Yield loss in apple caused by Monilinia fructigena (Aderh. & Ruhl.) honey,and spatio-temporal dynamics of disease development

Monilinia fructigena (Aderh. & Ruhl.) Honey causes considerable yield losse s in pome fruit culture. During a field study in the Netherlands in 1997 an d 1998, the increase in disease incidence in time was assessed and final pr e- and post-harvest losses were recorded in the susceptible apple cultivars James Grieve and Cox's Orange Pippin. Each individual tree was considered as a unique quadrat, and the spatial distribution of diseased fruits among fruit trees at every assessment date was characterised by a dispersion inde x, Lloyd's index of patchiness (LIP). Spatial autocorrelation was applied t o detect potential clustering of trees with diseased fruits within rows. In cv. James Grieve, the rate of increase of disease incidence was constant u p to harvest time, whereas in cv. Cox's Orange Pippin disease incidence inc reased markedly 3 weeks before harvest time, which coincided with the harve st of cv. James Grieve in neighbouring rows. Pre-harvest disease incidence was 4.2-4.3% in cv. James Grieve in both years, in cv. Cox's Orange Pippin this was 4.4% in 1997 and 2.7% in 1998. Post-harvest yield losses amounted on average 1.5-2.0% for both cultivars, no significant differences were fou nd between the cultivars (t-test, P=0.05). Both in 1997 and 1998, clusterin g of diseased fruits among fruit trees was detected; LIP values were signif icantly higher than 1 (P=0.05 in 1997, P=0.01 in 1998). Clustering of trees with diseased fruits was detected in 1998, when significant (P=0.05) posit ive correlation coefficients occurred for 2nd, 3rd and 4th lag-order distan ces in cv. James Grieve, and a significant (P=0.05) positive first-order co rrelation in cv. Cox's Orange Pippin. Wounding agents, such as insects and birds, may play an important role in the underlying disease dynamics, and c rop losses may be minimised by control of these agents.