Factors Affecting Toxicity and Translocation of Glyphosate in Cotton(Gossypium hirsutum)

Toxicity of nonradiolabeled and translocation of 14 C-labeled glyphosate [ N -(phosphonomethyl)glycine] in cotton (Gossypium hirsutum L.) were evaluated under different environmental conditions as affected by surfactant and by the maturity of the plant tissue at the place of herbicide application. Toxicity was affected primarily by temperature with 21 to 40% greater cotton injury at 25 C than at 35 C. The addition of surfactant often increased toxicity under environmental conditions where toxicity was initially low. Absorption and translocation of 14 C was affected primarily by relative humidity (RH). At constant temperature and rate of surfactant, an increase in RH from 40 to 100% resulted in a 3- to 6-fold increase in translocation of 14 C. Autoradiograms indicated that the movement of the 14 C-label was primarily into leaves above the treated area. Translocation of 14 C was significantly greater following application to the mature lower stem than to the mature lower leaves or to immature upper stem or leaves of cotton.