Investigation of Multiple Herbicide Resistant Palmer Amaranth and Waterhemp

A field site in west Kentucky with a mixed population of Palmer amaranth and waterhemp has exhibited resistance to postemergence applications of both glyphosate (an EPSPs enzyme inhibitor herbicide) and fomesafen (a PPO inhibitor type herbicide). Another site with Palmer amaranth located in central Kentucky has also been identified and requires further investigation. This population is suspected to be resistant to glyphosate and other possible herbicides. 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. Field studies 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 biochemical activity which include 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). In addition, glufosinate and treatments with 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 glyphosate, fomesafen, and other chemistries suspected of herbicide resistance. Plant genetic analysis and other laboratory procedures will be used to characterize the herbicide resistance among these populations of pigweeds and their heritability to glyphosate and PPO resistance.