Background and Aims The presence of viable sources and of conditions favourable for conidial production, dispersal and deposition is essential for a high number of Botrytis cinerea conidia to be available at host infection sites. This study investigated the effect of environmental conditions, growing media and grape organs on the sporulation of ten strains of different genotypes and geographical origin. Method and Results Media of different water activity and similar to berry juice at several maturity stages, grape bunch trash or mature berries were inoculated with B. cinerea and incubated under variable conditions of temperature and relative humidity. Optimal conditions for sporulation were: temperature between 15 and 20°C, relative humidity >65.5%; water activity=0.971; and medium similar to the juice of softening berries. Conidia produced on bunch trash and mature berries were significantly correlated with those on artificial media. Conclusions Differences among strains did not change the response pattern of sporulation to the environmental conditions. Equations were then developed for describing the effect of temperature and relative humidity on sporulation, and of degree-days on the length of latent period. Significance of the Study When combined with predictive models for infection, our equations could contribute to the development of an effective disease prediction system for Botrytis bunch rot.