Control of Powdery Mildew in Wild and Cultivated Grapes by a Tydeid Mite

Abstract

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 lambiis 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. lambiwas able to reduce the incidence and severity of grape powdery mildew on pottedV. ripariavines placed in the field.Orthotydeus lambiwas also able to reduce the severity of powdery mildew on the cultivated grapeV. vinifera(cv “Cabernet Sauvignon”) under greenhouse conditions and on the cultivated grape “Chancellor” (aVitisinterspecific hybrid) under vineyard conditions. A survey of wild and cultivated grapes in central New York indicated thatO. lambiis common on wild grape leaves but generally rare in commercial vineyards. We present experimental data showing that two commonly used fungicides, sulfur and mancozeb, suppressO. lambipopulations under vineyard conditions. Our results suggest thatO. lambiand 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.