Foliar Absorption and Translocation of Herbicides from Aqueous Solution and Treated Soil

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Abstract
It has been suggested that soil treated with a herbicide and subsequently carried by wind and deposited on plant foliage can cause crop injury. This study compared foliar uptake and translocation of herbicides applied to plants as an aqueous solution or in herbicide-treated soil. Leaves of 3-wk-old seedling alfalfa, grape, and pea were treated with 14C-labeled thifensulfuron, chlorsulfuron, glyphosate, 2,4-D, and bromoxynil. Significant amounts of all herbicides were absorbed by pea, alfalfa, and grape from the aqueous solutions, whereas very limited absorption occurred from herbicide-treated soil. Prolonged and multiple exposure to herbicide-treated soil did not increase herbicide uptake. High relative humidity enhanced herbicide absorption from aqueous solutions but not from herbicide-treated soil. All herbicides except bromoxynil were readily translocated in alfalfa, grape, and pea. Limited quantities of herbicides were absorbed from herbicide-treated soil by plant foliage, and this small amount is unlikely to cause crop damage.