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How to Manage Pests

UC Pest Management Guidelines


Leaf Spot

Pathogen: Mycocentrospora (=Cercospora) cladosporioides

(Reviewed 1/08, updated 1/08)

In this Guideline:

Leaf spot causes the leaves to appear slightly chlorotic (some varieties show more chlorosis than others). The undersides of some leaves become discolored with the conidial stage of the fungus, which appear to be covered with black dust. These leaves may fall, causing some defoliation in some cases. Fruit can also develop small, brown lesion spots and not mature uniformly.


This disease has been documented in coastal areas with humid growing conditions. The disease cycle seems to be similar to that of peacock spot.

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. Leaf lesions on these infected leaves have a white, crusty appearance. 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 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.


In coastal areas of Europe, where experience with this disease has been greater than in California, leaf spot is more difficult to control than peacock spot and requires more stringent treatment. In cool, wet areas, apply preventive treatments to olive trees after harvest but before winter rains begin and again in spring if wet, rainy weather persists.

Common name Amount to Use R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
When choosing a pesticide, consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
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 Note: 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.
  (Various) Label rates 24 see labels
  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.



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Olive
UC ANR Publication 3452
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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