Herbicide Resistance: What is Going on Around Wisconsin
2022
- Department of Agronomy, UW Madison
Project Media
Herbicide-resistant weeds have become commonplace across the Wisconsin row-crop landscape in recent years. Waterhemp [Amaranthus tuberculatus (Moq.) Sauer] has become one of the primary troublesome weeds for corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] producers due to its aggressive growth, extended emergence window, and rapid development of herbicide resistance. At current, waterhemp accessions have been determined resistant to ALS- (Group 2; imazethapyr), EPSPS- (Group 9; glyphosate), and PPO- (Group 14; fomesafen & lactofen) inhibitors in Wisconsin. The first comprehensive Wisconsin state-wide assessment of waterhemp response to a diverse group of herbicide site of action (SOA) was conducted by the UW-Madison Cropping Systems Weed Science Program in 2019 & 2020. Results suggest that imazethapyr and glyphosate POST are ineffective for waterhemp control and that atrazine PRE is ineffective for waterhemp control on silty clay loam soils in Wisconsin. Giant ragweed (Ambrosia trifida L.) is another troublesome weed for Wisconsin row-crop producers due to its aggressive growth and extended emergence window. Resistance to ALS- and EPSPS-inhibitor herbicides has been previously confirmed in Wisconsin. In 2020, a putative fomesafen-resistant (PPO-inhibitor) giant ragweed accession was detected in in food-grade, non-GMO soybeans in Rock County, Wisconsin and a greenhouse experiment was conducted to confirm resistance. Results indicate that this giant ragweed accession is highly resistant to fomesafen. To our knowledge, this is the first confirmed case globally of PPO-inhibitor resistance in giant ragweed. Fall panicum (Panicum dichotomiflorum Michx) is a reemerging troublesome weed in corn production and in 2020, a putative ALS-inhibitor (nicosulfuron) resistant fall panicum accession was detected in a sweet corn field in Dodge County, Wisconsin and greenhouse and molecular experiments were conducted to confirm resistance. This is particularly important as nicosulfuron is commonly used for POST grass control in sweet corn production. Results indicate that this fall panicum accession is highly resistant to nicosulfuron. This is the first confirmed case of ALS-inhibitor resistance in fall panicum in the USA. During this presentation, results will be shared to generate awareness on the current status of herbicide-resistant weeds in the state of Wisconsin and