Sensitivity of Kansas Palmer amaranth to commonly used herbicides

Palmer amaranth is one of the most troublesome summer annual broadleaf weed species in the U.S. Some herbicide-resistant Palmer amaranth has previously been reported in Kansas; however, the sensitivity response of Palmer amaranth populations over a wide geography of Kansas to the most commonly used herbicides is unknown.

New research in Agronomy Journal reports on the sensitivity of 28 Palmer amaranth populations randomly collected from cropland in south-central Kansas to field-use rates of glyphosate, chlorsulfuron, 2,4-D, dicamba, atrazine, and mesotrione. Researchers also characterize the sensitivity levels to these herbicides in two Palmer amaranth populations.

The team found that 47, 36, 7, 75, and 32% of all tested populations were less sensitive to glyphosate, chlorsulfuron, 2,4-D, atrazine, and mesotrione herbicide, respectively. In addition, the KW2 and PR8 populations showed 2.0- to 10.6-fold less sensitivity to 2,4-D, chlorsulfuron, atrazine, and mesotrione compared with a susceptible population in dose-response bioassays.

Reduced sensitivity to herbicides observed in Palmer amaranth populations will pose a serious management challenge for growers. This study clearly suggests that growers should quickly adopt integrated and more diversified weed control methods (chemical, mechanical, cultural, and biological) to manage these difficult-to-control Palmer amaranth populations on their production fields.