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How to Manage Pests

UC Pest Management Guidelines


Olive Knot

Pathogen: Pseudomonas syringae pv. savastanoi

(Reviewed 1/08, updated 1/08)

In this Guideline:


Olive knot appears as rough galls or swellings about 0.5 to 2 inches in diameter on twigs, branches, trunks, roots, leaves, or fruit stems. Small shoots may be defoliated and killed. Galls also form at trunk or limb wounds.


Olive knot can kill trees if infections occur on and girdle the trunks of young trees through injury by mechanical harvesters. It reduces tree productivity by girdling twigs and branches and causing dieback. Bacteria survive in the knots and are readily spread by water at all times of the year. Infection occurs at low temperatures, usually in fall or spring. Openings are necessary for penetration of bacteria, and these are provided by leaf scars, pruning wounds, or bark cracks made by freezing. All cultivars are susceptible, and damage can be severe when weather favors disease.


Olive knot is difficult to control and requires preventive fungicide applications to protect leaf scars and other wounds. It is also helpful to carefully prune during the dry season (July to August) to remove galls on twigs and branches. Because the bacteria may be carried on pruning shears, be sure to disinfect them frequently if pruning at other times during the year. Galls on limbs and/or trunks of small trees or on newly established grafts can be treated with Gallex.

Treatment Decisions
A minimum of two applications each year is needed for control. Make the first application in fall after harvest. Apply other applications in spring from March through May. Because leaf scars are susceptible when fresh, time treatment to protect as many leaf scars as possible.

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. Also, copper may injure trees in areas of low rainfall.
  (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.
B. 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.
C. GALLEX Label rates none none
+ 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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