To limit future problems with herbicide-resistant weeds, Gunsolus advises farmers to return to using a pre-emergence herbicide with residual chemistry to control early weed growth.

“The pre-emergence application will make your postemergence weed control better, by giving you a little wider window of application,” he says. “Plus, the weed density will be less when you apply postemergence products, which helps provide better herbicide contact to the weeds that are up. Particularly in soybeans, you can get better chemical diversity by using a pre-emergence herbicide with soil residual chemistry than you can by solely using postemergence products.”

However, the biggest strategy with herbicide resistance management is to use crop rotation to provide greater diversity in weed management chemistry, advises Gunsolus. “You really need to take full advantage of the different herbicides available to you for each crop, and don’t keep using the same product on crop after crop, year after year,” he says. “I also recommend that farmers try to limit their glyphosate use for any crop where an effective herbicide alternative to glyphosate exists. It’s best to target glyphosate use in those crops where its weed control is of greatest value to you.

“Also, it’s crucial that your postemergence timing occurs on 2-3 in. weeds,” he adds. “Larger weeds are more apt to survive a postemergence application and develop resistance.”