Overlap residual herbicides to get ahead of Palmer amaranth

Winter is an ideal time to evaluate what worked and what didn’t work — especially when it comes to weed control. Mark Bernards, associate professor of agronomy at Western Illinois University, and his weed science class conducted research this year to learn about growth of two common weeds. The group compared the development of Palmer amaranth with waterhemp plants as they grew in the same pot and had to compete. The result? Palmer amaranth grew more aggressively than waterhemp.

“One of the things we noticed is that Palmer amaranth adds leaves a lot quicker,” Bernards says. “At the end, Palmer amaranth had 17 to 18 leaves per pot whereas waterhemp had somewhere between 13 and 14. Palmer amaranth is a much more aggressive species.”

Whether the concern this year was Palmer amaranth, waterhemp or giant ragweed, corn farmers can implement helpful practices to control herbicide-resistant weeds in the future. Bernards says the two best ways to delay, or prevent, herbicide resistance is to apply herbicide mixtures that have active ingredients effective on the targeted weeds and to overlap residual herbicides with multiple modes of action.

“Our primary focus needs to be eliminating weed seed return, which means we don’t let any new weeds into our fields,” Bernards says. “A preemergence application followed by a post- is critical for herbicide resistance management.”

Using a preemergence herbicide helps farmers protect yield potential early. Following up with a postemergence herbicide will not only provide additional control but also help farmers navigate unfavorable weather circumstances.

“Farmers need a powerful herbicide program to fend off Palmer amaranth next season,” says Lyndsie Kaehler, U.S. product manager, Dow AgroSciences. “An example of a strong approach is applying SureStart II or FulTime NXT herbicide preemergence followed by Resicore herbicide for four modes of action that will work deep into the season. Many farmers also choose to add glyphosate and atrazine to this program to increase the number of different modes of action.”

For more information about Resicore® herbicide and controlling herbicide-resistant weeds, including Palmer amaranth, visit PowerOverWeeds.com.

Competitive nature of Palmer amaranth

Mark Bernards, associate professor of agronomy at Western Illinois University, and his weed science class conducted research this year to learn about growth of Palmer amaranth and waterhemp as they grew in the same pot. Palmer amaranth grew more aggressively than waterhemp.

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