Herbicide and Integrated Soybean Weed Management 2019
Sustainable Production
AgricultureCrop protectionHerbicide
Parent Project:
This is the first year of this project.
Lead Principal Investigator:
Michael Flessner, Virginia Tech
Co-Principal Investigators:
Project Code:
Contributing Organization (Checkoff):
Institution Funded:
Brief Project Summary:

This research explores options for control of common ragweed and Palmer amaranth. The first objective is to evaluate cover crops for weed suppression to answer common questions about using cover crops for weed suppression, like planting wheat or cereal rye, rolling cover crops or leaving them standing, and quantifying the effect on weed suppression. Trials evaluate combinations of the following: cereal rye versus wheat residue; rolled residue versus left standing; and no, low, medium, or high biomass levels for a total of 13 treatments. Another goal is to look at weed control with alternatives to glyphosate and ALS herbicides and to investigate herbicide program approaches to mitigate PPO resistance.

Key Benefactors:
farmers, agronomists, extension agents

Information And Results
Project Deliverables

All findings will be incorporated into Dr. Flessner’s Extension activities through Virginia Cooperative Extension. It is anticipated that these findings will be disseminated via web-based information, presentations, field day demonstrations, and other media where the information gleaned will be put in the hands of soybean producers. Producers can then implement weed management changes as they see fit. A report to the Virginia Soybean Board will be delievered.

Final Project Results

Updated August 28, 2020:

View uploaded report PDF file

Results from objective 1 indicate that maximizing cover crop biomass is most important for weed suppression. When sufficient biomass is achieved (~7,500 lbs/ac), similar weed suppression is achieved whether cover crop residues are rolled or left standing. Standing residue is recommended for common ragweed. It resulted in greater control than rolled residue in most cases, despite allowing more light penetration to the soil surface.

Common ragweed and Palmer amaranth survival and seed production were evaluated from various post-emergence herbicides (objective 2) and herbicide programs (pre-emergence followed by post-emergence; objective 3). Palmer amaranth and common ragweed control decreased as size increased for all herbicides. Palmer amaranth control was best and seed production least from glufosinate, dicamba + fomesafen, 2,4-D + fomesafen, and glufosinate + fomesafen. Dicamba, 2,4-D, and glufosinate with or without fomesafen and mesotrione + fomesafen resulted in the greatest biomass reduction.

Farmers should continue to target Palmer amaranth and common ragweed at small sizes (2 to 4 inches in height) for best outcomes. Herbicide program research results reinforce the utility of PPO PREs when used as part of a program with multiple, effective sites of action. Pre-emergence applications of flumioxazin, fomesafen, and sulfentrazone provide effective control and reductions of Palmer amaranth density. Dicamba, 2,4-D, and glufosinate on Palmer amaranth are effective on escapes from PPO-containing PRE herbicides.

Further research is necessary before recommending targeting taller Palmer amaranth and common ragweed for reducing seed production, but results are promising.

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.