Herbicide Resistant Weed Challenges to Look for in 2017

Herbicide resistant weeds are nothing new, but rather represent an evolving challenge for farmers and the soybean industry.

“Herbicide resistance is one of the primary weed control issues facing growers,” says Jason Bond, Mississippi State University research and extension weed scientist. “This will continue until our weed management programs become more diversified, including methods of control other than chemical methods.”

Aaron Hager, Ph.D., University of Illinois Extension weed science specialist, added that the frequency of resistance will probably only continue to increase in severity, frequency or number of acres infested. Once certain types of resistance are present in a field they will remain in that field from that point forward, so resistance is likely to be a problem on more acres next year.

Farmers need to stay up to date on the latest news and trends to stay ahead of weed resistance, so it’s never too early to start looking at issues that may crop up in the next growing season.

“The three species of greatest concern will be: 1) Waterhemp, which has shown resistance to multiple products (glyphosate, ALS inhibitors, PPO inhibitors); 2) Increased frequency of Palmer amaranth around the country; and, 3) Marestail,” says Hager.

“How to better control marestail in no-till soybeans will continue to be a challenge. I saw infestations of marestail as far north in Illinois as I’ve ever seen it in 2016 and I have no reason to assume that could not happen again in 2017.”

Increased incidence of herbicide-resistant weeds means farmers need to diversify their weed management program. Bond and Hager offer some tips to farmers looking for new ways to battle herbicide-resistant weeds:

• Diversify your herbicide programs as new technologies become available. “We’ve tried to use examples for years, where we’ve used this family of herbicides that was once effective, then resistance evolved and we stopped using that herbicide and we went to something else,” says Hager. “We’re very rapidly running out of something else. And data shows that farmers will spend more money after resistance becomes well established in a field than they would have if they’d proactively tried to slow down that evolution of resistance.”
• Every time you apply a herbicide treatment to a field, you really need to have at least two effective herbicides combined in that treatment that are effective against the weed species that you have the most concern about evolving resistance. “But that’s only a short-term, stop-gap measure,” says Hager. “Eventually, biology is going to win in the long run. It’ll literally force people to do things differently.”
• Investigate cultural weed management tactics, such as the use of cover crops, for weed suppression. “Our herbicide-based platform for managing weeds in soybeans has very nearly run dry,” says Hager. “We need to consider what the alternatives can be, including cover crops and row crop cultivation.”
• Consider options to reduce the weed seed in the seed bank. “That can be as simple as delaying planting by a few days, which allows several million seeds to germinate, and they can then be treated chemically or by tillage or other methods, and you’ll have reduced your seed bank tremendously,” says Hager.

“Everything changes and evolves over time and weed management programs should as well,” says Bond. “There are new herbicide-resistant crop technologies in varying stages of commercialization that will help growers diversify their herbicide programs.”

Still, it’s important to practice caution with new weed control tools. All herbicide applications should be with good stewardship in mind and in accordance with label directions, says Bond. Some of the herbicides that will ultimately be labeled for use in soybean with the new herbicide-resistant technologies can be a threat to non-target plant species, so they should be used carefully.