The very wet May has led to rapid degradation of the PRE applied herbicides in cotton. In our tests at Jackson that were planted 21 days ago all the PRE applied herbicides have broken. Some broke very quickly after application while others held on a little better, even with all the rain.
Relying on dicamba for residual pigweed control with all the wet weather did not pan out. It was very hard to distinguish the untreated checks from the dicamba PRE applied treatments. They were both jail breaks.
The very water soluble Cotoran also provided short lived residual Palmer amaranth control. By 21 DAA Cotoran pigweed control was down to 60%.
Two herbicides that worked relatively well in the wet weather were Caparol and Brake FX. Caparol, of course the one in short supply this spring, provided relatively good (77%) Palmer amaranth control while Brake FX, not surprisingly, was still providing fairly good control (87%) 21 DAA.
Warrant was more hit or miss and averaged about 70% control by 21 DAA. Diuron, which some used to replace the supply limited Caparol, also provided control in the 70% range.
Though all the residual herbicides used played out quicker than anyone of us would like or hope, they did buy some time to where POST applied herbicides have a chance to be applied timely. Moreover, those residual products reduced the numbers of Palmer amaranth that the POST applied herbicides have to control. Those results are a WIN!