Current status of herbicide resistance in global cotton production: trends and perspectives

The evolution of herbicide innovations continues to deliver benefits to cotton growers, but the threat of resistant weeds with repeated application of the same active ingredients has been steadily increasing over the last 20 years. In this study, a critical overview of herbicide resistance cases in cotton production globally is reported following data retrieved from the International Herbicide-Resistant Weed Database and the scholarly literature. The first case of herbicide resistance in cotton dates back to 1973, referring to trifluralin-resistant Eleusine indica in the United States. Since then, one hundred and nineteen (119) cases refer to resistant weeds in cotton during the period from 1973 to 2020. More than three-fourths of the resistant-weed cases (76.5 %) in cotton come from the United States. The cases increased dramatically after 2000. The most frequently reported broadleaf weeds with herbicide resistance are Amaranthus palmeri, Amaranthus tuberculatus, and Xanthium strumarium. The most frequently reported grasses with herbicide resistance are Eleusine indica and Sorghum halepense. Most cases of herbicide resistance refer to glyphosate (HRAC Group-9) and ALS inhibitors (HRAC Group-2), followed by microtubule assembly inhibitors (HRAC Group-3) and ACCase inhibitors (HRAC Group-1). To ensure the value of herbicides, growers must change weed control towards a more sustainable way, re-implementing an integrated approach to weed control with rotation of herbicide groups as a key principle for reducing herbicide resistance. Moreover, residual herbicides should be backed up with additional practices, such as tillage, cultivation plus chipping, and knockdown herbicides, other than glyphosate.