Evaluation of the Incidence and Severity of Olive Leaf Spot Caused by Spilocaea oleagina on Olive Trees in Palestine

Abstract

Olive Leaf Spot (OLS) is found in many parts of the world and cause readuced growth and yield in olive trees. In this study, investigations were carried out to measure the incidence (% infected leaves) and severity (number of lesions/leaf) of OLS in olive growing regions in Palestine, including the regions of Hebron, Bethlehem, Tulkarm, Salfit, Jenin, Nablus, Ramallah and Qalqiyah. OLS was found in all study areas with significantly higher percent incidences in Jenin and Nablus (67.16% ± 18.16% and 46.06% ± 23.70%, respectively). OLS was more severe in Nablus, Qalqilyah, Jenin and Tulkarm (severity grade 3.0 - 3.7). Analysis indicate that there is a positive correlation (R2 = 0.597) between dis-ease incidence and severity. OLS appeared to be particularly severe on trees that were growing in regions with higher annual rainfall. The correlation between severity and rainfall was positive (R2 = 0.543).