Lessons Learned From Two Decades of ALS-Resistant Weeds

Growers look to new mode of action in Huskie herbicide, better resistance management

RESEARCH TRIANGLE PARK, N.C. – Bayer CropScience is looking back at an unusual anniversary that most cereal growers across the Northern Plains would just as soon forget. It was two decades ago that the first ALS-resistant weeds were documented: kochia and Russian thistle. The problem started slowly then came to plague the region for 20 years until the unique mode of action in Huskie® herbicide – a unique mode of action that the industry looks to preserve using the lessons learned from ALS resistance.

“The first resistant weeds were discovered in my area,” said Brad Birch, owner of Dry Fork Ag in Ledger, Mont. “Everybody had been using ALS chemistry. When they first began seeing reduced performance, they weren’t sure what was going on, but then a bioassay confirmed that the kochia was resistant.”

Ed Davis, research agronomist at Montana State University, explains that adoption of ALSchemistry was so quick and widespread because it controlled the state’s big three weeds, kochia, Russian thistle and wild buckwheat. “Close to 90 percent of our growers relied on ALS herbicides.”

But the chemistry lost its utility on tough weeds quickly.

“ALS chemistry worked really well for about four years,” Davis said, “but then we got a few complaints about not getting complete control. About two years later, there was widespread non-performance in the field. Within five years, we had lost most of our ALS products.”

The same situation played out in fields throughout North Dakota and into Minnesota where ALS-resistant kochia appeared. “I have been there, done that with ALS-resistant kochia,” said Mike Hutter, a consultant with Northern Agricultural Management in Westhope, N.D. His region has been in the middle of ALS-resistant kochia since its beginning and has had to modify his weed management approach, as well.

Growers had a few options to replace ALS herbicides for control of resistant weeds, but none was particularly attractive. “We had to go back to older chemistries for kochia control, such as 2,4-D,” Davis said.

The first new mode of action for broadleaf weed control in small grains came almost 20 years later with the introduction of Huskie herbicide from Bayer CropScience. The new mode of action inhibits an enzyme critical for plant pigmentation, resulting in the bleaching and rapid control of weeds. A second mode of action blocks photosynthetic processes. As a result, Huskie controls more than 50 hard-to-manage broadleaf species, including many that have become resistant to ALS inhibitors, and provides partial control of 20 others.

“Huskie allowed us to get the early weed control we needed, including ALS-resistant kochia and Russian thistle,” Davis said. “Adding that second mode of action has really helped combat resistance development.”

If ALS resistance has a silver lining, it may be the fact that today, growers and consultants alike are much more sophisticated about resistance-management strategies.

 “At the time, ALS resistance had a fairly big impact on growers,” Birch said. “Growers had to change their mindset about tankmixing and alternating modes of action, and they also had to spend more money. Today, they are more concerned about achieving good control.”

After seeing the impact of resistant kochia, preventing resistance in other weeds is top of mind for Hutter.  “Huskie is a prevention tool to avoid future resistance. We use Huskie as part of a long-term weed management approach with a multi-crop rotation. I look at when chemistries and modes of action are used in the large rotation, so I know when to insert Huskie for the best year-to-year weed control,” Hutter said.

This approach combining crop rotation with mode-of-action rotation is one that Bayer CropScience recommends farmers to implement where possible. Lessons learned in weed control management could help preserve the power of Huskie herbicide against even the toughest ALS-resistant broadleaf weeds.

“With the past experience of losing their most valuable herbicide due to resistance, growers are doing a good job of resistance management,” Davis said. “It was a learning tool.”

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