Influence of alkyl oleates on efficacy of phenmedipham applied as an acetone:water solution on Galium aparine

Abstract

Galium aparine plants were treated at the two-whorl stage with technical-grade phenmedipham. The active ingredient was applied at 10 doses as an acetone:water solution, without emulsifier, alone or in mixture with an ester of oleic acid (methyl, butyl, octyl, dodecanyl, octadecanyl). The plant response was described by a log-logistic regression model. Phenmedipham applied alone did not kill the plants even at the highest dose (1621 g a.i. ha-1). In contrast, addition of any alkyl oleate to phenmedipham killed the plants at the 200-400 g a.i. ha-1 doses. The alkyl oleates differently affected activity of phenmedipham. Their effects could be ranked as follows: butyl ≥ methyl; octyl > methyl; dodecanyl ≤ methyl; octadecanyl < methyl oleate. Thus, butyl and octyl oleate promoted phenmedipham activity more than methyl oleate.