Effects of Ground Cover and Formulation on Herbicides in Runoff Water from Miniature Nursery Sites

Abstract

Granules of isoxaben plus trifluralin and liquid applications of isoxaben plus oryzalin were applied to miniature nursery plots covered with plastic, woven landscape fabric, or gravel with no cover. Herbicide concentrations were monitored in runoff water over a 30 d period. Runoff losses of isoxaben from the sprayable formulation applied to gravel were 5% greater than from plastic and 4% greater than losses from fabric in 1992. Similarly, oryzalin losses from the sprayable formulation applied to gravel were 7% greater than losses from plastic and 4% greater than losses from the fabric ground cover. In contrast, loss of isoxaben from the granular formulation applied to plastic was 7% greater than loss from gravel in 1993. Isoxaben losses from the granular formulation applied to fabric were intermediate. Trifluralin losses from the granular formulation applied to plastic and fabric were both 3% greater than losses from gravel. In addition, isoxaben losses from the granular formulation were 11 and 10% greater than loss from the sprayable formulation applied to the plastic and fabric-covered plots, respectively. Isoxaben losses from the sprayable formulation applied to gravel were 11% greater than losses from the granular formulation. In an experiment to determine herbicide release patterns and the effect of light on residues from the granular formulation of isoxaben and trifluralin in irrigation effluent, water was monitored for 36 d. Approximately 20% of the applied isoxaben and 7% of the applied trifluralin was detected in irrigation water during the 36 d period. These studies indicate that runoff losses and the ultimate fate of isoxaben, oryzalin, and trifluralin applied in nursery settings depend on factors including ground cover composition, herbicide formulation, and photochemical degradation.