Understanding infection pathways and tree factors for integrated disease management of brown rot and grey mould in sweet cherry

Brown rot and grey mould cause significant losses in sweet cherry, particularly in wet years and despite guidelines for integrated disease management. Studies in a Tasmanian orchard found that Botrytis cinerea was associated with 95% of fruit which was symptomatic at harvest, while Monilinia spp. were not detected. Total rot at harvest varied significantly between cherry varieties, while reduced crop load or removing fungicide during the last 53 days of fruit growth had no effect on harvest rot incidence. To determine how disease develops during the season, samples of fruit from two varieties (Simone and Regina) were obtained fortnightly over a 53 day period prior to commercial harvest and expression of “latent” non-symptomatic infections was induced. While incidence increased towards harvest, this study showed that a substantial amount of infection had already occurred prior to 53 days before harvest. Flowering is often assumed to be the time of most susceptibility to infection, while inoculum may be highest from fruit drop onwards. An assessment of the growth stages most susceptible and the optimal temperature and wetness conditions required for infection is currently being evaluated with key Australian varieties. This information is critical to guide decision-making about timing of fungicide application.