Significance of carry over inoculum, flower infection and latency on the incidence of Botrytis cinerea in berries of grapevines at harvest in New South Wales

The incidence of Botrytis cinerea was monitored at different stages in the growth of 7 grapevine cultivars in 14 vineyards in New South Wales, Australia, over a period of 10 years. The incidence of B. cinerea fluctuated during the growing season. While carry over infection from the previous season explained 70% of variation in flower infection, it only accounted for 26% of berry infection. Infection of flowers explained 78% of berry infection. Latent infection resulted in 58% of inoculum carried over to the following season. Disease prediction models were developed on the basis of these quantitative relationships so that growers can use them to measure disease risk and respond by rational application of fungicides. For instance, based on the model, a 50% incidence of B. cinerea monitored on grapevine tissues carried over from previous season can predict a 30% primary infection of flowers in the new season. This will require fungicide application during flowering so as to reduce the predicted risk of 22% berry infection at harvest.