Kniss developed the assignment into a user-friendly calculator thanks to funding from the Western Sugar Cooperative, which recognized the challenge that sugarbeet growers face when developing herbicide management plans. The Herbicide Resistance Risk Calculator helps farmers to develop a four-year crop rotation and herbicide management plan. The extended timeframe helps farmers understand how their actions in one growing season will affect the long-term herbicide resistance evolution in their fields. 

“If you are using multiple effective modes of action, that’s really good for delaying the evolution of resistance,” Kniss explains. 

To use the calculator:

The calculator then determines if your management plan contains multiple modes of action via a herbicide-resistance risk score, scaled from zero to four. 

A score of four indicates that only one herbicide mode of action was applied across all four years, and that a farmer has a high risk of developing herbicide resistance in their production. Spraying more than one effective site of action each year will reduce the risk score, and help farmers prevent herbicide resistance in their fields. Scores will break into decimals as herbicide modes of action are added to the management plan. 

Kniss explains that farmers should aim for a score lower than one. This target score indicates that a farmer deployed multiple effective modes of action against weeds across all four years. But know that the scores are just a rough visualization of your herbicide resistance risk. A score of 0.8 is not twice as likely as a score of 0.4 to develop herbicide resistance. 

A score of zero indicates that no effective site of action was applied.

The calculator also determines how well the management plan will suppress target weeds, and the plan’s average weed control costs. 

Farmers report that the calculator has been a useful and educational tool since its publication in 2020. Sugarbeet growers, especially, have realized that their previous herbicide programs didn’t utilize several modes of action, Kniss says. 

Kniss and fellow collaborator, Dr. Nevin Lawrence from the University of Nebraska Panhandle Research and Extension Center, update the calculator with regionally-relevant weed control efficacy and cost data annually. Kniss notes that the calculator was originally developed for sugarbeet producers in the High Plains regions. But the calculator’s design allows farmers nationwide to check their effective herbicide modes of action, though weed control and cost data might differ in their region. 

Kniss also reminds growers that using multiple effective modes of action is only one tool in the fight against herbicide resistance. “It’s important to understand that we’re not going to solve a problem created by herbicides by using more herbicides,” he states. “We can also think of non-chemical weed control as our second mode of action, whether that be crop rotations, planting dates, harvest dates, or even tillage.”

Explore GROW’s website for more information about managing herbicide resistance with integrated weed management.

Article and feature photo by Amy Sullivan, GROW; header photo by Claudio Rubione, GROW.

The resulting study found that hairy vetch and cereal rye are biomass-producing beasts, but it’s important to terminate your cover crop one or two weeks before planting corn, to avoid harming corn yield, according to Dr. Vijay Singh and then-Virginia Tech graduate student, Vipin Kumar.

The researchers pit four popular cover crops (hairy vetch, cereal rye, wheat, and rapeseed) head-to-head to understand how each would fare under different termination timings. Those timings included four weeks before planting, two weeks before planting, one week before planting, and at-planting. Researchers terminated cover crops via roll-crimping and the herbicide applications. 

Across all termination timings, Kumar and Singh found that hairy vetch reigned supreme at producing an average cover crop biomass of 4,479 pounds per acre. Cereal rye was the runner-up with 3,913 pounds per acre of biomass. 

Wheat had a biomass of 3,458 pounds per acre, and rapeseed came in last with just 2,297 pounds per acre of biomass. 

Rapeseed didn’t just accumulate little biomass, it also shrugged off termination. This cover crop only partially died 21 days after termination. Singh’s previous research has already studied rapeseed’s problem as a volunteer crop, and he emphasizes that poor termination could contribute to that volunteerism. 

Those results and corn considerations indicate one-to-two weeks before planting is a Goldilocks zone for cover crop termination that retains yields and suppresses weeds for mid-Atlantic growers.  

The highest corn yield in this study came from the hairy vetch cover crop terminated two weeks before planting (136 bushels per acre). Terminating cereal rye two weeks before planting also had the highest corn yield for that cover crop (118 bushels per acre). 

Terminating any of the cover crop species two weeks before planting resulted in 11% and 25% less grass and small-seeded broadleaf weed density compared to terminating four weeks before planting, respectively. 

“If we terminate cover crops late, like at the time of planting corn, we won’t be able to kill the cover crop well,” Singh explains of the late termination timing.

Terminating at planting could also make the cash and cover crops compete for nutrients, especially in droughts. That’s because it can take up to 12 days for cover crops to completely die after termination. Even that brief 12-day period can negatively impact your corn’s growth and yield. “If the corn isn’t healthy, what’s the point of managing weeds?” Singh asks. 

Singh and Kumar also demonstrated the power of integrated weed management in their study by combining cover crops with a standard pre- and postemergent herbicide regime. Researchers measured weed densities 28 days after corn planting, around the time when farmers would apply their postemergence herbicides, Singh says. “When you apply the postemergent herbicide, you are assuming that the cover crop has already done its work,” Singh explains. 

The cover crop and preemergent herbicide combo can handle weeds during the 28-day period after planting, and then postemergent herbicides can help pick up the slack.  

Singh sums his study’s findings into this recommendation: Choose a cover crop species with a booming biomass, and terminate around a week or two before corn planting to maximize your weed suppression and protect your corn yield. 

“We always suggest growers use integrated weed management approaches.” Singh recommends. “Don’t just use herbicides, use them with cover crops or other tillage practices to help control weeds effectively.” Virginia’s best-management-practices cost share program can help farmers implement cover crops and manage their price tags.

Explore GROW’s website for more information on cover crop management and termination. 

Article by Amy Sullivan, GROW; Header and feature photo by Claudio Rubione, GROW.

Results from the 2025 Weed Science Society of America (WSSA) broadleaf crops weed survey highlight the need for new herbicides and alternative weed management strategies. Those needs were revealed by comparing WSSA’s 2025 survey results with those obtained in 2022.

“Producers have continued to rely on the same herbicide chemistries for years to control problematic weeds,” says Matthew ‘Cole’ Woolard, Ph.D., WSSA Science Policy Fellow and Texas Tech University graduate assistant, who helped compile the survey results, along with Aleah-Butler Jones, WSSA Science Policy Fellow, a fourth-year Ph.D. candidate in horticultural biology at Cornell University. “Numerous weeds, such as Palmer amaranth, waterhemp, and kochia, have evolved resistance to herbicides that crop producers continue to rely on for weed control.”

WSSA’s Executive Director of Science Policy, Lee Van Wychen, coordinates WSSA’s weed survey every year. He distributed the 2025 online survey to all the members of the WSSA and its member affiliates in the U.S. and Canada, collecting responses during July and August 2025. Member affiliates include those from the Aquatic Plant Management Society (APMS); Canadian Weed Science Society (CWSS); North Central Weed Science Society (NCWSS); Northeastern Weed Science Society (NEWSS); Southern Weed Science Society (SWSS); and Western Society of Weed Science (WSWS).

“The 2025 survey results mirror the 2022 survey, indicating that we have not yet found any new weed management strategies that are effective on our most problematic and common weeds,” concludes Woolard. “These latest results are important for our researchers and farmers, because our key broadleaf crop weeds – pigweed species, common lambsquarters, kochia – remain problematic in fields.”

In WSSA’s 2025 survey, 347 members in 42 of the 50 U.S. states and seven of the Canadian provinces provided input. “This year’s responses also highlight our need for alternative herbicide chemistry or management strategies for the weeds that continue to be problematic annually,” emphasizes Woolard. “The weeds that continue to be the most common and most troublesome have evolved resistance or have limited control options. Therefore, we need to continue looking for alternative weed management strategies to fortify our conventional practices to control weeds.”

Researchers across North America are evaluating new technologies such as weed zappers, harvest weed-seed management products, weed flamers, and cover crops, among others, as tools that could be integrated into season-long weed management systems, notes Woolard. If these options prove viable, it will give producers additional tools to the current chemical options for weed control, he says.

The main results from the 2025 survey are as follows:

“We would like to thank all the member respondents for filling out the 2025 Most Common and Troublesome Weeds survey,” says Woolard. “These surveys help to provide milestones for weed management success and failure and to track weed population shifts over longer periods of time. It’s vital to continue this resource for future years.” 

To learn more about WSSA and its annual surveys, visit: https://wssa.net/weed/surveys/. For more information about WSSA’s 2025 broadleaf crops survey, visit this Excel link: https://wssa.net/wp-content/uploads/2025-Weed-Survey_Broadleaf-crops_pivotV1.xlsx, or this PowerPoint link that summarizes the top five most common and troublesome weeds for each crop: https://wssa.net/wp-content/uploads/2025-Broadleaf-Crops-Survey-Results.11.5.25.pptx.

Article by WSSA; Header and feature photo by Claudio Rubione, GROW.

Turning Canada thistle rust into a biocontrol agent was first envisioned over a century ago by a pioneer of American plant pathology, Dr. Byron Halsted. Two recent studies have now revealed that the fungus can nearly halve Canada thistle plant populations, and adding herbicide treatments can quicken and increase that control, according to researchers from the USDA, Colorado Department of Agriculture, and Utah State. 

But for now, this fungus can’t be found on store shelves. Instead, interested users must locate the fungus growing on Canada thistle plants in the field and then harvest, dry, crush, and spread the fungal spores themselves. 

Canada thistle weeds likely arrived in the U.S. by hitching a ride on ships from Europe and Asia in the 1600s. It has since spread from coast to coast and is mainly found in the northern U.S. How the Puccinia rust fungus got to North America is more of a mystery, but researchers do know that this fungus has eyes for only one plant – Canada thistle. 

The fungus’ onslaught begins when fungal spores attach themselves to Canada thistle leaves. Slowly, they invade the weed and its root system, stealing water and nutrients from Canada thistle. Aboveground, that process results in plants with stunted growth, no flowers, or wilting leaves. That deadly appetite for only Canada thistle plants makes the fungus a prime biocontrol agent for controlling this problematic weed. Several states and state universities, such as the Colorado Department of Agriculture and Montana State University, have information readily available for farmers and landowners to learn about using the rust fungus properly. 

Herbicides, mowing, and tillage are the traditional go-to methods for controlling Canada thistle. But these weed control methods only damage above-ground plant tissue. They rarely damage Canada thistle’s extensive root system. “[Canada thistle] gets into a place and then it really starts to spread, and a lot of that is happening underground,” explains Utah State’s Dr. Robert Schaeffer, an author on both studies.

Attacking that root system, though, is the rust fungus’ specialty. Schaeffer also notes that the rust’s complete reliance on Canada thistle means that this fungus has no non-target effects on the environment. 

Schaeffer and his team designed their two-year study with this multi-pronged attack in mind. They applied the rust fungus to Canada thistle 14 days after either spraying herbicides, mowing, or tilling the study plots – or combining all three. Schaeffer and his team used backpack sprayers to moisten the weeds with water so the spores would stick, and then tossed the ground fungus and leaves onto Canada thistle plants by hand. 

They found that using the fungus alone packed a punch. After two years it nearly halved Canada thistle plants when compared to the untreated control plots at the Utah study site. At the Colorado study site, the rust fungus reduced the plant population by 22% more than the untreated plots in that two-year period.

Combining the rust fungus with just tillage or mowing led to varying amounts of Canada thistle plants in the study plots. Schaeffer theorizes that tillage could actually help this hardy weed root itself in new locations. 

Herbicide treatments with or without the rust fungus resulted in the greatest Canada thistle control (over 90%). Combining herbicides with the rust fungus resulted in complete suppression of Canada thistle plants at each study site after two years.

In a resounding win for integrated weed management, stacking all control measures–herbicides, tillage, mowing, and the fungus–resulted in 95% suppression of Canada thistle plants after two years. 

Schaeffer theorizes that waiting more than two weeks after herbicides, mowing, or tillage to broadcast the fungus could help the fungus infect new shoots of Canada thistle.

Two years of sole fungus use nearly halved Canada thistle populations, but what about eight years? From 2014 to 2021, the same research team partnered with volunteers and private landowners to examine what happens to Canada thistle populations when only treated with Canada thistle rust fungus. Similar to that two-year study, researchers found that, on average, the rust halved Canada thistle populations at 77% of the study sites. The results indicate that long-term Canada thistle management is possible with just the rust. 

There’s more good news: Half of the 87 research sites only got one application of the thistle rust over the eight-year study. Re-applications only occurred when the site either showed no signs of successful infection from the previous year, or when variables such as livestock or wildfires damaged the sites. That suggests that one successful Canada thistle infection can last and spread for years to come. 

The rust fungus might be readily available to gather in a field near you, but there are some things to keep in mind when using this biological control agent. 

Gathering this fungus requires good eyesight, and an understanding of its complex life cycle.

The fungus’ most infectious stage comes via small, rust-colored spores on the underside of leaves–teliospores. These can be hard to spot, according to Bill Curran, a hay farmer and retired Penn State weed scientist who recently applied rust to Canada thistle for the first time. Curran is working with Dr. Tim Seipel, an Extension Cropland Weed Scientist at Montana State who has researched the rust fungus for several years.

The best way to identify Canada thistle rust fungus is to visit patches of Canada thistle in the spring. Keep your eyes peeled for leaves with bright orange undersides. When you spot the orange patches (uredinia spores), you’ve caught the fungus at an eye-catching and early point in its life cycle. Return to those same plants around September to find and gather the leaves with those rust-colored infectious teliospores. 

After gathering the leaves, you have to dry and blend them to create a fine powder of infectious fungus that’s ready to wage war against Canada thistle. Apply the fungus by hand (directly sprinkling onto Canada thistle or hand-tossing) to wet weeds in the late summer or early fall. The rust will have the best chance of germinating when applied early in the morning or late in the evening with temperatures between 55 and 64 degrees Fahrenheit.

“It’s a bit of a process for sure,” Schaeffer concedes. “I think that’s going to be one of the limitations to adoption…you can’t culture this on a petri dish.”

Once you’ve applied the fungus, the wait is on. It can take over a year for symptoms of the fungus to appear. And infection sometimes occurs just in the Canada thistle roots, resulting in no visible infection on plant leaves. Schaeffer noticed this in his two-year study, where many affected Canada thistle plants had little-to-no signs of uredinia or teliospores. 

Keep a close eye on the target plants and reapply the fungus each year if necessary. This biocontrol agent should spread each year until no Canada thistle remains. The fungus dies out once it no longer has a host. 

Next year, Curran plans to work with a Montana State Extension weed specialist to gain a better understanding of the Canada thistle rust fungus collection and preparation process. “It’s going to be a multi-year project, so I’m going to be learning a lot more as I go along,” Curran says. 

Curran isn’t the only farmer interested in applying rust to Canada thistle. The study authors say that farmers and ranchers in Colorado and surrounding states are also deploying this rust fungus to help control their own Canada thistle populations.

Explore GROW’s website for more information on Canada thistle, biocontrol, integrated weed management, and prevention. 

Article by Amy Sullivan, GROW; Feature photo by Tim Seipel and Dan Chichinsky, Montana State University; Header photo by Tim Seipel, Montana State University.

The workshop’s agenda, organized by the WiscWeeds team in partnership with Crops & Soils Extension Educators, covered a broad range of targeted spray topics, from weed control with targeted spray equipment to nozzle selection, herbicide spray coverage, and laser weeding. 

The workshop included 10 sponsor booths for attendees to visit throughout the event. GROW and Take Action, sponsored by the United Soybean Board, were among the organizations handing out informational materials on weed control and herbicide resistance. 

Workshop speakers included:

Attendees networked and competed head-to-head in weed identification and weed facts quizzes during the lunch break. Quiz winners received gifts from the workshop’s sponsors: John Deere, Ecorobotix, One Smart Spray, American Drone LLC, BASF, Bayer, Brandt, CHS, FMC, Syngenta, TeeJet Technologies, Valent, the Wisconsin Association of Professional Agricultural Consultants, the Wisconsin Corn Promotion Board, and the Wisconsin Soybean Marketing Board. 

After lunch, attendees heard a panel of two Wisconsin farmers and a co-op representative explain how they use precision sprayers in their operations, and their perceived benefits and limitations. 

The day ended with everyone climbing into trailers and heading into the field to watch demonstrations of the John Deere See and Spray, Ecorobotix ARA Ultra Precision, and One Smart Spray systems. 

Workshop attendees reported that this was one of the best educational events they attended. Attendees also noted that the information they gained will improve decisions made on their farms, or the farms that they advise. Be sure to keep your eyes peeled for the third annual weed management workshop in 2026! 

Explore GROW’s and Take Action’s website for more information on precision weed control, and to hear farmers talk about their own experiences with targeted spray technology. 

Article, header, and feature photo by Amy Sullivan, GROW.

Enter Dr. Steven Mirsky, a USDA-ARS researcher (and GROW co-founder), who has recently launched the Digital Agricultural Systems Hub (DASH), a new USDA platform that will help plant breeders and scientists turn their research and findings into real-world, deployable AI solutions for farmers.  Co-leaders of the system include USDA Computational Biologist Dr. Amanda Hulse-Kemp and NC State Plant Scientist Dr. Chris Reberg-Horton.

The first tools of this new platform include AgIR – the national Open-Access Plant Image Repository – built by public sector scientists around the country, and PlantMap3D, a modular camera system designed for both plant phenotyping and on-the-ground deployment on farming equipment for real-time biomass mapping and plant ID.

Mirsky was recently featured in a TEDx Talk, where he explained why USDA is well situated to take on the challenge of leading agriculture into the digital revolution. Watch it below!

Visit the DASH website here and learn more about Dr. Mirsky’s work from GROW here. 

Text and feature photo by Emily Unglesbee, GROW; banner image by Ubaldo Torres, Texas A&M

Do you know how many different modes of action are in your spray tank this fall? How about next spring’s burndown application, or the postemergence pass you’ll need to tackle your summer annual weeds?

If you answered no, you need the 2026 Take Action Herbicide Classification chart. If you answered yes, you still need it – to check your math! 

That’s because simply rotating herbicide products or tank mixing multiple products doesn’t mean you are automatically using multiple modes of action. Commercially branded herbicide premixes may have different names but contain the same active ingredients – and many active ingredients share the same herbicide site of action group. Getting it right matters, because rotating modes of action is a critical component of the fight against rising herbicide resistance.

It’s a complicated landscape for farmers, and products can change every year. That’s why the United Soybean Board sponsors the annually updated Herbicide Classification chart, through its farmer-focused Take Action Herbicide-Resistance Management program. Created and updated by Michigan State University weed scientist Dr. Christy Sprague, the chart helps farmers sort through all commercially available herbicides in the major row crops to learn exactly what active ingredients they contain – and what modes of action each one represents. 

The chart is broken down into two reader-friendly sections: 

The chart is a powerful tool for an industry facing a growing epidemic of weeds with resistance to one or more herbicide sites of action. Use it every year to help craft a herbicide program that incorporates multiple herbicide modes of action within tank mixes and across seasons.

Thanks to the soy checkoff’s sponsorship of Take Action, the Herbicide Classification chart is available for free print orders, up to a certain amount.

You can place your order here. Looking to stock up for the rapidly approaching winter meeting season? Order soon, to give plenty of time for your charts to arrive!

Text and photo graphics by Emily Unglesbee, GROW

The new webpage series starts with a main page that serves as a one-stop shop for everything HWSC. It covers a range of topics, including:

The two most common HWSC methods, chaff lining and seed impact mills, also have their own new webpages within the series. These pages give an in-depth look at how these two HWSC methods work and their method-specific variables. 

Visit GROW’s new Harvest Weed Seed Control webpage today to learn how these tools might fit your own farming operation and address your herbicide-resistant weed problems.

Do you use harvest weed seed control, or do you have questions about this weed control tactic? Let us know! And be sure to explore GROW’s Farmer Forum webpage and GROW Farmer Case Studies to see farmers discuss their own harvest weed seed control experiences. 

Article by Amy Sullivan, GROW; Header and feature photos by Claudio Rubione.

“Producers are more open to trying things that they’re normally not interested in because they are running out of other options,” Tidemann explains. “So there’s more interest in out-of-the-box ideas for dealing with [wild oat].” 

Her three-year study revealed that rotations with early-maturing crops halved wild oat populations. She also found that harvesting those early-maturing crops via swathing or straight-cutting could help keep weed seeds from returning to the seedbank, if combined with harvest weed seed control tactics like seed impact mills. But Tidemann warns of the logistical challenges like weather that can impact early-maturing crop rotations.

Earlier research from Tidemann found that harvest weed seed control can’t fully control wild oat because the weed’s seeds shatter (drop from the weed) before the region’s typical crops of spring wheat and canola are harvested. Then an idea struck her, she recalls: “We keep saying wild oat seed is shed before we harvest… what if we harvested earlier?” 

From that thought came the three different crop rotations for her three-year study: 

The rotations with early-maturing crops consistently had 50% fewer wild oat plants than the other crop rotations. Tidemann theorizes that this could be due to crop competition, as fall-seeded cereals such as winter wheat compete with wild oats by emerging earlier and capitalizing on nutrient and moisture intake. 

Tidemann also examined how harvesting both crops in each rotation through swathing or straight-cutting affected wild oat plants and their seeds. She thought that swathing the crops to lay in windrows and dry before going through the combine might retain weed seeds within the windrow and allow them to reach the combine. Straight cutting – when farmers cut and combine crops at the same time – is a newer method that has become popular in the Canadian Prairies and also warranted research. Once in the combine, the grains or legumes are separated (threshed) from their stalks, and the stalks become chaff. 

The research found that neither swathing nor straight-cutting resulted in consistently fewer wild oat plants in the ensuing study years. Swathing seemed to help a few more seeds be captured as populations were lower in some study locations, but this effect was minor compared to the rotation of early-maturing crops. 

“Having any impact on the weed seedbank was exciting,” Tidemann says. “When the seeds can live there for over five years, it’s nice to be able to have an effect!” 

Canadian Prairie farmers will need to have a seed impact mill installed on their combine after swathing or straight-cutting to kill the weed seeds passing through the combine, Tidemann notes, or be willing to capture the seeds with something like a chaff cart. Early-maturing crops improve harvest weed seed control efficacy, but without using a harvest weed seed control method, those weed seeds aren’t being killed. More research is needed to determine if early harvests with swathing or straight-cutting captured more weed seeds than normally-timed harvests.

Managing rotations of early-maturing crops can be one of the largest hurdles in implementing this cropping system, Tidemann acknowledges. 

The major concern is weather, particularly over-winter survival or winterkill events. Events such as drought can reduce or delay fall emergence, and limited snow cover in extreme cold temperatures can cause crop failure due to winterkill. Spring cereals are more common in the Canadian Prairies because winter cereals have a higher risk of winterkill.

Understanding weather patterns, the associated risk, and how early-maturing crops fit into your production is key to making this system work. 

For even more robust wild oat control, farmers could potentially pair crops that mature earlier with other weed management tactics such as harvest weed seed control, the few remaining herbicides effective against wild oat, and increased seeding rates, Tidemann adds. She didn’t use any wild oat herbicides in this study, and Tidemann anticipates that using these herbicides would further improve control. 

Ultimately, there isn’t a simple, reliable prescription that farmers can follow to reduce weeds in their fields, Tidemann says. Herbicide-resistant weeds such as wild oat require treatment on a case-by-case basis, which could come in the form of crop rotations for one field and increased seeding rates for another field. “We’re at a point where we need to be thinking beyond herbicides,” Tidemann says. “We’re being forced into that.”

Article by Amy Sullivan, GROW; Feature photo by Claudio Rubione; Header photo by Virginia Tech Weed ID.

Chu found that cotton production meets the power and moisture requirements to operate a seed impact mill, and that the impact mill crushed over 98% of weed seeds from gin and bur trash beyond viability. But a post-harvest implement like a flail forage mower is needed to catch any weed seeds left on plants after harvest. Equipment logistics also remain a hurdle – if seed impact mills were engineered to outfit cotton harvesters and gins, they might grant farmers more options when it comes to weed control in their cotton productions, Chu concludes. 

The questions Chu sought to answer all came down to the different types of cotton crop residues, known as “trash,” which emerge from a cotton harvester and would be processed by a seed impact mill. 

The different trash types result from the different goals of each harvester. Cotton pickers guide rows of cotton towards vertically rotating heads containing barbed spikes. These barbed spikes only grab seed cotton from the plant as it passes through the cotton picker head. Cotton strippers operate similarly to pickers, but with horizontally spinning rollers that strip plants of their cotton bolls, leaves, and sticks. The cotton stripper then separates the seed cotton from the excess vegetation. Cotton strippers are most commonly used in dry areas where harsh weather conditions require farmers to harvest quickly. 

Once seed cotton has been harvested by a picker or stripper, a cotton gin separates the cotton lint from the cotton seed and any remaining plant trash. 

In general, cotton stripper trash (sometimes called bur debris) is much bulkier than cotton gin trash (sometimes called gin debris).

Flail forage mowers are used by cotton farmers to cut down cotton stalks after harvest with a cotton picker. While this was the only mower examined in this research, farmers can use any mower for this task. Flail forage mower trash is largely stalks and weeds (sometimes called trash-stem debris).

Chu began this project in fall 2023 by teaming up with Dr. Michael Walsh who was in Texas on a Fulbright Scholarship. The pair set out to find where Palmer amaranth and waterhemp seeds fell during harvest with cotton strippers and pickers, Chu recalls. 

Their research found that 52% of seeds hitched a ride with the seed cotton, and 15% of seeds remained on the weeds after harvest with a cotton stripper. But with over 80% of weed seeds remaining on their plants after harvest with a cotton picker, Chu’s research had to pivot. Instead of looking at the seed impact mill’s effectiveness with cotton strippers and pickers, she looked to evaluate the impact mill’s effectiveness in cotton strippers, flail forage mowers, and cotton gins. 

Previous research at the University of Arkansas already confirmed the presence of several species of weed seeds in cotton gin trash, including palmer amaranth and barnyardgrass. These weeds were also found to be viable for up to two years after the gin trash had been composted. And since cotton gins are the final step in processing seed cotton into lint, they’re also the final chance to target weed seeds. 

Chu’s revised research targets posed another hurdle: Was it even possible to operate the seed impact mill with each trash type when the impact mills were designed for small grain productions?

Cotton strippers and gins seemed like a good match for seed impact mills since so many weed seeds end up in their trash. And the findings agreed. 

Over 98% of the weed species observed in cotton stripper and cotton gin trash–Texas millet, sicklepod, prickly sida, Palmer amaranth, morningglory, large crabgrass, and barnyardgrass–were pulverized by a stationary Harrington Seed Destructor impact mill. 

The cotton picker’s selectiveness meant that just 7% of weed seeds made it into the combine and 85% of weed seeds remained on the weeds after harvest. Combining a post-harvest weed control method like the flail forage mower with the seed impact mill might be able to target the weed seeds still left on plants. However, more research is needed to test that theory. 

The seed impact mill couldn’t handle flail forage mower trash when it was too wet (29% moisture). This trash repeatedly clogged the impact mill and made weed seed viability analysis impossible. Chu’s findings align with previous impact mill research in soybean and rice where over 16% chaff moisture clogged the mill. The cotton bur and gin debris had less than 10% moisture. 

That doesn’t mean that the flail forage mower isn’t a contender for harvest weed seed control.  “If we could figure out a way to decrease that moisture, it might work then,” Chu says. One potential option would be to use the flail forage mower after giving the weeds and cotton plants more time to dry out. 

The results were unexpected, but promising. The seed impact mill was able to easily terminate weed seeds regardless of gin or bur trash bulkiness, and trash moisture is an obstacle that could be overcome. (Watch the GROW video below to see what Chu’s research process looked like for this part of the study). 

Chu also found that operating the seed impact mill with cotton gin and stripper debris didn’t require more power than wheat or soybean chaff would. Both debris types had peak power requirements under 60 kilowatts, or roughly 80 horsepower. “We’re within normal operating range, which really shows the promise to implement this technology,” she explains. 

But that’s not to say that there aren’t a few roadblocks. Seed impact mills operate via internally spinning mechanics. High concentrations of lint in cotton debris could catch on these mechanics and make string that clogs the mill. There’s also the issue of physical logistics. Small grain combines, cotton harvesters, cotton gins, and flail forage mowers are very different machines, and engineers would need to revisit the seed impact mill’s design to connect these mills to cotton harvesters and flail forage mowers, Chu says. 

The results overall suggest that harvest weed seed control could have potential in cotton, even if a lot more work would be needed to outfit seed impact mills onto cotton harvesters, gins, and flail forage mowers. For cotton farmers, that could mean more flexibility in their future weed control options. 

“I think of my research as putting a toe in the door,” Chu says. “[This research] is going to go forward beyond me.”

Visit GROW’s website for more information on harvest weed seed control and to learn more about the weeds plaguing cotton production.

Article by Amy Sullivan, GROW; Feature photo by Claudio Rubione, GROW; Header photo by Sarah Chu, Texas A&M.