Brief Summary of Minutes of Annual Meeting

We met at Hyatt Regency, Newport Beach, CA on March 6 from 3 to 5 pm before the 2022 Western Society of Weed Science annual meeting. The discussions in the meeting were focused on past and future research projects relevant to the region. The potential to develop multi-state projects for research was also discussed.

• Some of the specific topics covered were:
• Weed management using CoAXium wheat production system
• Seeding direction and weed management
• Harvest weed seed control (HWSC)
• Integrating cover crops and HWSC in western cropping systems
• Developing methods for weed science research
• Importance of doing dose-response studies
• Feral rye germination and genetic diversity studies to study climate change
• Importance of using reverse osmosis water for herbicide efficacy

1.  Selection of New Secretary/Chair-Elect

Albert Adjesiwor was nominated by Andrew Kniss and was unanimously elected as the new secretary/chair-elect for next year. Consequently, Lovreet Shergill will organize and conduct the 2023 meeting and Albert Adjesiwor will take notes and file the annual report.

1          State Reports

1.1         Montana – Lovreet S. Shergill

Research

Harvest weed seed control (HWSC) for weed management in wheat

Grain harvest presents an opportunity for non-chemical weed control. Concurrent maturation of crops and infesting weeds means that crop harvest can result in “harvesting” and subsequent redistribution of problematic weed seeds across the field. The retention of high proportions (> 70%) of total seed production at a height that ensures collection during crop harvest has been recorded for several weed in multiple crops including wheat. In this study, we test the least expensive and most easily implemented HWSC method, known as chaff lining, to determine its efficacy on downy brome in winter wheat using dryland crop rotation systems. We also determined seed retention of problematic weeds in winter and spring wheat cropping systems.

Objective 1. Determine chaff lining efficacy on downy brome: The experiment simulating wheat-fallow rotation designed as a factorial, strip-split-block design with 4 reps was initiated in fall 2020. Factors correspond to chaff levels i.e., no-chaff, low, and high (based on average low and high yield data across Montana), and management include untreated, fallow weed control (glyphosate application in summer), and planting (wheat planting at end of summer fallow). Chaff mixed with 500 downy brome seeds/m² was placed by hand between the crop stubble rows in 12 to 15-inch line width. Weed seed viability was evaluated by including 200 seeds/species in a mesh bag and placed between the soil surface and chaff monticule.

            No downy brome emergence was observed in fall 2020 and spring 2021. However, greatest downy brome emergence was observed in no chaff treatment irrespective of the management level. Lowest number of downy brome emerged at both timings in the low and high chaff treatments indicating the weed suppression ability of chaff presence. However, high chaff levels were more effective in suppressing downy brome compared to low and no chaff levels. The viability testing of the seeds recovered at the end of the experiment shows that high chaff level was effective in reducing the seed viability compared to low or no chaff levels. It was also observed that seeds were more deteriorated in high chaff treatments as compared to other treatments at the end of the experiment.

Objective 2. Determine weed seed retention at harvest: The field trials were established in randomized design at Southern Agricultural Research Center, Huntley, Montana. Dryland conditions were selected for both trials. In both trials, a minimum of 10 plants of each species were randomly selected to study seed shattering phenology. In spring wheat, only wild oats, and in winter wheat, only feral rye and downy brome were able to survive due to the dry season. The seeds of all three weed species were broadcasted uniformly across the trial before planting wheat. Wheat was planted at 8 inches (row spacing) and 2 inches depth with a commercial seeder. Seed traps were installed around the weed plants a week before wheat physiological maturity to capture shattered seeds. The shattered seeds were collected from traps at weekly intervals up to 28 days after wheat physiological maturity. Finally, we estimated per capita daily seed shattering rate and per capita daily cumulative seed shattering percentage up 28 days after wheat physiological maturity. These metrics are an indicator of how soon farmers should harvest the wheat after physiological maturity to be able to perform harvest weed seed control.

            In spring and winter wheat, seed shattering percentage increased over time. The seed shattering percentage of wild oats in spring wheat was <5% at physiological maturity, which was increased to 30%, 50%, 55%, and 60% at 7, 14, 21, and 28 days after physiological maturity, respectively. The lower seed shattering percentage at wheat physiological maturity makes wild oats a suitable candidate for harvest weed seed control in spring wheat. However, a timely harvest is necessary to capture maximum seeds due to the tendency of wild oats to shatter seeds rapidly over time. In winter wheat, seed shattering percentages ranged from 2 to 35% and 4 to 65% for feral rye and downy brome, respectively, over the tested period. Feral rye shattered 2% of seeds at wheat physiological maturity, which was reached at 17%, 30%, 35%, and 35% at 7, 14, 21, and 28 days, respectively, after physiological maturity. Seed shattering of downy brome was recorded around 4% at wheat physiological maturity, which gradually increased and reached 30%, 60%, 65%, and 65% at 7, 14, 21, and 28 days, respectively, after physiological maturity. Both weed species are suitable candidates for harvest weed seed control in winter wheat, considering their low seed shattering percentage at wheat physiological maturity. However, farmers need to harvest the wheat as early as possible after physiological maturity to capture maximum downy brome seeds due to its rapid seed shattering.

Impact: This is initial study to explore possibility of using HWSC to manage weeds in Montana cropping systems. The results were shared with growers and researchers through various in-person and virtual presentations and Agricultural Experiment Station Annual Research Report. This research was also demonstrated at 2021 MSU-SARC field day, which was attended by at least 90 people.

Herbicide strategies for grass and broadleaf weed control in spring wheat: Montana small grain producers are facing an ever-increasing challenge of managing herbicide-resistant weed species. Current weed control practices in spring wheat production rely on post-emergence (POST) herbicides to control annual weed species. The control of grass weed species in spring wheat is further complicated by having limited available herbicide options, from two mode-of-action (MOA) groups. Grass weed species resistance to group 1 or group 2 mode-of-action herbicides leaves wheat growers with highly limited herbicide options. Across several agricultural systems weeds have rapidly evolved resistance to POST than pre-emergence (PRE) herbicides. Therefore, there is a need to proactively develop weed management strategies that utilize PRE soil residual herbicides along with effective POST applied foliar herbicides.

            Our trials at two different locations (Huntley and Kalispell) showed that two-pass herbicide strategies (PRE followed by POST) provided better control over kochia and wild oats compared to onepass (only PRE or POST). Two two-pass herbicide strategies, such as glyphostate + saflufencil fb pinoxaden and pendimethalin fb pinoxaden proved to be the foremost in controlling kochia and wild oats at both research sites. In Huntley, two-pass strategies, such as glyphosate + pyroxasulfone fb pinoxaden and pyroxasulfone + carfentrazone-ethyl fb pinoxaden provided >95% and 100% control over kochia and wild oats, respectively. In Kalispell, two-pass strategies, such as glyphosate + pyroxasulfone fb pinoxaden and pyroxasulfone + carfentrazone-ethyl fb pinoxaden, displayed 100% control over kochia and wild oats; however, some other weed species, such as lambsquaters and pennycress, survived and produced trivial biomass. Regardless of its onepass nature, pyrasulfotole + bromoxynil octanoate + bromoxynil heptanoate + pinoxaden, provided 100% control at both research sites. No crop phytotoxicity was observed at both research sites; therefore, herbicide strategies did not influence grain yield despite enough weed pressure. This might be because of the dry season.

Impact: These research findings were shared with Montana wheat growers and research community through various in-person and virtual presentations and Agricultural Experiment Station Annual Research Report. This research was also demonstrated at 2021 MSU-SARC field day, which was attended by at least 90 people. The research aided in providing additional options for growers to manage broadleaf and grass weed control.

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

Research

Italian ryegrass seed shatter in spring wheat: Italian ryegrass (Lolium multiflorum) is a serious weedy threat to crop production in parts of the Pacific Northwest. In addition to high competitiveness with crops, it is now resistant to most herbicides that were once effective for its control. Another mechanism that has contributed to its persistence is the tendency for seeds to disarticulate (shatter) soon after seed maturity and well before crop harvest. This presents a problem as only seeds left on the plant potentially could be captured in the combine grain tank, or better yet, managed with a harvest weed seed control system. We began monitoring Italian ryegrass seed shatter rates on the Palouse in 2017 in winter wheat. Seed shatter in winter wheat averaged about 60% at harvest. We wanted to see if seed shatter rates are different in spring wheat. In 2020, two locations near Pullman, WA were selected. At each location, sampling began when it was evident that most of the florets had finished anthesis (flowering and seed set) and were filling seeds. Ten Italian ryegrass plants were randomly collected from a northeast facing slope, a draw bottom, and a southwest facing slope. Sampling occurred weekly until the wheat crop was ripe, and harvest had begun. From each plant, the number of tillers and spikelets per tiller were counted. In the first two weeks, a representative intact spikelet on each plant was removed from the stem and all florets counted to get an estimate of the potential number of seeds per spikelet if all florets filled; however, it was uncommon for all florets to fill. From all our collections, the total number of florets per spikelet consistently averaged around 12. Maximum floret fill occurred by July 27, but no statistical difference occurred between positions. By August 5, shatter was greatest on the southwest facing position and averaged 3.9 seeds per spikelet, which was a 49% shatter rate for that position. On August 12, seed shatter had significantly increased at all three positions with the southwest position having greater shatter than the northeast. By August 18, there was no statistical change in number of seeds per spikelet for each position, but the southwest position still had greater shatter (fewer seeds per spikelet) than the northwest position. By August 18, or harvest, the southwest position had a shatter rate of 75%, while the draw bottom and the northwest positions had shatter rates of 69 and 61%, respectively. If Italian ryegrass seed management is to be successful, strategies will be needed to collect or destroy the seed before a majority of the seed has shattered.

Impact Statement: Grower and industry awareness of herbicide resistance continued to increase in 2021 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 (smallgrains.wsu.edu). Growers were also provided with efficacy and crop safety information for newer herbicide products in wheat.

1.3         Idaho - Joan Campbell and Traci Rauch

Research

Objective 1. Results. A winter wheat/Italian ryegrass control study evaluated Zidua and Anthem Flex at the highest labeled rates with the following application times:  pre-fertilization, post fertilization, postplant no germination and postplant germinated wheat. Italian ryegrass population was very light and not uniform. Winter wheat yield was similar for all treatments including the untreated check. In another trial, fall or split applications of Zidua controlled Italian ryegrass 90% or better. Fall Zidua followed by spring Axiom controlled Italian ryegrass 93% compared to 82% with Axiom followed by spring Zidua.

Outcomes/Impacts: Zidua (group 15) was registered for annual grass control, including Italian ryegrass and rattail fescue, in winter and spring wheat in spring 2014. Zidua registration has aided in control of group 1 and 2 resistant Italian ryegrass. Very few herbicides control rattail fescue. Zidua and Anthem treatments controlled rattail fescue 89-97% in 2018. Winter wheat yield was not reduced by Zidua when 0.5 inch of sprinkler irrigation was applied immediately after planting a spraying on the same day (worst-case scenario). Wheat had minimal injury in 11 conventional-tilled (chisel plowed/field cultivated) sites and in seven direct-seed locations. U of I studies were instrumental in implementing Zidua label changes including an increased use rate and a preplant application time in winter wheat and rotational crops. These label changes have aided growers by giving them more options to improve weed efficacy. Anthem Flex also was registered in wheat fall 2014. Our Anthem Flex studies were useful to FMC when drafting initial rates and timings for their label and subsequent changes. This information will help growers use these products safely and effectively to control grass weeds with minimal crop injury. These registrations provide needed tools to help control herbicide resistant weeds, especially Italian ryegrass.

Objective 2. Results: Castle CL, Magic CL, and Sparrow winter wheat varieties with and without safener, fluxofenim, were seeded at the U of I Moscow and Genesee farms October 2020. Zidua, Outlook, and Dual Magnum were applied after seeding along with an untreated control. Outlook and Dual Magnum herbicides applied at a 3X rate postplant preemergence caused substantial injury and yield reduction to Sparrow and Magic CL winter wheat varieties at both locations, however injury was more severe at Moscow. Magic and Sparrow yield was increased with safener for Outlook and Dual Magnum at Genesee. At Moscow, Magic and Sparrow yield was increased with safener only for Dual Magnum. Castle CL showed a level of inherent tolerance. Castle yield at Genesee was actually higher in plots treated with Dual Magnum averaged over all safener treatments. Zidua applied at a 3X rate did not cause visual injury or yield effect to any variety at either location. Tekoa, Net CL, Ryan, and Seahawk spring wheat varieties with and without safener, fluxofenim, were seeded at the U of I Moscow and Genesee farms spring 2021. Zidua, Outlook, and Dual Magnum were applied after seeding along with an untreated control. No spring wheat variety was visibly injured by Outlook, Dual Magnum or Zidua at a 2X rate applied postplant preemergence at two locations. At Genesee, Ryan yield was lower than the nontreated with no safener and higher than the nontreated with safener for Dual Magnum only. Other variety-treatments combinations did not show any yield differences. No effect from safener was observed at Moscow.

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 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, 106 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. Due to limited greenhouse space, 58 sample screenings are still in progress for Zidua, Dual Magnum, Outlook, Axiom, and Amber. Currently, no sample is resistant to Zidua or Outlook. Amber resistance is widespread at 86%. Axiom and Dual Magnum resistance is 25 and 14%, respectively.

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: Tillage intensity and duration effects on rattail fescue is ongoing. Severe flooding killed winter wheat in 2019 and downy brome took over. The area is being reestablished to rattail fescue to continue the research.  Success of harvest weed seed control requires weed seed to enter the combine. All other seed will be available to grow the following season. Rattail fescue seed measured at 18 and 7.5 inch header cutting height was 5988 and 3447 seeds per sq foot, respectively. This only included seed still on the plant residue. More seed had shattered and was on the ground.

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. Tillage is important but research on how invasive and how often is unknown. Harvest weed seed control data can aid in reducing rattail fescue and other herbicide resistant weed populations. Harvest weed seed control may not provide substantial control for weeds that shatter seed, lodge, or grow low to the ground. This data will help growers take an integrated weed management approach to reducing rattail fescue and increasing crop yield.

Objective 5. Results: A group 14 numbered compound was examined as a burndown herbicide in wheat. A burndown application of the compound prior to planting spring wheat was confounded by volunteer winter wheat so Italian ryegrass control and crop response were not evaluated. In a fall burndown application, cotyledon to 2 leaf prickly lettuce was controlled 91 to 99% with this compound plus glyphosate compared to 87% with glyphosate alone. Winter wheat vigor and yield are being evaluated. This compound with be evaluated additionally in 2022.

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 numbered compound is registered in Australia and may an option for possible control of herbicide resistant broadleaf and grass weeds, especially Italian ryegrass.

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 blackgrass sample was screened to six herbicides. It was resistant to Beyond, Osprey Xtra, PowerFlex (group 2) and susceptible to glyphosate, clethodim and Axial XL. Three wild oat seed samples were screened with 8 herbicides. Samples were susceptible to clethodim, glyphosate and Axial XL Two samples were resistant to Osprey Xtra, PowerFlex, Everest, and Tacoma (fenoxaprop). One sample was resistant to Beyond. Eight downy brome seed samples were screened to 9 herbicides. All samples were susceptible to Zidua and metribuzin. Four samples were resistant to Osprey Xtra, PowerFlex, Outrider, Olympus and Beyond. Two samples were resistant to glyphosate. These were from a dryland continuous winter wheat rotation.

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. Due to COVID 19, other presentation opportunities were limited.

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.

1.4         Oklahoma – Misha Manuchehri

Research:

Tillage System Impact on Efficacy of Delayed Preemergence Herbicides in Winter Wheat

Delayed PRE herbicides can provide season-long Italian ryegrass (Lolium perenne L. ssp. multiflorum (Lam.) Husnot) control in Oklahoma winter wheat when applied at proper rates and incorporated successfully. Many producers use conventional tillage to prepare fields prior to planting but adoption of conservation and no-till acres is evident. However, crop residue in reduced tillage systems may reduce efficacy of delayed PRE herbicides. To evaluate how previous crop residue might impact DPRE herbicides in Oklahoma winter wheat, a trial was conducted at Perkins, OK during the 2019-20, 2020-21, and 2021-22 growing seasons. Herbicide treatments included metribuzin, pinoxaden, pyroxasulfone, and/or pyroxasulfone + carfentrazone-ethyl applied alone or in tank-mixture in no-till, conservation, and conventional tillage systems. Conservation tillage included a pass of a sweep plow set approximately 10 cm below the soil surface with subsequent rotary hoe action. Conventional tillage systems were disked twice with a tandem disk with a field cultivator following. Crop injury was observed in 2019-20 following pyroxasulfone + metribuzin. In 2019-20, visual ryegrass control prior to harvest was 97 to 99% following pinoxaden POST, pyroxasulfone alone or + carfentrazone-ethyl, pinoxaden, or metribuzin. In 2020-21, pinoxaden applied POST resulted in 100% visual control of ryegrass and 94% less biomass compared to the nontreated. Nontreated and pinoxaden applied DPRE had 98% more ryegrass biomass than any other treatment. In 2019-20, pyroxasulfone + metribuzin resulted in the highest yield, 9% and 22% more compared to pinoxaden DPRE and POST, and the nontreated, respectively. Tillage system affected wheat yield in 2019-20 and 2020-21. Yield decreased ~19% following conventional tillage in 2019 and decreased by ~29% following no-till in 2020 compared to other systems. Soil surface residue influenced by tillage did not affect the efficacy of DPRE herbicides in winter wheat but did affect overall grain yield.

Cheat Management in Winter Wheat

Cheat (Bromus secalinus) is a difficult-to-control winter annual Bromus species of the southern Great Plains. In past years, cheat has been documented to infest approximately 1.4 million hectares of harvested Oklahoma winter wheat. Biotypes cross-resistant to acetolactate synthase inhibiting herbicides have left growers with minimal management options in conventional and herbicide tolerant systems. Field trials conducted at Lahoma, Oklahoma in 2019-20 and 2020-21 evaluated integrated cheat management using a combination of three management strategies: planting date (optimal, mid-, and late), cultivar selection (one high- and one low-competitive cultivar), and two common herbicides (sulfosulfuron at 35.2 g ai ha^-1 and pyroxsulam at 18.4 g ai ha^-1). In 2019-20, eight to nine weeks after treatment, visual control increased 11% at mid-planting compared to the optimal and increased 14% at late planting compared to the mid-planting. In 2020-21, similar visual control (~99%) was recorded for mid- and late plantings with 23% greater control than the optimal timing. Cheat biomass during the 2019-20 growing season had no response to planting date, cultivar, or herbicide treatment. During 2020-21, biomass was low (≤ 0.2 g m^-2) and 98% less following an application of pyroxsulam or sulfosulfuron compared to nontreated controls. Winter wheat grain at the optimal planting was greatest compared to mid- and late plantings for both growing seasons. In 2019-20, a delay in planting from the optimal to mid- or late timings decreased grain yield up to 21%. In 2020-21, a planting date by herbicide interaction occurred. Delaying planting reduced grain yield, but an application of pyroxsulam or sulfosulfuron increased yield at the optimal planting, resulting in the greatest yields (~6,057 kg ha^-1). Pyroxsulam or sulfosulfuron provided a reduction in cheat biomass in 2020-21 but a delay in planting by two to six weeks after the optimal sowing window decreased overall grain yield.

CoAXium Wheat Varietal Tolerance to Quizalofop-P-ethyl

CoAXium Wheat Production Systems offers postemergence control of many annual grass weeds. However, in the state of Oklahoma, crop tolerance concerns have been raised by agricultural stakeholders. To evaluate the response of winter wheat varieties that contain the AXigen trait (tolerance to quizalofop-P-ethyl), a study was conducted at Perkins and Tipton, Oklahoma and Hays, Kansas during the 2020-21 and 2021-22 growing seasons. Varieties included AP18, Crescent, Fusion, Helix, and Photon. Two herbicide treatments, 1X rate (92 g a.i. ha^-1 of quizalofop-P-ethyl plus MSO at 1% vol/vol) and 2X rate (185 g a.i. ha^-1 of quizalofop-P-ethyl plus MSO at 2% vol/vol) were applied at three timings: fall (three to five-leaf wheat), early spring (first hollow stem), and late spring (second node detectable). The 2X rate was only applied in the 2021-22 season. For the 2020-2021 growing season at peak visual injury, AP18 exhibited the highest level of damage of 17%, 22%, and 51% at Hays, Perkins, and Tipton, respectively. A similar trend followed for the fall application of the 2021-2022 growing season, with AP18 exhibiting the highest damage (72%) at Perkins across both rates. At Hays, a variety by herbicide rate effect was observed when evaluating percent visual injury. The 2X rate applied to Crescent and Photon resulted in ~80% injury while varieties Fusion and Helix were only injured ~41%. At Tipton, a herbicide rate effect was observed where across all varieties, the 2X rate resulted in an average of 16% more injury than the 1X rate. When evaluating grain yield for the 2020-2021 growing season, a herbicide application timing effect was present at all locations. At Perkins, the early spring timing reduced yield up to 9% compared to the fall, late spring, and nontreated control. A similar trend was observed at Tipton where there was a 9% reduction in yield for the early spring timing compared to the fall. Lastly, at Hays, the late spring application reduced yield 16%, 7%, and 11% compared to nontreated, fall, and early spring, respectively.

Impacts: Group 15 herbicides are currently the only chemical tool to manage Italian ryegrass in Oklahoma winter wheat. When using a carrier volume of at least 15 gallons per acre, tillage system likely will not impact ryegrass control.

Pyroxsulam and sulfosulfuron are effective tools to manage ALS susceptible cheat. For ALS cross resistant biotypes, CoAXium wheat offers a short-term strategy while crop rotation offers a long-term strategy.

Early and late spring applications of quizalofop in CoAXium wheat can result in yield loss. Future research is currently being conducted regarding how CoAXium variety and environmental conditions impact crop response.

Adhikari, S., Revolinski, S. R., Eigenbrode, S. D., & Burke, I. C. (2021). Genetic diversity and population structure of a global invader Mayweed chamomile (Anthemis cotula): management implications. AoB Plants, 13. https://doi.org/10.1093/aobpla/plab049

Adhikari, S., Burke, I. C., Piaskowski, J., & Eigenbrode, S. D. (2021). Phenotypic trait variation in populations of a global invader Mayweed chamomile (Anthemis cotula): implications for weed management. Frontiers in Agronomy 3:29. https://doi.org/10.3389/fagro.2021.662375

Adhikari, S., Burke, I. C., Revolinski, S. R., Piaskowski, J., & Eigenbrode, S. D. (2021). Within-population trait variation in a globally invasive plant species Mayweed chamomile (Anthemis cotula): implications for future invasion and management. Frontiers in Agronomy, 3. https://doi.org/10.3389/fagro.2021.640208.

Dentzman, K., & Burke, I. C. (2021). Herbicide Resistance, Tillage, and Community Management in the Pacific Northwest. Sustainability, 13(4), 1937. https://doi.org/10.3390/su13041937.

Flessner, M., Burke, I. C., Dille, J., Everman, W., VanGessel, M., Tidemann, B., Manuchehri, M., Soltani, N, and Sikkema, P. (2021). Potential wheat yield loss due to weeds in the United States and Canada. Weed Technol, 1-8. doi:10.1017/wet.2021.78.

Lyon, D.J., J. Barroso, M.E. Thorne, J. Gourlie, and L.K. Lutcher. 2021. Russian thistle (Salsola tragus L.) control with soil-active herbicides in no-till fallow. Weed Technol. 35:547-553.

Rodriguez, J., Hauvermale, A., Carter, A., Zuger, R., & Burke, I. C. (2021). An ALA122THR substitution in the AHAS/ALS gene confers imazamox‐resistance in Aegilops cylindrica. Pest Manag Sci. 77:4583-4592. https://doi.org/10.1002/ps.6498.

San Martin, C., M.E. Thorne, J.A. Gourlie, D.J. Lyon, and J. Barroso. 2021. Seed retention of grass weeds at wheat harvest in the Pacific Northwest. Weed Sci. 69:238-246.

Raiyemo, D. A., J. M. Campbell, R. Ma, W. J. Price, T. A. Rauch, and T. S. Prather. 2021. Herbicide Safener Increases Weed-Management Tools for Control of Annual Grasses in Wheat. Weed Technology 35 (2) p.309.