The Effect of Adjuvants and Oil Carriers on Photodecomposition of 2,4-D, Bentazon, and Haloxyfop

Abstract

Laboratory photolysis rates of 2,4-D [(2,4-dichlorophenoxy)acetic acid], bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], and haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} in dilute aqueous solution were enhanced by the presence of adjuvants. Addition of 1.0% (v/v) petroleum oil concentrate (POC), 1.0% (v/v) soybean oil concentrate (SBOC), and 0.15% (v/v) emulsifier package (EP) enhanced herbicide photolysis rates more than addition of 0.15% (v/v) oxysorbic (20 POE) (polyoxyethylene sorbitan monolaurate). Bioassays showed that phytotoxicity of photolyzed herbicide solutions was negatively correlated with time of exposure to ultraviolet light. Addition of 0.85% (v/v) acetophenone to aqueous herbicide solutions containing 0.15% (v/v) oxysorbic strongly sensitized photodegradation of 2,4-D, and to a lesser extent, haloxyfop. Acetophenone had no effect on bentazon photolysis in the presence of oxysorbic. In another study, herbicides were dissolved in white mineral oil or once-refined soybean oil and exposed to ultraviolet light. After a 6-h exposure, there was 92% loss of haloxyfop in mineral oil and 36% loss in soybean oil. There was no difference between oils in affecting the photolysis rate of 2,4-D or bentazon.