Sources of variation in a field evaluation of the incidence and severity of olive leaf spot

Abstract

Incidence ( infected leaves) and severity (number of lesions/leaf) of olive leaf spot disease caused by Spilocaea oleagina were assessed every 2 weeks on 20 trees in a Canterbury olive grove for 12 weeks during summer 2003/04 All the trees were infected by olive leaf spot disease (OLS) and although disease incidence and severity varied between trees (Plt;0001) it did not vary between branches over time (P0088) There was a strong correlation (R20869) between disease incidence and severity It was estimated that at least five trees and 50 leaves/tree were required to correctly estimate the mean values of the parameters measured Throughout the duration of the experiment no new leaf lesions formed and although old lesions increased in size (Plt;0001) spore numbers decreased from 5104 to 1102 conidia/cm2 of lesion and viability of conidia declined from 55 to 10