How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS AND DAMAGE

Peacock spot appears on leaves as sooty blotches that develop into black, circular spots about 0.1 to 0.5 inch (2.5–12 mm) in diameter. There may be a yellow halo around the spot. The pathogen also infects fruit and fruit stems, but lesions are observed most often on upper leaf surfaces of leaves low in the tree canopy. Leaves fall prematurely. When significant defoliation occurs, strong bloom fails to develop and crop production is substantially reduced. Twig death may occur as a result of defoliation, and productivity is eventually further reduced.

COMMENTS ON THE DISEASE

This disease occurs throughout California's olive-growing regions. Cultivars vary in their susceptibility to this disease, but all are subject to infection.

Outbreaks are sporadic, and the disease may take several years before it becomes serious enough to cause economic damage. Not all infected leaves fall from the tree, and the fungus survives in those that remain on the tree. The margins of these lesions enlarge in fall, and a new crop of spores develops there. New infections are associated with rainfall and mostly occur during fall and winter. By summer, most diseased leaves have fallen from the trees, leaving partially defoliated shoots with mostly healthy foliage remaining. High temperatures restrict spore germination and growth, thus the disease is inactive during the warm, dry summers in California.

MANAGEMENT

If olive trees exhibit peacock spot leaf symptoms, it is important to treat for it yearly. Apply a treatment in late October before winter rains begin and again in the spring if wet weather persists.

PUBLICATION

UC IPM Pest Management Guidelines: Olive
UC ANR Publication 3452
Diseases
L. Ferguson, Pomology, UC Davis
P. M. Vossen, UC Cooperative Extension, Sonoma County
Acknowledgment for contributions to Diseases:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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