Fungicide reduction favors the control of phytophagous mites under both organic and conventional viticulture

Pesticides can have detrimental effects on non-target biodiversity, especially in intensively managed agroecosystems such as vineyards. However, new fungus-resistant grape varieties can greatly reduce the need and use of fungicides. Fungicides can have direct and indirect effects on economically important predatory mites (mainly Phytoseiidae) and on phytophagous mites (Tetranychidae, Eriophyidae) on which they prey. We investigated the impact of fungicide treatments on beneficial and phytophagous mite densities in 32 vineyards of organic and conventional wineries planted with susceptible and fungus-resistant grape varieties in the Palatinate region, Germany. Organic vineyards were sprayed with different formulations of sulfur, copper and potassium bicarbonate, while conventional vineyards received mostly synthetic fungicides. Fungicide applications were reduced by 47-80 % in fungus-resistant varieties, with stronger reductions under organic than under conventional management. Regardless of organic or conventional management, predatory mites (Phytoseiidae and Tydeidae) were significantly enhanced in vineyards planted with fungus-resistant varieties. Contrastingly, phytophagous mites (Eriophyidae) were enhanced in vineyards with fungus-susceptible varieties and in those under organic management. Densities of further predatory mite families increased under organic farming (Anystidae) or showed an interactive response to farming system and grape variety (Trombidiidae). Reduced fungicide applications through cultivation of fungus-resistant varieties enhance predatory mite densities and thus contribute to higher natural pest control potential. Thus, the cultivation of fungus-resistant grape varieties is an effective approach towards more environmentally friendly viticulture.