In 2004 and 2005, glyphosate diuron and flumioxazin MSMA were applied POST-directed to cotton at 20, 30, 40, and 50 cm in height. Herbicides were directed to either the lower 2 cm of the cotton stem or to the lower 50% of the cotton stem to determine the impact of application timing and placement on cotton response. Glyphosate diuron resulted ≤ 22% injury when applied high on the stem and ≤ 8% injury when applied low on the stem. Regardless of application placement or timing, no yield reductions were observed as a result of glyphosate diuron application. Conversely, flumioxazin MSMA applications resulted in 93 and 64% injury when applied high POST-directed (HPD) to 20- and 30-cm cotton, respectively. Low POST-directed (LPD) applications caused 33 and 23% injury to 20- and 30-cm cotton, respectively. In both years, HPD applications of flumioxazin MSMA on 20-cm cotton resulted in excessive yield loss (94 to 87%), whereas yield loss was only noted in 30-cm cotton in 2004. No yield loss was observed in 40- or 50-cm cotton. Additionally, LPD applications of flumioxazin MSMA, though causing significant visual injury, did not result in a yield reduction at any application timing. Although cotton became more tolerant to flumioxazin MSMA as the season progressed, the research suggests that applications of flumioxazin should be made with precision or delayed until cotton reaches 40 cm in height.

Nomenclature: Diuron, flumioxazin, glyphosate, MSMA, Cotton, Gossypium hirsutum L. ‘DPL 555’, GOSHI