THE RELATIONSHIP BETWEEN THE HERBICIDAL EFFECT OF 2,6-DICHLOROBENZONITRILE AND ITS PERSISTENCE IN THE SOIL

Summary. A series of experiments with 2,6-dichlorobenzonitrile is described. It is demonstrated that 2,6-DBN is highly phytotoxic when applied as a soil drench or preemergence spray in the greenhouse, but measurement of crop and weed responses in the field, accompanied by quantitative assessment of the chemical residues in the soil, indicates that the persistence of 2,6-DBN following surface application is short under both tropical and temperate (winter) conditions. It is, however, extended from a few days to several weeks if the chemical is incorporated into the soil immediately after application. Under tropical conditions the effect of 4 lb/ac applied to the surface is roughly equated to 2 lb/ac immediately watered-in, 1.5 lb/ac immediately raked-in, or 1 lb/ac both watered- and raked-in, and a delay of 4 hours between application and incorporation is shown to reduce the effectiveness of the chemical by about half. The lack of persistence of 2,6-DBN when applied to the soil surface, and the modifying influence of soil incorporation and watering is attributed to its high vapour pressure (5 × I0⁻⁴ mm Hg at 20° C) and its relatively low solubility in water (20 ppm at 25° C).
Le rapporl entre l'activité herbicide du 2,6-dichlorobenzonitrile et sa persistance dans le sol