FUNGICIDE CONTROL OF STRAWBERRY FRUIT ROTS, AND THE FIELD OCCURRENCE OF RESISTANCE OF BOTRYTIS-CINEREA TO IPRODIONE, BENOMYL AND DICHLOFLUANID

Ten fungicides were screened in three experiments on two commercial farms in southern Victoria, Australia, for the control of the major fruit rots of strawberry, namely grey mould (Botrytis cinerea), black spot (Colletotrichum acutatum), leather rot (Phytophthora cactorum) and leak (Rhizopus stolonifer). Fruit were sampled at weekly intervals and rots were assessed after 3 days' incubation in the laboratory. When the incidence of rots from unsprayed plots from all trials were combined, leak (19% fruit rotted) was most important, followed by grey mould (16%), black spot (12%) and leather rot (8%). The best overall control of grey mould, black spot and leather rot was achieved by fluazinam. Thiram and dichlofluanid gave next best control of these diseases, although resistance of B. cinerea to dichlofluanid on one farm resulted in poor control of grey mould. Chlorothalonil was as effective as thiram in controlling grey mould, but its efficacy against black spot and leather rot was not determined. The dicarboximide fungicides iprodione and procymidone, and the benzimidazole fungicide benomyl, were on the whole less effective owing to the presence of fungicide-resistant strains of B. cinerea. The dicarboximides showed little activity against black spot or leather rot, whereas benomyl gave partial control of black spot. Fosetyl-aluminium controlled leather rot, but showed inconsistent activity against black spot. SC 0858 controlled only grey mould, but was phytotoxic on leaves. Copper hydroxide was ineffective against grey mould, and was phytotoxic on leaves and fruit; its activity against black spot and leather rot was not determined. Dichlofluanid, iprodione, procymidone and thiram showed some activity against leak. but results were inconsistent. The occurrence of B. cinerea isolates resistant to iprodione, benomyl and dichlofluanid was confirmed by tests in vitro. The apparent cross-resistance between isolates resistant to iprodione and dichlofluanid was also shown in vitro.