Metolachlor, herbicide traits and Weed Science webpage, oh my!

• By Tommy Butts and Tom Barber •

Palmer amaranth
Palmer pigweed is growing resistant to the herbicide active ingredient, metolachlor.

There are two new Extension publications available from the Arkansas Weed Science team, FSA2185 – Metolachlor Herbicides: What are the Facts, and MP554 – Herbicide Resistance Traits: Quick Reference Guide.

Metolachlor herbicides are typically used as a preemergence, residual herbicide in corn (Zea maysL.), cotton (Gossypium hirsutum L.), soybeans [Glycine max (L.) Merr] and a variety of other crops to control grasses and small-seeded broadleaves such as pigweeds (Amaranthus spp.).

However, due to chemical principles of the metolachlor active ingredient and recent herbicide resistance evolution in Palmer amaranth (Amaranthus palmeri S. Wats.), losses in weed control have been observed in Arkansas. Check out FSA2185 – Metolachlor Herbicides: What are the Facts, which provides information regarding the metolachlor chemistry, how to effectively use the herbicide and recent discoveries of herbicide resistance in the state of Arkansas:

Herbicide-resistant traits

Herbicide-resistant crops have provided more flexibility for postemergence herbicide applications across cropping systems.

However, the abundance of options has led to confusion of which herbicides certain traits confer resistance to and has increased the potential for misapplications to occur.

Check out MP554 – Herbicide Resistance Traits: Quick Reference Guide to quickly identify what herbicides each herbicide-resistant trait provides resistance to in corn, cotton, rice and soybean:

Overhauled Weed Science website

Arkansas weed science logoAlso, be sure to check out the updated UAEX Weed Science webpage at: The webpage has been overhauled to allow for weed management materials to be easier to find and to be completely mobile-friendly.

The weeds website contains publications, videos, presentations, and more. Also, the new Weed Science Blog will be updated with any new weed management updates so everything weeds-related can be found in one location.

Finally, you may have seen a new AR Weed Science logo surfacing on a few Extension materials. Be on the lookout for it on weed management materials to signify the information has been distributed from the University of Arkansas System Division of Agriculture Weed Science team and is scientifically supported.

Drs. Thomas R. Butts and L. Tom Barber are University of Arkansas Extension weed scientists. Butts may be reached at Barber may be reached at

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