Viticulture in Washington State dates back to the 1800s, but wine grape production has doubled in the last decade, and the industry is still expanding. Washington growers frequently utilize broad-spectrum insecticides for arthropod pest control and sulfur for powdery mildew, a common fungal disease that can render a crop unmarketable. However, chemical pest control can have undesirable consequences, including secondary pest problems, pest resistance, and reduction of predator densities. In order to investigate how chemical input was affecting the grape arthropod fauna, mite densities were monitored via leaf sampling in five grape growing regions of south-central Washington and northern Oregon. During 2001, 48 vineyard sites were sampled monthly from June-Sept., while in 2002, 30 sites were sampled. Sites were classified as high, low, and no according to insecticide/miticide input, and received variable numbers of sulfur applications. Insecticide/miticide input did not appear to significantly affect mite densities. However, as the number of sulfur applications increased, pest spider mite densities increased in a linear fashion while predatory phytoseiid mite and fungivorous tydeid mite densities decreased. Generalist-feeding phytoseiid mites appeared more susceptible to sulfur applications than specialist-feeding phytoseiids. Implications for spider mite biological control in vineyards will be discussed.
Species 1: Acari Tetranychidae Tetranychus
Species 2: Acari Phytoseiidae Galendromus
Species 3: Acari Tydeidae
Keywords: grapes, sulfur
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