Plant Responses to Haloxyfop as Influenced by Water Stress

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Abstract
Green foxtail [Setaria viridis (L.) Beauv. # SETVI] and proso millet [Panicum miliaceum (L.) #PANMI] growing under high water stress for 3 days before + 3 days after foliar applications of the methyl ester of haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} developed less herbicide injury than plants growing under low water stress. There was a 32% reduction in the retention of haloxyfop sprays by proso millet when growing under high water stress than when growing under low water stress. Haloxyfop spray retention by green foxtail was not affected by the degree of water stress. The translocation of 14C out of 14C-haloxyfop-treated leaves was significantly greater in plants of both species when growing under low water stress than when growing under high water stress. The conversion of 98% of the absorbed 14C-haloxyfop-methyl to 14C-haloxyfop and unidentified polar metabolites occurred in both species within 12 h of application. The green foxtail growing under low water stress contained greater concentrations of 14C-haloxyfop than did plants growing under high water stress. Levels of 14C-haloxyfop were the same in proso millet growing under high and low water stress. The reduced injury of green foxtail and proso millet growing under high water stress from postemergence sprays of haloxyfop can be attributed to a reduction in herbicide translocation in both species, plus a reduction in spray retention by proso millet or changes in the metabolism of the herbicide in green foxtail, which results in a reduction in the concentration of haloxyfop.