Influence of spray schedules on fungicide resistant populations of Botrytis cinerea Pers. on grapevine

Treatments with dicarboximide fungicides provided only 20 to 40% control of grey mould on grape (cv. Moscato d'Asti) in vineyards where benzimidazole and dicarboximide resistant strains ofBotrytis cinerea Pers. constituted about 50% of the fungal population and a high disease pressure existed. The percentage of dicarboximide resistant strains increased after treatment. Fungicide combinations of a benzimidazole with diethofencarb, sprayed twice per season or once alternated with a dicarboximide, provided satisfactory control of grey mould and decreased the percetage of benzimidazole resistant strains. A combination of thiram and procymidone controlled grey mould, but increased dicarboximide resistance in the population.