In vitroand In vivoActivity of Cyprodinil and Pyrimethanil on Botrytis cinereaIsolates Resistant to other Botryticides and Selection for Resistance to Pyrimethanil in a Greenhouse Population in Greece

No cross-resistance was observed between pyrimethanil or cyprodinil and the fungicides benomyl, iprodione or carbendazim + diethofencarb. In vitro, both anilinopyrimidine fungicides were effective against strains of Botrytis cinerearesistant to benzimidazoles and/or dicarboximides and against a wild type strain insensitive to diethofencarb (EC50values ranged between 0.03–0.19 and 0.006–0.054 μg ml−1for pyrimethanil and cyprodinil, respectively). Preventive applications of anilinopyrimidines completely protected young cucumber plants and fruits that were inoculated with all strains of B. cinerea. The effectiveness of pyrimethanil against grey mould was studied in greenhouse grown tomatoes in relation to (a) the type of infection and the progress of the disease on different plant parts and (b) the response of the naturally occurring B. cinereapopulation to the selection pressure caused by eight successive applications of this fungicide. Pyrimethanil effectively controlled grey mould on leaves, fruits and stems but did not significantly reduce the number of dead plants and fruits with 'ghost spot' symptoms. The selection pressure caused by the consecutive applications of pyrimethanil resulted in reduction of its effectiveness on leaves that became apparent after the sixth application. This was correlated with a shift of the B. cinereapopulation (not previously exposed to anilinopyrimidines) towards reduced sensitivity, probably due to the development of a low level of resistance (RL= 7.7). Pyrimethanil delayed the onset of the disease but it did not reduce the infection rate.