Waterhemp has done it again. University of Illinois researchers just published an article in Pest Management Science confirming 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,” said Aaron Hager, U of I Extension weed specialist.

Waterhemp is not a weed species that can be adequately managed with one or two different herbicides, Hager said. This troublesome weed requires a much more integrated approach.

“Large-scale agronomic crop production systems currently depend on herbicides for weed management,” Hager said. “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, a U of I professor of molecular weed science in the Department of Crop Sciences, 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 said. “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.”