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

Abstract

Toxicity of nonradiolabeled and translocation of14C-labeled metriflufen3{2-[4-(4-trifluoromethylphenoxy)phenoxy] propanoic acid} in cotton (Gossypium hirsutumL. ‘Stoneville 213’) were evaluated under different environmental conditions as affected by surfactant and by the maturity of stem or leaf tissue at the place of herbicide application. Cotton was very tolerant to metriflufen, with the greatest tolerance at high temperatures. The herbicide entered the plant quite rapidly and autoradiographs indicated that radioactivity from the herbicide moved freely throughout the plant. Relative humidity (RH) between 40 and 100% had little effect on metriflufen toxicity. Two weeks after treatment with metriflufen at 0.5 kg/ha, cotton was essentially free of injury symptoms at 35 C, but injury was as great as 41 and 13% at 18 and 25 C, respectively. All plants recovered fully after 6 additional weeks in the greenhouse. When surfactant was added to the spray solutions, cotton injury was frequently increased during the first 2 weeks but not after 8 weeks. Accumulation of14C at the site of14C-metriflufen application was 31 to 65% after 48 h. Between 16 and 51% of the applied14C moved from the treated area by translocation into other parts of the plant, or by volatilization into the atmosphere. Movement was greatest from stem tissue at 35 C and 100% RH. There was no correlation between14C movement and herbicide toxicity within the plant. The selectivity of metriflufen to cotton probably results from deactivation by, or tolerance within, the plant rather than from differential absorption and translocation of the herbicide.