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Do You Have Resistant Weeds?

Waterhemp, Palmer amaranth, marestail, and other noxious weeds are doing their best to stay rooted in your fields. With all their might they fight off herbicides – and sometimes they win by developing herbicide resistance. It isn’t a matter of if, but when the weeds in your fields will thumb their leaves at you.

Aaron Hager is an associate professor of weed science at the University of Illinois. He says there are ways to tell if you might have a problem.

"One of the tell-tale signs at the end of the year that you could be facing a problem with herbicide resistance in the field, is simply that you’re harvesting a lot of these weed plants at the end of the growing season," he says. "If you had a field, let’s say, early on in the growing season where you had 4-5 different weed species in the field but at the end of year you only have one, that could suggest that you could have an emerging problem with herbicide resistance."

Hager says even with your best management efforts, weed resistance doesn’t obey field boundaries.

"We do know that resistance can actually move from field-to-field based on movement by seed or by pollen. But the other thing to remember also is that independent selection can occur in any field where herbicide is used," says Hager. "So really, there are no boundaries to the evolution of resistance. It can occur within a particular field and maybe a unique type of resistance, compared with what a neighbor across the road would experience in their field."

Unfortunately, there are no blanket herbicides or recommendations that will work for everyone. Hager says the best treatment is one that’s tailored specifically for the weeds in a given field.

Read more about weed herbicide resistance

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