Sources ofCycloconium oleaginum (Cast.) conidia for infection of olive leaves and conditions determining leaf spot disease development in the region of Sétif, Algeria

In the region of Setif, peacock leaf spot disease caused byCycloconium oleaginum was found to be most prevalent in the period from late autumn to spring and of minor significance in the period from the beginning of July until the middle of November. Severity of infection on the lower parts was greater than on the upper parts of the trees. Damage on leaves facing north was much greater than on those facing south. Production of conidia leaf spots was found to be high in spring and late autumn but very low in summer and early autumn. Temperatures from 15 to 18°C were found optimal for the growth of the fungus. Reduced growth was seen at 3, 1 and 25°C with total inhibition at 30°C. Our results suggest that fallen leaves play no role in new infections and the role of the remaining spots on the tree during summer is of little importance. Four phases for the infection of new leaves were determined. In the first, during late spring, three newly opened pairs of leaves were infected, this infection remains hidden until late autumn. The second phase occurs in early autumn after rain. The third stage in late autumn and in the beginning of winter is characterized by the occurrence of new leaf spots which are usually concentrated on the basal pair of newly grown leaves. The fourth phase of infection, at the beginning of spring, is the most important of all. The infected leaves at this stage, comprise the infection source for all the following stages.