Brief Summary of Minutes of Annual Meeting

We had a meeting in Room 110D, Boise Centre West, Boise, ID on February 27 from 3 to 5 pm before the 2023 Western Society of Weed Science annual meeting. The discussions in the meeting were focused on these themes:

The Pacific Northwest Herbicide Resistance Initiative (PNW HRI).

The PNW HRI is a collaboration between USDA-ARS and 3 Land Grant Universities (University of Idaho, Oregon State University, and Washington State University)

The overall goals of the PNW HRI were discussed as well as opportunities for collaborative research around the initiative goals. Broadly, the initiative is focused on crop rotations and weed biology and ecology for managing herbicide resistance in the PNW.

Precision Ag and Remote Sensing in Weed Science

There were discussions on emerging technologies and practices for weed management that present collaborative opportunities for weed scientists in the region. Specific technologies or practices included:

• Weed IT sprayer, and how to better control grassy weeds
• Variable rate technology, weed mapping,
• Open-source libraries, firms selling services for mapping weeds.
• Target late season escapes – weed seed production.
• Weed ID between resistant and susceptible

Harvest Weed Seed Control (HWSC) research in the West

There were discussions on the opportunities and challenges with HWSC in the West. Specific issues or topics discussed included:

• PNW adoption – saving 1 glyphosate application.
• Farmer collaboration
• Issues with farmer adoption, chaff deck (Colorado), slow down of harvest in Idaho in wet years, hail (need to harvest asap), slopes in PNW
• Organic farmers may benefit.
• Need to estimate how much seed retention is needed for HWSC to be effective.
• Low seed retention on weed species
• Spring wheat tend to retain more seeds
• Remote sensing for collecting data – species level or broad groups
• Growers in PNW more interested in impact mills than chaff lining
• Funding – WIPM, WSARE,
• Wheat fallow rotation, maybe farmers could save one herbicide application.

There was a suggestion to create a sub-committee to work on HWSC.

Other research focus in the region

• Cover crops for weed suppression.
• Russian thistle dispersion –fences – community management

The potential to develop multi-state projects for research was also discussed.

Eric Westra was unanimously elected as the new secretary/chair-elect for next year. Consequently, Albert Adjesiwor will organize and conduct the 2024 meeting in Denver and Eric Westra will take notes and file the annual report.

1          State Reports

1.1         Idaho – Albert Adjesiwor, Joan Campbell, and Traci Rauch

Research

Objective 1. Results: Castle CL, Magic CL, and Sparrow winter wheat varieties with and without the safener ConcepIII were seeded at the U of I Moscow and Genesee farms in October 2021. Outlook and Dual Magnum were applied after seeding along with an untreated control. Outlook and Dual Magnum herbicides applied at a 2X rate post-plant preemergence caused substantial injury and yield reduction to all winter wheat varieties at both locations, however, injury was more severe at Moscow. Yield of all varieties was increased with safener at both locations. Tekoa, Net CL, Ryan, and Seahawk spring wheat varieties with and without the safener were seeded at the U of I Genesee farm in spring 2022. Zidua, Outlook, and Dual Magnum were applied after seeding along with an untreated control. Yield of all varieties and for all herbicides was increased with safener. Yield averaged over all herbicides and varieties was 70 and 51 bu/a with and without safener, respectively.

Objective 1. Outcomes/Impacts: Resistance to Group 1 and 2 herbicides used for annual grass control is a problem to farmers in the region. Annual grasses confirmed with resistance to these groups include Italian ryegrass, wild oat, downy brome, jointed goatgrass, windgrass and cereal rye. Safener-induced tolerance of winter wheat to Group 15 herbicides that cause injury to wheat but control these annual grasses could provide additional herbicides to address yield losses. Safener application to seed may be a tool to expand herbicide mode of action to aid herbicide-resistant weed management in wheat.

Objective 2. Results: Kerb was applied at 1.25 and 2.5 pt/a in fall and spring before planting spring canola, pea, chickpea and lentil at Moscow and Genesee. There was no injury to any of these crops. Winter wheat was planted in October 2021 to assess crop response. Wheat yield was reduced more with the high rate than the low rate at both locations. The very dry year in 2021 was not conducive to herbicide breakdown and the dry, hard soil in fall 2021 resulted in a very shallow planting depth. This experiment has been repeated and wheat was planted in October. No injury was evident after crop emergence fall 2022. In a second experiment, Kerb was applied prior to spring wheat planted at two depths. The shallow planting had more injury. This experiment is being repeated with winter wheat and no injury was evident fall 2022 at either depth.

Objective 2. Outcomes/Impacts:  Kerb is an old herbicide that is active on many grass (Italian ryegrass, downy brome, wild oat, jointed goatgrass, etc) and broadleaf weeds. Canola and pulse crops are tolerant to this herbicide. The following wheat crop must be tolerant to residual amounts of herbicide to obtain a label for these crops. Kerb would be an additional chemistry to help with control of some problematic weeds.

Objective 3. Results. Italian ryegrass seed was collected in the same locations as in a 2006/2007 herbicide-resistant survey. Italian ryegrass samples were collected in 2017-2019. Currently, 103 samples have been collected. Seed was collected by hand in the center of the infestation in each field. Seeds from each sample along with a known susceptible biotype are screened in the greenhouse against herbicides used to control Italian ryegrass. Untreated plants are included from each sample. All samples have been screened for Zidua, Dual Magnum, Outlook, Axiom, and Amber. No sample was resistant to Zidua or Outlook. Amber resistance is widespread at 91%. Axiom and Dual Magnum resistance is 20 and 10%, respectively.

Objective 3. Outcomes/Impacts. Identifying Italian ryegrass changes in herbicide resistance overtime aids growers in understanding how their weed control management practices, including tillage, crop, and herbicide rotation, have altered the makeup of the population.

Objective 4. Results: The 2 sites were taken over by downy brome. It is difficult to separate information on rattail fescue only. Downy brome was unaffected by any of the tillage treatments. Rattail fescue was reduced by tillage, but not eliminated with these treatments. Data over the length of the experiments will be summarized in the coming months.

Objective 4. Outcomes/Impacts: Knowledge of cultural controls, crop rotation and tillage is limited for rattail fescue control. Current information is speculative at best. Herbicide usage is the only known research-based tool for rattail fescue control in direct seed.

Objective 5. Results: A group 14 numbered compound from BASF was examined as a burndown herbicide in wheat. In a fall burndown application, cotyledon to 2 leaf prickly lettuce was controlled 91 to 99% with BASF compound plus glyphosate compared to 87% with glyphosate alone in November. By May, the highest BASF compound rate tended to have the best residual prickly lettuce control at 68%. A group 27 numbered compound from Corteva was examined for broadleaf weed control (Russian thistle) in wheat but was not evaluated due to a nonuniform weed stand. Crop tolerance was excellent. This compound with be evaluated additionally in 2023. Plant health chemicals, fungicides, and nutrients were also evaluated with and without herbicides.

Objective 5. Outcomes/Impacts: Examining tolerance and efficacy of newly registered and soon-to-be registered herbicides is critical to the development of unbiased information on the use of these products by Idaho wheat growers. Evaluating combinations of fungicides with herbicides for crop response and weed control is also important. This data assists in timely federal registration of new compounds. Herbicides with new and different modes of action are necessary to reduce or stop the development of herbicide-resistant weeds. The BASF compound is registered in Australia and may be a tool for possible control of herbicide-resistant broadleaf and grass weeds, especially Italian ryegrass. The Corteva compound is registered in corn in the USA and may be another option for broadleaf weed control.

Objective 6. Results: Suspected-resistant weed seed samples collected from research plots and submitted by growers, fieldmen, and industry representatives were screened in the greenhouse. The weed seed samples were sprayed with herbicides at twice the labeled rate. Susceptible plants were included to verify spray coverage. Seeds were counted at planting with preemergence herbicides and plants counted at emergence with postemergence herbicides. Untreated plants were included from each sample. Resistance was evaluated on plant survival and vigor compared to the untreated. One ventenata sample was screened to six herbicides. It was resistant to Beyond and susceptible to PowerFlex, Osprey Xtra, glyphosate, clethodim and Axial XL. One wild oat seed sample was screened with 7 herbicides. It was resistant to Assure II and susceptible to clethodim, glyphosate, Axial XL, Beyond, Osprey Xtra, and PowerFlex. One downy brome seed sample was screened to 6 herbicides. The sample was resistant to Beyond and susceptible to Zidua, metribuzin, Osprey Xtra, PowerFlex, and Aggressor.

Objective 6. Outcomes/Impacts: Screening weed seed samples enables growers to combat herbicide resistance by adjusting their weed control approach so that it includes rotating chemicals, changing crop rotations, and implementing other cultural practices.

Objective 7. Results: Project personnel participated virtually in cereal schools in north Idaho in January. Research information was presented at the Western Society of Weed Science meeting in March. Cereal research was also presented at field days in June and July.

Objective 7. Outcomes/Impacts: Information presented at cereal schools, field tours, and extension meetings will aid growers in making the best economic and ecological decisions for weed control in their wheat production systems.

Objective 8. Alternatives to glyphosate for pre-plant wheat control in wheat and barley cropping systems. Field experiments were conducted at the University of Idaho Research and Extension Centers in Kimberly Center and Aberdeen, Idaho in 2021 and 2022, to evaluate weed control, crop response, and economics of different herbicide programs. At Kimberly, the soil was a Portneuf silt loam (coarse-silty, mixed, superactive, mesic Durinodic Xeric Haplocalcids). The soil at Aberdeen was a Declo loam (Coarse-loamy, mixed, superactive, mesic Xeric Haplocalcids).

The wheat and barley studies were established side-by-side at each location. For each crop, there were 18 different herbicide and herbicide combination treatments, including the untreated check. Treatments were arranged in a randomized complete block with four replications. Each plot was approximately 3 m wide by 9 m long. Herbicides were applied using a CO₂-pressurized bicycle sprayer delivering 144 L ha^-1 at 207 kPa with TeeJet 11002DG nozzles on August 25th, 2021, and September 14th, 2022 in Kimberly, and September 2, 2021, and September 15th, 2022 in Aberdeen. At the time of herbicide application, the average weed heights in Kimberly in 2021 and 2022 were common lambsquarters (12, 3 cm), kochia (14, 3 cm), redroot pigweed (12, 3 cm), green foxtail (8, 3 cm). In Aberdeen, common lambsquarters, kochia, redroot pigweed, and green foxtail were about 3 to 6 cm tall in both years.

Each year and for each crop, weed control efficacy (by weed species) was visually assessed at 7 days and 14 days after treatment on a scale of 0 to 100%, with 0% being no weed control and 100% being complete weed control. Within 28 days after herbicide applications, winter wheat (“Brundage”) and winter barley (“Charles”) were planted at a rate of 112 kg ha^-1. In the spring of 2022 and 2023, visible crop injury was assessed on a scale of 0 to 100% with 0% being no crop injury and 100% being total crop destruction. Immediately following crop injury assessments, all plots were sprayed with post-emergence herbicides to control emerging weeds and eliminate or reduce competition from weeds. This was done to ensure that any growth or yield reduction was due to crop response to herbicides and not weed competition. The costs of the weed control programs were calculated using the average unit herbicide cost from local agrochemical dealers.

Objective 8. Results: Majority of the herbicide treatments applied alone or in mixtures provided weed control statistically similar to glyphosate. Glufosinate, paraquat, tiafenacil, and topramezone applied alone as well as the low rate of glyphosate provided less than 90% control of common lambsquarters. However, mixtures containing these herbicides provided very good (>90%) control of common lambsquarters. This demonstrates the importance of herbicide tank-mixtures for effective weed control. There was herbicide by location interaction effect on common lambsquarters control. This was possibly due to differences in weed size and weather conditions at the two locations.

Redroot pigweed control was also significantly influenced by herbicide and the herbicide by year by location interaction. The interaction effect of these factors on redroot pigweed control was due to weed size and weather condition differences across years and experimental sites. Only topramezone applied alone provided less weed control compared to glyphosate. All other herbicides, whether applied alone or in mixtures provided similar weed control as glyphosate. We can infer that almost all these treatments would be good preplant burndown treatments for a field that had a high population of redroot pigweed. Since redroot pigweed grows later in the growing season, having a burndown in the late summer to early fall is ideal, especially if redroot pigweed is a predominant weed in the field.

Nearly all herbicide treatments except for topramezone applied alone provide very good (>90%) control of kochia. Topramezone was the least effective herbicide for kochia control. Only around 50% kochia control was achieved with the topramezone treatment. Mixtures of topramezone with other herbicides provided better kochia control. There was no effect of year, location, or their interactions on kochia control.

One characteristic that makes glyphosate an ideal preplant burndown herbicide is its ability to control both grassy and broadleaf weeds. While there are multiple herbicide options for broadleaf weed control before or after planting small grains, grassy weed control remains very challenging. It was observed that glyphosate remains one of the best options for grassy weed control. Interestingly, green foxtail control was much more effective with topramezone compared to the broadleaf weeds. Nonetheless, the results showed that there are other effective alternatives to glyphosate for pre-plant grassy weed control. For example, glufosinate, paraquat, and their mixtures provided similar green foxtail control as glyphosate.

After herbicide treatments were applied, the wheat and barley were evaluated for crop injury to determine if the herbicide treatments were as safe as glyphosate treatments. No physical signs of herbicide damage were observed, and the growth of both the wheat and barley was observed as normal. Crop yield was evaluated in 2022, and there were no effects of herbicide treatments on wheat or barley yield. Wheat yield was 7,666 kg ha-1 in the untreated check and 6,927 to 8,877 kg ha-1 in the herbicide treatments. Barley yield was 8743 kg ha^-1 in the untreated check and 6,591 to 9,550 kg ha^-1 in the herbicide treatments. Visible injury evaluations in the spring of 2023 also showed that there were no injuries from the pre-plant herbicide applications. Thus, these herbicide alternatives have all been shown to be safe alternatives for pre-plant burndown weed control in these cereal crops.

The cost of the pre-plant herbicide programs was compared to the price of glyphosate due to glyphosate being the standard pre-plant burndown herbicide treatment that growers use for weed control. It is observed that there were at least six other treatments that may be economical alternatives to glyphosate for pre-plant weed control. The cheapest treatment was paraquat at $15.9 ha^-1 and depending on the weed species had between 85 to 99% control. This proves that there are indeed cheaper alternatives to glyphosate that still have high levels of control for all the weed species in this study. While more money might be spent on herbicide mixtures in the short term, there is a long-term benefit as a proactive herbicide resistance management strategy.

Objective 8. Outcomes/Impacts: These research findings were shared with Idaho Wheat and Barley Commissions through in-person meetings and recorded presentations. Results were also published on the Weeders of the West Blog and demonstrated at 2022 Snake River Weed Tour which was attended by nearly 100 stakeholders. The research aided in providing additional herbicide options to growers for pre-plant weed control to reduce reliance on glyphosate.

1.2         Washington – Drew J. Lyon and Ian C. Burke

Research

Evaluation of BAS 85101H for Russian thistle control in chemical fallow. A field study was conducted at the Lind Dryland Research Center near Lind, WA to assess BAS 85101H alone and in tank mix combinations with glyphosate for the control of Russian-thistle in chemical fallow. BAS 85101H is an herbicide in development by BASF Corporation. The soil at this site is a Ritzville silt loam with 1.3% organic matter and a pH of 5.6. The field was previously in winter wheat. The Russian-thistle population was uniform across the trial area but was at a low level of 12 plants per square yard. The plants ranged from 6 to 16 inches in diameter (mean = 9.0 inches) and a height that ranged from 2.5 to 10 inches (mean = 6.0 inches). Treatments were applied on June 30, 2022, with a CO2-powered backpack sprayer set to deliver 10 gpa at 47 psi at 2.3 mph. The applications were made at an air temperature of 86°F and relative humidity of 21%, and winds were out of the south at 8 mph. The station received 1.73 inches of rain in June (average = 0.78 inches), and 0.35 inches in July (average = 0.28 inches) following the herbicide applications. Air temperatures were not significantly different from the normal for this time. RoundUp PowerMax applied at either 16 or 22 fl oz/a did not control Russian thistle (Table). BAS 85101H, Sharpen and Reviton all showed quick-acting burndown on Russian thistle 7 days after treatment (DAT). Fourteen DAT, it was evident that Russian-thistle plants were recovering in the Sharpen- and Reviton-treated plots. This trend continued with these two treatments up to the final rating 27 DAT. BAS 85101H provided nearly complete control of Russian thistle through the final rating 27 DAT. The addition of RoundUp PowerMax at either rate, did not significantly change the level of Russian thistle control provided by BAS 85101H, Sharpen or Reviton as stand-alone treatments. With the above-average precipitation preceding the study, it was thought that the Russian thistle plants were not under significant drought stress and that glyphosate would provide acceptable control. It may have been that the glyphosate rates chosen in the study were too low to provide control. BAS 85101H really stood out in this study. Our hope is that this product will be brought to the market and provide another herbicide other than glyphosate or paraquat that will offer excellent control of Russian-thistle.

Pyroxasulfone for Downy Brome Control in Winter Wheat. The study objective was to evaluate pyroxasulfone with GA3 for downy brome (Bromus tectorum) control in winter wheat. GA3 is a plant growth regulator that stimulates seed germination and alleviates seed dormancy in laboratory and greenhouse conditions. The combination of pyroxasulfone and GA3 has potential to reduce downy brome seedbanks in winter wheat production systems. A study site was established at WSU Wilke Farm near Davenport, WA and downy brome populations were present at the time of study establishment. Preemergence applications of pyroxasulfone, pyroxasulfone with GA3, and pyroxasulfone with GA3 and metribuzin were applied to winter wheat in the fall of 2021 (table 1). Treatments were applied with a CO2-powered backpack sprayer and a 5-foot boom with four Teejet 11002VS nozzles. The sprayer was calibrated to 15 gallons per acre. The study was conducted in a randomized complete block design with four replications and plots were 10 ft wide by 30 ft long. Treatments were assessed by visual estimation of winter wheat density at 224 days after treatment with pyroxasulfone and downy brome density per m2 at 250 and 263 days after treatment with pyroxasulfone. All data were subjected to an analysis of variance using Agricultural Research Manager software system (ARM ver. 2022.7, Gylling Data Management). There was no difference in winter wheat density between treatments at 224 days after treatment with pyroxasulfone as a preemergence herbicide.

At 250 days after treatment, downy brome density per m² was reduced in all treatments (density ranged from 1 to 5 plants/m2) compared to the nontreated plots (15 plants/m²). Yield was similar among treatments and greater than the nontreated. GA3 did not affect downy brome control with pyroxasulfone, but pyroxasulfone was effective for reducing overall downy brome density in winter wheat.

Grower and industry awareness of herbicide resistance continued to increase in 2022 through a variety of presentations and articles in the popular press and through Timely Topic posts, the Weeders of the West Blog, and WSU Wheat Beat Podcast episodes on the Wheat and Small Grains Website. Growers were also provided with efficacy and crop safety information for newer herbicide products in wheat.

Kniss, A.R., Mosqueda, E.G., Lawrence, N.C., Adjesiwor, A.T. 2022. The cost of implementing effective herbicide mixtures for resistance management. Adv Weed Sci 2022; 40(spe1): e0202200119

Lyon, D.J., and M.E. Thorne. 2022. Smooth scouringrush (Equisetum laevigatum) control with glyphosate in Eastern Washington. Weed Technol. 36:457-461.

Spring, J.F, S.R. Revolinski, F.L. Young, D.J. Lyon, and I.C. Burke. 2022. Weak population differentiation and high diversity in Salsola tragus in the inland Pacific Northwest, USA. Pest Manag. Sci. 78:4728-4740.

Tautges, N. & Borrelli, K. & Goldberger, J. & Machado, S. & Fuerst, E.P. & Roberts, D. & Burke, I. C. (2022). Chapter 3 - Growing small grains organically in the semiarid West: A review of markets and management practices to optimize productivity and sustainability. Advances in Agronomy 171, 111-141. https://doi.org/10.1016/bs.agron.2021.10.005.

Revolinski, S.R., Maughan, P.J., Coleman, C.E. and Burke, I.C., 2023. Preadapted to adapt: underpinnings of adaptive plasticity revealed by the downy brome genome. Nature Communications (In Press)

Extension Publications and Proceedings:

Adjesiwor, A.T., D.J. Lyon, J. Barroso, and J.M. Campbell. 2022. Integrated management of wild oat in the Pacific Northwest. (PNW759).

Brunharo C, Barber T, Bond J, Brosnan J, Campbell J, Geddes C, Rana N, Stephenson D, Subramanian N, Bagavathiannan M, Pennsylvania State University; University of Arkansas; Mississippi State University; University of Tennessee; University of Idaho; Agriculture and Agri-Food Canada; Bayer Crop Science; Louisiana State University; Texas A&M University. 2022. Revised Herbicide Mode of Action Classification. Western Society of Weed Science. Page 30. https://wsweedscience.org/wp-content/uploads/WSWS-Proceedings-2022-v2.pdf 

Lyon, D, Barroso, J, Burke, I, & Campbell, J. 2022. Managing Herbicide-Resistant Annual Grass Weeds in Dryland Wheat Production Systems of the PNW [Abstract]. ASA, CSSA, SSSA International Annual Meeting, Baltimore, MD. https://scisoc.confex.com/scisoc/2022am/meetingapp.cgi/Paper/141977

Rauch, T.A and J. M. Campbell. 2022. Field Disturbance and Greenhouse Irrigation Effects on Italian Ryegrass Control with Pyroxasulfone. Western Soc. Weed Sci. Proceedings. 75:19.