Influence of Flumioxazin Application Timing and Rate on Cotton Emergence and Yield

Abstract

Palmer amaranth is one of the most troublesome weeds in the southeast. Significant reductions in cotton yield because of Palmer amaranth competition warrant intense control efforts consisting of both PRE and POST herbicides. Flumioxazin is a soil-active, protoporphyrinogen oxidase-inhibiting herbicide that is labeled for use in cotton 14 to 21 d before planting; however, shorter preplant application intervals could increase the duration of control from this herbicide. Flumioxazin was applied at 3 rates (0.03 and 0.06 kg ai ha−1in 2009 and an additional rate of 0.09 kg ai ha−1in 2010 and 2011) and 6 application timings (30, 20, 15, 10, 5, and 0 d before planting cotton). Cotton emergence, height, and yield were documented. In 2009, at the Jay and Citra, FL, sites, cotton emergence, plant height, and yield were not affected by any herbicide rate or timing. At Dawson, GA, in the same year, significant reduction in cotton stand counts were observed with application timings < 10 d before planting. Cotton height was reduced similarly at Dawson, GA, but recovered to levels equal to the control by 45 d after planting (DAP). It is believed that rainfall during cotton emergence resulted in this significant level of injury at Dawson, GA. In 2010 and 2011, at Citra, FL, cotton emergence was only reduced when 0.06 and 0.09 kg ha−1were applied at planting. Cotton height showed a similar pattern with additional reductions in height at 0.03 kg ha−1applied at planting and 0.09 kg ha−1applied 5 d before planting. In 2010 and 2011, at Citra, FL, yield was reduced when 0.09 kg ha−1flumioxazin was applied 5 d before planting and when 0.06 and 0.09 kg ha−1were applied at planting. These results indicate that flumioxazin application intervals can be shortened with little crop impact likely to be seen at lower use rates. However, rainfall at crop emergence has the potential to significantly injure cotton and reduce yield.