| Spider mites (Acari: Tetranychidae) are phytophagous pests of several crops, including wine grapes (Vitis vinifera L.). Specialist and generalist predatory mites (Acari: Phytoseiidae) have often been used in spider mite biological control programs, although research in this area has been lacking in Washington State wine grapes. Thus, I surveyed the mite and insect fauna of Washington wine grapes and the mite species on unsprayed vegetation in the region, assessed the current status of spider mite control within vineyards, investigated how pesticides affected the mite community, and explored effects of generalist phytoseiid mites and grapevine canopy structure on pest mite densities. I surveyed the grape mite community within: (1) unmanaged grapevines without chemical input, (2) managed vineyards exposed to fungicides and herbicides, and (3) managed vineyards exposed to fungicides, herbicides, insecticides, and acaricides. A guild of generalist phytoseiid mite species were found on unmanaged grapevines and unsprayed vegetation in the region, while generalists were virtually absent from managed vineyards. Although unmanaged grapevines had lower spider mite, higher generalist phytosend mite, and comparable specialist phytoseiid mite densities, mite densities did not differ between managed vineyards. I suspected this was partially due to widespread usage of sulfur. Field experiments supported this theory, with sulfur, alone and in combination with the insecticide chlorpyrifos, suppressing pest and predatory mites. In other open-field experiments we manipulated densities of generalist phytoseiid mites and canopy size. Increasing densities of generalists resulted in lowered spider mite densities and temporary suppression of specialist phytoseiid mites. These experiments demonstrate that generalists can significantly slow spider mite population growth in grapes, but suggest that spider mite control may be most effective through the combined impacts of generalist and specialist phytoseiid mites. |
