Cotton (Gossypium hirsutum) Injury from Simulated Quinclorac Drift

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Abstract
Cotton (Gossypium hirsutum) response was evaluated when quinclorac was applied prior to cotton emergence (preemergence) and to cotton in the cotyledon and pin-head square stages in 1988, 1989, and 1990. Quinclorac applications at 9, 17, 35, 70, and 140 g ha−1 prior to cotton emergence had little effect on cotton growth, with only 140 g ha−1 causing stand reduction or stunting. Quinclorac application to cotton in the cotyledon stage caused more damage, and 70 g ha−1 caused crop injury. Greatest phytotoxicity was observed when quinclorac was applied to cotton at pin-head square, with all rates including 9 g ha−1 causing injury. Cotton injury consisted of leaf strapping and malformation of reproductive structures. Regression analysis revealed yield was reduced by quinclorac applications to cotton in the cotyledon or pin-head square stage. The approximate regression equation to predict cotton yields after pin-head square application of quinclorac was [yield] = [yield with no injury] − 10(quinclorac rate in g ha−1).