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]

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.