Reentry After Methomyl Application in Greenhouses

Abstract

Abstract To establish practical reentry intervals in greenhouses, decay patterns of methomyl were assessed. Methomyl is a toxic carbamate insecticide with a reversible, mild to moderate cholinesterase-inhibiting activity. The investigation was carried out under conditions of normal work practice in four greenhouses during six test runs with various combinations of the factors: substrate (soil or rock wool), plant type (cucumber or tomato), wet or dry spraying, area of the greenhouse, and dosage of application. Personal and area samples of the air, hand rinse samples, leaf samples, and samples of the soil surface or the plastic cover of the rock wool were taken during a period of 7 days after application of methomyl. Decay rates of methomyl concentrations in the air, on the leaves of the plants, and on the surface could be described by first-order kinetics with half-life times ranging from 1.6 to 4.3 days. The decay curves of the area concentrations could not be used to derive safe reentry intervals becaus...