Farm Industry News Blog

More weed resistance headaches

New waterhemp resistance issues sound warning bell

New research from the University of Illinois points to a very chilling result: weeds can develop resistance to any herbicide.

Case and point: waterhemp. In an article recently published in Pest Management Science, reserchers confirm that waterhemp is the first weed to evolve resistance to HPPD-inhibiting herbicides.

"A fifth example of resistance in one weed species is overwhelming evidence that resistance to virtually any herbicide used extensively on this species is possible," says Aaron Hager, Extension weed specialist.

Waterhemp is not a weed species that can be adequately managed with one or two different herbicides.

"Large-scale agronomic crop production systems currently depend on herbicides for weed management," Hager says "A weakness in this approach lies in its strength; because herbicides are so effective, they exert tremendous selection pressures that, over time, result in resistant weed populations as natural outcomes of the evolutionary process."

In an article in the Journal of Agricultural and Food Chemistry, Hager and Pat Tranel, professor of molecular weed science at the University of Illinois, shared the results of a survey of multiple-herbicide resistance in waterhemp. The results showed that all populations resistant to glyphosate were also resistant to ALS inhibitors and 40 percent contained resistance to PPO inhibitors.

Adding HPPD resistance to the mix complicates problems for growers and scientists. When weeds stack several forms of resistance, it greatly reduces the number of viable herbicide options.

"We are running out of options," Hager says. "This multiple-herbicide resistance in waterhemp has the potential to become an unmanageable problem with currently available postemergence herbicides used in conventional or glyphosate-resistant soybean."

Hager says they've already discovered one waterhemp biotype that's resistant to four different herbicide families. He said growers may see five-way resistance in the future.

At least two companies are developing crop varieties that are resistant to HPPD inhibitors. In the future, both of these companies see HPPD-inhibiting herbicides growing in importance.
 

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