Rising Herbicide Resistance Concern is Nothing to Ignore

Proliferation of weeds that stand tall after a herbicide application requires new control tactics.

Published on: Dec 20, 2013

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By Mark Yontz

There's no question the Midwest is a great place to raise crops. With the right combination of soil, climate and topography, there's nowhere else quite like it on earth. However, where good things grow, so can the bad.

For example, of the approximately 250,000 species of plants worldwide, about 3% (or 8,000) behave like weeds. But only 200 to 250 of these 8,000 weed-like species are deemed major problems to cropping systems worldwide. This, however, doesn't minimize the issue for U.S. growers.

TACKLING TOUGH WEEDS: A combination approach will be necessary as more weeds resistant to a variety of herbicides appear in more farm fields.
TACKLING TOUGH WEEDS: A combination approach will be necessary as more weeds resistant to a variety of herbicides appear in more farm fields.

According to the International Survey of Herbicide Resistant Weeds, there are currently 144 different species of herbicide-resistant weeds growing in the U.S., which makes us the clear leader among countries dealing with this challenging issue. Note: Australia comes in a distant second with 62 herbicide-resistant weeds.

What does this mean for Midwest growers? It depends on the individual grower and, in some respects, where he or she is located, as not all areas of the Midwest have been equally impacted by herbicide-resistant weeds. According to the experts, though, growers who refuse to recognize the seriousness of the issue run the risk of experiencing significant setbacks in yields and profitability.

"One of the most pervasive problems today is the continuing evolution of weed resistance. It's not a new issue, but over the last 15 to 20 years, it has become more and more prevalent," says Aaron Hager, an Extension specialist and associate professor of weed science at the University of Illinois.

Given his work with growers in Illinois, Hager cites waterhemp as a good example of the weed evolution problem, as it has not only spread, but also become resistant to multiple classes of herbicide.

"We don't have any reason to assume four-way resistance is the end of it. The concern is that we will eventually run out of herbicide classes to control it [waterhemp]," explains Hager, who says nearly every county in Illinois now has fields with waterhemp issues. This wasn't always the case.

Bryan Young, an associate professor of weed science at Purdue University, concurs with Hager that herbicide-resistant weeds continue to be a growing problem throughout the Midwest.

"I'm not surprised we're seeing problems with weed resistance. The abandonment of other proven weed management practices has led to this. Growers got too used to simply spraying Roundup and being done," says Young, who has a doctorate in weed science. "We're utilizing 30-year-old herbicide technology to kill modern weeds."

Set your strategy

Young believes the best investment growers can make today is in early-season, residual herbicides, as he says you can no longer rely upon postemergent herbicides, especially in soybean production.

"There's no crop insurance for weed management. You're on your own, so you need to have a good plan," he advises.

Hager reiterates the importance of growers today having a good weed management plan, and stresses that all this talk about herbicide-resistant weeds isn't just "university hype." The issue is very real and getting worse.

"The long-term, sustainable solution isn't going to be poured out of a jug," warns Hager. "We need to go back to managing weeds instead of controlling them."

Nonetheless, both Hager and Young acknowledge there are pockets of resistance throughout the Midwest when it comes to growers making changes.

"There are still areas where it's not a big problem, so they don't feel a sense of urgency or feel a need to change," explains Young, who believes the situation may need to get worse before it gets better.

Young suggests growers can stay ahead of weed issues by being proactive and looking for ways to improve. "When harvesting their fields, growers always need to ask themselves, 'What one thing can I do to improve weed management next year?' "

Yontz writes from Urbandale, Iowa.

Rising Herbicide Resistance Concern is Nothing to Ignore