Investigation of Mixed Population of Palmer Amaranth and Waterhemp with Multiple Herbicide Resistance

A field site in west Kentucky has been identified with a mixed population of Palmer amaranth and waterhemp that has exhibited resistance to postemergence applications of both glyphosate and fomesafen (a PPO inhibitor type herbicide). Field, greenhouse, and laboratory studies will be conducted to investigate and characterize these populations and to evaluate alternative control strategies that can be effectively used to manage these weeds. The field study will be used to evaluate soil-residual and postemergence herbicide control options. The emphasis of this research will be to evaluate programs involving herbicides with multiple sites of action including protoporphrinogen oxidase (PPO) inhibitors (e.g. sulfentrazone, flumioxazin, and fomesafen), photosystem II inhibitors (e.g. metribuzin), and cell division inhibitors (e.g. acetochlor, metolachlor, and pyroxasulfon) and combinations of these active ingredients. In addition, glufosinate and treatments that mimic new technologies that utilize in-season applications of dicamba and 2,4-D will be evaluated. Greenhouse studies will be conducted on plants to validate and characterize the level of resistance to POST applications of glyphosate and fomesafen. Laboratory analysis and other procedures will be used to characterize the heritability of herbicide resistance among these populations of Palmer amaranth and waterhemp.