There are some who have or soon will apply Zidua (pyroxasulfone) via impregnated fertilizer in cotton. My understanding is that this has been done successfully in Texas in years past. Along with those applications we have applied some in research as well a few days ago. One would expect no cotton injury applied via fertilizer to dry foliage. Indeed, that was the case in our trials.
The directions on the label state that when applying Zidua via impregnated fertilizer, “the fertilizer must be applied at a minimum of 200 lbs per acre”. This is to assure the best chance to obtain adequate coverage. In reality, most are using 250 to 350 lbs of dry fertilizer/acre. In theory, the more fertilizer applied to the acre the more even and consistent the residual weed control. The max fertilizer rate limited by the label is 750 lbs/A.
The Zidua rate most are using is 3.2 ozs/A. The calculation to apply the correct rate is: (Fl oz of Zidua x 2000)/ pounds of fertilizer/acre = oz of Zidua for 1 ton of fertilizer).
Another pyroxasulfone-based herbicide (Anthem Flex) currently is not labeled to be applied via impregnated fertilizer. However, the folks at FMC have applied for a label and expect to hear something early next year.
The one drawback to applying in this fashion is that one can likely expect some leaf burn if the fertilizer is applied and the cotton leaves are wet. This will be something to watch for with both commercial and research applications this summer.
This way of getting a herbicide that provides good residual control of Palmer amaranth and grasses would have a lot of advantages in cotton. Since many do not have time or equipment to run post-direct applications this would be a good alternative. It also does not tie up a sprayer which should improve the chances that POST applied pesticide applications can be made more timely to cotton and soybeans. It is also a good option to get a residual on cotton with little crop injury in those fields that have been planted to 30”-wide rows. We will keep you posted on this research and the level of weed control this method provides.