Synergistic Phytotoxicities of Herbicide-Insecticide Combinations in Soil

Abstract

Combinations of 3-(3,4-dichlorophenyl)-l,l-dimethylurea (diuron) with O,O-diethyl S-2-(ethylthio)-ethyl phosphorodithioate (disulfoton) or O,O-diethyl S-(ethylthiomethyl) phosphorodithioate (phorate) in soil resulted in synergistic phytotoxicities. These synergistic phytotoxicities persisted 21 to 27 weeks in alternately fallow-cropped soils treated with 0 to 12 ppm disulfoton or phorate and 0 to 1.0 ppm diuron where oats (Avena sativa L., var. Mark-ton) was the bioassay plant, and persisted 5 to 15 weeks in alternately fallow-cropped soils treated with 0 to 12 ppm disulfoton or phorate and 0 to 1.33 ppm diuron where corn (Zea mays L., var. US 13) was the bioassay plant. The persistence of the combined pesticides corresponded closely with persistence of the individual pesticides. Corn and cotton (Gossypium hirsutum L., var. Acala 4-42) were more tolerant than was oats to diuron and diuron-insecticide combinations.