Glyphosate and Pyrithiobac Resistance in Arizona Palmer Amaranth Populations

Greenhouse studies verified that the lack of Palmer amaranth control in a Buckeye, AZ cotton field in 2012 was due to resistance to the herbicide glyphosate as compared to a susceptible population of amaranthus Palmeri. Further greenhouse studies showed that the Buckeye glyphosate resistant Palmer amaranth population was also resistant to the herbicide pyrithiobac (Staple). Results of site visits with growers and PCAs in 2013 and their implications will also be discussed.