After more questions this past week on follow-up applications to remove Palmer amaranth, junglerice and goosegrass in Xtend crops it occurred to me we need a new thought process on weed management with this technology. Roundup Ready soybeans came out in 1996 and cotton in 1998. If we look back at the first three years with that technology, glyphosate was controlling every weed no matter the weed height. That Roundup Ready performance in the early years is still the expectation with Xtend technology. It has become abundantly clear, in year three, that Engenia or XtendiMax mixed with glyphosate is not providing even close to the level of weed control that glyphosate alone did back in it’s hay day.
In many fields I visited the past few weeks as well as research conducted here at Jackson, it is clear that the first application of Engenia or XtendiMax mixed with glyphosate is often just a “set up” application on Palmer amaranth. Many Palmer amaranth have escaped that application though most will be growing slow enough that a follow up application of either a labeled dicamba product, Liberty or a PPO herbicide will finally control them. The control many experienced in year one where that tankmix was consistently taking Palmer amaranth out is not happening in 2019.
With respect to junglerice and goosegrass, glyphosate tankmixed with Engenia or XtendiMax is clearly a swing and a miss in a good number of fields. We had more reports of poor grass control just in the past couple days (pictures attached). Preliminary results from research on these grass species is that their tolerance level to glyphosate is high enough that when mixed with dicamba good control can no longer be achieved. Some have tried applying glyphosate at 8 gpa, with flat fan tips and without dicamba and have reported better, though not complete, control. Preliminary research would also suggest that follow-up applications of clethodim without dicamba will provide good control of these escaped grasses.
The expectation that all grasses and Palmer amaranth will be controlled 2 weeks after the dicamba and glyphosate application is not a reality. Some old tried and true weed management tactics are needed. One management change is to try to pick up grass control with a separate application from Engenia or Xtendimax. Another in cotton would be to start using hooded or layby rig again as that is a great way to help manage weeds the Xtend system is struggling to control. Finally, and likley most inpactful tactic is to overlay residual herbicides. Hands down, the best weed control in and Xtend crop is when overlaying residual herbicides are being used and getting activated. This is very clear with research this year as well as from observations from field visits. An Engenia or XtendiMax tankmixed with glyphosate application needs to be thought of as supplementing the control of the overlaying residual herbicides and not the other way around.