Risk analysis for latent infection of prune by Monilinia fructicola in California

The quantitative relationships between incidence of latent infection (ILI) of prune by Monilinia fructicola and wetness duration (WD) for different bl oom and fruit developmental stages and different inoculum concentrations we re obtained. Three levels of ILI were considered as criteria for low, moder ate, and high risks of latent infection, respectively. Seasonal patterns of WD leading to different risk levels of latent infection were obtained for low (IPL) and high (IPH) inoculum potential conditions in orchards. Longer WD was needed at a resistant than at a susceptible fruit developmental stag e to induce similar levels of latent infection. The curves of WD leading to different levels of ILI over the growing season (risky WD curves) were use d in risk analysis for latent infection. Multi-year historical WD data from 10 prune-growing locations in California were compared with risky WD curve s. The percentage of days (P) with WD leading to a certain risk level of la tent infection was calculated for each month from historical weather data. Under the IPL condition, the P distributions for low risk of latent infecti on were higher in March and April than in May and were the lowest in June f or most locations. Under the IPH condition, the number of days that WD lead ing to low risk of latent infection in May increased compared with those un der the IPL condition. The risk analysis approach was evaluated by using se parate experimental data as incidence of fruit brown rot obtained from diff erent prune orchards over years. Consistency between predicted overall risk levels of latent infection and observed incidence of fruit brown rot was o btained. The results demonstrated the usefulness of the risk analysis in de cision support system for disease management.