Cotton planting is well under way in Colquitt County and overlapping residual herbicides is key to manage glyphosate resistant Palmer amaranth. Palmer present at harvest often emerge within 17 d of planting, hence timeliness of POST 1 herbicides is critical. Palmer amaranth usually breaks through PRE herbicides between 13 and 17 day after application and activation. In the table below, post emerge herbicide options for Roundup and Liberty based programs for controlling Palmer amaranth in cotton.
Reducing the potential for POST herbicides to negatively impact yield:
1) Research suggests cotton injury near or during fruit set is more likely to be detrimental as compared to early season injury. Therefore, one should make all topical applications before the 8-leaf stage of cotton growth; programs above provide application intervals between PRE, POST1, and POST 2 applications to assist with this objective. After 8-leaf cotton, make sloppy directed or precision directed applications according to herbicides applied.
2) Research in 2015 suggested greatest negative impact from POST herbicide applications occurred when significant injury was observed for several weeks. Thus, it is important when making sequential POST applications to minimize injury with the 2nd POST application.