AbstractTen years of watershed‐scale research has been conducted on the fate of forestry‐use pesticides in forested catchments under mainly operational conditions throughout the southern United States. Studies have evaluated chemicals such as hexazinone, picloram, sulfometuron methyl, metsulfuron methyl, azinphosmethyl, triclopyr, carbofuran, lindane, malathion, fenvalerate, copper‐chromium‐arsenic, and pentachlorophenol. Off‐site movement in stream flow, leaching to ground water, and thermal combustion have been examined. Model verifications of pesticide fate and dissipation and risk analyses have been conducted using simulation models such as GLEAMS, CREAMS, and PRZM. Field study data indicate that movement is controlled by the main hydrologic pathways (e.g., surface runoff, infiltration, interflow, and leaching below the root zone). Peak residue concentrations tend to be low (<500 μg/L), except where direct applications are made to perennial streams or to ephemeral channels, and where buffer strips are not used and do not persist for extended periods of time. Indirect effects noted from the use of pesticides in forested watersheds include temporarily increased nitrate nitrogen losses, reduced sediment yields, temporal changes in terrestrial invertebrate abundance, reduced plant diversity, and changes in particulate organic matter transport in streams. Very limited cumulative effects research has been conducted. The effects of increasing watershed size on herbicide concentrations and the impact of nonforestry pesticides on fish have been examined. Analyses conducted in regional environmental impact statements indicate that the low concentrations and short persistence of forestry pesticides in surface and ground water do not pose a significant risk to water quality, aquatic biota, or hu
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