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.

Common name		Amount to Use	R.E.I.+	P.H.I.+
(trade name)			(hours)	(days)
When choosing a pesticide, consider information relating to environmental impact.
CAUTION: Application of methidathion with, or closely following, a fungicide containing lime will negate the insecticide's effectiveness. Apply methidathion before fungicides containing lime are applied.
A.	BORDEAUX MIXTURE#	Label rates	see labels	see labels
	MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M1)
	COMMENTS: For information on making Bordeaux mixtures, see UC IPM Pest Notes: Bordeaux Mixture, ANR Publication 7481. When used on organically grown produce, all ingredients must be certified organic. Observe the most restrictive label precautions and limitations of all products used.
B.	FIXED COPPER#
	(Various)	Label rates	24	see label
	MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M1)
	COMMENTS: Not all copper compounds are approved for use in organic production; be sure to check individual products.
+	Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
#	Acceptable for use on organically grown produce.
1	Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions (for more information, see http://www.frac.info/). Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode of action Group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode of action Group number; for fungicides with other Group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode of action Group number.

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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