Auxin Herbicide-Glufosinate Interactions on Palmer Amaranth Control

The interaction of glufosinate with either 2,4-D (Enlist One) or dicamba (Engenia or Xtendimax) on the control of Palmer amaranth was studied during the 2016 and 2017 cotton seasons in fallow fields at the University of Arizona Red Rock Agricultural Center (RRAC) and Maricopa Agricultural Center (MAC). Randomized complete block designs with 6 replications and small plot research methods were used in the studies. The herbicide treatments were applied with a CO₂ pressurized backpack sprayer. Palmer amaranth was sprayed when plants reached 4 to 6 inches in height. In 2017, individual plants were marked prior to spraying and characterized by measuring height and number of leaves of each plant. The responses of Palmer amaranth to the herbicide treatments were followed over the course of 3 to 4 weeks after spraying. Roundup Powermax was the most effective treatment since the Palmer amaranth populations at these sites were not yet resistant to glyphosate. Glufosinate tank mixed with Roundup Powermax was not as effective as Roundup Powermax alone confirming this tank-mixture is antagonistic. The auxin herbicides 2,4-D and dicamba while not as effective as glyphosate still provided acceptable control albeit with some escapes that were severely injured. Tank-mixtures of glufosinate with 2,4-D or dicamba did not appear to be antagonistic and may be beneficial.