Cornell Cooperative Extension’s Field Crops Specialist, Josh Putman, shares information on one of the most problematic weed species in the U.S. and newly found resistance to Liberty herbicide. (photo provided by the University of Arkansas, Weed Science Program).

One of the most problematic weed species in the US & a resistance to Liberty herbicide

Palmer Amaranth Confirmed Resistant to Liberty Herbicide

One of the most problematic weeds in the US shows new resistance

NEW YORK (March 19, 2021) – Cornell Cooperative Extension’s Southwest New York Dairy, Livestock, and Field Crops Program (SWNYDLFC) shares information that farms need to know about Palmer amaranth and other weed species that affect New York crop production. Additional information and resources can be found from the University of Arkansas as well as the International Herbicide-Resistant Weed Database managed by Dr. Ian Heap.

Researchers from the University of Arkansas have identified Palmer amaranth populations that survived several applications of glufosinate, the active ingredient in Liberty herbicide. Seed collected from these Arkansas populations and tested in the greenhouse showed resistance of 16 times the typical field use rate of 32 fluid ounces per acre. Glufosinate resistance has been documented in grass species, however, these findings represent the first confirmed case of broadleaf resistance to Liberty herbicide in the world.

Palmer amaranth is now present in 3 counties across New York State, with the most severe case located in Southwest, NY. Seed collected from this population in the fall of 2020 and is now being tested for resistance to our commonly used herbicides like Roundup, atrazine, dicamba, and Liberty. Dr. Lynn Sosnoskie, Weed Scientist at Cornell University, will test for resistance over the next few weeks. Field research is planned for 2021 to evaluate Palmer amaranth's emergence, growth, competitive features, and in-field herbicide control options.

Farms should continue to monitor this new resistance and monitor their fields for Palmer amaranth during the upcoming growing season. This potentially detrimental weed species can significantly reduce crop yields and spreads rapidly. For more information about Palmer amaranth identification, control, and prevention connect with Cornell Cooperative Extension Field Crop Specialists.

SWNYDLFC is a partnership between Cornell University and the CCE Associations of Allegany, Cattaraugus, Chautauqua, Erie, and Steuben counties. Their team includes Katelyn Walley-Stoll, Farm Business Management (716-640-0522); Joshua Putman, Field Crops (716-490-5572); Alycia Drwencke, Dairy Management (517-416-0386) and Amy Barkley, Livestock Management (716-640-0844). CCE is an employer and educator recognized for valuing AA/EEO, Protected Veterans, and Individuals with Disabilities and provides equal program and employment opportunities. For more information, visit

For more information about Cornell Cooperative Extension, contact your county’s Association Executive Director. Allegany County – Laura Hunsberger, or 585-268-7644. Cattaraugus County – Dick Rivers, or 716-699-2377. Chautauqua County – Emily Reynolds, or 716-664-9502. Erie County – Diane Held, or 716-652-5400. Steuben County – Tess McKinley,, or 607-664-2301. 


Katelyn Walley-Stoll
Team Leader, Business Management Specialist

Last updated March 22, 2021