Effect of management practices on behavior of nine pesticides in runoff water at a container nursery

Pesticide runoff from container plant nurseries may alter aqueous ecosystems and damage sensitive container plant species if runoff water is recycled for irrigation. A series of field studies was conducted at a container nursery from 1998 to 2000 quantifying runoff of nine commonly used ornamental pesticides and investigating management practices that may mitigate pesticide runoff. Pesticides were applied to large (0.2 Ha) replicated production beds and overhead irrigation created runoff water. Runoff samples were collected from the first through third runoff event after pesticide application. Samples were analyzed for pesticide residues by high pressure liquid chromatography.; Large amounts of metalaxyl, isoxaben, oryzalin, chlorothalonil and thiophanate-methyl were detected in runoff water. Smaller quantities of chlorpyrifos, trifluralin, oxyfluorfen and pendimethalin were detected in runoff water. Concentrations detected did not exceed known toxicity levels for aquatic organisms.; Several container plant production management practices were evaluated for their effect on pesticide runoff. Allowing weeds to grow in containers did not adversely affect container plant quality but reduced herbicide amounts in runoff water. Implementation of integrated pest management strategies for determining pesticide applications reduced levels of fungicides in runoff water and did not result in decreased container plant salability. Total isoxaben amounts were greater from a granular formulation than a sprayable formulation but no differences due to formulation were detected for trifluralin. Total thiophanate-methyl amounts transported in runoff were lower when post application irrigation volume was reduced as compared to a pulsed irrigation volume, but amounts of chlorpyrifos, isoxaben and oryzalin were not affected.; A simple model is proposed to predict runoff amounts and pesticide concentrations in runoff water for the first runoff event after pesticide application. The runoff model is based on applied irrigation amount and was found to accurately predict runoff volume within 40% of actual values. Pesticide levels were modeled based on the correlation of the pesticide's aqueous solubility value to concentration in runoff. The model accurately predicted concentrations found in the field research for seven of the nine pesticides.