Weed resistance is a growing concern among row crop producers. The lack of new herbicide modes-of-action has caused over-reliance on existing products. Although dicamba and 2,4-D tolerance was recently introduced into soybean, these herbicides were commercialized nearly 50 years ago. Currently, Palmer amaranth is resistant to glyphosate, ALS-inhibitors, and DNA herbicides. The three effective modes-of-action for Palmer amaranth are Liberty (group 10), PPO-inhibitors (group 14), and growth regulators (group 4). This survey will determine the levels of Palmer amaranth resistance to these herbicides present in South Carolina soybean production.

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

1) 4 Quarterly reports to the SC soybean board
2) 1 final report to the SC soybean board
3) Present soybean injury results to soybean growers at county and/or regional Extension soybean meetings January 1 through March 31, 2022.

Updated April 15, 2021:
The soybean Palmer amaranth survey sites are selected with a good representation across the soybean growing areas of the state during the first quarter of the project. Since Palmer amaranth is a summer annual, the survey cannot be conducted until late summer of 2021.

Updated October 15, 2021:
We have been working on locating the survey sites for Palmer amaranth collections. The graduate student on this project is currently working on the sampling protocol. The number of sites we collect from will be noted in the next progress report. September and October are the best time to collect Palmer amaranth seed.

Updated October 15, 2021:
As of the writing of this report (10-15-21), we are still actively collecting female Palmer amaranth seedheads from around the state. We have collected from over half of the counties where row crops are grown in the state. Samples are placed in the greenhouse for drying and processing. Palmer amaranth response to the various herbicides results will be delivered in the next progress report.

Updated December 15, 2021:

View uploaded report

Updated January 17, 2022:

View uploaded report

This project will characterize the prevalence of herbicide resistance in Palmer amaranth in South Carolina. Soybean producers will benefit from this increased knowledge with regard to their herbicide programs.