Herbicide-resistant Palmer amaranth observations and calls have started. Most recent calls have been from some who have switched from Xtend to Enlist crops. They are finding that the sketchy pigweed control in Xtend crops they experienced in previous years is also problematic in an Enlist crop. This would be consistent with our research that has often shown that Palmer amaranth that is resistant to dicamba is cross resistant to 2,4-D.
Our research has shown that on these auxin resistant Palmer populations an application of either Enlist One or Liberty alone followed by another shot or a tankmix of the two is not the most reliable approach (Picture 1). Rather on these problematic pigweed populations our research suggests that the strategy that provides the best probability of respectable weed control (75 to 90%) is to apply a tankmix of Enlist One + Liberty in the first pass followed approximately 14 days later with an application of that same tankmix. The variance on the level of control is mostly dependent on if the pigweed are 4” or less when the first application occurs and on how timely that 2nd application can be made. Delays on either end can decrease control. Interestingly, we also saw similar results with atrazine and Armezon on these populations (Figure 1).
Figure 1..
