Joseph Zimbric (UW-Madison Agronomy Graduate Student), David Stoltenberg (UW-Madison Agronomy Professor), Mark Renz (UW-Madison Extension Weed Scientist) and Rodrigo Werle (UW-Madison Extension Weed Scientist)
20 Unique Cases of Herbicide Resistance in Wisconsin
- 20 unique cases (weed species by herbicide site of action) of herbicide resistance have been confirmed in Wisconsin, including 13 weed species with evolved resistance to one or more herbicide sites of action (Figure 1, Table 1).
- The first confirmed case of herbicide resistance in Wisconsin was PSII inhibitor resistance in common lambsquarters in 1979.
- Since then, ALS-inhibitor resistance has been confirmed in more weed species than other type of herbicide resistance, totaling eight weed species including common ragweed, giant ragweed, Palmer amaranth, and waterhemp.
- In comparison, PSII inhibitor resistance has been confirmed in four species, whereas ACCase inhibitor resistance has been confirmed in only two species (giant foxtail and large crabgrass).
- The first confirmed case of glyphosate (an EPSP synthase inhibitor) resistance in Wisconsin was a non-rapid response phenotype of giant ragweed in 2011 (Figure 2). Glyphosate resistance has subsequently been confirmed in horseweed, waterhemp, Palmer amaranth, and most recently, common ragweed in 2018.
Waterhemp in Wisconsin
Waterhemp presence has increased rapidly in Wisconsin to include over 400 locations in 61 of 72 counties in the state (Figure 3).
In recent years, glyphosate resistance concerns have focused on waterhemp which has also increased rapidly to include confirmed cases in 28 counties (Figure 4). Among these, multiple resistance to glyphosate and PPO inhibitors has been confirmed in 10 counties.
Palmer amaranth in Wisconsin
Palmer amaranth was first identified in Wisconsin in 2011. Since then, 12 populations have been found among nine counties (Figure 5).
Herbicide resistance in Palmer amaranth has been limited to two cases of confirmed glyphosate resistance and one case of confirmed multiple resistance to ALS inhibitors and the HPPD inhibitor tembotrione (Figure 5).
Glyphosate resistance in waterhemp, and multiple resistance to glyphosate and PPO inhibitors, have increased rapidly in Wisconsin indicating that effective waterhemp management will continue to be a top concern of Wisconsin growers.
Herbicide resistance in Palmer amaranth is currently limited to three counties in southern Wisconsin, but glyphosate resistance in two populations, and multiple resistance to ALS and HPPD inhibitors in another population, also have serious management implications for Wisconsin growers.
It is critical that diversified management tactics be implemented to reduce the spread, persistence, and impact of these and other herbicide-resistant species.
This overview was presented as a poster at the 2018 Annual Meetings of the North Central Weed Science Society in Milwaukee, WI (December 3-6, 2018). Click HERE to download the PDF version of the poster.