Control Weeds & Resistance

The struggle to survive is as fierce in weeds as it is in any species. With the introduction of herbicide-tolerant traits in 1996, weeds have adapted by becoming resistant to certain herbicides. The result is a vigorous weed population—among certain species—that is increasingly difficult to control. Just as weeds have adapted, so must your approach to controlling them.

herbicide sprayer weed control weed resistance AgVenture Forward Progress

“Resistance in weeds like Palmer amaranth and waterhemp is the result of several factors, including using one single mode of action year after year, cutting herbicide rates and not following label directions for mixing the product,” says Louis Sutton, AgVenture seed and technology manager. “When we see herbicide efforts fail, we have to scramble to fix the problem. Rather than take a reactive approach, farmers need to think proactively about weed control.

“Following a long-term, year-round weed control plan that you create in conjunction with your AgVenture Yield Specialist (AYS) is a sure way to manage resistance. This three- to five-year plan will include changing the modes of action in pre- and post-emergent herbicides and rotating soybean technologies,” Sutton adds.

Each herbicide class has a mode of action on how it kills weeds. Multiple modes of action are necessary to prevent building up
resistance to certain modes. “There are seven modes of action in herbicides. Some are specifically for corn and some are specifically for soybeans,” Sutton says. “Your long-term plan needs to include rotating all seven to prevent the development of resistance.”

Sutton goes on to say that in addition to rotating modes of action, it’s necessary to rotate technologies. Farmers have more choices in soybeans with herbicide-resistant traits now than they had a few years ago, making it easier to develop an effective rotation plan. Today, there’s Roundup Ready 2 Yield® and Roundup Ready 2 Xtend®, LibertyLink® and Enlist technologies.

Enlist E3™ soybeans feature the newest trait in AgVenture’s portfolio of soybean products. In addition to other benefits, it offers tolerance to three herbicides—2,4-D choline, glyphosate and glufosinate—to give farmers more rotation options. “I feel this is the best soybean technology to be introduced since Roundup Ready soybeans,” Sutton says, “because it offers a broader spectrum of herbicide resistance and greater environmental safety.”

herbicide sprayer weed control weed resistance AgVenture Forward Progress

He stresses the importance of early season weed control, not only to kill weeds but to manage resistance. “Weeds are extremely competitive for nutrients, water and sunlight. The earlier you eliminate the competition, the sooner your crop can freely access all the ingredients it needs to thrive. The smaller the weeds, the easier they are to kill. And the sooner you kill them, the less impact they’ll have on yield,” Sutton says. “While there may be intervening variables, the ideal time to spray is within the first six weeks after planting and before weeds reach a height of 6 to 8 inches. Some farmers let weeds get too big before spraying. By that time, the herbicide won’t kill them. It only makes weeds stronger and more resistant.”

If you see weeds like henbit, chickweed and dandelions when you’re scouting your fields, it’s because they weren’t controlled in the fall. To get rid of these weeds, apply a herbicide about two weeks before planting. And to prepare for next spring, spray them in the fall with 2, 4-D or other fall weed control herbicide to prevent them from germinating. Chances are you won’t see them next planting season.

Sutton also reminds farmers not to spray cover crops too close to planting. “Your cover crop is harboring and serving as a food source for insects. Once the cover is gone and your beans emerge, they’ll attack your crop. You might need to add a little insecticide when you burn down to knock the insects back prior to planting,” he says.

Whenever you spray, in the spring or fall, be sure to follow the label. Cutting back on rates to save money not only reduces the efficacy of the herbicide, but it contributes to resistance. “If you don’t follow the label, you’re actually wasting all the research and data on how to effectively kill weeds,” says Sutton.

Weeds are extremely competitive for nutrients, water and sunlight. The earlier you eliminate the competition, the sooner your crop can freely access all the ingredients it needs to thrive.

Weeds are driven to survive and reproduce. They will continue to evolve and adapt to the environment that we impose on them. Don’t make it easy for weeds to survive at the expense of your crop. Control them by following a long-term plan to get an early jump on weeds, stay on top of the issue by frequent and knowledgeable scouting and reduce herbicide resistance by rotating modes of action and technologies.

™, ®, SM Trademarks and service marks of Dow AgroSciences, DuPont or Pioneer, and their affiliated companies or their respective owners. Enlist E3™ soybeans were jointly developed by Dow AgroSciences and MS Technologies. Enlist Duo® and Enlist One™ herbicides are not registered for sale or use in all states or counties. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your area. Enlist Duo® and Enlist One™ are the only 2,4-D products authorized for use with Enlist crops. Consult Enlist herbicide labels for weed species controlled. Always read and follow label directions. Roundup Ready 2 Yield® and Roundup Ready to Xtend® are registered trademarks of Monsanto Technology LLC used under license. LibertyLink® is a trademark of Bayer. © 2019, AgVenture, Inc.

Want more? Click here to read Sutton's nine steps for effective, early season weed control.