Persistence of Some Plant Growth-Regulators when Applied to the Soil in Herbicidal Treatments

Abstract

Treatment of greenhouse soil with high rates of 2,4-dichlorophenoxyacetic acid prevented normal germination of seeds and development of plants during the first 8 weeks following soil treatment. After this period, plants growing in treated soil appeared normal. In the field 2,4-dichlorophenoxyacetic acid did not persist in the soil >80 days after treatment, while isopropyl-N-phenylcarbamate had apparently disappeared 60 days after treatment. In another field expt., a comparison was made of the persistence of 2,4-dichlorophenoxyacetic acid, 2-methyl-4-chlorophenoxy-acetic acid and isopropyl-N-phenylcarbamate. After 68 days the soil still contained enough 2-methyl-4-chlorophen-oxyacetic acid to be toxic to soybeans. On the other hand, 68 days after the soil had been treated with 2,4-dichlorophenoxyacetic acid or isopropyl-N-phenylcarbamate, there was practically a complete disappearance of herbicides from the soil. The 2,4,5-trichlorophenoxyacetic acid retained its herbicidal effectiveness in the soil longer than did 2,4-dichlorophenoxyacetic acid.