A number of folks in the past few days have asked about the best way to take out the Palmer amaranth that has lived through an Engenia or XtendiMax application. The answer depends upon the crop and if there is still time on the label to try to respray a labeled dicamba product.
In cotton the “go to” is Liberty. Hot and humid conditions greatly favor the efficacy of Liberty or any glufosinate product on Palmer amaranth. Therefore, the July spray window is right in Liberty’s wheelhouse for best performance. Remember, if the choice is to come back with Engenia or XendiMax the cut-off in cotton is 60 days after planting.
In soybean the options are limited to either re-treat with a labeled dicamba product or spray with Ultra Blazer, Cobra or Flexstar. Again, please refer to the labels of Engenia or XtendiMax which state that those herbicides can only be used in Xtend soybeans up to the R1 growth stage or 45 days after planting. By the time one can determine if the Palmer amaranth is going to die from the first dicamba application the soybeans will often be well past the R1 deadline.
In past years in our research, as well as many applications out in the field, good control of Palmer amaranth that has escaped a dicamba application has been achieved with either Ultra Blazer, Flexstar or Cobra. One thing to consider here, in July, is if the field is slated to be planted to corn or grain sorghum next year then do not use Flexstar or any fomesafen product as carryover could be an issue in 2020.
There have been several inquires about using rates above 12.8 oz/A of Engenia or 22 oz/A of XtendiMax on the Palmer amaranth that has escaped earlier applications. Those are the labeled rates and no higher rates can be used! It is July so this is dicamba drift season in Tennessee. Dicamba drift/volatility complaints have started in the last week from homeowners, dove field owners and others utilizing non-Xtend broadleaf crops. We do not need to do anything that could make more issues. Stick to the labeled rates!!!