It’s an awful feeling knowing you’re being robbed and there’s little you can do to stop the losses. For years, Randy Wenger spent consistently more money and time on weed control on his Yuma, Colo., farm with diminishing results.
“I was struggling big time,” he says. “I would do a burndown herbicide application, and sometimes it didn’t look like we had done anything. If you can’t control weeds, yields will suffer.”
Herbicide-resistant weeds were stealing valuable nutrients, moisture and sunlight from Wenger’s crops — dryland and irrigated hard red winter wheat, corn, grain sorghum and blackeyed peas. Palmer amaranth and kochia were the worst culprits.
Crop protection woes
After herbicide-tolerant crops were introduced in the 1990s, growers needed just one or two herbicide applications to control weeds. Those glory days were soon gone.
By the mid-2000s, herbicide-resistant weeds were a growing problem nationwide due to repeated exposure to the same herbicide or herbicides with similar sites of action.
Weeds have evolved resistance to 21 of the 31 known herbicide sites of action and to 168 herbicides, according to the International Herbicide-Resistant Weed Database. Palmer amaranth is resistant to eight sites of action, while kochia is resistant to two sites. As of the end of 2024, there were 533 unique cases of herbicide-resistant weeds globally, including 273 species, according to the database.
“I went from using mostly one to three herbicide applications [which included one preemergence application, if weather conditions allowed] to four or five passes a season,” Wenger recalls. “That was too expensive.”
Jerome Benish, Wenger’s agronomist at CHS High Plains based in Yuma, suggested a solution.
Instead of trying to control growing weeds, Benish recommended not letting the yield-robbers emerge in the first place. In 2023, on that advice, Wenger began an overlapping two-pass preemergence herbicide program followed by postemergence applications as needed. He added Soiltrate™, a soil-applied herbicide adjuvant by CHS, to the preemergence tank mix.
“The program we’re using now is keeping my fields clean,” Wenger reports. “I’m impressed.”
Related: Adjuvant selection tips to optimize crop protection performance
Grower Randy Wenger, left, and agronomist Jerome Benish review crop protection plans for Wenger’s operation.
Weed management
For more than a decade, farmers have been asking for innovative solutions to quell the growing herbicide-resistant weed crisis. CHS listened.
“Our approach to product development is taking feedback from our growers and agronomists to find solutions to problems,” says Steve Carlsen, director of proprietary products with CHS. “When Soiltrate came into our lineup about eight years ago, it was ahead of its time.”
Back then, he says, growers were still able to control weeds with a combination of preemergence and postemergence herbicides. “We’ve seen that approach become less effective over time.”
Wenger credits Soiltrate for much of the recent weed management success on his farm. The soil and spray deposition agent improves absorption and efficacy of soil-applied herbicides, improves drift control and enhances application efficiency. It’s designed to keep herbicide active ingredients in the weed-kill zone longer.
“Palmer amaranth is an amazing survivor. The only way we’ve found to control it is not letting it come up,” Benish says, using a practice he likes to call “spray dirt.”
“We apply a preemergence herbicide right before or after planting and then make another preemergence application before the first one fails. The idea is to start and stay clean until the crop canopies and can shade out late-emerging weeds.”
Most preemergence herbicides promise residual control of germinating weeds for about 30 days. Benish says Soiltrate extends that residual control by five days to two weeks.
Proactive weed control
Dylan Tacke, a CHS agronomist based in Wausa, Neb., says the mindset of Midwest farmers is changing from reactive to proactive measures to control pigweed species — predominantly waterhemp and its nasty cousin Palmer amaranth. Instead of relying on postemergence applications, he says more farmers are upping their preemergence game by layering active ingredients and using Soiltrate.
Tacke advocates an integrated weed management approach that includes rotating crops and herbicides with different sites of action, cover crops, tillage and more. Using the right adjuvants can make a difference, he adds.
Related: Adjuvant choice can make or break a herbicide mix
“The results we have had using [Soiltrate] were awesome. You could really tell where it was used.” Soiltrate also acts as a hedge against volatile weather, Tacke says. It usually takes a half-inch of rain to sufficiently activate preemergence herbicides, moving active ingredients to the depth of germinating weed seeds. Soiltrate provides extra time for needed rain to fall or for herbicide applications if rain delays occur. It also reduces herbicide leaching after a downpour.
Adding Soiltrate to the tank costs about $4 to $6 per acre, Benish says. “When you can get effective preemergence herbicides onto fields and make them last longer, Soiltrate delivers return on investment through more effective control,” he adds.
Wenger agrees. He estimates he is saving $15 to $30 per acre with a Soiltrate-enhanced preemergence control approach compared to his old program because fewer postemergence applications are needed. And cleaner grain sorghum fields are producing an extra 15 to 20 bushels per acre, he says.
“I’m very happy with [Soiltrate],” he says. “It takes some of the stress out of weed management.”
Best practices to manage herbicide resistance
Eric Jones, an Extension weed management specialist at South Dakota State University, says preemergence herbicides are an important part of a diversified approach to managing herbicide-resistant weeds.
“There isn’t a one-size-fits-all strategy that works,” Jones says. “Don’t rely on a single herbicide group because that’s how you select for resistance. Use multiple modes of action. Scout fields for weeds and tailor your weed management plan accordingly.”
Here’s a 12-step approach to better manage herbicide-resistant weeds.
- Understand the biology of weeds present.
- Use a diversified weed management approach. Focus on preventing weed seed production.
- Plant into weed-free fields, then keep fields as weed-free as possible.
- Plant weed-free crop seed.
- Scout fields routinely.
- Use multiple herbicide modes of action (MOAs) that are effective against the most troublesome weeds or those most prone to herbicide resistance.
- Apply the labeled herbicide rate at recommended weed sizes.
- Emphasize cultural practices that suppress weeds by helping crops compete for moisture and sun.
- Use mechanical and biological management practices where appropriate.
- Prevent field-to-field and within-field movement of weed seed or vegetative reproductive structures.
- Manage weed seed during and after harvest to prevent buildup of the weed seedbank.
- Manage field borders to prevent an influx of weeds.
Source: Weed Science Society of America
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