W4008: Integrated Onion Pest, Disease and Weed Management

(Multistate Research Project)

Status: Active

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SAES-422 Reports

Annual/Termination Reports:

[02/24/2023] [05/03/2024] [05/29/2025]

Date of Annual Report: 02/24/2023

Report Information

Annual Meeting Dates: 01/05/2023 - 01/05/2023
Period the Report Covers: 03/01/2022 - 01/05/2023

Participants

Participants Attachment:

W4008 Final Report (2022) Rev 1 02-23-23.pdf

Brief Summary of Minutes

Minutes Attachment:

W4008 Final Report (2022) Rev 1 02-23-23.pdf

Accomplishments

Objective 1. Evaluate onion germplasm for resistance to pathogens and insects.   Georgia: Screened 52 Vidalia cultivars under field conditions for bacterial foliar symptoms and bulbs were screened for the ability of P. ananatis 97-1 strain to induce necrotic lesion on scales. Six varieties (Georgia Boy, Rio Dulce, Emy 55843, Alba Blanca, White Gaspare and Maragogi) displayed significantly lower necrotic lesions compared to others.   California: Analysis of data from Kern variety trial and lab-based assays (bulb assay and scale assay on bulbs from variety trials) is underway.  Preliminary results are that the lab-based assays are not well correlated with the field trial results.   Idaho: In fall of 2021, bulbs of 12 yellow cultivars and pre‐ commercial lines were collected and stored (36°F). On 24 June 2022, samples were evaluated for defects. Only two entries (Crockett and NUN 7212) reached >80% marketable bulbs after 9 months of storage. With few exceptions, translucent scale was the primary defect in bulbs not considered marketable, while internal decay was the second most common defect. Oloroso and Seminis 1526 showed very high levels of translucent scale, while OLX 13-331 and Trident had the highest incidence of internal decay. Vaquero, the industry standard, had ~70% marketable bulbs, below the long‐term average for this cultivar.   Trials at Malheur Agricultural Experiment Station, Oregon State University during 2022, assessed the susceptibility of 16 varieties (12 yellow, four red) to Setophoma terrestris, the causal agent of pink root.  Ten plants were pulled from the discard rows from four replicated plots on two separate dates, roots were washed and percentage infection was visually assessed.  Among the yellow varieties, Legend, Trident and Caldwell appeared among the most susceptible to pink root whilst Sedona and Calliber were the least susceptible. Purple haze was least susceptible of the red onion varieties.    New York: A variety trial conducted in Elba, NY investigated the relative susceptibility of 16 onion varieties to onion thrips, bacterial bulb rot, pink root and Stemphylium leaf blight. The trial was arranged as a split-plot design with variety as the main factor and insecticide treatment as the sub-plot factor. Treatments were replicated 4 times. Data were also collected on leaf color, upright plant architecture, vigor, neck diameter, maturity and yield. Grading was completed in early January 2023 and data analysis is pending.  The trial will be repeated in 2023.   New Mexico: NMSU breeding lines exhibited a lower Fusarium basal rot (FBR) incidence and severity than a FBR-susceptible and a FBR-resistant cultivar, indicating breeding efforts to be successful. When exposed to high onion thrips pressure conditions conducive for Iris yellow spot (IYS) disease development, other NMSU breeding lines exhibited fewer thrips per plant and a lower disease severity early in the growing season, and greater bulb size at harvest than a commercial cultivar grown under the same conditions.   Washington: Bulbs from the 2021 Washington State University Onion Cultivar Trial were evaluated in Feb. 2022 after 5 months in storage, for quality and bulb rots. Results were summarized and shared with onion stakeholders on the WSU Onion Alerts (>600 subscribers), demonstrating how >50 cultivars fared under Columbia Basin conditions. The 2022 Washington State University Onion Cultivar Trial was planted in April 2022 near Quincy, WA, with three replicate plots of each of 54 cultivars submitted by seed companies. Plots were evaluated for diseases and pests. Bulbs were harvested in September to assess yield, and 50 bulbs/plot placed in storage to evaluate storage quality and bulb rots in Feb. 2023. The WSU Onion Field Day was held on Aug. 25, the first in-person field day since 2019 (>100 attendees).   Objective 2. Investigate the biology, ecology and management of onion insect pests.   California: Several treatments provided effective control of seedcorn maggot in field trials evaluating insecticide seed treatment efficacy for spring seed onions.    Oregon: Threshold-based sampling plans reduced insecticide applications for thrips and IYSV and input costs without reducing yields. Further trials demonstrated that tank-mixing of most insecticides does not improve thrips management and is not cost effective.   Idaho: Thrips and IYSV control with a standard foliar insecticide program (Aza/M‐pede, Movento, Minecto Pro, Radiant – 2 applications of each) was compared to programs where the Movento foliar applications were substituted with 2 applications of experimental insecticides from Gowan (GWN‐12030 and GXP-60513) applied via the drip irrigation system. All insecticide programs reduced thrips populations and IYSV incidence compared to the untreated, and some drip programs were equal in efficacy to the standard foliar program. The total yield and the proportion of ≥3‐inch diameter onions were also increased by insecticide programs.   New York: Syngenta’s new insecticide, isocycloseram (PLINAZOLIN® technology), was evaluated for managing onion thrips as a foliar spray. Several foliar applications of a high rate of isocycloseram provided a commercially acceptable and equivalent level of control as high rate of cyantraniliprole (Exirel), and both provided better control than a high rate of spinetoram (Radiant SC).  Isocycloseram alone and in combination with thiamethoxam (Cruiser 5FS) were evaluated as an onion seed treatment for onion maggot control. Results in 2022 showed that a high rate of isocycloseram provided a similar and excellent level of maggot control as the two standards, FarMore FI500 with Regard SC and FarMore FI500 with Trigard. Field studies in 2022 identified cyclaniliprole (Harvanta 50SL) and flupydifurone (Sivanto Prime) as effective in reducing onion thrips infestations in green onion. Future registrations for these products are being explored on onion for thrips control. Field research in 2022 documented a new formulation of spinosad (Lumiverd) that can be used as an onion seed treatment for maggot control. Results were used to assist Corteva, in getting Lumiverd registered as a seed treatment on onion for the 2023 field season.   Washington: Insecticide efficacy trials in 2022 evaluated control options for onion thrips (Thrips tabaci). One trial featured new unregistered insecticides, one of which was nearly as efficacious as Radiant (spinetoram), currently the most effective insecticide available to onion producers in WA. Another trial evaluated insecticides currently registered for use on onions but that are not used to manage onion thrips, but none proved effective compared to currently used products.   In trials assessing control of Seedcorn maggot, all insecticide treatments improved stands numerically compared to non-treated, but not all treatments improved stands statistically. Diazinon applied pre-planting, Diazinon applied post-planting, and Capture LFR were the most effective. They did not differ significantly from one another but caused significantly better stands than the non-treated check plots. Seedcorn maggot pressure was high in the trial, with only 58% stand in the non-treated. The best treatment resulted in 80% stands. Plots treated with Regard only had 68% plant stands, which is not acceptable commercially. FarMore FI500 and Capture LFR treatments resulted in acceptable stands of 72 and 74% respectively.  Under the significant pest pressure, there was evidence that Diazinon, Farmore FI500, and Capture LFR can be used to reduce seedcorn maggot pressure and achieve adequate plant stands.   Objective 3. Investigate the biology, epidemiology and management of onion plant pathogens.   Pennsylvania:  As part of the Stop the Rot SCRI project, during 2022 a third year of field sampling was conducted to identify bacteria associated with symptomatic onion foliage and bulbs. Ten whole onion plant samples were collected from each of five fields in PA and in NY at two times during the season. From each plant, isolations were made onto nutrient agar and up to three unique bacterial colonies were selected. Approximately 153 bacterial isolates were collected from PA and 77 from NY under an APHIS 526 permit and stored (-80C). The post-harvest samples are currently being processed. The majority of isolates were non-pathogenic based on the red scale necrosis assay and all are in the process of being identified to genus.   A bactericide efficacy trial was repeated in 2022 but disease pressure was variable despite multiple inoculations. There were no significant differences in total marketable bulb weight although numerically, the non-inoculated, untreated control was the highest and the inoculated untreated control was near the lowest (P=0.136). The percent of bulbs with bacterial rot symptoms at harvest (interior and exterior) was numerically highest in the copper treated plots and lowest in the plots treated with LifeGard or the non-inoculated, untreated control plots (P=0.670).   A nitrogen rate and timing trial with four nitrogen rates (0, 50, 105, and 160 lb/A) at two timings (half and full season) was repeated to evaluate the effect on center rot disease incidence and marketable yield. Although there was a significant rep effect, the percent of plants with foliar symptoms of center rot was significantly higher in the treatments with higher rates of nitrogen (P=0.003) and also numerically higher for symptomatic bulbs at harvest. Total marketable bulb weight was significantly higher in plots that received nitrogen (P=0.001) compared to the no nitrogen control. Nitrogen application timing and inoculation status (inoculated vs non-inoculated) did not significantly affect disease incidence or marketable weight.   Georgia: The efficacy of fungicides to manage Botrytis leaf blight (BLB) on onion was evaluated in Georgia. Four rows of ‘Vidora’ onion were transplanted into 6-ft beds (panels) on 10 Dec (2020) at the Vidalia Onion and Vegetable Research Center, Lyons, GA.  Natural inoculum was relied upon. Disease severity was assessed on 22 Mar, 4 Apr, and 20 Apr as percent leaf area with symptoms per plot. Area under disease progress curve (AUDPC) was calculated using disease severity ratings from the four assessment periods.   BLB symptoms first appeared on 22 Mar with significantly higher disease severity for the non-treated check (63.8%) and Scala (55.0%) than for the other fungicide-treated plots, with no significant differences among other treatments. Disease progressed over a four-week period and reached 88.8% (disease severity) on 20 Apr, in non-treated plots and Scala-fungicide treated (81.3%) plots, which were significantly higher than the other fungicide-treated plots. Non-treated check and Scala-fungicide treated plots had significantly higher AUDPC compared with the fungicide treatments. Phytotoxicity was not observed with any treatment.   An evaluation of the effect of N-fertility on bacterial internal rot in onion was conduted. There was no observable difference in percent bulb incidence in field or in storage for any of the N-fertility and timing of the final N application. Different copper products and biological control products were evaluated under field conditions. Multiple bactericide programs were evaluated with LifeGard. Foliar symptoms were not observed; however, bulb incidence of internal rot after 30-days of storage differed significantly. Bactericides (Nu Cop, Mankocide, Nordox, Champ) along with LifeGard significantly reduced internal bulb rot compared to non-treated check. Cultural practices to reduce bacterial internal rot in onion were evaluated.  Based on the multiple assessments, onion clipping length (2 cm or longer) resulted in significantly reduced internal bulb rot compared to the shorter neck length.   Utah: Laboratory studies were conducted to determine if temperature could influence outbreaks of Fusarium bulb rot. Fusarium proliferatum grew best between 25-30C. A field trial was conducted to determine the effect of cultural and chemical practices used in Utah onion production. Fungicides showed very little to no effect on the disease. There was a 10% reduction in bulb rot when onions were topped with a 3-in neck vs 1.5-in neck.   California:  Pathogen screening for bacterial diseases affecting CA fresh market and dehydration onions was undertaken in seven counties. Pathogens isolated included: Pantoea agglomerans, Burkholderia cepacia, Burkholderia gladioli, and Pectobacterium carotovorum.  Bactericides for management of bacterial diseases was studied in Kern and San Joaquin counties.  Preliminary conclusion based on just a single successful trial is that the bactericides are not effective for bacterial disease control in CA.  An irrigation study at the Intermountain REC in Tulelake evaluated the influence of sprinkler irrigation and drip irrigation on bacterial diseases.  A significant decrease in bacterial disease incidence and severity was observed when onions were grown under drip compared to sprinkler irrigation in 2021 and 2022. Two studies in Southern California evaluated weather-based models for management of onion downy mildew. Fewer treatments were made in the model treatments compared to the standard calendar and no disease was observed in the study areas, indicating the potential to forgo applications when disease pressure is low.   Oregon: Over irrigation and excess N-fertilization increase the incidence of fungal neck rot. Optimizing irrigation and fertility through soil moisture monitoring, and plant and soil nutrient testing can reduce risks for bulb rots.   The application of dry formulations of encapsulated DADS and garlic oil resulted in a 74% and 75% reduction in white rot sclerotia populations, respectively, compared to the non-treated control in naturally infested soils. Encapsulated DADS and garlic oil is easier to handle and apply than traditional liquid formulations, which could promote the adoption of sclerotial germination stimulants in a white rot IPM program.    Idaho: Pink root control from drip applications of Fontelis at the first irrigation followed by a second application 4 weeks later were compared to Velum Prime or Velum Prime followed by Minuet at the same application timings.  None of the fungicide programs significantly reduced disease incidence and severity in July and August compared to the untreated.  Additional trials with biological based programs (Symborg) and fall solarization treatments also failed to show any reduction in pink root compared to the untreated.  The second half of the 2022 growing season was exceptionally hot and 100% of the roots showed disease symptoms by early August.   Studies were completed in which onion bulbs were inoculated with Rahnella spp. and incubated  at 25°C (77°F), 30°C (86°F) or 35°C (95°F) and evaluated for bulb rot at 3, 5, or 8 weeks.  Bulb rot increased over time, resulting in up to 60% of the bulb being impacted by 8 weeks post inoculation. Incubation at 30°C (86°F) after inoculation with Rahnella spp. resulted in only 36% bulb rot.  A second assay incubated the onion bulbs for 2 days or 2 weeks after inoculation with Rahnella spp. followed by storage at 5C (41F) and evaluated bulbs for rot at 4 and 6 months.  Bulbs incubated at 30C for 2 days or 2 weeks resulted in 35% bulb rot compared to 60-70% when incubated at 25°C (77°F) or 35°C (95°F).  This demonstrates that temperature can significantly impact disease development.    The level Stemphylium vesicarium spores were monitored over the spring/summer from 2019 to 2022 in an effort to inform fungicide timing and understand the relationship of the pathogen with environmental conditions. A Burkard Multivial Cyclone spore trap was situated on Field block D at Parma and operated continuously over 24-hour periods. DNA was extracted from the spore trap samples and DNA of S. vesicarium was quantified using real-time PCR. DNA was recovered in all four years. In 2019 there was relatively low-level detection before mid-July which coincided with the observation of symptoms in late summer. In 2020, which was arguably when the most severe outbreaks of Stemphylium were observed in the Treasure Valley, relatively high levels of Stemphylium spores were detected throughout June and again from mid-August. Fewer spores were detected from mid-August in 2021 which coincided with arguably less disease observed that year.   Colorado: Bactericidal products were evaluated for the management of onion bacterial rots in inoculated field trials.  In addition, we evaluated three post-harvest fogging treatments to assess their effectiveness in managing internal rot of stored onion bulbs.  Bulbs will be cut and bulb rots quantified in February of 2023.   New York: In New York, three field trials were conducted in commercial onion fields to evaluate efficacy of fungicides for control of Botrytis leaf blight and Stemphylium leaf blight (SLB), in Elba (2 trials) and Oswego, NY (Hoepting). Each trial was arranged as a randomized complete block design with 24 treatments and 4 replications. Fungicide sprays began in mid-June and continued weekly for 8-9 weeks until mid- to late-August. Trials investigated the efficacy and development of fungicide resistance to FRAC 3 active ingredients when applied alone, in tank mixes with other FRAC group fungicides and in rotation with other FRAC group fungicides. A few novel products were trialed to identify another FRAC group with activity on SLB including Oso (FRAC 19), as well as several tank mixes and premixes. Data analysis is pending.   Control of Stemphylium leaf blight (SLB) in NY is difficult because S. vesicarium has developed resistance to fungicides within the FRAC 2, 7, 9 and 11 groups. Currently the most effective fungicides are in FRAC 3. However, there is also concern of resistance development in this group. Isolates of S. vesicarium collected from diseased onion fields in four regions of NY in 2020 (n=114) and 2021 (n=81) were tested for fungicide sensitivity to three FRAC 3 active ingredients (a.i.). Results suggest insensitivity is developing to all three a.i’s but is developing more slowly to difenoconazole than to tebuconazole, with propiconazole intermediate between these. Some regional differences were also apparent. Results will be used to inform changes in fungicide programs to maintain disease control and slow the development of resistance. Other studies determined that transplants from interstate were a source of SLB, but that seed was not. The disease forecaster BSPcast was tested in a field trial but was found to be a poor predictor of disease.   Field studies showed that supplemental foliar applications of insecticides sprayed early in the season targeting adult onion thrips in an attempt to reduce transmission of IYSV were not effective. Levels of IYSV at the end of the season were similar between onion fields that received the supplemental sprays (5% incidence) and those that did not (9% incidence). However, final levels of IYSV were low.   This study will be repeated in 2023.   Another field study showed that IYSV levels were similar between transplanted and direct-seeded fields early in the season, indicating that transplanted fields should not be considered the only major source of early-season IYSV epidemics. Rather, adult onion thrips that are viruliferous may be overwintering in New York and colonize onion fields early in the season. There is some evidence that thrips may prefer to initially colonize onion fields that have the largest plants in the vicinity, often those with an early planting date.   Texas:. A total of 218 bacterial strain samples from Texas (n=208) and New Mexico (n=10) were isolated from onion and identified using 16S rRNA in 2022, encompassing 34 bacterial genera. On the red scale assay, 97.2% of bacteria were non-pathogenic. Out of the 218 samples, the predominant genus was Pantoea (56), Pseudomonas (27), Enterobacter (22), and Bacillus (20). The survey identified a novel bacterial species - Curtobacterium allii.   Washington: As part of the ‘Stop the Rot’ USDA NIFA SCRI Project No. 2019-51181-30013, we continued the 3-season, 11-state survey across the USA to determine the diversity and prevalence of bacteria associated with onion diseases. Five onion bulb crops were surveyed across the Columbia Basin in Jul – Sep. 2022. Isolations from 75 plant samples with symptoms of bacterial infection resulted in 84 bacterial isolates.  Isolates are being identified to genus and species with 16S rDNA sequencing, and all isolates are being tested for pathogenicity . This will complete 3 seasons of survey in WA. We are also completing sequencing and foliar and bulb pathogenicity tests for 33 isolates obtained from symptomatic onion bulb crops in CA that were surveyed by Brenna Aegerter at UC-ANR. Strains of bacteria from Seasons 1 and 2 were submitted to the National Onion Bacterial Strain Collection at the Univ. of Georgia. In addition, soil, plant, and water samples were collected in some fields surveyed in WA in 2022, and sent to James Woodhall, Univ. of Idaho, for testing with real-time PCR assays being developed to detect pathogenic strains of Pantoea.   Six field trials were carried out in 2022 on management of onion bacterial diseases evaluating: 1) cultivar susceptibility, 2) chemigation vs. spray boom application of 3 bactericides, 3) timing of rolling tops, 4) timing of topping bulbs, 5) timing of undercutting bulbs, and 6) postharvest application of disinfectants. These trials were repeats of the 2021-22 trials. Bulbs were harvested in Aug.-Sep., placed in storage, and will be cut and rated in Feb. 2023. Results of the Season 2 (2021-22) trials for these same objectives demonstrated: 1) there was more bacterial leaf blight in inoculated plots of earlier maturing cultivars, with ~50% bulb rot for cultivars in maturity groups 1 and 2, 34.5% for those in maturity group 4, and 18.5% for those in maturity group 3; 2) Five weekly, preventative applications of Badge SC, ManKocide, or Lifegard WG did not control bacterial leaf blight or bulb rot, and there was no effect of the herbicide Outlook on leaf blight or bulb rot; 3) rolling tops increased leaf blight but not bulb yield or bulb rot; 4) early topping increased bacterial bulb rot compared to normal or late topping; 5) timing of undercutting did not affect bacterial leaf blight, yield, or bulb rot; and 6) none of four disinfectant treatments reduced bacterial bulb rot, as observed the year prior. We are continuing to develop a risk assessment model for onion bacterial diseases in the Pacific Northwest, using results from the 3 seasons of field trials, and we will invite growers to test the risk model in 2023.   Objective 4. Investigate the biology, epidemiology and management of weedy plant species that impact onion production.   Utah: Claudia Nischwitz presented information on Fusarium bulb rot and Dan Drost gave a presentation on Seed priming and plant population responses at the Utah Onion Association meeting February 8, 2022 attended by 28 people.. On August 9, 2022, Dan Drost held a field day demonstrating his onion variety trial and introduced the new irrigation specialist, attended by 36 people.   New York: In New York, a pre-emergent herbicide trial was conducted in a commercial onion field in Elba, arranged as a randomized complete block design with 18 treatments and 4 replications. The objective of this trial was to optimize weed control and crop safety.  It compared a one-step to a two-step barley-kill herbicide program, heavy vs. light rates of pre-emergent herbicides up until barley-kill, different timings of multiple applications of Outlook and Prowl, and incorporation of bicyclopyrone into the onion herbicide program. Data were collected on onion stand, visual crop injury, stunting and vigor, as well as on weed control by species. Data analysis is pending. New Mexico: A post planting, delayed preemergence application of pendimethalin resulted in similar or better control of annual weeds than current weed control methods using Bensulide and DCPA herbicides or pendimethalin applied at the 2-leaf stage for autumn-sown and winter-sown onions in New Mexico. This same application of pendimethalin did not impact onion stand and bulb yield and did not leave detectable residues on onion bulbs after harvest.

Publications

Belo, T., LaHue, G., and du Toit, L.J. 2023. Reducing the risk of onion bacterial diseases through irrigation, fertility, and other cultural management strategies. Agronomy Journal: accepted. doi: 10.1002/agj2.21301.   du Toit, L.J., Derie, M.L., Gundersen, B., Waters, T.D., and Darner, J. 2022. Effects of bactericide and herbicide applications on bacterial leaf blight and bulb rot of onion, Pasco, WA, 2021-22. Plant Disease Management Reports 16:V150.   du Toit, L.J., Derie, M.L., Gundersen, B., Waters, T.D., and Darner, J. 2022. Effects of late-season cultural practices on bacterial leaf blight and bulb rot in an onion crop, Pasco, WA, 2021-22. Plant Disease Management Reports 16:V149.   du Toit, L.J., Derie, M.L., Gundersen, B., Waters, T.D., and Darner, J. 2022. Efficacy of disinfectants applied to onion bulbs in storage for control of bacterial bulb rots, Pasco, WA, 2021-22. Plant Disease Management Reports 16:V148.   du Toit, L.J., Derie, M.L., Gundersen, B., Waters, T.D., and Darner, J. 2022. Susceptibility of 12 onion cultivars to bacterial leaf blight and bulb rot in Pasco, WA, 2021-22. Plant Disease Management Reports 16:V151.   Dung, J.K.S. and Hua, K.. 2022. Comparison of fungicides for control of white rot on garlic in Oregon, 2020-2021. Plant Disease Management Reports 16:CF029. doi: 10.1094/PDMR16   Dutta, B., Foster, M.J., and Donahoo, W.M. 2022. Evaluation of fungicides to manage Botrytis leaf blight on onion in Georgia, 2021. PDMR 16:V043.   Dutta, B., Foster, M.J., and Donahoo, W.M. 2022. Evaluation of bactericides and plant defense inducers to manage internal bacterial rot of onion in Georgia, 2021. PDMR 16:V044.   Dutta, B., and Tyson, C. 2022. Evaluation of neck-clipping length on post-harvest incidence of external and internal bacterial bulb rot in onion, Georgia, 2021. PDMR 16:V107.   Dutta, B., and Tyson, C. 2022. Evaluation of harvesting methods on post-harvest incidence of external and internal bacterial bulb rot in onion, Georgia, 2021. PDMR 16:V108.   Dutta, B., and Tyson, C. 2022. Evaluation of digging methods on post-harvest incidence of external and internal bacterial bulb in onion, Georgia, 2021. PDMR 16:V109.   Feibert, E., C. Shock, S. Reitz, A. Rivera-Ramires, and K. Wieland. 2022. Performance of Onion Cultivars in the Treasure Valley of Eastern Oregon and Southwestern Idaho in 2010—20. Hortechnology, 32:435-446   <h1>Hay, F.S. D.W. Heck, A. Klein and S. Sharma, C.A. Hoepting and S.J. Pethybridge.  2022.  Spaciotemporal dynamics of Stemphylium leaf blight and potential inoculum sources in New York onion fields.  Plant Disease, 106(5): 1381-1391.</h1>   Hay, F.S., D.W. Heck, S. Sharma, A. Klein, C.A. Hoepting and S.J. Pethybridge.  2022.  Stemphylium leaf blight of onion.  The Plant Health Instructor, 22: online: doi: 10.1094/PH-P-2022-01-0001.   Hay, F., A. Klein, S. Murphy, S., and B. Nault. 2022. Efficacy of OMRI-listed products for Stemphylium leaf blight control in onion in New York, 2018. Plant Disease Management Reports 16: V121.   Hay, F., A. Klein, S. Murphy, and B. Nault. 2022. Effect of OMRI-listed products for Stemphylium leaf blight control in onion in New York, 2019. Plant Disease Management Reports 16: V152.   Hoepting, C.A. 2022. Rolling onions to “Stop the Rot” (cover).  Veg Edge, 18(12): 1, 3.   Hoepting, C.A. 2022. Bactericides not effective for control of onion bulb rot in on-farm field trials in New York (cover).  Veg Edge, 18(17): 1, 3-4.   Hoepting, C.A. 2022. Primary vs. secondary Stemphylium leaf blight in onion.  Veg Edge, 18(16): 5-6.   Hoepting, C.A. 2022. Scouting tips for onion thrips in onion.  Veg Edge, 18(13): 9.   Hoepting, C.A. and F.S. Hay. 2022. 2021 fungicide research highlights for Stemphylium leaf blight in onion – The fall of the FRAC 3s and keeping onions green despite poor SLB control.  Veg Edge, 18(13): 3-5.   Hoepting, C.A. 2022. Slim pickings for fungicides to control Stemphylium leaf blight of onion in 2022.  Veg Edge, 18(12): 4-5.   Hoepting, C.A. 2022. Best fungicide options for control of Botrytis leaf blight in onion: It depends on what kind of spot you got.  Veg Edge, 18(11): 4-6.   Hoepting, C.A. 2022. Effective post-emergent weed control in onion: Knocking back and knocking out (cover).  Veg Edge, 18(8): 6-9.   Hoepting, C.A. 2022. The weed race – Trial notes on spraying small onions with post-emergent herbicides.  Veg Edge, 18(7): 6-7.   Hoepting, C.A. 2022. Onion updates and killing of barley nurse crop.  Veg Edge, 18(6): 6.   Hoepting, C.A., S.K. Caldwell and E.R. van der Heide.  2022.  Evaluation of cultural practices to reduce bacterial bulb rot in onions that are failing to lodge, 2021.  Plant Disease Management Reports 16: V167.   Hoepting, C.A., S.K. Caldwell and E.R. van der Heide.  2022.  Efficacy of fungicide products for control of Botrytis leaf blight and Stemphylium leaf blight in onion in Oswego, 2021.  Plant Disease Management Reports 16: V140.   Hoepting, C.A., S.K. Caldwell and E.R. van der Heide.  2022.  Efficacy of FRAC 3 and 7 tank mixes for control of Botrytis leaf blight and Stemphylium leaf blight in onion, 2021.  Plant Disease Management Reports 16: V139.   Hoepting, C.A., S.K. Caldwell and E.R. van der Heide.  2022.  Efficacy of fungicide tank mixes for control of Botrytis leaf blight and Stemphylium leaf blight in onion, Elba, 2021.  Plant Disease Management Reports 16: V138.   Hoepting, C.A., S.K. Caldwell and E.R. van der Heide.  2022.  Evaluation of in-furrow drenches for control of pink root and Fusarium basal rot in direct seeded onion, 2020-2021.  Plant Disease Management Reports 16: V132.   Hoepting, C.A., S.K. Caldwell and E.R. van der Heide.  2022.  Evaluation of in-furrow and soil line drenches for control of pink root and Fusarium basal rot in direct seeded onions, 2021-2022.  Plant Disease Management Reports 16: V174.   Hoepting, C.A., S.K. Caldwell and E.R. van der Heide.  2022.  Evaluation of selected pesticides for control of bacterial bulb rot in onion, 2021.  Plant Disease Management Reports 16: V168.   Hoepting, C., and B. Nault. 2022. Lorsban is banned: How to control cabbage maggot in brassicas now? Cornell Cooperative Extension, Cornell Vegetable Program. VegEdge 18(4): 4-6. <a href="https://rvpadmin.cce.cornell.edu/pdf/veg_edge/pdf235_pdf.pdf">https://rvpadmin.cce.cornell.edu/pdf/veg_edge/pdf235_pdf.pdf</a>.   Iftikhar, R., A. Ghosh, and H.R. Pappu. 2022. Mitochondrial genetic diversity of Thrips tabaci (Thysanoptera: Thripidae) in onion growing regions of the USA. J. Econ. Entomol. In Press.   Khanal M., B.P. Bhatta, and S. Malla. 2022. Isolation and characterization of bacteria associated with onion and first report of onion diseases caused by five bacterial pathogens in Texas, U.S.A. Plant Dis. <a href="https://doi.org/10.1094/PDIS-09-22-2206-SR">https://doi.org/10.1094/PDIS-09-22-2206-SR</a>   Khanal, M., B.P. Bhatta, S. Timilsina, S. Ghimire, K. Cochran, and S. Malla. 2023. Curtobacterium allii sp. nov., the actinobacteria species causing onion bulb disease. Antonie van Leeuwenhoek 116:83–96. DOI: <a href="https://doi.org/10.1007/s10482-022-01775-z">https://doi.org/10.1007/s10482-022-01775-z</a>   Khanal, M., S. Timilsina, B.P. Bhatta, K. Bophela, T. Coutinho, K. Cochran, and S. Malla. 2022. Pseudomonas uvaldensis sp. nov., a bacterial pathogen causing onion bulb rot, isolated from Texas, USA. Int. J. Syst. Evol. Microbiol. 72:005311. https://doi.org/10.1099/ijsem.0.005311   Lai, P.-C., and B. Nault. 2022. Are onion thrips allies of bulb-rot causing bacteria in organic onion production? Cornell Cooperative Extension, Cornell Vegetable Program. VegEdge 18(16):  9-10. <a href="https://rvpadmin.cce.cornell.edu/pdf/veg_edge/pdf247_pdf.pdf">https://rvpadmin.cce.cornell.edu/pdf/veg_edge/pdf247_pdf.pdf</a>.   Lai, P.-C. and B. Nault. 2022. Do thrips facilitate bulb rot disease? Onion World 38(8): <a href="https://issuu.com/columbiamediagroup/docs/onion_world_december_2022?fr=sMzU1YzQ5MDQ1MjQ">https://issuu.com/columbiamediagroup/docs/onion_world_december_2022?fr=sMzU1YzQ5MDQ1MjQ</a>.   Lai, P.-C., L. Iglesias, R.L. Groves, M.J. Havey, and B.A. Nault. 2022. Performance of a semi-glossy onion hybrid in certified organic onion fields infested with Thrips tabaci and bulb-rot causing bacteria. Crop Protect. 160 (1-9). <a href="https://doi.org/10.1016/j.cropro.2022.106037">https://doi.org/10.1016/j.cropro.2022.106037</a>   Machado-Burke, A., M. Uchanski, and J. Davey. 2022. Evaluation of bactericides to manage slippery skin in onion in Colorado, 2021. Plant Disease Management Reports (PDMR), the American Phytopathological Society (APS), V128.   MacKay, H., du Toit, L., Havey, M., and Rogers, P. 2022. Joint Allium research meeting held in Denver showcases latest research on onion production, pests and diseases. Onion World May/June 2022:14-16. <a href="https://issuu.com/columbiamediagroup/docs/onion_world_may-june_2022/14">https://issuu.com/columbiamediagroup/docs/onion_world_may-june_2022/14</a>   MacKay, H., du Toit, L., and Hoepting, C. 2022. Stop the Rot Half-Time Report: News from the Stop the Rot project on onion bacterial diseases. Onion World March/April 2022:16-17.   Machado-Burke, A., M. Uchanski, and J. Davey. 2022. Evaluation of bactericides to manage slippery skin in onion in Colorado, 2021. Plant Disease Management Reports (PDMR), the American Phytopathological Society (APS), V128.   Murdock, M.R., Pizolotto, C.A., and Woodhall, J.W. 2022. Evaluating Pristine and Luna Tranquility against Botrytis leaf spot, Stemphylium leaf blight and other foliar diseases on drip-irrigated onions in Idaho, 2020. Plant Disease Management Reports 16, V105.   Murray, K., I. Sandlin, P. Ellsworth, P. Jepson, A. Fournier, H. Luh and S. Reitz. 2022. The Economic Impact of Onion Pests in the Treasure Valley - A Look at Pests and Associated Management Practices, 2018–2019. Oregon State University Extension Service, EM 9347, 34 pp. <a href="https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/em9347.pdf">https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/em9347.pdf</a>   Myers, B. Shin, G.Y., Stice, S., Agarwal, G., Gitaitis, R., Kvitko, B., and Dutta, B.  2022. Genome-wide association and dissociation studies in P. ananatis reveal potential virulence factors affecting Allium porrum and A. fistulosum x A. cepa hybrid. Frontiers in Microbiology (in press)   Nault, B.A. 2022. Onion thrips control in onion, 2021. Arthropod Management Tests 47(1): tsac052, <a href="https://doi.org/10.1093/amt/tsac052">https://doi.org/10.1093/amt/tsac052</a>.   Nault, B.A. 2022. Onion maggot control using seed treatments in onion, 2021. Arthropod Management Tests, 47(1): tsac055, <a href="https://doi.org/10.1093/amt/tsac055">https://doi.org/10.1093/amt/tsac055</a>.   Nault, B., and C. Hoepting. 2022. Guidelines for maggot and disease control in onion with an emphasis on seed treatments. Cornell Cooperative Extension, Cornell Vegetable Program. VegEdge 18(22):  7-10. <a href="https://rvpadmin.cce.cornell.edu/pdf/veg_edge/pdf253_pdf.pdf">https://rvpadmin.cce.cornell.edu/pdf/veg_edge/pdf253_pdf.pdf</a>.   Nault, B., and C. Hoepting. 2022. Guidelines for maggot and disease control in onion with an emphasis on seed treatments. Cornell Cooperative Extension, Cornell Vegetable Program. VegEdge 18(22):  7-10. <a href="https://rvpadmin.cce.cornell.edu/pdf/veg_edge/pdf253_pdf.pdf">https://rvpadmin.cce.cornell.edu/pdf/veg_edge/pdf253_pdf.pdf</a>.   Nault, B.A. and C. Hoepting. 2022. Seed treatments: What to know to protect your 2023 onion crop. Onion World 38(7): 28-31. <a href="https://issuu.com/columbiamediagroup/docs/onion_world_november_2022?fr=sYmE1NDQ5MDQ1MjQ">https://issuu.com/columbiamediagroup/docs/onion_world_november_2022?fr=sYmE1NDQ5MDQ1MjQ</a>.   Nault, B.A., R.K. Sandhi, R.S. Harding, E. Grundberg, and T. Rusinek. 2022. Optimizing spinosyn insecticide applications for allium leafminer (Diptera:  Agromyzidae) management in allium crops. J. Econ. Entomol. 115(2): 618–623. <a href="https://doi.org/10.1093/jee/toac016">https://doi.org/10.1093/jee/toac016</a>   Qian, Y., Hua, G.K.H., Scott, J.C., Dung, J.K.S., and Qian, M. 2022. Evaluation of sulfur-based biostimulants for the germination of Sclerotium cepivorum sclerotia and their interaction with soil. Journal of Agricultural and Food Chemistry Manuscript (in print). <a href="https://doi.org/10.1021/acs.jafc.2c05862">https://doi.org/10.1021/acs.jafc.2c05862</a>   Regan, K.H. and B.A. Nault. 2022. Impact of reducing synthetic chemical inputs on pest and disease management in commercial onion production systems. Agronomy 12(6), 1292; <a href="https://doi.org/10.3390/agronomy12061292">https://doi.org/10.3390/agronomy12061292</a>   Shahabeddin Nourbakhsh, S. and C.S. Cramer. 2022. Onion germplasm possess lower early season thrips numbers. Horticulturae 8:123. https://doi.og/10.3390/horticulturae8080123.   Shahabeddin Nourbakhsh, S. and C.S. Cramer. 2022. Onion size measurements as predictors for onion bulb size. Horticulturae 8:682. https://doi.og/10.3390/horticulturae8080682.   Shin, G.Y., Smith, A., Coutinho, T.A., Dutta, B., Kvitko, B. 2022. Validation of species-specific PCR assays for the detection of Pantoea ananatis, P. agglomerans, P. allii and P. stewartii. Plant Disease (first look).   Sidhu, J., Dubose, J., Fernberg, J. and Aegerter, B.J. 2022. Evaluation of bactericides for management of bacterial leaf blight and bacterial bulb rot in onions, 2021. Plant Disease Management Reports 16:V026. <a href="https://doi.org/10.1094/PDMR16">https://doi.org/10.1094/PDMR16</a>   Wilson, R., K. Nicholson, and B. Aegerter. 2022. The influence of irrigation method on bacterial diseases of onion in Northeast California, 2021 Plant Disease Management Reports 16: V154. <a href="https://doi.org/10.1094/PDMR16">https://doi.org/10.1094/PDMR16</a>   Woodhall, J., M. Murdock, K. Beck and M. Thornton. 2021. Pink root disease of onion – biology and control. Extension Bulletin 1000, University of Idaho. Colorado   Zhao, M., Tyson, C., Chen, H.C., Paudel, S., Gitaitis, R., Kvitko, B., and Dutta. B. 2022. Pseudomonas allivorans sp. nov., a plant-pathogenic bacterium isolated from onion leaf in Georgia, USA. Systematic and Applied Microbiology 45 (1):126278. doi: 10.1016/j.syapm.2021.12627.   Zhao, M., Shin, G.Y., Stice, S., Coutinho, T., Gitaitis, R., Kvitko, B., and Dutta, B.  2022.  A novel biosynthetic gene cluster across the Pantoea species complex is important for pathogenicity in onion.  Mol. Plant Microbe Interact. (in press)   Zhao, M., Tyson, C., Gitaitis, R.,  Kvitko, B., and  Dutta, B. 2022. Rouxiella badensis, a new bacterial pathogen of onion causing bulb rot. Frontiers in Microbiology 13:1054813.

Impact Statements

A post planting, delayed preemergence application of pendimethalin could provide comparable or better control of annual weeds as currently used herbicides in autumn-sown and winter-sown onions in New Mexico while reducing herbicide costs by 92-95% ($99-$156/acre) and reducing the legacy costs on the environment by 74-88%. This simple switch could save the NM onion industry $1 million per year.

Date of Annual Report: 05/03/2024

Report Information

Annual Meeting Dates: 03/05/2024 - 03/05/2024
Period the Report Covers: 01/01/2023 - 12/31/2023

Participants

Brenna Aegerter (University of California),
Jo Ann Asselin (USDA – ARS),
Juan Carlos Brevis (BASF/Nunhems),
Emmanuel Byamukama (USDA NIFA National Program Leader),
Teresa Coutinho (University of Pretoria, South Africa),
Mike Derie (Washington State University),
Joe DiSalvo (DiSalvo Farms),
Jeremiah Dung (Oregon State University),
Lindsey du Toit (Washington State University),
Bhabesh Dutta (University of Georgia),
Jake Fountain (University of Georgia),
Adri Grobler (University of Pretoria, South Africa),
Erik Hansen (Bioworks)
Frank Hay (Cornell University)
Chris Hayes (Bioworks)
Scott Hendricks (Seminis/Bayer),
Christy Hoepting (Cornell University Co-operative Extension),
Gabe LaHue (Washington State University),
Subas Malla (Texas A&M AgriLife),
Claudia Nischwitz (Utah State University),
Ram Neupane (Pennsylvania State University),
Peter Rogers (BASF/Nunhems),
Gina Shin (University of Georgia),
Jaspreet Sidhu (University of California),
Paul Stodghill (USDA – ARS),
Sahil Thapa (Washington State University),
Mark Uchanski (Colorado State University),
Tim Waters (Washington State University),
James Woodhall (University of Idaho).

Brief Summary of Minutes

Accomplishments

SAES-422 Multistate Research Project W-4008: Integrated Onion Pest and Disease Management   Annual report for 2023    W4008 Committee Officers – 2023: Chair: Frank Hay, Cornell University.   Vice-Chair: Gabriel LaHue, Washington State University. Secretary: Rob Wilson University of California. Past Chair: David Burrell, National Onion Labs.   Contributors:  CA: Brenna Aegerter*, Alex Putman, Jaspreet Sidhu*, and Rob Wilson CO: Jane Davey, Eduardo Gutierrez-Rodriguez, and Mark Uchanski GA: Bhabesh Dutta, Brian Kvitko, Jake Fountain, and Stormy Sparks ID: Brenda Schroeder, Mike Thornton, and James Woodhall NM:  Chris Cramer and Brian Schutte NY: Brian Nault, Christy Hoepting, Sarah Pethybridge and Frank Hay. PA: Beth Gugino OR: Stuart Reitz and Jeremiah Dung TX: Subas Malla UT: Claudia Nischwitz WA: Lindsey duToit, Timothy Waters, and Gabriel la Hue.  *not current members of W4008   Accomplishments   Objective 1. Evaluate onion germplasm for resistance to pathogens and insects.   California An onion variety trial was conducted within a commercial field in San Joaquin County to evaluate susceptibility of 12 onion varieties to bacterial bulb rots. Although there was no disease in the field trial, bulbs from each plot were stored and tested in the laboratory using two different potential screening assays. The objective was to continue our evaluation of these post-harvest assays as a possible means to complement field screening trials, which are challenging for numerous reasons. Unfortunately, the postharvest assay results do not correlate well with field trial results based on what we have seen in multiple years at multiple locations across the U.S.   Colorado Laboratory and field studies were conducted to evaluate differences between 15 onion varieties (yellow, white, and purple/red) in relation to the human pathogen Salmonella.   Despite the documented antimicrobial properties of onion metabolites, no cultivar showed a significant reduction in Salmonella populations in laboratory or field studies.   Idaho Thirteen commercial onion varieties and pre-commercial onion lines were screened for storability in cooperation with seed companies and McCain Foods.  Ten entries had more than 85% marketable bulbs after 9 months storage at 2 deg C.  A total of 10 varieties grown in the Onion Variety Trial at the OSU Malheur Experiment Station were evaluated for resistance to Botrytis aclada.  Over 90% of inoculated bulbs showed symptomatic Botrytis neck rot disease progression among all varieties, with an average of 98% incidence. Disease severity among all inoculated bulbs was also much greater than the control group, with an average of 11.8% of halved bulb surface area discolored. Variety ‘Montero’ had the highest average disease severity (17.3% discolored inner surface), while ‘Tucannon’ had the lowest (7.4%). It should be noted that while ‘Montero’ tied for the lowest rate of natural infection, it rated poorly when inoculated.  Twenty varieties in the onion variety trial at OSU were also evaluated for pink root susceptibility.   New Mexico NMSU breeding lines exhibited a lower Fusarium basal rot (FBR) incidence and severity than an FBR-susceptible and an FBR-resistant cultivar. Our breeding efforts have shown a reduction in FBR disease severity and incidence with selection. When exposed to high onion thrips pressure conditions conducive for Iris yellow spot (IYS) disease development, other NMSU breeding lines exhibited fewer thrips per plant and a lower disease severity early in the growing season, and greater bulb size at harvest than a commercial cultivar grown under the same conditions.   New York An onion variety trial was conducted in Elba, NY that investigated the relative susceptibility of multiple commonly grown onion varieties to onion thrips and bacterial bulb rot. The trial was arranged as a split-plot design with variety as the main factor and insecticide treatment as the sub-plot factor and treatments replicated four times. Data were also collected on plant characteristics including leaf color, upright plant architecture, vigor, neck diameter, maturity and yield. Data entry, analysis and summary are pending.   Texas The Texas A&M (TAM) AgriLife Vegetable Breeding program evaluated 21 advanced TAM onion lines, including 28 commercial checks against Pink Root (Setophoma terrestris) in a randomized complete block design with four replications. Four TAM germplasm (31034, 34066, 50084, and 50089) were resistant with a low severity of 5 (on a scale of 0 to 100). Additionally, 65 early generation TAM lines were evaluated in an augmented trial with ten commercial checks. A total of 39 TAM germplasm showed resistance to pink root with a severity of 5. Germplasm were further evaluated for variety development.   Utah Six onion varieties were screened in a field trial for susceptibility to slippery skin caused by Burkholderia gladioli. In three varieties quite a few transplants died which significantly reduced the stand.  Stand density was correlated with rot, with the denser the stand, the less rot was observed.  This effect masked any potential differences between varieties in disease susceptibility.   Washington Bulbs in storage for the 2022 Washington State University (WSU) Onion Cultivar Trial were evaluated in Feb. 2023 after 5 months in storage for quality and bulb rots. Results were summarized and shared with onion stakeholders on the WSU Onion Alerts (>600 subscribers), demonstrating how 53 cultivars fared under Columbia Basin production conditions. The 2023 Washington State University Onion Cultivar Trial was planted in April 2023 near Moses Lake, WA, with three replicate plots of each of 52 cultivars submitted by onion seed companies. The plots were evaluated regularly for diseases and pests. Bulbs were harvested in September to assess yield, and 50 bulbs/plot were placed in storage to evaluate for storage quality and bulb rots in Feb. 2024. The WSU Onion Field Day, at which stakeholders could look at the plots and hear presentations on onion research and other issues, was held on Aug. 31 in-person, and was well attended (>100 attendees).    Objective 2. Investigate the biology, ecology and management of onion insect pests.   California A field trial was conducted in Tulelake to evaluate the efficacy of insecticide seed treatments for suppressing seed corn maggot feeding on seedling onions.   Idaho An experimental insecticide (GWN12030) applied as a foliar or drip application was compared to grower standard practices for impact on onion thrips populations and incidence of Iris Yellow Spot Virus (IYSV). Both application rate and timing were important factors in efficacy.  All treatments that significantly reduced insect populations on disease incidence also improved the yield of > 3 inch diameter onions.    New York Surveys of maggot species infesting onions across northern production regions of North America revealed that seedcorn maggot is the dominant pest of onion in the Klamath and Columbia Basins, while onion maggot is the dominant pest of onion in the Treasure Valley and Great Lakes regions. This information is valuable for determining which insecticide seed treatments should be considered for different regions.  Field research studies in 2023 documented onion maggot insensitivity to spinosad in one New York onion field. The LC50 of that population to spinosad increased 165- fold since 2018 and 2.3-fold since 2021. Lumiverd (spinosad) seed treatment failed to protect the crop from onion maggots in that field in 2023, indicating that the population has developed resistance to spinosad.  Field research studies in 2023 also revealed onion thrips insensitivity to spinetoram in several onion fields in the Elba production region. While we cannot confirm that onion thrips populations have developed resistance to spinetoram, there is considerable concern that this may be the situation.  An on-farm small-plot trial revealed that a tank mix of Lannate LV + Agri-Mek SC + Warrior II was found to be as effective as the industry standard, Exirel 16 fl oz/A for controlling thrips when pressure was high (4 thrips/leaf at the time of the first spray). This treatment may be used instead of Radiant in the 2023 growing season. Syngenta’s new insecticide, isocycloseram (PLINAZOLIN® technology), was evaluated as a seed treatment for maggot control and as a foliar spray for onion thrips control. Isocycloseram alone and especially in combination with either thiamethoxam (Cruiser 5FS) or clothianidin + imidacloprid (Sepresto) provided protection of the crop against onion maggot and seedcorn maggot. Onion maggot control using isocycloseram alone and in combination with other products occurred in the field where the population is resistant to Spinosad. Isocycloseram also was one of the most effective products for protecting onions from onion thrips, including locations where onion thrips populations were not controlled effectively by spinetoram.  Co-applying methomyl (Lannate LV) with spirotetramat (Movento/Senstar) early in the season significantly reduced populations of onion thrips early in the season as well as the numerical incidence of IYSV later in the season. Bulb yield was numerically greater in fields with lower levels of IYSV, but differences were not statistically significant.   Oregon Onion thrips and thrips-transmitted IYSV are the key pests of onion in the Treasure Valley of eastern Oregon and southwestern Idaho. At present, insecticides remain the cornerstone for management of these pests. In 2023, we demonstrated that good thrips management reduces the incidence and severity of foliar fungal pathogens (Stemphylium leaf blight) and onion bulb rots. We also demonstrated that yield and size profiles of onions increase with shorter intervals between insecticide applications. In general, tank-mixing insecticides does not improve thrips management.   Texas The TAM AgriLife Vegetable Breeding program evaluated insecticide programs to manage thrips. The trial was direct seeded at the Uvalde Center on October 15, 2022. The experiment was laid out in split-plot design with four replications. The main plot was variety with three levels (‘Hornet’, ‘Mata Hari’, and ‘Don Victor’), and the sub-plot was insecticide program with three levels (threshold application based on 1 thrips per leaf, weekly application, and control). We selected three products based on different modes of action (abamectin [Agri-Mek SC], spirotetramat [Movento], and spinetoram [Radiant SC]). Insects were counted on 10 tagged plants each week from February 23 to April 10, 2023. Insecticide programs included Agri-Mek SC followed by Movento and Radiant SC. Each insecticide was sprayed two subsequent times. The action threshold and weekly methods were not significantly different in managing thrips, however, both methods were significantly different from the control. The action threshold method needed only three applications of chemicals, whereas the weekly method used six applications of chemicals. In addition, onion germplasm comprising 18 Texas A&M selections and 24 commercial varieties were screened for thrips tolerance in a germplasm evaluation nursery. Two Texas A&M onion germplasm (40052 and 50023) showed tolerance to thrips.   Washington Insecticide efficacy trials were conducted in 2023 to evaluate control options for onion thrips (Thrips tabaci) management. One trial featured a new insecticide set to be registered for use in 2024, plinazolin insecticide. Plinazolin was as efficacious as Radiant (spinetoram), currently the most effective insecticide available to onion producers in WA. Another trial evaluated organic products currently registered for use on onions. None of the organic insecticides provided consistent efficacy against onion thrips.  Seedcorn maggot research was conducted in collaboration with stakeholders. Based on all data for both spray application plot locations, Diazinon as a pre application is still effective at reducing seedcorn maggot pressure and damage.  Based on stand counts and harvest data from two trial locations for seed treatments, Lumiverd, Sepresto 75 WS, Lumiverd + Sepresto 75 WS, and Plinazolin+ Cruiser 5FS as a seed treatment, effectively reduced seedcorn maggot pressure for a better plant stand and improved harvest yield. The commercial standards currently are Diazinon pre-plant and seed treatment with Lumiverd or Lumverd + Cruiser. Plinazolin will not be registered as a seed treatment in 2024, but when it becomes available in future years will be an alternative option for growers to manage seedcorn maggot in onions.     Objective 3. Investigate the biology, epidemiology and management of onion plant pathogens.    California A field trial was conducted in Kern County to evaluate the efficacy of bactericides against bacterial diseases (foliar symptoms and bulb rot). However, there was insufficient disease to draw good conclusions about efficacy.  Two field trials were conducted to examine efficacy of timing fungicide applications for downy mildew control based on environmental conditions measured using on-site weather stations.  Environmental disease models were used to determine if the measured weather conditions were favorable for disease and warranted fungicide application.  This strategy was compared to the standard approach of applications at regular intervals. The weather models indicated that conditions in 2023 were generally not favorable for disease, and indeed we did not observe disease in any trial location or year.  This result shows that this modeling approach can identify when environmental conditions are unfavorable for onion downy mildew development.  To evaluate if downy mildew can be detected in air samples and used as an indicator of when to start applying fungicides, we placed air samplers to trap spores of the pathogen at the field trial locations described above.  The samplers collected air continuously, and samples were brought back to the lab one to three times per week.  In the lab, pathogen spores were quantified microscopically, and using quantitative PCR (qPCR).  Few spores of the pathogen were detected during the months-long monitoring period, a result which agrees with observations of no symptoms in the field trials and unfavorable conditions from the weather models.   Colorado Trials were conducted to examine bacterial bulb rot management with bactericide (in season) and postharvest fogging trials during storage.   Georgia The effect of neck-clipping length on post-harvest incidence of external and internal bacterial bulb rot in onion was evaluated in a field/storage trial.  Four rows of ‘Century’ onions were transplanted into 6-ft beds (panels) on 15 Dec at the Vidalia Onion and Vegetable Research Center, Lyons, GA. The fertility program was consistent with University of Georgia Extension Service recommendations. Experimental design consisted of a randomized complete block with four replications. Treated plots were 20-ft long and were separated on each side by non-treated border panels. Plots were separated by a 3 ft bare-ground buffer within the row. Thrips and disease management program was followed according to the UGA Cooperative Extension recommendation. Natural infection was relied upon. At harvest maturity, onion bulbs were undercut using a bed ridge frame undercutter (Parma Inc.,) followed by a three-day field curing period. Following curing, dried necks of onion bulbs were clipped manually at four different lengths; 1-in., 2-in., 3-in. and close-to the shoulder of the bulb (0-in.). Roots were also clipped but care was taken not to clip too close to the basal plate. Onion bulbs from each replicate plot (four replicates) were bagged and stored at 4℃ for 35 days. After storage, onion bulbs were individually cut using a sterile knife to determine the incidence of internal rot. Internal bulb rot was evaluated after a month of storage.  Individual onion bulbs were cut open with a sterile knife and assessed visually. The onion neck-clipping length had a significant effect on internal bulb rot incidence but not on the external rot. Significantly higher incidence of internal bulb rot was observed with the neck-clipping length of one inch or when the necks were cut close to the shoulders compared with the two and three inches. Internal rot was associated with mainly Pantoea spp., and Enterobacter spp. based on arbitrarily-collected symptomatic samples. Bulb rot due to post-harvest fungal pathogens (Aspergillus spp.) was not observed.   The ability of Bacillus subtilis QST 713 (Serenade ASO) or Bacillus mycoides isolate J (LifeGard WG) applied in rotation or tank-mix with copper (Nordox 75 WG) to manage center rot in onion leaves and bulbs was assessed in a field trial. Alternating the application of BCAs with copper at longer day intervals (10 or 15 d) could achieve a similar level of center rot control as their rotation at shorter day intervals (5 d). Under low disease pressure, two to three applications could be eliminated from the spray program without compromising disease suppression.  B. subtilis QST 713 and B. mycoides isolate J strains from respective products were copper-sensitive at concentrations >250 ppm. Our concurrent study on the tank mix of BCAs with copper showed that the standalone copper treatment had a similar level of disease control as their tank mix application. Frequent applications of copper may control disease relatively better than treatments without copper but the integration of BCA with copper in spray programs may largely depend upon their compatibility and modes of action of the BCA products.  Center rot complex in onions is attributed to various Pantoea species, including P. ananatis, P. agglomerans, P. allii, and P. stewartii ssp. indologenes. These bacterial pathogens utilize the HiVir and alt gene clusters to induce necrosis and colonize onion tissues. However, not all Pantoea spp. possess these gene clusters. Research on virulence factors like motility, quorum sensing, and EPS production have been extensively studied in P. ananatis but not in P. agglomerans and P. stewartii ssp. indologenes, leaving their gene functions unexplored. In this study, we investigated the impact of quorum sensing (luxIR), EPS production (epsG), and flagellar motility (motB) genes on the pathogenicity of P. ananatis PNA 97-1, P. agglomerans AR1a, and P. stewartii subsp. indologenes PNA 03-3. Deletion of luxIR reduced acyl-homoserine lactones (AHLs) production, motB gene removal eliminated swimming motility, and epsG deletion decreased EPS production in all three Pantoea species. However, quorum sensing and flagellar motility gene deletions did not affect the pathogenicity of these Pantoea spp. on onions, contradicting previous findings. Further, we identified epsG as a novel gene contributing to exopolysaccharide production but was not involved in onion necrosis symptoms in three Pantoea spp. Our study used strains that are HiVir and alt positive, unlike previous strains that were HiVir positive only and lacked the alt gene cluster. Further studies would focus on investigating the roles of these three genes in three Pantoea spp. without the the alt gene cluster background.   Idaho Curing duration and storage assays were completed by inoculating onion bulbs (cv. Vaquero) with Rahnella spp. and incubation of bulbs at 25°C (77°F), 30°C (86°F) or 35°C (95°F) for 2 days or 2 weeks and storage at 5°C for 4 and 6 months.  The 2 day curing assays determined that bulbs cured for 25°C (77°F) and stored for four or six months exhibited 42% or 58% bulb rot, respectively.  Bulbs cured for 2 weeks at 25°C (77°F) exhibited similar amounts of bulb rot.  Bulbs cured at 35°C (95°F) for 2 days or 2 weeks and stored for four or six months exhibited around 40% and 50% bulb rot.  Interestingly bulbs cured at 30°C (86°F) for 2 days or 2 weeks and stored for four or six months exhibited around 30% bulb rot.    Field trials were conducted investigating the impact of irrigation and planting date on decay.  A LAMPL assay for P. agglomerans was developed and demonstrated at the Parma IPM field day.   New York  Three on-farm small-plot trials were conducted to evaluate fungicides for control of Stemphylium leaf blight (SLB) and Botrytis leaf diseases in muck-grown onions. Objectives included screening novel active ingredients for efficacy on these diseases and evaluating 2-3 product tank mixes of mediocre products with medium to low risk of fungicide resistance in an attempt to find a treatment that may be rotated with most effective double product-FRAC 3 treatment. We also staged some of the treatments to help us understand their effect on the development of fungicide resistance. For these treatments, SLB isolates were taken from leaf samples that were collected after the last fungicide sprays, and screened for fungicide sensitivity to propiconazole and tebuconazole. Results of fungicide sensitivity assays are still being analyzed, but a new FRAC 3 active ingredient was identified that had excellent control of SLB.  Fungicide resistance monitoring Testing of S. vesicarium against the FRAC 3 active ingredients difenoconazole (Quadris Top, Inspire Super), propiconazole (Tilt), and tebuconazole (Viathon, Luna Experience) has been undertaken to detect shifts in sensitivity of Stemphylium vesicarium, cause of Stemphylium Leaf Blight of onion.  Between 2021 and 2022, S. vesicarium isolates from Elba and Wayne exhibited a similar profile of sensitivity to difenoconazole, suggesting no change in sensitivity.  However, S. vesicarium isolates from Oswego showed a continuing trend towards increased insensitivity to difenoconazole between 2020, 2021 and 2022.  In Elba, Wayne and Oswego there appeared to be an increase in S. vesicarium isolates sensitive to tebuconazole (EC50 > 10 µg/ml) remained similar between 2021 and 2022 in Elba and Wayne, and there was a general trend towards increased highly insensitive isolates in Oswego.    Between 2021 and 2022, S. vesicarium isolates from Elba and Oswego exhibited a similar profile of sensitivity to propiconazole, suggesting no changes.  In Wayne, highly insensitive isolates (EC50 > 10 µg/ml) were detected in 2021, but not in 2022.   Identification of inoculum sources of Stemphylium In April/May 2023, prior to or shortly after direct seeding onion, the incidence of S. vesicarium in volunteer onion ranged from 20-80% in each of 10 fields in Elba, NY.  An initial study utilizing SSR’s indicated that genotypes of S. vesicarium present in volunteers were present in the succeeding crop at the end of the season indicating that S. vesicarium overwintering in volunteer onion could be a major contributor to SLB in the succeeding onion crop.   Approximately 25% of onion in NY is grown from bare-root transplants produced and imported from other States.  Samples of 11 batches of bare-root onion were obtained at delivery to farms in NY.  S. vesicarium was detected in all 11 batches, ranging in incidence from 74%-100%.   However, an initial study utilizing SSR’s indicated a poor relationship between genotypes of S. vesicarium present in transplants and those in the crop at the end of the season suggesting that S. vesicarium in transplant onion was a minor contributor to SLB in the succeeding onion crop compared to local sources of inoculum.  One hypothesis is that S. vesicarium isolates on transplants may exhibit less fungicide resistance in comparison to local sources in NY and become outcompeted by local sources when fungicides are applied.   The bulb rotting pathogen Botrytis aclada was also detected in leaves from 8 of the 11 batches of transplant onion ranging in incidence from 1.1-21.5% with identity confirmed by sequencing.  A species of Botrytis previously unrecorded in onion, but is pathogenic to onion, was also detected and is currently being characterized.   Assessment of nematode issues in NY onion. A survey of fields in Elba, Oswego, Wayne, Yates and Orange was undertaken in June and July 2023 to determine the prevalence of nematode species.  Root Knot Nematode (RKN; Meloidogyne hapla) and root lesion nematode (Pratylenchus spp.) were detected at low population density, unlikely to cause adverse effects on onion yield. Stubby Root Nematode (SRN; Paratrichodorus allius) was prevalent and occurred at population densities which have been associated with yield losses in other onion growing regions in USA. Monitoring of nematode populations in a grower’s field of non treated areas, and areas treated with Vydate or Velum Prime at planting demonstrated that both nematicides were effective at reducing SRN numbers early in the season.  Velum Prime and Vydate treatment increased the weight of standard sized bulbs in a 30-bulb sample by an average of 86.4 and 71.8% respectively compared to non treated. Velum Prime and Vydate treatment decreased the weight of boiler sized onion in a 30-bulb sample by an average of 76.8 and 62.5% respectively compared to non treated. Regression analysis indicated that for every 10 stubby root nematode/200 ml soil in June there was a loss in mean bulb weight in a 30-bulb sample of 0.128 kg, or 9.3%, mean weight of a bulb of 0.398 kg or 9.5%, mean weight of standard sized bulbs of 0.443 kg or 11.7%, and an increase in boiler sized of 0.111 kg or 58.1%.   SRN was widespread in onion fields in NY and occurred at population densities that would indicate yield loss.    Oregon White rot is a devastating soilborne fungal disease that limits the yield, marketability, and production of onion, garlic and other Allium crops. Growth chamber and field trials demonstrated that both encapsulated diallyl disulfide (DADS) and garlic oil inclusion complexes were equally or more effective at reducing populations of white rot sclerotia in soils when compared to liquid DADS or garlic powder.   Pennsylvania Pathogenicity testing and data analysis was completed for the three-year onion bacterial disease survey conducted in both Pennsylvania and New York. Of the 43 bacterial genera tested using the red scale necrosis assay, Burkholderia and Pantoea were the predominant pathogenic genera, with 74.5% of Burkholderia and 44.1% of Pantoea being pathogenic. A subset of the non-pathogenic isolates were further tested in both whole bulb and foliar pathogenicity assays. Among those 37% of Pantoea (n=27) and 94.1% of Burkholderia (n=17) were found to be pathogen in either foliar, bulb or both assays.   A copper tolerance plate assay was used to evaluate the tolerance of Burkholderia isolates collected from PA and NY. Preliminary analysis has indicated that the majority of isolates (87%, n=38) tested exhibited a reduced copper sensitivity phenotype. Speciation of the Burkholderia isolates is also underway with the majority of isolates speciating as Burkholderia cenocepacia and B. cepacia.   Washington: Genetic diversity of Iris yellow spot virus. Barcoding of Thrips tabaci (onion thrips) from different onion producing regions was carried out. Onion thrips is a key pest of onion and acts as a vector of several viruses, including Iris yellow spot virus (IYSV), a serious viral pathogen of onion. There is limited information available on the genetic variation within and among T. tabaci populations in the United States, and key evolutionary parameters. In our study, 83 T. tabaci specimens were collected from A. cepa from 15 locations comprising four states in the United States. A total of 92 mtCOI gene sequences of T. tabaci was analyzed to understand the genetic diversity and structure of T. tabaci from onion. Seven distinct haplotypes of T. tabaci were identified from the collection, while nine T. tabaci sequences retrieved from GenBank comprised 5 haplotypes. Overall, 15 haplotypes of T. tabaci infesting A. cepa were identified in the world, including 10 haplotypes in the United States. In the phylogenetic analysis, all populations collected during the study clustered with the thelytokous lineage, while T. tabaci sequences retrieved from GenBank corresponded with the leek-associated arrhenotokous lineage. The greatest genetic variation was found in Elba, NY and Malheur, OR populations with 3 haplotypes in each. Results suggest that haplotypes 1 and 7 are more frequently prevailing haplotypes in the northwestern United States, with haplotype 1 being predominant all over the country. The eastern United States appears to have a more diverse group of haplotypes. Ongoing research included collection and typing of onion samples for the presence of IYSV. More than 20 isolates were identified, and selected regions of the IYSV RNA genome were amplified, with the nucleotide sequences determined. Sequence and bioinformatics analyses are being carried out. Information from this effort will provide insights into genome diversity, population structure, and evolutionary patterns of the virus, which could help refine IYSV detection.   Onion bacterial diseases. As part of the ‘Stop the Rot’ USDA NIFA SCRI Project No. 2019-51181-30013, ongoing identification and characterization of bacterial strains was conducted from a survey over 3 seasons in 11 states across the USA to determine the diversity and prevalence of bacteria associated with onion diseases.  Hundreds of bacterial isolates from WA and CA were tested for pathogenicity on onion using scale, foliar, and bulb assays; and sequencing for genus and species determination. Results from five field trials in 2022-23 were finalized after rating bulbs in storage in Feb. 2023. Rolling onion tops at onset of ‘tops down’ did not affect bulb rot; undercutting early increased yield and reduced bulb rot compared to undercutting at 100% tops down or not undercutting; early topping of bulbs (while green) reduced yield by 54% and increased bulb rot by 32-35%. In 2023, we repeated field trials to evaluate timing of topping onion bulbs, effect of chemigated vs. spray boom applications of pesticides on bacterial diseases, and postharvest application of disinfectants on control of bacterial bulb rots in storage. The bulbs were harvested in Aug.-Sep. 2023 and placed in storage for bulb rot evaluations in Feb. 2024. Bulb rot ratings in storage have been completed and data analyses are in progress. Results will be published in Plant Disease Management Reports. A PNW bacterial disease risk model was developed using 4 risk categories: current/cumulative risk, field variables, environmental variables, and production variables. Weekly scores were plotted over the season. The model was demonstrated at farms in WA and tested on ~12 bulb crops in 2023. Storage results from the farms are pending for validation. Data from trials in previous years also are being used to test the model. This was led by Project Manager, MacKay, who resigned in 2023 for medical reasons. du Toit is seeking expertise to continue developing the model and develop an app for stakeholders. Three field trials were carried out in 2023 to investigate the impacts of irrigation and nitrogen management on onion bacterial diseases: (1) an irrigation frequency trial in Pasco, WA, (2) an N application timing trial in Othello, WA, and (3) an N application rate trial in Othello, WA. Total and marketable bulb yield, bulb size class distribution, and the incidence and severity of bacterial bulb rot were assessed at harvest and after 5 to 6 months of storage. Preliminary results suggest total yield increased with more frequent irrigation. However, marketable yield was comparable among plots subjected to irrigation frequency treatments, due to more frequent irrigation leading to an increase in bulbs culled due to bacterial rot. Similarly, in the N rate trial, total yield at harvest increased with increasing N rates for the cv. Calibra, but so did the weight of bulbs culled due to bacterial rot, such that statistically separable differences in marketable yield were not detected. No statistically separable differences were observed among N timing treatments.    Objective 4. Investigate the biology, epidemiology and management of weedy plant species that impact onion production.   California A study was conducted in Tulelake to evaluate the efficacy of herbicides applied post-plant to control annual broadleaf weeds in direct seeded processing onions.   New Mexico A post planting, delayed preemergence application of pendimethalin resulted in similar or better control of annual weeds than current weed control methods using Bensuilde and DCPA herbicides or pendimethalin applied at the 2-leaf stage for autumn-sown and winter-sown onions in New Mexico. This same application of pendimethalin did not impact onion stand and bulb yield while also not leaving any detectable residues on onion bulbs after harvest.   New York Three small-plot onion herbicide trials were conducted in commercial muck onion fields: 1) To optimize weed control and crop safety with pre-emergent herbicides; 2) To improve control of volunteer potatoes with post-emergent herbicides with emphasis on incorporating new herbicide Optogen into the program; and 3) To extend weed control season long with late applications of pre-emergent herbicides. Data analysis is underway.  However, none of the treatments evaluated in this trial were more effective than repeated applications of Goal 2XL for controlling volunteer potato. Keeping volunteer potatoes as small as possible, ideally 4-6” by applying low doses of Goal 2XL 0.5-2 fl oz in young onions (flag+ to 1.25 leaf) when volunteer potatoes are 2-4” is key to achieving high rates of control (90% or more) when high rates of Goal 2XL may be applied to 2.5 leaf onion. This study demonstrated that adding Buctril 2E and Optogen to Goal 2XL 4 fl oz did not increase crop injury beyond that of Goal 2XL 4 fl oz alone. Thus, these tank mixes may be incorporated into POST herbicide spray program without increased risk of crop injury or negative impact on volunteer potato control. Although weed pressure was very low in this trial, our preliminary results suggest that pre-emergent herbicide applications made to 6-leaf (Jun 28, 77 d PHI) and 9-leaf (Jul 20, 55 d PHI) onion significantly reduced weed pressure at harvest. Generally, the 9-leaf applications, Chateau +/- Prowl H2O and Zidua demonstrated the most effective season-long residual weed control. Optogen 3.42 fl oz/A @ 6-leaf numerically reduced weed density but was not significantly different than the nontreated.   Washington: Two onion newsletter articles were written and distributed to >600 subscribers, mostly in the Pacific Northwest USA, via the WSU Onion Alerts. The WSU Onion Field Day at Skone and Connors Farms, Moses Lake, WA on August 31 was attended by ~100 attendees, who inspected 3 replicate plots of 52 cultivars. du Toit, Waters, and Wohleb assisted onion stakeholders with disease, entomology, and production questions through the 2023 season. The USDA NIFA SCRI ‘Stop the Rot’ annual team meeting was held on 5-7 March 2024 at the WSU Mount Vernon NWREC, with 25 attendees, immediately following the W-4008 annual meeting at the same location the morning of 5 March 2024. The team shared updates on all objectives of the project, including to those who had been attending the W-4008 meeting.

Publications

Impact Statements

In New York the development of fungicide resistance in Stemphylium leaf blight has become critical. In the Elba region there has been good adoption of resistance management strategies with 87.5% of eight spray programs using two or fewer FRAC 3 fungicide sprays, of which 75% were tank mixes of two FRAC 3 fungicides, resulting in little increase in fungicide resistance over 3 years. This is in contrast to increased fungicide resistance in regions which have not adopted these recommendations.
In New Mexico, a post planting, delayed preemergence application of pendimethalin was shown to provide comparable or better control of annual weeds as the currently used herbicides in autumn-sown and winter-sown onions, while reducing herbicide costs by 92-95% ($99-$156/acre) and reducing the legacy costs on the environment by 74-88%. This simple switch could save the New Mexico onion industry $1 million per year.
There has been substantial national outreach from the multi-state USDA SCRI funded ‘Stop the Rot’ project through presentations at grower meetings in 7 states (>780 stakeholders), 7 articles in Onion World and Vegetable & Specialty Crop News, and extension newsletters and online, e.g. through the Alliumnet website. Growers have indicated they are incorporating project recommendations into their production practices, particularly late-season irrigation and cultural practices that minimize the risk of bacterial rots
Results from a national survey of stakeholders have shown the multi-state USDA SCRI project ‘Stop the Rot’ has made good progress on increasing awareness of bacterial pathogens of onion, and developing standardized assays for bacterial isolations and virulence screening. Project recommendations for bacterial management such as avoiding cutting necks too short (<2 inches), avoiding early topping of bulbs, and drip irrigation instead of overhead irrigation, were considered effective by stakeholders.
Colorado onion stakeholders were interested in whether postharvest disinfectants were effective at managing bacterial bulb rot. However, trials demonstrated that none of the fogging or ozone treatments evaluated were effective at reducing onion bacterial bulb rot in storage.
Topping of onions to retain a neck length of two inches or more has been a common practice for Vidalia onion growers in Georgia to reduce bacterial internal rot. This slight modification in harvesting practice has been widely adopted in Georgia and other States.
Surveys of maggot species infesting onions across northern production regions of North America revealed that seedcorn maggot is the dominant pest of onion in the Klamath and Columbia Basins, while onion maggot is the dominant pest of onion in the Treasure Valley and Great Lakes regions. This information is valuable for determining which insecticide seed treatments should be considered for different regions.
New products in the pipeline for registration showed good efficacy against seedcorn maggot and thrips in field trials in different states, and are likely to provide new options for onion growers in the future.
Screening of onion varieties in different States are providing growers with valuable information on susceptibility of different varieties to particular diseases. On-going breeding efforts in several states are showing continual progress towards the development of agronomically acceptable, disease and insect resistant varieties.

Date of Annual Report: 05/29/2025

Report Information

Annual Meeting Dates: 02/11/2025 - 02/11/2025
Period the Report Covers: 01/01/2024 - 12/31/2024

Participants

California: Robert Wilson, Dr. Alex Putnam, Dr. Cassandra Swett, Dr. Brenna Aegerter, Dr. Pastrana Leon, Dr. Ali Montazar
Colorado: Mark Uchansk
Georgia: Bhabesh Dutta, Brian Kvitko, Jake Fountain, Stormy Sparks
Idaho: Brenda Schroeder, James Woodhall, Mike Thornton
New Mexico: Chris Cramer, Brian Schutte
New York: Brian Nault, Christy Hoepting and Frank Hay
Oregon: Jeremiah Dung, Stuart Reitz
Pennsylvania: Beth Gugino
Texas: Subas Malla
Utah: Claudia Nischwitz
Washington: Lindsey du Toit, Timothy Waters, Hanu Pappu, Gabriel LaHue
Wyoming: Eunsook Park

Brief Summary of Minutes

W4008 2025 Annual Meeting Notes

Tuesday, February 11th, 2025 (11:30 AM – 2:00 PM Pacific Time)

Notes taken by Rob Wilson (Vice Chair)

General business:
- New Member: Eunsook Park new W4008 member from Wyoming
- Update from Emmanuel (National leader for NIFA group) - Really no updates at this time due to government review. Waiting for updates and collaboration. There is a link that can provide updates on the review. Link sent to Gabe. Gabe shared link in chat. No updates on status of SCRI new proposal deadlines and review process. Review panels are suspended.

CA Update - Wilson and Putnam
- Insect pests
  - Seedcorn maggot research in Tulelake, Wilson UC IREC (new active ingredients and new company products)
  - Reports of maggot and thrips problems in Low Desert Imperial Valley production Region
  - Reports of bulb mites in onions in Central Valley
- Disease
  - Wrapping up Stop the Rot bacterial disease project (statewide)
  - Downy Mildew research by Dr. Putnam, UC Riverside and Dr. Pastrana Leon, UCCE in low desert
  - Fusarium in Onion and Garlic led by Dr. Swett, UC Davis (preliminary identification investigations and start of management work)
  - Impact of irrigation on downy mildew management in the low desert Dr. Montazar, UCCE
- Weeds
  - Alternative herbicide options to replace Dacthal , Wilson, UC IREC (Tulelake)
- Georgia Update - Bhabesh Dutta
  - Botrytis leaf blight widespread- screen fungicides; loss efficacy of merivon and scala; recommending luna flex for resistant management
  - Downy mildew was found but managed well by growers. Several fungicides were effective in trial.
  - 100% of soil samples had Burkholderia species but not all species are pathogenic.
  - Copper products are equally effective in reducing center rot but not sour skin
  - Lifegard can be rotated with copper to reduce center rot severity
  - Jake Fountain working on black mold in Vidalia onions
  - New Horticulture extension agent McAvoy working on cultural management for management of bacterial disease
  - Luan Pereira de Oliveira, working on precision agriculture work with pest management in onions
  - New vegetable entomologist, thrips and insecticide efficacy trials
- Jane Davy, Colorado Update
  - Not much work in the last 12 months; some screening of Fusarium bulb rot from CO onions in storage; Onion acreage down
- Brenda Schroeder, Idaho Update
  - Reporting for James Woodhall and Mike Thornton
  - Brenda working on post harvest bulb rot and coinfection studies on how pathogens work together and individually and big picture of how storage curing affects disease.
  - Mike worked on how soil temperature affects bulb size and yield; treatments that cool the soil increase yield and size; treatments that cool soil have less decay. Biochar increased soil temp. and increased decay
  - Fungicide work on pink root;
  - James is looking at chemical and biological control of bacterial pathogens
- Michigan - No rep.
- New Mexico, Chris Cramer
  - Cramer looking at thrips and iris yellow spot and variety susceptibility
  - Cramer working on fusarium basal rot and variety resistance; some varieties appear to have resistance/less severe infection severity
  - Brian Schrudy and Cramer looking use of pendimethalin at 75% radical emergence; good crop safety and good weed control
- New York, Chisty Hoepting
  - Weed control of volunteer potatoes
  - Thrips pressure and quick accumulation of degree days
  - Got rain that can increase bacterial rot
  - Nault evaluated insecticide seed treatments for control of maggots
  - Nault evaluated insectides for onion thrips management
  - Carbon robotic laser weeder testing
  - Onion disease research Stemphylium leaf blight fungicide spray trials;
  - Optogen 3.5 fl oz post + buctril providing good control of emerged weeds; Hoepting
- Oregon, Jeremiah Dung
  - Ontario crop report, lower yields, low levels of thrips, some bacterial problems, wildfire smoke affected production
  - Gina Greenway looking at factors affecting disease free yield of white rot; fungicides seem to be most effective factor to increasing disease free yield
  - Dung, impact of DADS on soil microbial communities
  - Joel Felix, Carbon robotic laser weeder; comparison of herbicide with laser weeder; observation laser worked well on broadleaf weeds; laser did work well on high weed density; Optogen caused a lot of injury; delayed preemergent with Optogen seems to work ok; ET defoliant using it on onions at the 2-leaf stage; Nimitz application before nutsedge emerges gave good control; Nimitz will not be labeled on onions according to Adama;
  - Rob made the suggestion of trying to do some regional evaluations of herbicides in onions.
  - Tim mentioned the evaluation of Eco robotic machines and smart sprayers
- Pennsylvania - Beth Gugino
  - Revising Stop the Rot survey
- Subas - Texas update
  - Thrips studies on identification and insecticide efficacy
  - Pink root screening
- Claudia Nischwitz - Utah update
  - Hail damage on onions
  - Little research update
- Tim Waters- Washington
  - Fusarium, onion thrips management
  - Directed sprays with robotic weeders and delayed pre-emergent herbicides
  - Plant pathogen research with onion bacterial diseases
  - Mike Derie retired
- Eunsook Park
  - No onions in Wyoming
  - Cell biologist
  - Update on research related to onions
- Nominations for Secretary
  - Subas Malla nominated as secretary
  - Hawaii possible meeting location for 2025 and NOAA NARC

Accomplishments

Accomplishments   Objective 1. Evaluate onion germplasm for resistance to pathogens and insects Idaho: Onion bulbs from a total of 10 cultivars grown in the Onion Variety Trial at the OSU Malheur Experiment Station were inoculated with a spore suspension of Botrytis allii. Onion bulbs were cured and stored for 4 months. Onion bulbs were cut down the center and evaluated for the amount of rot the pathogen caused. It appears that cultivars respond differently to the neck rot pathogen suggesting that they have the ability to resist the pathogen to some degree. Further investigation with larger sample sizes is planned now that we know that there is a differential resistance response to B. allii across the cultivars. New Mexico: When inoculated with the disease-causing pathogen, NMSU breeding lines exhibited a lower Fusarium basal rot (FBR) incidence and severity than an FBR-susceptible and an FBR-resistant cultivar. Our breeding efforts have shown a reduction in FBR disease severity and incidence with selection. When exposed to high onion thrips pressure, conditions conducive for Iris yellow spot (IYS) disease development, other NMSU breeding lines exhibited fewer thrips per plant and a lower disease severity early in the growing season, and greater bulb size at harvest than a commercial cultivar grown under the same conditions. Washington: Bulbs for the 2023-24 Washington State University (WSU) Onion Cultivar Trial were evaluated in Feb. 2024 after 5 months in storage, for quality and bulb rots. Results were summarized and shared with onion stakeholders on the WSU Onion Alerts (>600 subscribers), demonstrating how 51 cultivars fared under Columbia Basin production conditions. The 2024 WSU Onion Cultivar Trial was planted in April 2023 near Prosser, WA, with three replicate plots of each of 47 cultivars submitted by onion seed companies. The plots were evaluated regularly for diseases and pests. Bulbs were harvested in September to assess yield, and 50 bulbs/plot were placed in storage to evaluate for storage quality and bulb rots in Feb. 2025. The WSU Onion Field Day, at which stakeholders could look at the plots and hear presentations on onion research and other issues, was held on August 29 in-person, and was well attended (>100 attendees).   Objective 2. Investigate the biology, ecology and management of onion insect pests. California: Robert Wilson evaluated insecticide seed treatments for management of seedcorn maggot in onions. New York: Surveys of maggot species infesting onions continued across northern production regions of North America and continued to indicate that seedcorn maggot is the dominant pest of onion in the Klamath and Columbia Basins, while onion maggot is the dominant pest of onion in the Treasure Valley and Great Lakes regions. This information may be valuable for determining which insecticide seed treatment should be considered in regions dominated by each species. In New York in 2024, we confirmed that one onion maggot population in New York had developed practical resistance to spinosad seed treatment. We also observed that spinosad seed treatment (Lumiverd) performed poorly in Oregon, but performed well in CA. In New York in 2024, onion thrips infestations were inadequately managed using spinetoram in several onion fields in western New York. While resistance to spinetoram has not been confirmed in those populations, it is suspected. Syngenta’s new insecticide, isocycloseram (PLINAZOLIN® technology), was evaluated as a seed treatment for maggot control and as a foliar spray for onion thrips control. Isocycloseram in combination with either thiamethoxam (Cruiser 5FS) or clothianidin + imidacloprid (Sepresto) provided protection of the crop against onion maggot and seedcorn maggot. Onion maggot control using isocycloseram alone was inadequate. Isocycloseram also was one of the most effective products for protecting onions from onion thrips, including locations where onion thrips populations were not controlled effectively by spinetoram. Tank mixes of methomyl (Lannate LV), lambda-cyhalothin (Warrior II with zeon technology) and abamectin (Agri-Mek SC) significantly reduced populations of onion thrips and provided an equivalent level of control as isocycloseram (PLINAZOLIN) and cyantraniliprole (Exirel). Oregon: Insecticides remain the cornerstone for management of insect pests of onion. In 2024, we demonstrated that yield and size profiles of onions increase with shorter intervals between insecticide applications. In general, tank-mixing insecticides does not improve thrips management and reduces insecticide options for growers. New insecticide chemistries show promise for managing onion and seedcorn maggots. Washington: Insecticide efficacy trials were conducted in the Columbia Basin in 2024 to evaluate control options for onion thrips (Thrips tabaci) management. One trial featured a new insecticide set to be registered for use in 2025, plinazolin. The efficacy was similar to Radiant (spinetoram), currently the most effective insecticide available to onion producers in WA. We also evaluated application of this insecticide via chemigation, since that is the preferred method for growers to use, and it worked well applied in that manner.   Objective 3. Investigate the biology, epidemiology and management of onion plant pathogens. California: Robert Wilson and Brenna Aegerter conducted studies of onion bacterial diseases under the “Stop the Rot” USDA NIFA SCRI project. Alex Putnam, Pastrana Leon, and Ali Montazar investigated the epidemiology and management of Downy Mildew in onions. Cassandra Swett investigated the epidemiology and management of Fusarium spp. in onions. Georgia: Pantoea stewartii subspecies indologenes (Psi) isolates can cause disease in several Poaceae hosts, including millets and rice and were recently known to cause foliar and bulb symptoms characteristic of center rot in onions. Cover crops such as millet and cash crops like corn are commonly grown in the summer after onion harvest in Vidalia, Georgia, USA. However, the risk of pathogen transmission to onions in the cropping systems where summer crops precede onion planting is mostly unknown. We evaluated the survivability of Psi in foliage and residue of corn and pearl millet as well as their colonization ability on onion roots and shoots transplanted in the infested soil. Our microplot study showed that crop residue can support Psi survival for at least 58 days and the presence of the pathogen in the soil coincided with onion transplanting. However, despite planting onion seedlings in Psi-infested soil, no bacterial colonization was observed in the rhizosphere or foliar surfaces of onion seedlings. Moreover, no visible symptoms of center rot were observed in onion foliage and bulbs, indicating a lesser risk of vertical transmission of Psi to onions in the Poaceae-Allium cropping system. We further investigated genetic determinants for bacterial survival in millet residue and bare soil by creating deletion mutants of the genes responsible for exopolysaccharides, flagellar motility, quorum sensing and pathogenicity in a Psi pathovar cepacicola strain PNA14-12. All mutant strains survived for at least 24 days in millet residue at high populations and bacterial colonies of all the tested strains were detectable until 44 days in bare soil, similar to the wild-type strain. Exopolysaccharide seemed to play a minor role in pathogen survival, but none of the other targeted genes contributed to the bacterial survival in millet residue and bare soil. Overall, our findings suggest that crop residue may play an important role in Psi survival in fields with onion-millet/corn cropping scheme, but bacterial transmission to onion crops from millet/corn residue was not observed. Despite this observation, crop residue should be incorporated into the soil to facilitate decomposition prior to onion transplanting. Onion is a widely cultivated crop that suffers from substantial losses due to Pantoea ananatis infection, a bacterial pathogen responsible for onion center rot disease. The virulence of the pathogen is driven by the chromosomally located HiVir gene cluster, which produces the phytotoxin ‘pantaphos’, causing extensive necrosis in infected tissues. Despite its economic importance, Allium genotypes with resistance against P. ananatis are unknown. In this study, we conducted a comprehensive screening across 982 Allium genotypes to evaluate resistance against P. ananatis. Only one A. cepa genotype, DPLD 19-39, demonstrated a consistent resistant phenotype by exhibiting lower foliar necrosis and bulb rot. Moreover, we also performed in vivo transcriptome sequencing and analysis of onion plants infected by P. ananatis under distinct conditions and identified several mis-regulated pathways involved with plant resistance, including cell wall reinforcement, oxidative stress regulation, and programmed cell death. Our findings indicate a potential mechanism for resistance against P. ananatis in A. cepa and suggest that future efforts should focus on these defense pathways to develop P. ananatis -resistant onion genotypes. Pseudomonas alliivorans, first identified on onion foliage in Georgia, has emerged as a pathogen that also infects cucurbits in Florida and Alabama (2020-2023). To assess whether P. alliivorans diversity is influenced by host and geographic locations, and to identify genetic traits related to host adaptability and pathogenicity, we conducted comparative genomics, pathogenicity and growth curve assays on filtered-onion juice for strains isolated from both hosts. The core proteome-based phylogeny revealed that P. alliivorans strains cluster according to their host of isolation and geographic location. Pathogenicity assays demonstrated that strains isolated from cucurbits (n=10) exhibited a wide range of symptoms on onion tissues; additionally, strains isolated from onions (n=40) could induce leaf spot on watermelon leaves. The allicin tolerance (alt)-like cluster, which confers bacterial tolerance to thiosulfinate ‘allicin’ in onion tissues particular in bulbs, was present in most of the onion strains. In contrast, all cucurbit strains lacked this gene cluster and displayed compromised growth in filtered half-strength onion juice, indicating its role in bacterial survival and growth in thiosulfinate-rich onion environment. This was further confirmed by the bacterium’s ability to induce bulb rot: approximately 80% of the onion isolates caused significant rotting of yellow onion bulbs and red scale necrosis, while less than 50% of the cucurbit isolates caused similar symptoms. Additionally, onion isolates were able to grow in half-strength onion juice at 25º C and 30º C whereas cucurbit isolates had compromised growth at these temperatures. Since onions and cucurbits are commonly grown in rotation in Georgia, we assessed whether P. alliivorans from either host could survive on crop debris. Both onion and cucurbit isolates could survive in cucurbit debris up to 72 h post-incorporation under greenhouse conditions. Moreover, isolates from both hosts survived better on cucurbit debris than on onion debris. Subsequently, onion seedlings exposed to P. alliivorans-contaminated cucurbit debris developed foliar symptoms, indicating a potential risk of cross-contamination between the two crops. Postharvest rots are major concern for Vidalia onion production in Georgia. Fungal rots due to black mold (Aspergillus niger) are common postharvest due to logistical delays. This results in extended suboptimal storage conditions prior to curing and refrigeration. Although not yet reported on onions, A. niger is also capable of producing mycotoxins such as ochratoxins and fumonisins. This study focuses on investigating the genetic diversity and mycotoxin production potential of Vidalia onion-associated Aspergillus section Nigri isolates. A total of 156 isolates were collected over two years from four locations within the Vidalia onion production zone of Georgia. PCR analysis on the first year’s 55 isolates revealed 42% had the fumonisin biosynthesis gene fum10 and 5% had the ochratoxin A gene ota1. Of the isolates with the fum10 gene, 70% were isolated from culls and only 1 also had ochratoxin genes amplified. Initial whole genome sequencing (WGS) studies of the first 55 isolates generated 35,717 SNPs using the A. niger KJC3 genome as reference. Structure and DAPC analyses revealed that isolates separated based on sample location and onion source. WGS is in progress for all isolates. Continuing analyses of the complete collection will focus on species identification, genomic structural variation, mycotoxin biosynthetic cluster comparisons, quantification of mycotoxin production, and fungicide sensitivity assays. Findings from this investigation will help develop informed extension recommendations to growers on methods of preventing black mold issues in postharvest storage. Idaho: <ol> <li>Determine the impact temperature and curing parameters on progress of Rahnella spp. in onion bulbs during storage. To determine the impact of temperature on bulb rot caused by Rahnella spp., bulbs were inoculated with Rahnella spp. and incubated at various temperatures (25, 30 and 35°C). Bulbs were assayed weekly to evaluate disease progress to determine how Rahnella spp. is impacted by temperature.  Bulb rot caused by Rahnella spp. is exacerbated by incubation time as bulb rot increased over time. It was observed that the bulb rot decreased as the temperature increased. To determine the impact of temperature and curing on bulb rot caused by Rahnella spp., bulbs will be inoculated with Rahnella spp.  and incubated at various temperatures (25, 30 and 35°C) bulbs were assayed weekly to evaluate disease progress and determine how Rahnella spp. is impacted by temperature.  Bulbs were cured at either 25, 30 or 35°C for each of two durations (2 days vs. 2 weeks) and placed in storage at 5°C.  Bulbs were cut down the center and evaluated for severity of storage rot after 4 and 6 months in storage.  A water-inoculated control treatment and a non-inoculated control treatment were included for comparison.  The amount of bulb rot observed was reduced at the higher temperatures for both the two day and two-week curing periods.</li> <li>Determine the genetic diversity present in Rahnella spp. and potentially identify the species of Rahnella isolated from infected onion in Idaho. Genetic characterization of Rahnella spp. included genomic DNA extraction. PCR amplification and sequencing of the 16S rRNA, gyrB, infB, rpoB, and atpD genes from the Idaho strains of Rahnella spp. Strains were obtained from onion bulb rot in the Treasure Valley. Phylogenetic analysis of these sequences along with the respective sequences downloaded from GenBank and analysis was completed using Geneious software. It appears that Rahnella aceris is the primary species present in the Tresure Valley along with R. perminowiae and R. aquatilis.</li> <li>Field plots were established to evaluate the relationship between soil temperature at bulb initiation and yield and bulb size at harvest. Treatments that cool the soil (straw mulch or Surround) increase yield and size, while treatments that heat the soil (biochar) have the opposite effect. The field treatments continue to have an effect after harvest. The biochar treatment resulted in an increase in decay after 3 months of storage.</li> <li>Field plots were established to evaluate a new group 7 fungicide from BASF (Tesaris) for pink root management. It appears to be as effective as Fontelis (another group 7) in suppressing disease when applied through drip at the 2-leaf stage.</li> </ol> New York: Using an intensive insecticide program (multiple weekly applications of methomyl [Lannate LV]) during the first half of the season significantly reduced thrips populations, symptoms of IYS, and incidence IYSV later in the season compared with those following a standard insecticide program. Bulb yields also were numerically greater in three of four field pairings treated with the intensive insecticide program compared with the standard program. The extra cost of the Lannate LV applications was minimal compared with the remarkable increases in profit from the higher yields. Twenty five fungicide treatments were evaluated for efficacy on Botrytis leaf blight (BLB) and Stemphylium leaf blight (SLB) in an on-farm small-plot trial. Each treatment was applied weekly for 7 weeks beginning at first onset of disease until 50-70% lodging. In the untreated, 41% of the plants “died standing up” due to BLB and SLB. At plant health assessments made 16 days after the last treatment, Amara (FRAC BM 02, a.i. Bacillus velenzensis), Badge (FRAC M1, copper bactericide), Velum Prime (FRAC 7, a.i. that is in Luna-brand fungicides), Miravis (FRAC 7, a.i. that is in Miravis brand products), Rampart (FRAC P07) and Tilt (FRAC 3, a.i. propiconazole) were not significantly different than the untreated and had only 0-8% green foliage/plot at this time. Proline (FRAC 3, a.i. prothioconazole) and Viathion (FRAC 3 a.i. tebuconazole + P07) + Tilt (FRAC 3) + Bravo (FRAC M5) had the healthiest plants in the trial with 68% and 63% green foliage/plot due. Green foliage increased by ~ 10% for every 2 additional sprays of FRAC P07 fungicide applied earlier in the spray program. Oso (FRAC 19) + Rampart (FRAC P07) + Bravo was as good as Viathon + Tilt + Bravo. There was a general trend that plant health improved as the number of products in the tank mix increased. Oso, FRAC P07 fungicides and double-product FRAC 3 combinations with Tilt were the only treatments with activity on SLB. BLB data analysis is underway.               As part of on-going monitoring of fungicide resistance, isolates of Stemphylium vesicarium were collected from NY onion fields and tested for sensitivity to DMI fungicide active ingredients propiconazole, tebuconazole and prothioconazole. Insensitivity of S. vesicarium to propiconazole continues to develop slowly over time.  The percentage of isolates of S. vesicarium with EC50 between 1-10 µg propiconazole/ml was 82.5% in 2024, compared to 94.8% in 2018.  The percentage of isolates of S. vesicarium with EC50>10.0 ug propiconazole/ml was 14.0% in 2024, compared to 1.0% in 2018. By contrast, insensitivity to tebuconazole has increased rapidly with the percentage of isolates of S. vesicarium with EC50>10.0 ug tebuconazole/ml being 4.1% in 2018, and 83.3% in 2024. The differences in the change in sensitivity do not seem to be related to use patterns, as fungicides containing either propiconazole or tebuconazole are utilized commonly in NY onion production.  Differences in the developmental rate of insensitivity are indicative of an incomplete cross resistance occurring between DMI active ingredients.  However, careful resistance management strategies are required in order to slow resistance development in all DMI’s.               Prothioconazole, a DMI active ingredient not registered for onion, was tested for the first time in 2024 and also displayed incomplete cross resistance to other DMI's.  In 2024, 67.1% of isolates of S. vesicarium were sensitive to prothioconazole with E50<1.0 ug/ml, compared to only 3.5% and 0% for propiconazole and tebuconazole respectively.  However, 6.4% of S. vesicarium isolates were highly insensitive (EC50>10 ug prothioconazole/ml), indicative of prior exposure of S. vesicarium in some fields perhaps through historical application to crops grown in rotation with onion.  This indicates that prothioconazole would require careful resistance management if it were to be registered for onion in the future. Oregon: Using data from field experiments conducted in the Tulelake Basin of California, Ordinary Least Squares regression was used to develop a model to improve understanding of factors that impact disease-free yield of onion produced in fields that have been naturally infected with the white rot pathogen Sclerotium cepivorum. Variables included fumigants, germination stimulants, fungicides, onion stand, and sclerotia counts. Onion stand at the two-to-four leaf stage served as a good predictor of disease-free yield. Findings indicated a significant positive relationship between stand and disease-free bulb yield. Treatment with fungicides applied in furrow at planting also had a significant and strong positive impact on disease free yield. Treatment with fumigants and germination stimulants did not have a significant impact on disease free yield. The responsiveness of yield to reductions in sclerotia populations was incremental; results indicated that every one percent decrease in sclerotia populations resulted in a 0.07 percent increase in disease free yield. None of the treatments in our analysis increased yields to the estimated 58.4 metric tons per hectare that would be required to break even on total production costs. However, the responsiveness of yield to fungicide use indicates that fungicides may be an economically viable component of future white rot integrated management programs. Natural products derived from Allium spp., such as garlic oil, garlic powder, and diallyl disulfide (DADS), are strong elicitors of sclerotia germination in the fungus Sclerotium cepivorum, the causal agent of Allium white rot. However, these compounds can also have broad antimicrobial activity against a wide range of bacteria, oomycetes, and other fungi when they are applied to soil. DADS was applied to two soil types and incubated under aerobic and anaerobic conditions. Metabarcodes for bacterial, fungal, and oomycete communities were analyzed to identify changes. A significant effect of DADS treatment on the overall compositions of bacterial, fungal, and oomycete communities was observed compared to the mock-inoculated treatment. Soil type and incubation conditions did not have a significant effect on soil microbial communities and significant interactions were not observed with DADS treatment in this study. These results suggest that potential changes in soil microbial communities should be considered when applying DADS to field soils. Pennsylvania: From the large multi-state survey conducted as part of the USDA NIFA SCRI Stop the Rot project, a previously undescribed Burkholderia species causing bulb rot in onion was identified in Pennsylvania and pathogenicity testing determined that both strains were pathogenic on onion. Based on their phenotypic, genotypic, and phylogenomic characteristics as well as comparative analysis, the two strains represent an uncharacterized Burkholderia species pathogenic to onion. This research was published in the journal Plant Disease as a First Look in Dec 2024 (<a href="https://doi.org/10.1094/PDIS-12-24-2675-SC">https://doi.org/10.1094/PDIS-12-24-2675-SC</a>). The phylogenic analysis using recA genes and disease severity assessment of 89 Burkholderia strains isolated from symptomatic onion leaves and bulbs in Pennsylvania and New York has been completed and the manuscript is in the final stages of preparation. Five Burkholderia species and two Paraburkholderia species were identified. Burkholderia cepacia and B. orbicola were predominant in New York, while B. gladioli was only identified in Pennsylvania. Interestingly, B. gladioli isolates were significantly more aggressive in whole bulb pathogenicity tests compared to all the other species identified. Additionally, a subset of Burkholderia strains from Pennsylvania and New York was selected for copper tolerance screening. In total, 116 Burkholderia strains were tested for copper tolerance using plate assays. Over 85% of the strains exhibited copper insensitivity at 200 ppm of copper sulfate pentahydrate in the plate assay. Utah: We conducted a small trial for Fusarium proliferatum to determine if we can get infection using inoculum in the soil. We were not able to. The only time we had successful infection was when the inoculum was applied to the neck. The resulting symptoms matched symptoms in the field. Washington: For the ‘Stop the Rot’ USDA NIFA SCRI Project No. 2019-51181-30013, we continued identifying and characterizing bacterial strains from a survey over 3 seasons in 11 states across the USA to determine the diversity and prevalence of bacteria associated with onion diseases. For the WA and CA strains, the WSU regional lab finished testing 100’s of isolates for pathogenicity to onion using scale, foliar, and bulb assays; and sequencing for genus and species identification. Results from 3 field trials in 2023-24 were finalized after rating bulbs in storage in Feb. 2024, to evaluate timing of topping onion bulbs, effect of chemigated vs. spray boom applications of pesticides on bacterial diseases, and postharvest application of disinfectants on control of bacterial bulb rots in storage. In the bactericide trial, five weekly applications of Badge SC, ManKocide, or Lifegard WG by chemigation or by spray boom did not have any effect on marketable bulb yield or the incidence of bulbs that developed bacterial rot. Spray boom applications of the two copper products, Badge and ManKocide resulted in significantly more phytotoxicity (injury) to the onion leaves than chemigated applications. The timing of topping trial demonstrated a very steep decrease in amount of bacterial bulb rot (at harvest + in storage) the lower the moisture content in the necks at the time of topping, i.e., the drier the necks at the time of topping, the lower the risk of bacterial bulb rot. For the trial evaluating postharvest applications of disinfectants to bulbs placed in storage, none of the disinfectants reduced the incidence of bacterial bulb rot, as demonstrated in the 3 previous years of trials. Field research trials also were carried out in 2024-25 to investigate the impacts of irrigation and nitrogen management on onion bacterial diseases. Results were presented at the Tri-Societies Annual Meeting in fall 2023 and fall 2024. Increasing N application rates increased total yield for the later-maturing cv. Calibra, not the earlier-maturing cv. Highlander, but also increased the incidence of bacterial bulb rot for Calibra. Conversations about these results will help producers understand the disadvantages of tailoring N application rates to maximize total bulb yield. The irrigation frequency trials demonstrated that longer and less frequent irrigation can reduce losses to bacterial bulb rots without reducing marketable yield.   Objective 4. Investigate the biology, epidemiology and management of weedy plant species that impact onion production. California: Robert Wilson researched alternative herbicide options to replace Dacthal for summer annual weed control in direct seeded onions. New Mexico: A post planting, delayed preemergence application of pendimethalin did not reduce onion stand or bulb yield and did not result in bulbs with pendimethalin residues greater than U.S. federal tolerances.  Compared to the nontreated control and preemergence applications of bensulide, a delayed preemergence application of pendimethalin reduced both densities of annual weeds and the amount of time for one individual to hand weed onion at 85 days after onion seeding.  These results suggest a delayed preemergence application of pendimethalin is a promising option for controlling annual weeds in New Mexico onion. New York: Two on-farm trials were conducted to evaluate late-season applications of preemergent herbicides for extended weed control through harvest. Yield data indicated that single, double and triple late-season applications of Dual Magnum and Prowl EC were safe on onion. Weed pressure was unfortunately very low, but data is trending that double-applications of Dual Magnum late mat reduce yellow nutsedge and pigweed at harvest. More studies are planned for 2025.

Publications

Publications (January 1, 2024 to December 30, 2024) 1. Publications in scientific journals de Jesus, H.I., Cassity-Duffey, K., Dutta, B., da Silva, A.L.B.R., Coolong, T. 2024. Influence of Soil Type and Temperature on Nitrogen Mineralization from Organic Fertilizers. Nitrogen 5: 47–61. <a href="https://doi.org/10.3390/nitrogen5010004">https://doi.org/10.3390/nitrogen5010004</a>. Greenway, G., B., Nault, S. Rondon, and S. Reitz. 2024. Extension impacts on onion IPM:  Current perspectives from the industry. The Journal of Extension, 62(3), Article 21. https://open.clemson.edu/joe/. Hua, G.K.H., Wilson, R.G., and Dung, J.K.S.. 2024. Evaluation of bait crops for the integrated management of white rot (Sclerotium cepivorum) in Allium crops. Plant Disease 108(1):118-124. https://doi.org/10.1094/PDIS-04-23-0688-RE. Hoepting, C.A, S.K. Caldwell and S.L. Mertson. 2024. Evaluation of fungicide tank mixes for control of Botrytis leaf blight and Stemphylium leaf blight in onion, Elba, NY, 2023. Plant Disease Management Reports, 18: V114. https://doi-org.proxy.library.cornell.edu/10.1094/PDMR18. Hoepting, C.A, S.K. Caldwell and S.L. Mertson. 2024. Evaluation of FRAC 3 fungicides for control of Botrytis leaf blight and Stemphylium leaf blight in onion, Elba, NY, 2023. Plant Disease Management Reports, 18: V114. https://doi-org.proxy.library.cornell.edu/10.1094/PDMR18. Hoepting, C.A, S.K. Caldwell and S.L. Mertson. 2024. Evaluation of FRAC 3 fungicides for control of Botrytis leaf blight and Stemphylium leaf blight in onion, Wolcott, NY, 2023. Plant Disease Management Reports, 18: V116. https://doi-org.proxy.library.cornell.edu/10.1094/PDMR18. Hoepting, C.A, S.K. Caldwell and S.L. Mertson. 2024. Evaluation of fungicide tank mixes for control of Botrytis leaf blight and Stemphylium leaf blight in onion, Wolcott, NY, 2023. Plant Disease Management Reports, 18: V118. https://doi-org.proxy.library.cornell.edu/10.1094/PDMR18. Hoepting, C.A. and S.K. Caldwell.  2024.  Effect of pulling onions early and fast curing with artificially heated forced air on a drying wall in a box storage on bacterial bulb rot in onion, 2023.  Plant Disease Management Reports, 18: V113. Hoepting, C.A., N.K. Gropp and S.K. Caldwell.  2024.  Evaluation of two phenotypic screening assays for bacterial bulb rot of onion, Elba, NY, 2022-2023.  Plant Disease Management Reports, 18: V112. Koirala, S. Shin, G. Y., Kvitko, B., and Dutta, B. 2024. Integrating biocontrol agents with copper for center rot management in onion. Crop Protection (in press) Komondy, L., M. Fuchs, and B. A. Nault. 2024. Localization of Iris yellow spot virus in naturally infected onion plants: A sampling approach for reliable diagnosis. Plant Health Progress https://doi.org/10.1094/PHP-05-24-0046-RS. Komondy, L., C. Hoepting, S. J. Pethybridge, M. Fuchs, and B. A. Nault. 2024. Development of a sequential sampling plan for classifying Thrips tabaci (Thysanoptera: Thripidae) populations in onion fields. J. Econ. Entomol. https://doi.org/10.1093/jee/toae161. Lenon, K.M., Dutta, B., Coma, M. Q., Johnson, W., and Schmidt, J. 2024. From weeds to natural enemies: implications of weed cultivation and biopesticides for organic onion production. Journal of Economic Entomology (in press) Liakos, C., Ibanez, V., Lebre, P.H., Derie, M.L., van der Waals, J., du Toit, L.J., Dutta, B., Kvitko, B., Cowan, D.A., and Coutinho, T.A. 2024. The bacterial and viral communities associated with onion bacterial bulb rot. Phytobiomes Journal: accepted 14 May 2024. Liakos, C., Ibanez, V., Lebre, P. H., Derie, M. L., Waals, J. L., duToit, L., Dutta, B., Kvitko, B., Cowan, D.A., and Coutinho, T.A. 2024. The bacterial and viral communities associated with onion bacterial bulb rot. Phytobiomes (in press). Paudel, S., Zhao, M., Dutta, B., and Kvitko, B. 2024. Thiosulfinate tolerance gene clusters are common features of Burkholderia onion pathogens. Molecular Plant Microbe Interactions (first look) (Editor’s Pick) Paudel, S., Franco, Y., Zhao, M., Dutta, B. , Kvitko, B.H. 2025. Distinct Virulence Mechanisms of Burkholderia gladioli in Onion Foliar and Bulb Scale Tissues. Molecular Plant-Microbe Interactions https://doi.org/10.1094/MPMI-10-24-0129-R. Paudel, S., Dutta, B., and Kvitko, B. 2024. Onion pathogenic Burkholderia species: Role and regulation of characterized virulence determinants. Plant Pathology (in press) Qian, Y., Hua, G.K.H., Dung, J.K.S., and Qian, M. 2024. Encapsulation of garlic oil and diallyl disulfide with β-cyclodextrin for white rot control in Allium crops. Crop Protection 178:106597. https://doi.org/10.1016/j.cropro.2024.106597. Racine, J., Nerney, A., Kilgore, S., Waters, T., Critzer, F., Harris, L. J., Reitz, S., and Waite-Cusic, J. 2024. Escherichia coli Survival on Dry Bulb Onions Treated with Crop Protection Sprays Prepared using Contaminated Water in the Treasure Valley Growing Region. Journal of Food Protection. 87: 100373 <a href="https://doi.org/10.1016/j.jfp.2024.100373">https://doi.org/10.1016/j.jfp.2024.100373</a>. Salgado, L. D., L. A. Rosen, O. Vetrovec, N. Hessler, P. Wang, A. G. Taylor, and B. A. Nault. 2025. Practical resistance to spinosad in an onion maggot (Diptera: Anthomyiidae) population in New York. J. Econ. Entomol., toaf057, https://doi.org/10.1093/jee/toaf057. Sharma, S. and C.S. Cramer. 2024. Validating single nucleotide polymorphism markers for Fusarium basal rot resistance in short-day onion cultivars through kompetitive allele-specific PCR. Crop Breed. Genet. Genom. 6(3):e240006. https://doi.org/10.20900/cbgg20240006. Sharma, S., S. Mandal, and C.S. Cramer. 2024. Recent advances in understanding and controlling Fusarium diseases of Alliums. Horticulturae 10:527. <a href="https://doi.org/10.3390/horticulturae10050527">https://doi.org/10.3390/horticulturae10050527</a>. Shin, G.Y., Asselin, J.A., Smith, A., Aegerter, B., Coutinho, T., Zhao, M., Dutta, B. , Mazzone, J., Neupane, R., Gugino, B., Hoepting, C., Khanal, M., Malla, S., Nischwitz, C., Sidhu, J., Burke, A.M., Davey, J., Uchanski, M., Derie, M.L., Toit, L.J.D., Stresow-Cortez, S., Bonasera, J.M., Stodghill, P., Kvitko, B. Plasmids encode and can mobilize onion pathogenicity in Pantoea agglomerans. The ISME Journal 19:1 Thapa S., du Toit L., Waters T., Derie M., Schacht B., and G.T. LaHue. Effects of irrigation frequency on onion bacterial bulb rot in the Columbia Basin of Washington State, 2023-24. Plant Disease Management Reports. 18:CF075. Thapa S., du Toit L., Waters T., Derie M., Schacht B., and G.T. LaHue. Effects of nitrogen management on onion bacterial bulb rot in the Columbia Basin of Washington State, 2023-24. Plant Disease Management Reports. 18:CF076. Valenzuela, M., MacLellan, M.P., Guajardo, J., Dorta, F., Seeger, M., and Dutta, B., 2024. First Report of Erwinia aphidicola causing bulb rot of Onion in Chile. Plant Disease 108(9): 2915. Wilson, R. G., Aegerter, B. J., & LaHue, G. (2024). The Influence of Sprinkler and Drip Irrigation on the Incidence and Severity of Bacterial Disease in Onions Grown in Northeast California. Plant Health Progress, PHP-01. <a href="https://doi.org/10.1094/PHP-01-24-0002-RS">https://doi.org/10.1094/PHP-01-24-0002-RS</a>   2. Abstracts and Papers at International/National Professional Meetings Komondy, L., and B. A. Nault. 2024 Improving onion thrips management: Developing machine learning-enhanced, spatially optimized sequential sampling plan. In Member Symposium: Metamorphosis- From John Henry Comstock Award Winners to Future Leaders in Entomology. Entomological Society of America Annual Meeting, Phoenix, AZ, November 12, 2024. Komondy, L., and B. A. Nault. 2024. Development of a sequential sampling plan for surveilling onion thrips in onion to reduce sampling effort involved in management decision-making. XXVII International Congress of Entomology, Kyoto, Japan. August 25–30. Komondy, L., and B. A. Nault. 2024. Optimizing early-season control of iris yellow spot virus transmission: A targeted spray program for enhanced efficacy against adult onion thrips. Entomological Society of America Eastern Branch Meeting, Morgantown, West Virginia, USA. March 10, 2024. (Note:  Awarded First Place in the Ph.D. Student Competition 10-minute paper). Neupane, R., J.D. Mazzone, C.A. Hoepting, B.K. Gugino. 2024. Peeling the rotten onion: A three-year bacterial survey of onion fields across Pennsylvania and New York. (Abstr.) Phytopathology 114:S1.148. Pineros-Guerrero, N., Hay, F. S., Heck, D. W., Klein, A., Hoepting, C., and Pethybridge, S. J. 2024. Determining the contribution of onion volunteers to the population genetics of Stemphylium vesicarium in New York, USA, using microsatellite markers. Proc. APS North-East Division Meeting, Ithaca, NY. Pp. 10. 6 March 2024. Salgado, L. D, A. G. Taylor, R. G. Wilson, and B. A. Nault. 2024. Performance of insecticide seed treatments for managing Delia spp. (Diptera: Anthomyiidae) in onion fields (poster). XXVII International Congress of Entomology, Kyoto, Japan. August 25–30.   3. Presentations at Grower Meetings and Field Days Cramer, C.S. Onion leaf wax and thrips feeding preference. 2024 NMSU Onion Research Workshop, Las Cruces, NM, 5 June 2024. Dung: Evaluation of Encapsulated Sclerotial Germination Stimulants for White Rot Management. California Garlic and Onion Symposium, 2024. February 12, 2024. Tulare, CA. du Toit, L.J. 2024. Soilborne plant disease control – Best practices. Invited presentation, Pest Management Session, Pacific Northwest Vegetable Association Annual Convention & Trade Show, 13-14 Nov. 2024, Kennewick, WA (~250 people) du Toit, L.J. 2024. Stop the Rot: Overview of the national onion bacterial project. Invited presentation, Onion Session, Pacific Northwest Vegetable Association Annual Convention & Trade Show, 13-14 Nov. 2024, Kennewick, WA (~250 people) du Toit, L.J. 2024. Stop the Rot: 2023-24 Trial results for Columbia Basin onion growers. Invited presentation, Onion Session, Pacific Northwest Vegetable Association Annual Convention & Trade Show, 13-14 Nov. 2024, Kennewick, WA (~250 people) du Toit, L.J. 2024. Black mold. Invited presentation to KORKOM onion growers’ association in Western Cape, South Africa. 20 Sep. 2024, online (35 people) du Toit, L.J. 2024. “Stop the Rot”: Grower-relevant results from a national onion bacterial project. Invited 2-h presentation and discussion with Wisconsin muck onion growers, 25 Mar. 2024, online, OR (10 people) du Toit, L.J. 2024. Conquering recalcitrant diseases using the art and science of plant pathology. Invited seminar to Dept. of Plant Pathology, The Ohio State University, 12 Feb. 2024, Columbus, OH. (~60 people) du Toit, L.J. 2024. Applied outcomes and practical solutions from emerging from the ‘Stop the Rot’ onion bacterial project. Invited presentation, Wisconsin Muck Farmers’ Association Annual Research Meeting and Wisconsin Potato and Vegetable Growers’ Annual Meeting, 7 Feb. 2024, online presentation. (22 people) du Toit, L.J. 2024. “Stop the Rot”: Grower-relevant results from a national onion bacterial project. Invited presentation, Annual Meeting of Idaho-Malheur Co. Onion Grower Association, 6 Feb. 2024, Ontario, OR (~150 people) du Toit, L.J. 2024. Stop the Rot: A national effort to minimize the impact of onion bacterial diseases. Invited presentation to vegetable seed industry personnel, followed by discussions on disease management in vegetable seed crops, 31 Jan. 2024, Oudtshoorn, South Africa. (70 people) du Toit, L.J. 2024. Stop the Rot: A national effort to minimize the impact of onion bacterial diseases. Invited presentation to du Toit Farms production team, followed by general discussion on onion disease management, 30 Jan. 2024, Ceres, South Africa. (20 people) du Toit, L.J. 2024. Stop the Rot: A national effort to minimize the impact of onion bacterial diseases. Invited presentation to KORKOM Onion Producers’, followed by general discussion on disease management in onion crops, 30 Jan. 2024, Ceres, South Africa. (25 people) du Toit, L.J. 2024. Stop the Rot: A national effort to minimize the impact of onion bacterial diseases. Invited presentation to Northern Cape Onion Producers’ Association, followed by general discussion on disease management in onion crops, 29 Jan. 2024, Kimberly, South Africa. (60 people) du Toit, L.J. 2024. Stop the Rot: A national effort to minimize the impact of onion bacterial diseases. Invited presentation to ZZ2 Farms production team, followed by general discussion on vegetable disease management, 27 Jan. 2024, Mooketsi, Limpopo Province, South Africa. (15 people) du Toit, L.J. 2024. Conquering recalcitrant diseases using the art and science of plant pathology. Keynote presentation, 53rd Congress of the Southern African Society of Plant Pathology, 22-25 Jan. 2024, Golden Gate National Park, South Africa. (150 people) du Toit, L.J. 2023. ‘Stop the Rot’ and other onion disease research at WSU. Invited presentation to AusVeg and HortInnovation meeting with onion growers/stakeholders in South Australia, 27 Nov. 2023, Murray Bridge, Australia. (35 people) du Toit, L.J. 2023. Stakeholder engagement in research and extension programming: An essential aspect of management recalcitrant plant diseases. Invited presentation, 2023 Conference of the Australasian Plant Pathology Society, Adelaide, Australia, 20-24 Nov. 2023. (~250 people) du Toit, L.J. 2023. Late season fungal and bacterial diseases of onion. Invited presentation, Onion Session, Pacific Northwest Vegetable Association Annual Convention & Trade Show, 15-16 Nov. 2023, Kennewick, WA. (~250 people) du Toit, L.J. 2023. Stemphylium leaf blight of onion – Biology and control. Invited presentation, Onion Session, Pacific Northwest Vegetable Association Annual Convention & Trade Show, 15-16 Nov. 2023, Kennewick, WA. (~250 people) du Toit, L.J. 2023. Environmental influences on plant diseases in the Pacific Northwest. Invited presentation, WSU Research Symptosium on “Integrated Pest Management in a Changing Climate”, Tilth Conference, 26-28 Oct. 2023, Port Townsend, WA. (~70 people) Field Day: Snake River Weed Control Tour, June 19, 2024. Ontario, OR. Field Day: Malheur Experiment Station Summer Field Day, July 10, 2024. Ontario, OR. Field Day: Malheur Experiment Station Onion Field Day, August 28, 2024. Ontario, OR. Hay, F.S., Hoepting, C., Grundberg, E., Klein, A.  2024.  Assessing and reducing the impact of plant-parasitic nematodes on onion production in New York.  Feb. 26, 2024.  Presentation to Onion Research Development Program Committee. Speaker, 20 minutes.  Attendees: 10. Hay, F.S. 2024.  Agriculture in New York State.  Invited speaker Onions, N.Z. Pukekohe Research Station, Pukekohe, New Zealand.  Jan. 17, 2024.  Speaker 20 minutes.  Attendees: 20. Hay, F.S., Hoepting, C., Heck, D., Klein, A., Pethybridge, S.J. 2024.  Stemphylium leaf blight – a continually evolving problem for onion growers in New York.  Invited speaker Onions, N.Z. Pukekohe Research Station, Pukekohe, New Zealand.  Jan 17, 2024. Speaker, 60 minutes.  Attendees: 20. Hay, F.S., Hoepting, C., Heck, D., Klein, A., Pethybridge, S.J. 2024.  Stemphylium leaf blight – a continually evolving problem for onion growers in New York.  Invited speaker Onions, N.Z. Ashburton Hotel.  Jan 19, 2024. Speaker, 60 minutes.  Attendees: 20. Hoepting, C.A. 2024. Finishing strong: Harvest practces that reduce bacterial bulb rot. Empire State Producers Expo, Syracuse, NY. January 24, 2024 (30 minutes) – 24 attendees. Hoepting, C.A. 2024. Managing Stemphylium leaf blight of onion with emerging fungicide resistance in New York. Wisconsin Onion Muck Meeting. Virtual Zoom: February 7, 2024 (30 minutes) – 22 attendees. Hoepting, C.A. 2024. Refining fungicide programs for Stemphylium leaf blight management in onion. Orange County Onion School. Pine Island, NY: February 28, 2024 (30 minutes) – 50 attendees. Hoepting, C.A. 2024. Stop the Rot Finale: Progress towards understanding and managing bacterial bulb rot in onion. Orange County Onion School. Pine Island, NY: February 28, 2024 (30 minutes) – 50 attendees. Hoepting, C.A. 2024. Preparing for Optogen herbicide in New York: A review of bicyclopyrone weed control in onion. Orange County Onion School. Pine Island, NY: February 28, 2024 (30 minutes) – 50 attendees. Hoepting, C.A. 2024. Stop the Rot Finale: Progress towards understanding and managing bacterial bulb rot in onion. Oswego Muck Onion Pre-Season Meeting, Phoenix, NY: March 20, 2024 (45 minutes) – 24 attendees. Hoepting, C.A. 2024. Stop the Rot Finale: Progress towards understanding and managing bacterial bulb rot in onion. Elba muck Onion Pre-Season Meeting, Elba, NY: March 29, 2024 (45 minutes) – 13 attendees. Hoepting, C.A. 2024. 2023 research highlights and new recommendations for Stemphylium leaf blight and Botrytis leaf blight in onion. Annual Muck Onion Twilight Meeting in Oswego Co. Oswego, NY: June 20, 2024 (45 minutes) – 69 attendees. Hoepting, C.A. 2024. Onion herbicide trial tour featuring pre- and post-emergent control of marsh yellowcress, Lamb’s quarters and ragweed2023 research highlights and new recommendations for Stemphylium leaf blight and Botrytis leaf blight in onion. Annual Muck Onion Twilight Meeting in Oswego Co. Oswego, NY: June 20, 2024 (60 minutes) – 69 attendees. LaHue, G.T., Thapa, S., du Toit, L.J., and Waters, T. 2024. Irrigation management impacts on onion bacterial bulb rot. WSU Onion Field Day, Prosser, WA, August 29th, 2024. Nault, B.A. 2024. Onion maggot management update. Oswego Onion Growers Winter Meeting. Oswego, NY. December 12, 2024. Speaker, 20 minutes. Attendees: 25. Nault, B. A., and L. Salgado. 2024. Onion insect pest management update featuring seed treatment combinations for onion maggot control. 2024 Muck Onion Growers Twilight Meeting in Oswego. Cornell Cooperative Extension, Cornell Vegetable Program. Oswego, NY. June 20, 2024. Speaker, 40 minutes. Attendees: 75. Nault, B.A. 2024. Controlling onion maggot with seed treatments. Muck Grower Information Days (Ontario, Canada). Virtual. April 4, 2024. Speaker, 25 min. Attendees: N/A Nault, B. A., and L. Komondy. 2024. Onion thrips and IYSV management update. Elba Onion Growers Preseason Meeting. Cornell Cooperative Extension, Cornell Vegetable Program. March 29, 2024. Speaker, 60 minutes. Attendees: 12. Nault, B. A. 2024. Seedcorn maggot, onion maggot, and onion thrips management updates for 2024. 2024 Orange County Onion School. Cornell Cooperative Extension Eastern New York Commercial Horticulture Program. Pine Island, NY. February 28, 2024. Speaker, 60 minutes. Attendees: 60. Nault, B.A. 2024. Insect management (Onion Session). Empire State Producer’s EXPO. New York Vegetable Growers Association. Syracuse, NY. January 24, 2024. Speaker, 30 minutes. Attendees:  35. Nault, B. A. 2024. Seeking alternatives to neonicotinoid insecticides for insect pest management in vegetable crops. New York State Agriculture and Markets Review of CALS Research. Geneva, NY, Speaker, 15 minutes.  Neupane, R.C, and Gugino, B. 2024. Peeling the rotten onion: Bacterial diseases and copper bactericides. Mid-Atlantic Fruits and Vegetable Growers Convention, 31 January 2024, Hershey, Pennsylvania.Putman, A.I. Evaluation of weather-based models for management of onion downy mildew. California Garlic and Onion Symposium, UC Cooperative Extension, February 12 2024, Tulare, CA. Putman, A.I. Downy mildew diseases of vegetables. Vegetable Production and IPM Workshop, UC Cooperative Extension Imperial County, February 28 2024, Imperial, CA. Putman, A.I. Overview of onion and garlic diseases. Onion and Garlic Production Meeting, UC Cooperative Extension Riverside County, October 17 2024, Blythe, CA. Reitz: Thrips Management and the Impact of Thrips on Stemphylium Leaf Blight  and Bulb Rots. Idaho-Malheur County Onion Growers Meeting, February 6, 2024. Ontario, OR. Reitz: What you cannot see is harming your onions: Wireworms, Maggots, and Bulb Mites. Idaho-Malheur County Onion Growers Meeting, February 6, 2024. Ontario, OR. Reitz: Onion Thrips Management in Dry Bulb Onions. Pacific Northwest Vegetable Association, November 13, 2024. Kennewick, WA. Schutte, B. Improving weed control programs for onions. 2024 NMSU Onion Research Workshop, Las Cruces, NM, 5 June 2024. Sharma, S. and C S. Cramer. Breeding for Fusarium basal rot resistance. 2024 NMSU Onion Research Workshop, Las Cruces, NM, 5 June 2024. Thapa, S., du Toit, L.J., Waters, T., and LaHue, G.T. 2024. Irrigation management: An inexpensive way to reduce the risk of bacterial rot of onions grown in the Columbia Basin of Washington State. Oral and poster presentation at the 2024 ASA, CSSA, SSSA International Annual Meeting, San Antonio, TX, November 12th, 2024. Thapa, S., du Toit, L.J., Waters, T., and LaHue, G.T. 2024. Stop the Rot: Revisiting nitrogen fertility practices in onion production in the context of bacterial diseases. Oral and poster presentation at the 2024 ASA, CSSA, SSSA International Annual Meeting, San Antonio, TX, November 11th, 2024. Thapa, S., du Toit, L.J., Waters, T., and LaHue, G.T. 2024. Nitrogen management impacts on onion bacterial bulb rot. WSU Onion Field Day, Prosser, WA, August 29th, 2024. Waters, T. D. 2024. Seedcorn Maggot Control in Onions. Pacific Northwest Vegetable Association Annual Meeting, Kennewick, WA. (November 13, 2024). Invited. Waters, T. D. 2024.  Potato and Onion Insect Management Update. Agrinorthwest Agronomy Update, AgriNorthwest Farms, Plymouth, WA. 14 Feb. 2024. Invited. Waters, T.D., and du Toit, L.J. 2023. ‘Stop the Rot’ onion bacterial project: Grower-relevant results. Invited presentation, Onion Session, Pacific Northwest Vegetable Association Annual Convention & Trade Show, 15-16 Nov. 2023, Kennewick, WA. (~250 people) Woodhall, J., Onion diseases update. Idaho Onion Growers Association and Malheur County Onion Growers Association conference. Ontario, OR. Feb. 6, 2024 Woodhall, J., Updates on Stemphylium leaf blight. Idaho Onion Growers Association and Malheur County Onion Growers Association conference. Ontario, OR. Feb. 6, 2024 Woodhall, J., Fungicide resistance. Idaho IPM webinar. 2024.   4. Newsletter Articles du Toit, L.J. Abnormal onion development from the wide temperature swing in April 2023, resembling herbicide injury. Veg Edge 20(13):5 (26 Jun. 2024). Hoepting, C.A. 2024. Controlling volunteer potato in onion: Start Early! Cornell Cooperative Extension – Cornell Vegetable Program Extension Grower newsletter, Veg Edge, 20(7): 1, 3-4 (cover story) (May 15, 2025). Hoepting, C.A. and F.S. Hay. 2024. Stemphylium leaf blight (SLB) of onion 2023 research highlights and implications for management in 2024: Part I – The FRAC 3 situation. Cornell Cooperative Extension – Cornell Vegetable Program Extension Grower newsletter, Veg Edge, 20(14): 8-10 (July 10, 2024). Hoepting, C.A. and F.S. Hay. 2024. Stemphylium leaf blight (SLB) of onion 2023 research highlights and implications for management in 2024: Part II – Piecing together tank mixes with low-risk mediocre products (FRAC M5, 2, 12, 19, P07). Cornell Cooperative Extension – Cornell Vegetable Program Extension Grower newsletter, Veg Edge, 20(15): 9-10 (July 17, 2024). Hoepting, C.A. and F.S. Hay. 2024. Botrytis leaf blight (BLB) necrotic spots of onion are driving us crazy! But they are important and can be controlled with fungicides. Cornell Cooperative Extension – Cornell Vegetable Program Extension Grower newsletter, Veg Edge, 20(16): 8-10 (July 24, 2024). Hoepting, C.A.  2024.  How much rot you got? Pre-harvest assessment of bacterial bulb rot in onion and management options.  Cornell Cooperative Extension – Cornell Vegetable Program newsletter, Veg Edge, 20(20): 6-8 (August 21, 2024). Neupane, R., J.D. Mazzone, and B.K. Gugino. 2024 Rotten to the Core: The Center Rot Disease of Onion. Penn State Extension. https://extension.psu.edu/rotten-to-the-core-the-center-rot-disease-of-onion   5. Other (e.g. Youtube videos etc.) Cumagun, C.J.R, Wood B., Woodhall, J.W., Onion quick facts. BUL1084. 2024. Cumagun, C.J., M. Thornton, S.R. Reitz, and J.W. Woodhall. 2024. Iris yellow spot virus: A threat to onion seed and bulb crops in Idaho. University of Idaho Extension. Dung, J., Scott, J., Qian, Y.P., and Qian, M. 2023. Evaluating Encapsulated Sclerotial Germination Stimulants for White Rot Management. Central Oregon Agricultural Research and Extension Center 2023 Annual Report:23-25. Greenway, G., B.A. Nault, S. Rondon, and S.R. Reitz. 2024. Extension Impacts on Onion IPM:  Current Perspectives from the Industry. Journal of Extension. 62(3), Article 21. https://open.clemson.edu/joe/vol62/iss3/21. Hoepting, C.A. 2024. Cornell onion (dry bulb) fungicide “Cheat Sheet” for control of leaf diseases in New York, 2024. Cheat Sheet: Cornell Cooperative Extension – Cornell Vegetable Program Website. Posted: July 1, 2024 (2 pages). https://cvp.cce.cornell.edu/submission.php?id=904&crumb=crops|crops|onions|crop*20. Hoepting, C.A. and S.K. Caldwell.  How to identify foliar symptoms of bacterial diseases in onion. 4:19 min.  Posted April 1, 2024: https://www.youtube.com/watch?v=pTYmdIwjbao. (893 views on May 9, 2025). Hoepting, C.A. 2023. Tour of on-farm onion fungicide trial for Botrytis leaf blight and Stemphylium leaf blight.  Elba, NY: August 20, 2024 (60 minutes) - 8 attendees. Neupane, R., and Gugino, B. 2024. Peeling the rotten onion: Bacterial diseases and copper bactericides. Proceedings of the Mid-Atlantic Fruits and Vegetable Growers Convention, 31 January 2024, Hershey, Pennsylvania. Neupane, R.C., “Bacterial diseases of onion and copper bactericides”. Food Science Institute, University of Debrecen, Hungary. October 21, 2024 Salgado, L. D., B. Nault and R. Wilson. 2024. Maggots-Be-Gone: An update on insecticide seed treatment performance. Onion World 40(8): 6-9. Wilson, R. et al. 2024. Insecticide Treatments to Protect Spring-Seeded Onions from Maggots. IREC Research Progress Report #206. Cooperative Extension, University of California, PO Box 850, Tulelake CA 96134

Impact Statements

California: Tulelake grower adoption of insecticide seed treatment for the management of seedcorn maggot has increased over 50% in the last five years. Use of chlorpyrifos dropped 100% while growers obtained improved suppression of seedcorn maggot compared to chlorpyrifos. Tulelake growers also have adopted irrigation management practices for reducing the severity of bacterial diseases.
Georgia: Onions with neck-length of 2-inches or more has become a common practice for Vidalia onion growers to reduce bacterial internal rot. This slight modification in harvesting practice has been widely adopted in Georgia and beyond. LifeGard is used in rotation with Copper products. A thrips management program is now a cornerstone for the center rot management used by both organic and conventional onion growers. Use of copper products have reduced to 15% (conservative estimates) in onions grown in Georgia.
New Mexico: Our research demonstrated that our evaluation method was successful in reliably producing disease symptoms which is essentially for disease resistance development. Germplasm has been developed that expresses lower disease severity as a result of selection. Our target audience can use this information and germplasm to develop disease resistant onion cultivars. A post planting, delayed preemergence application of pendimethalin could provide comparable or better control of annual weeds as currently used herbicides in autumn-sown and winter-sown onions in New Mexico while reducing herbicide costs by 92-95% ($99-$156/acre) and reducing the legacy costs on the environment by 74-88%. This simple switch could save the NM onion industry $1 million per year.
New York: 2024 Success Stories including the following: “Muck Onion Growers Enjoy Control of Troublesome Weeds with New Herbicide” Executive Summary Cornell Vegetable Program (CVP) Onion Specialist figured out how a new and novel herbicide, Optogen would be most beneficial in muck onion production and was instrumental in getting it registered for this use in New York. In 2024, on one farm, for every $1 spent on Optogen to control troublesome weed perennial sowthistle, they saved $13.64 in hand weeding expenses for a total of $48,650, which would have otherwise eaten up 7% of their profit. Issues/Needs and Audiences Herbicides are the first line of defense for weed control in muck-grown onion. Strategic programs include 5-8 applications of both pre- and post-emergent herbicides with five active ingredients that belong to 4 different modes of action. Despite this, ragweed and perennial sowthistle remained troublesome weeds that needed to be hand weeded at an added average expense of $250 per acre. Onions are one of the most valuable vegetable crops grown in New York with a farmgate value of $68.9 million in 2023. Pungent dry bulb cooking onions are grown predominantly on muck soils that are high in organic matter where production is unique and intensive. Approximately 165,000 tons are produced on 7,900 acres of which ~ 60% are produced on 16 farms within the CVP region. Extension Responses CVP Onion Specialist, Christy Hoepting helps her muck onion growers to improve their weed management through on-farm research trials including evaluation of pipeline products. She conducted her first experiment with the active ingredient bicyclopyrone in 2015. Although underwhelming when used alone, she noticed that it had post-emergent activity on ragweed. So, in 2016, she experimented with bicyclopyrone and several herbicide tank mix partners and discovered that bicyclopyrone + bromoxynil provided phenomenal control of ragweed while not hurting the onions. She consequently shared her results with Syngenta, the company that makes bicyclopyrone, and fortunately, they agreed to pursue the use of this herbicide in onion. Hoepting continued her collaboration with Syngenta and conducted another 25 on-farm onion herbicide trials with bicyclopyrone, which included both pre- and post-emergent applications, different rates, crop timings, spray volumes, tank mix partners and sequences. She studied the safety on the onion crop and evaluated the effectiveness of dozens of bicyclopyrone treatments for their ability to control 7 types of broadleaf weeds, 2 grasses, yellow nutsedge, and even volunteer potato and perennial sowthistle. It took Hoepting 4 years of trial and error and not giving up to figure out how bicyclopyrone could be helpful for controlling perennial sowthistle. The successful program included a tank mix of bicyclopyrone, which was to be followed by Stinger herbicide 2 weeks later. Hoepting kept the muck onion growers informed of her research developments regarding bicylopyrone and sought their input on the practicality of the use patterns she was proposing: From 2017 to 2024, she gave 10 tours of her herbicide trials and presented the research results at 7 winter educational meetings to 365 and 285 growers and allied industry representatives, respectively. Accomplishments and Impacts On May 17, 2024, the eager anticipation was lifted when bicyclopyrone was finally registered for use in onion in New York, under the trade name Optogen. The research data that Hoepting generated guided the use instructions for onion on the Optogen label. Optogen arrived in New York just in time for growers to use it to effectively control ragweed and perennial sowthistle. Hoepting advised them to be cautious as they tried for the first time a new herbicide with a completely different mode of action than anything they had used before in onion. In 2024, 4 out of the 6 farms in the CVP region where ragweed is troublesome were able to try Optogen + bromoxynil. All farms were impressed with the ability of this dynamic combination to control ragweed with 2 farms reporting nearly 100% control. None of these farms reported any issues with crop injury. Plans are in place for the all 6 farms to achieve near-100% control of ragweed with Optogen + bromoxynil in 2025. In 2024 in Elba, where perennial sowthistle is especially problematic, one grower successfully implemented Hoepting’s herbicide strategy with Optogen + bromoxynil and Stinger under her careful guidance. Eventually, 70 acres of heavily infested onion fields were treated. Although the treatment did not kill the thistle outright, it injured it so badly that it remained mostly inactive until the end of July, which allowed the onion crop to grow as if it were free of weeds. Thus, the grower decided to not hand weed the thistle. At the end of the season, it was estimated that the addition of Optogen + bromoxynil ($55/A) saved the grower $750/A in hand weeding expenses, because it would have taken 3-times longer than average to weed these heavily infested fields, for a total of $48,650 in savings, which would have otherwise eaten up 7% of their profit. For every $1/A invested in Optogen + bromoxynil herbicide treatment, $13.64/A was saved in hand weeding expenses. Collaborators: Larissa Smith, Syngenta Crop Protection “Just One More Trial” Yielded the Winning Insecticide “Trifecta” for Thrips Control in Onion” Onion thrips are tiny insect pests that feed on the leaves of onion plants. They also vector a destructive disease, iris yellow spot virus (IYSV). When uncontrolled the onion thrips/IYSV complex can reduce onion yields by 30-50%, costing growers $2,900 to $5,700 per acre. Thrips/IYSV is the worst in the Elba muck land, where over a million pounds of onions are produced annually, about 30% of the New York onion industry. Insecticides are the first line of defense for controlling onion thrips, and the growers diligently follow research-based recommendations developed by CVP Onion Specialist, Christy Hoepting and Cornell Entomologist, Brian Nault, to prevent insecticides from developing resistance. But in 2022, it looked like one of the top-performing insecticides, Radiant was starting to slip. According to data collected via the CVP Onion Scouting Program, Radiant could easily knock back high thrips populations of 3 to 6 onion thrips per leaf to below the spray threshold of 1 thrips/leaf. But in 2022, as an example, thrips increased from 1.7 to 4.2 thrips/leaf after two consecutive applications of Radiant. Was it because onion thrips were developing insecticide resistance to Radiant? Or was there another explanation? Hoepting was determined to get to the bottom if it. She devised a plan to track the effectiveness of Radiant across the 2023 growing season in the Elba muck through a series of on-farm research trials. Unfortunately, it was clear that thrips had indeed developed insecticide resistance to Radiant after Hoepting completed the first trial when the 1x and 1.5x rates had as many thrips as the nontreated controls and the 2x rate reduced thrips by only 50%. When Nault’s on-farm insecticide trial in Elba corroborated Hoepting’s results, she knew that she did not want to be facing the Elba muck onion growers in 2024 and not have a recommendation for an insecticide treatment to use instead of Radiant. So, she added “just one more” field trial to her plate at the end of the 2023 growing season. Hoepting’s last-ditch efforts paid off and she found a tank mix combination that was as good as the top-performing insecticides: Agri-Mek + Warrior + Lannate. Each of these insecticides belong to different modes of action than the other main insecticides used in the onion thrips management program, which is crucial for resistance management. Onion thrips were atrocious in 2024, and the Elba onion growers were thrilled with the effectiveness of Agri-Mek + Warrior + Lannate. It annihilated high populations of 4.2 to 7.8 thrips/leaf with reductions of 66-95% after one application and 97-99% after two applications. They nick-named Hoepting’s Radiant-replacement “Trifecta”.
Oregon: Results from these research and Extension projects have allowed growers to improve their pest management decisions and make more efficient use of pesticides. Encapsulated sclerotia germination stimulants are easier to apply and just as effective at reducing soilborne white rot inoculum than their non-encapsulated counterparts. The public benefits from access to more reliable and sustainable food supplies that have lower chemical inputs and reduced input costs.
Washington: Outreach to growers and onion industry stakeholders, field representatives and extension staff occurred through informal visits with growers, grower meetings, and field days. The ‘Stop the Rot’ video playlist contains videos for growers and the industry (https://www.youtube.com/playlist?list=PLajA3BBVyv1zf2obB16bNEdQPQeLW_XB_). Outreach and dissemination of preliminary results to onion stakeholders and the industry has been conducted through informational articles in trade publications and extension newsletters (see publications) and websites/online alerts. A new video on diagnosing onion bacterial diseases in the field was produced by C. Hoepting at Cornell Extension, with review/edits on the video provided by Tim Waters and Lindsey du Toit from WSU, and was posted on Alliumnet in April 2024. Growers have indicated they are incorporating recommendations from the trial results into their production practices, particularly late-season irrigation and cultural practices that minimize the risk of bacterial rots. Visits to the Alliumnet website with results from the project have increased significantly.