Johnsongrass Resistance to Glyphosate and Aryloxyphenoxypropionate Herbicides: Implications for Management in Cotton.

In recent years, johnsongrass (Sorghum halepense) escapes and infestations have been a growing issue for cotton (Gossypium hirsutum) producers across the mid-South. This could be due to reliance on specific herbicides such as glyphosate and acetyl CoA carboxylase inhibitors. A greenhouse study was conducted in Fayetteville, Arkansas, in 2020 and 2021 to determine the extent of johnsongrass in Arkansas with resistance to aryloxyphenoxypropionate herbicides and glyphosate. Johnsongrass seeds were collected from 63 locations within six counties in eastern Arkansas. These accessions were then seeded in the greenhouse and treated with fluazifop at 0.9 lb ai/ac, quizalofop at 0.04 lb ai/ac, and glyphosate at 0.77 lb ae/ac. Quizalofop was the only herbicide that provided 100% mortality of all accessions. Some plants escaped fluazifop, but all accessions had greater than 90% mortality, except one accession from Crittenden County. Glyphosate resulted in variable levels of mortality, ranging from 10% to 100%. Overall, Arkansas johnsongrass accessions showed high levels of variability in control when treated with glyphosate, while fluazifop and quizalofop applications appeared effective on almost all of the accessions tested. [ABSTRACT FROM AUTHOR]