Peacock eye disease, caused by the hemibiotrophic fungus Venturia oleaginea, is the most destructive and widespread disease of olive in Israel. In a national project to develop an environmentally friendly peacock eye disease-management protocol for the local olive industry, it was found that one or a few fungicide applications in the autumn effectively suppressed disease development in the concurrent season. Since fungicide application timing should be based on environmental criteria rather than a predefined seasonal schedule the goal of the current study was to define criteria for predicting the occurrence of infection events. It was observed that peacock eye severity and leaf abscission were significantly lower in tree canopies facing sunrise between October and December, the presumed period of autumn infection events, than in those facing other directions. Accordingly, we used the uneven distribution of the disease with varying canopy orientation as a tool to ascertain the relative importance of the respective weather variables to infection. Duration of leaf wetness caused by dew was the most salient ambient condition showing consistent, albeit short-duration (≤2 h) differences between canopy sides. In-vitro experiments were conducted to examine how this small difference leads to marked differences in disease severity and to define conditions promoting conidial germination, germ tube elongation, and sporulation. Based on these and our previous results, we defined criteria for predicting the occurrence of infection events in highly susceptible olive cultivars: a rain event of 15 mm or more (for 1 day or accumulated over several consecutive days), wetness duration of at least 6 h, and temperatures between 12 and 18oC during the wetting period. These criteria could serve to time fungicide applications.
Ygzao et al. (Wed,) studied this question.