Soybean (Glycine max) and Cotton (Gossypium hirsutum) Response to Simulated Drift of Glyphosate and Glufosinate1

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Abstract
Field research was conducted for a period of 2 yr to evaluate the response of soybean and cotton to simulated drift rates representing 12.5, 6.3, 3.2, 1.6, and 0.8% of the usage rates of 1,120 g ai/ha glyphosate (140, 70, 35, 18, and 9 g/ha, respectively) and 420 g ai/ha glufosinate (53, 26, 13, 7, and 4 g/ha, respectively). Early-postemergence applications were made to 2- to 3-trifoliate soybean and 2- to 3-leaf cotton, and late applications to soybean at first flower and cotton at early bloom. A mid-postemergence application was also made to cotton at pinhead square (first flower bud development). Soybean and cotton injury and height reductions occurred in most cases for only the two highest rates of the herbicides with variation noted between years. Soybean height was reduced by no more than 11%, regardless of herbicide rate or timing. On the basis of visual injury, soybean was more sensitive to glyphosate than to glufosinate when applied early in 1998, but sensitivity was equal for both the herbicides...