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TECHNICAL REPORTS

Ecological Risk Assessment

Spray Deposition from Ground-based Applications of Carbaryl to Protect Individual Trees from Bark Beetle Attack

^a Pacific Southwest Research Station, USDA Forest Service, 1731 Research Park Drive, Davis, CA 95618
^b Forest Health Protection, USDA Forest Service, 4746 South 1900 East, Ogden, UT 84403
^c Agricultural and Environmental Services Lab., The Univ. of Georgia, 2300 College Station Road, Athens, GA 30605

^* Corresponding author (cfettig{at}fs.fed.us).

Received for publication June 8, 2007. Bark beetles (Coleoptera: Curculionidae, Scolytinae) are recognized as the most important tree mortality agent in western coniferous forests. A common method of protecting trees from bark beetle attack is to saturate the tree bole with carbaryl (1-naphthyl methylcarbamate) using a hydraulic sprayer. In this study, we evaluate the amount of carbaryl drift (ground deposition) occurring at four distances from the tree bole (7.6, 15.2, 22.9, and 38.1 m) during conventional spray applications for protecting individual lodgepole pine (Pinus contorta Dougl. ex Loud.) from mountain pine beetle (Dendroctonus ponderosae Hopkins) attack and Engelmann spruce (Picea engelmannii Parry ex Engelm.) from spruce beetle (D. rufipennis [Kirby]) attack. Mean deposition (carbaryl + -naphthol) did not differ significantly among treatments (nozzle orifices) at any distance from the tree bole. Values ranged from 0.04 ± 0.02 mg carbaryl m^–2 at 38.1 m to 13.30 ± 2.54 mg carbaryl m^–2 at 7.6 m. Overall, distance from the tree bole significantly affected the amount of deposition. Deposition was greatest 7.6 m from the tree bole and quickly declined as distance from the tree bole increased. Approximately 97% of total spray deposition occurred within 15.2 m of the tree bole. Application efficiency (i.e., percentage of insecticide applied that is retained on trees) ranged from 80.9 to 87.2%. Based on review of the literature, this amount of drift poses little threat to adjacent aquatic environments. No-spray buffers of 7.6 m should be sufficient to protect freshwater fish, amphibians, crustaceans, bivalves, and most aquatic insects. Buffers >22.9 m appear sufficient to protect the most sensitive aquatic insects (Plecoptera).

Abbreviations: a.i., active ingredient • dbh, diameter at breast height (1.37 m) • HPLC, high-performance liquid chromatography • LC₅₀, median lethal concentration that kills 50% of test organisms • SDI, stand density index