April 1, 2024
As resistant weed varieties continue spreading to different geographies each season, researchers continue discovering new cases of resistance. For growers like you, a sound management strategy is key to staying ahead of this ongoing challenge.
“Most growers understand the importance of using different chemistries. However, it takes more than applying different herbicide brands. It takes a familiarity with local weed populations and a solid understanding of herbicide classifications,” says Brett Gordon, an Enlist® field specialist based in Arkansas. “Additionally, it’s critical to employ a diverse weed control program approach.”
Gordon says a first step to creating an effective program is choosing a trait technology that provides several herbicide tolerances. Enlist E3® soybeans and Enlist® cotton varieties offer tolerances to 2,4-D choline, glufosinate and glyphosate. Enlist® corn offers the same tolerances plus an additional tolerance to FOP herbicides. Enlist One® herbicide and Enlist Duo® herbicide are the only 2,4-D herbicides approved for use with crops with the Enlist® trait.
“For example, Palmer amaranth is one of the most troublesome, resistant weeds in the South. To control it, you need to start with a burndown or tillage. Then apply preemergence residual herbicides and overlap residuals post,” Gordon says. “For good stewardship of the Enlist system, always tank-mix Enlist herbicides with another effective mode of action to reduce the odds of developing resistance.”
Gordon advises carefully selecting herbicides to include different active ingredients, from different herbicide groups in your pre- and postemergence applications. This balances weed control effectiveness with resistance management.
Here are five reminders for resistance prevention:
Choose herbicide traits carefully and consider your rotations. If you rotate crops, make sure you’re not inadvertently encouraging resistance development by continually using the same active. Enlist E3 soybeans, Enlist corn and Enlist cotton varieties, for example, all offer tolerance to multiple herbicides. This gives you application flexibility and allows you to switch up active ingredients in back-to-back crops.
Site of action vs. mode of action: Know the difference and know what you’re applying. Mode of action (MOA) refers to how the herbicide controls the weed, such as inhibiting cell division; site of action (SOA) refers to the place in the plant where the action occurs, such as a specific protein. Effectively managing resistance involves using a combination of herbicides with different SOA or multiple MOA.
Avoid letting resistant weeds go to seed. Remove them by hand or through application of a product known to control the resistant weed. Thoroughly clean equipment to avoid bringing seeds from one field to another.
Don’t assume single resistance. Cross-resistance can occur. So, don’t assume if a resistant population appears, then you can simply apply a different herbicide for control. Work with your local advisers to find effective tools to control resistant weeds.
Remember that resistance is proportional. The longer a resistant weed variety is allowed to thrive in a field, a greater percentage of that total weed population will develop resistance.
In closing, Gordon says, the best resistance management plan is the one that uses a diverse program built on a foundation of weed control best practices.