Plan Now to Stop Resistant Weeds Next Season

AURORA, Colo. (Nov. 2, 2022) — Resistant weeds continue to march across the country, threatening yields and grower profits. As you prepare for the next growing season, taking proactive measures now can help keep challenging weeds from taking hold by spring.

Kevin Erikson, a Wilbur-Ellis Agribusiness agronomy manager located in South Dakota, offers three tips for controlling weeds before they emerge to best combat resistance and gain control.

“You have a 100 percent chance of killing weeds if you get them before they emerge,” Erikson said. “Once they’re out of the ground, weather becomes a big factor. Weeds grow quickly, and if it’s raining or too windy for herbicide application, you can easily miss your window for good control.”

Plan ahead for herbicide inputs the same way you would plan for seed needs. You can take advantage of early order programs that provide cost saving benefits and have peace of mind knowing your supply of herbicides is guaranteed. Take the following tips into consideration as you plan for 2023 growing season needs.

“Late fall/early winter is a good time to start control for the following season with a post-harvest application that keeps winter annuals under control,” said Erikson. “It makes a big difference for starting out clean in the spring.”

Whether growers use tillage or no-till methods, it’s important to control weeds from the end of the previous season and beyond. Plan for scheduled applications in the spring—don’t wait until you see weeds to apply herbicides. After emergence, target weeds at three inches or shorter.

Between the cost of labor and equipment as well as the impacts on soil health and water holding capacity, it’s a balancing act for each farm to decide about using tillage in their weed management plan.

Lastly, treat small weeds at full herbicide rates to keep fields weed free all season. To avoid weed seed set and promote better herbicide uptake for optimum control, apply herbicides when weeds are small and actively growing. Using the full recommended application rate combined with optimum spray coverage is also key to gaining maximum control and avoiding resistance development.

Once planting season starts, Erikson recommends weed treatments for no-till fields beginning right after corn and soybean seed is planted.

“After the seed is in the ground, we apply a burndown treatment for any weeds that happen to emerge early season,” he explained. “Then we’ll layer in our pre-emergent herbicides, going with a minimum of two—ideally three—different modes of action (MOAs).

Burndown treatments are great for removing any winter annuals that may have escaped fall treatments. Whether you are using pre-emergent or post-emergent treatments, all herbicides work differently on a chemical level within the plant. These modes of action are an important tool in preventing herbicide-resistant weeds since each MOA targets a different mechanism of the plant. Erikson recommends using three or more different MOAs throughout the season as you control weeds. He also advises a two-fold strategy for post-emergent applications.

“For in-season weed control, we always include a contact herbicide to catch any escaped weeds from the pre-emergent treatment. Then we add another layer of a pre-emergent product with residual activity in the tank-mix to keep in-season weeds from emerging,” he noted.

These layered treatments are especially important when combating tough weeds that have already become resistant to some MOAs.

“Because of the shift in weed species over the last 20 years, resistant waterhemp has become a big problem,” Erikson noted. “Waterhemp emerges later in the season, typically after the post-emergent treatment has been made. Residual herbicides in that post-emergent treatment deliver the most effective protection.”

“Glyphosate, glufosinate and dicamba are the most used chemistries around,” said Gregg Gerber, Wilbur-Ellis Agribusiness agronomist. “If we have resistance to common MOAs, then we’re going to have to manage our chemistry selection better and maybe adopt older practices to control weeds.”

Crop rotation may be another way to overcome herbicide-resistant weeds. For example, if you’re observing weed resistance in cotton, plan to plant corn or sorghum the following year so you can apply other chemistries.

  

Erikson recommends following herbicide label recommendations closely when it comes to including adjuvants in the tank-mix to enhance performance.

“At Wilbur-Ellis, we spend a lot of time researching which products will make herbicides work better, whether it’s helping get the chemistry into the plant more efficiently for quicker burndown or helping pre-emergent herbicides stay in the soil longer,” Erikson said. “All the products we recommend have been shown to provide a good return on investment for the grower.”

For example, adding an adjuvant to the spray tank as part of your herbicide program can increase herbicide coverage, adhesion to foliage and absorption into the soil as well as improve residual activity in the soil to extend weed-control protection.

Contact your local Wilbur-Ellis representative for more weed control and 2023 planning tips.