2022
Survey of Palmer Amaranth Resistance in South Carolina Cotton Production
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Contributor/Checkoff:
South Carolina Soybean Board
Category:
Sustainable Production
Keywords:
AgricultureCrop protectionHerbicide
Parent Project:
This is the first year of this project.
Lead Principal Investigator:
Michael Marshall, Clemson University
Co-Principal Investigators:
Project Code:
Contributing Organization (Checkoff):
South Carolina Soybean Board
$8,472
Institution Funded:
Clemson University
$8,472
Brief Project Summary:
Weed resistance is a growing concern among row crop producers. Currently, Palmer amaranth is resistant to glyphosate, ALS-inhibitors and DNA herbicides. The three effective modes of action for Palmer amaranth are glufosinate, PPO-inhibitors, and growth regulators. This survey determines the levels of Palmer amaranth resistance to these herbicides present in South Carolina soybean production. Research intends to collect Palmer amaranth seed samples across the state and conduct greenhouse herbicide screens for levels of resistance to glyphosate, glufosinate, PPO-inhibitors, ALS[1]inhibitors, 2,4-D, and dicamba. Then, efforts aim to disseminate these research results to South Carolina farmers to support decisions about managing Palmer amaranth in soybeans and all rotational crops.
Key Beneficiaries:
#agronomists, #extension agents, #farmers
Unique Keywords:
#herbicides, #weed control, #weed resistance, #weeds
Information And Results
Project Summary

Palmer amaranth seed were planted and sprayed in the greenhouse at EREC from October 2022 through early January 2023. All populations from the 22 counties showed resistance to both the 1X and 2X rates of glyphosate (MOA 9) and Staple (MOA 2) [ALS-inhibitor]. This confirms results from past Palmer amaranth collections in that glyphosate and ALS-resistance is persisting in South Carolina populations. In contrast, all populations were sensitive to the 1X rates of Reflex,
Liberty, Enlist One, and Dicamba postemergence herbicides. In the preemergence experiments, there were populations from 10 counties that we observed survivors from the atrazine at the 1X rate. In addition, there were populations from 5 of those counties with survivors from the 2X rate of atrazine. The remaining Palmer populations were controlled by atrazine at the 1X rate. In the Dual Magnum treatment, we observed populations from 3 counties with survivors at the 1X rate. There were no survivors at the 2X rate of Dual Magnum. The HPPD herbicide Balance (isoxaflutole, MOA 27) provided excellent control of all populations tested. Although atrazine is not used in cotton, we observed more survivors from the atrazine treatments compared to the 2021 population survey. Also, there were several populations that survived the Dual Magnum (MOA 15) preemergence treatments (@1X) which could indicate that this herbicide family may lose effectiveness soon. Further research is needed on populations that are surviving both atrazine (MOA 5) and Dual Magnum (MOA 15) herbicides.

Project Objectives

1. To collect Palmer amaranth seed samples across the state and conduct greenhouse herbicide screens for levels of resistance to glyphosate, Liberty, PPO-inhibitors, ALSinhibitors, 2,4-D, and dicamba.
2. To disseminate these research results to South Carolina cotton growers through field days and grower meetings.

Project Deliverables

Progress Of Work

Final Project Results

Updated May 10, 2023:

View uploaded report PDF file

Benefit To Soybean Farmers

The United Soybean Research Retention policy will display final reports with the project once completed but working files will be purged after three years. And financial information after seven years. All pertinent information is in the final report or if you want more information, please contact the project lead at your state soybean organization or principal investigator listed on the project.