Latent Infection of Olive Leaf Spot Disease on Palestinian Olives

Olive Leaf Spot (OLS) or peacock disease is one of the most destructive diseases on olive trees in many parts of the world. The disease is caused by the fungus Spilocaea oleagina and can reduce the growth and yield of olive trees (Olea eurapaea L.). Investigations were carried out during October 2011 and October 2012, to determine the latent incidence and severity of OLS infection in Palestine. Five growing regions (Tulkarm, Qalqilyah, Salfit, Nablus and Jenin) were visited routinely every two weeks to collect olive leaves from two groves in each region. In each grove, 100 new and another 100 old leaves from 5 trees were collected and transported to the laboratory. Disease incidence was determined by recoding the per cent of infected leaves per tree. OLS was found in all study areas with Salfit and Qalqilyah the most infected. The grade of latent severity in these regions (2.3 and 2.1 in old and new leaves, respectively) was significantly higher than that in the other regions. Interestingly, the highest latent severity and incidence in all regions (new and old leaves) occurred in March during the winter season. The rate of visible incidence and severity (70 and 4%) in old leaves was higher than that in the new leaves (40 and 3%). This survey might provide reliable information on the prevalence of OLS in Palestine.