Control of powdery mildew in wild and cultivated grapes by a tydeid mite

The leaf surface of woody perennials is inhabited by an extraordinary diversity of mites. Although a majority of these mite species are thought to feed on fungi or other microbes, their ability to control plant pathogens has not been rigorously investigated. We present experimental evidence that a tydeid mite, Orthotydeus lambi, can suppress the development of grape powdery mildew on wild and cultivated grapes. Orthotydeus lambi is abundant on the leaves of a number of different tree and vine species in the northeastern United States, including the riverbank grape, Vitis riparia, When released at realistic densities, O. lambi was able to reduce the incidence and severity of grape powdery mildew on potted V. riparia vines placed in the field. Orthotydeus lambi was also able to reduce the severity of powdery mildew on the cultivated grape V; vinifera (cv "Cabernet Sauvignon") under greenhouse conditions and on the cultivated grape "Chancellor" (a Vitis interspecific hybrid) under vineyard conditions. A survey of wild and cultivated grapes in central New York indicated that O. lambi is common on wild grape leaves but generally rare in commercial vineyards. We present experimental data showing that two commonly used fungicides, sulfur and mancozeb, suppress O. lambi populations under vineyard conditions. Our results suggest that O. lambi and other mycophagous mites play an important role in regulating some epiphyllous fungi in the wild. We may be able to exploit mycophagous mites as biological control agents of important fungal pathogens of crop plants. (C) 1999 Academic Press.