Large-scale analyses of pesticide use and risk patterns are essential for the development of sustainable pest management strategies and regional ecosystem conservation plans. This study investigated the spatio-temporal patterns of pesticide use on walnuts and associated risks to surface water in California. Pesticide use data from 1996 to 2013 were obtained from the Pesticide Use Report (PUR) database, and pesticide risks to surface water were evaluated using the Pesticide Use Risk Evaluation (PURE) indicator. Results show that in-season fungicides were applied at the highest intensity, while in-season insecticides posed the highest risk to surface water, mainly due to the intensive use and high toxicity of organophosphates and pyrethroids. The spatial distribution of temperature and humidity largely determined the spatial patterns of insecticide and fungicide use, and regulatory programs further complicated herbicide use patterns. Spatial differences in drainage density, precipitation, and soil permeability seem to drive the spatial patterns of pesticide risk. The significant decrease (<i>p</i> &lt; 0.05) in risks associated with toxic chemicals suggested the effectiveness of regulation and awareness of farmers on limiting the use of high-risk pesticides such as chlorpyrifos, malathion, maneb, and diuron. Increasing herbicide use, especially in some of the ground water protection areas (GWPAs), indicated the increasing reliance on herbicides and intensive selection pressure might have accelerated the evolution and spread of resistant weeds. Increasing use was observed in high-risk pesticide pyrethroid as well as herbicide paraquat dichloride and oxyfluorfen, possibly as organophosphate and glyphosate alternatives, respectively. The results from this study will not only guide the formulation of effective pest management policy in California in the future, but also demonstrate the potential of spatially distributed risk indicators in large-scale risk assessment.

Spatio-temporal analyses of pesticide use on walnuts and potential risks to surface water in California

254th National Meeting (2017)

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