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Waterhemp is escaping — again!

Waterhemp has done it again. University of Illinois researchers have confirmed that waterhemp is the first weed to evolve resistance to HPPD-inhibiting herbicides — after escaping glyphosate, ALS inhibitors and PPO inhibitors.

“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,” reports Aaron Hager, U of I Extension weed specialist. It’s no longer a weed species that can be adequately managed with one or two different herbicides, he adds. It requires a much more integrated approach.

Key Points

Waterhemp has developed resistance to a fourth herbicide class.

The potental exists for it to become unmanageable via post products.

Weeds, too, can stack trait resistance; waterhemp shares genes among biotypes.


“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.”

Hager and co-researchers at Illinois found that all populations resistant to glyphosate were also resistant to ALS inhibitors, and 40% contained resistance to PPO inhibitors.

Adding HPPD resistance to the mix greatly complicates problems for growers.

Weeds, too, can ‘stack’ resistance

“We are running out of options,” adds Hager.

“This multiple-herbicide resistance in waterhemp has potential to become an unmanageable problem with the currently available postemergence herbicides used in conventional or glyphosate-resistant soybean.”

One waterhemp biotype already is resistant to four different herbicide families. And he speculates that growers may see five-way resistance in the future.

Fortunately, very few annual weed species in this country have shown this level of multiple resistance — yet.

Waterhemp is a dioecious species, and ideally suited for evolving herbicide resistance by sharing resistance genes among populations and biotypes.

For example, you can have HPPD resistance evolving in field A, and in adjacent field B you can have selection for glyphosate resistance. Pollen is always moving in the air, allowing pollen from field A to mix with resistant plants from field B, resulting in HPPD and glyphosate resistance in the same progeny. That’s how easy it is to stack resistance.

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QUADRUPLE TROUBLE: Waterhemp biotypes have the potential for being resistant to glyphosate, ALS inhibitors and PPO inhibitors, and now HPPD inhibitors as well.

This article published in the April, 2011 edition of AMERICAN AGRICULTURIST.

All rights reserved. Copyright Farm Progress Cos. 2011.