Exudation of Glyphosate from Wheat (<i>Triticum aestivum</i>) Plants and Its Effects on Interplanted Corn (<i>Zea mays</i>) and Soybeans (<i>Glycine max</i>)

Abstract

Glyphosate [ N -(phosphonomethyl)glycine] applied at 1.1 kg/ha to wheat [ Triticum aestivum (L.) ‘Arthur 71′] plants increased height and fresh weight of soybean [ Glycine max (L.) Merr. ‘Ransom′] seedlings planted in the pot at time of application of the glyphosate as the number of wheat plants treated increased from 5 to 30/pot. Height and fresh weight of the soybean seedlings also increased as the rate of glyphosate applied to wheat plants (5/pot) increased from 1.1 to 6.7 kg/ha. Increasing the rate of glyphosate from 1.1 to 6.7 kg/ha, however, reduced the height and fresh weight of soybeans when 30 wheat plants/pot were treated. In addition, when 6.7 kg/ha of glyphosate were applied to wheat plants, soybean-seedling plant height and fresh weight decreased as the density of wheat plants per pot increased from 5 to 30. The 14 C-glyphosate exuded into the soil from treated wheat plants was characterized by thin-layer chromatography. Trace amounts of the radio-label were present on thin-layer plates of leaf and stem extracts of corn ( Zea mays L.) plants, which were growing in the same pots with the treated wheat plants. The zone of activity had the same Rf value as the glyphosate standard.