How to Control Pest Infestations


How to Control Pest Infestations

A Guide for Managing Pests in Olive Trees

Prevention is the key weapon to maintaining healthy olive trees. It’s far easier to keep trees and fruit free of pests than it is to eradicate an infestation. In this article, we’ll look at good practices for pest prevention as well as treatment once pests have attacked your trees.

Aphids on a branch

Above: Aphids attacking a branch

Preventing Pest Infestations on Olive Trees

Preventing Pest Infestations on Olive Trees

Olive trees will fend off pests on their own when they are healthy specimens and have their own version of antibodies to protect themselves. Pests may arrive airborne, in a good downpour or through the soil. Begin with healthy tree practices:

Healthy Tree Practices

Let’s make sure we’re on the same page with our pest control verbiage. First, find “best practices” immediately below. Then, find various types of pest problems identified below that you may encounter in caring for olive trees.

Click the ” + ” below to expand the selection.


Provide plenty of sunshine. Olive trees thrive on long hours of hot sunshine.


Water and food are essential. Olive trees need water but don’t like their roots standing in water. Surrounding soil can dry out between watering in well drained environments, but they can’t remain soaked or standing in water.


Feeding may only be necessary within the first three years in the ground to establish health roots. Liquid feed or fish blood and bone as additives can assist in providing nutrients. Follow manufacturer directions for appropriate dosages.


Good drainage is essential. Olive trees have flourished in the most desolate of locations with very low moisture. But if your goal is to produce olives for food or oil, finding the right balance of water, food and drainage is imperative.


Without consistent and careful pruning, airflow between twigs and branches will be dramatically reduced, potentially allowing insects and other airborne pests an opportunity to set up shop in your olive trees.

The last piece of maintaining healthy olive trees is regular inspection of your olive trees. It’s essential to catch any infestation as early as possible to prevent the spread of disease or pests. If you are managing an orchard, determine a regular inspection schedule, walking various rows and blocks of trees to inspect leaves, fruit, branches and trunks for any problems. Keep a log of findings and observations so that you know a timeframe for when a pest arrives in your orchard. Then you will know whether or not your treatment is effective in the timeframe set out by instructions.

Common Olive Tree Pests

Brown or black spots? Woolly white “snow”? Leaf or fruit loss? Discoloration? Limb death? Once you’ve found an anomaly to a healthy olive tree, you must treat it immediately to prevent the spread of problems. In California, we are lucky to have fewer pest problems arise than in other parts of the U.S. or Europe and Australia where olive trees are also commonly grown. Here is a list of some common pests, followed by suggested treatments.

Woolly Aphid

…to begin spraying olive trees as a preventative measure to spring’s crop of arriving pests. Woolly Aphids aren’t themselves extremely damaging to olive trees.

SYMPTOMS – Woolly aphids produce tufts of white, snowy-like fiber among branches which is generally harmless. But they love the sap produced olive trees. This may arise immediately after pruning along open cuts that have yet to canker over.

In the chain of life, the woolly aphids then secret a type of honeydew that olive fruit flies are attracted to. And if woolly aphids aren’t too damaging to an olive tree, fruit flies definitely are!

When the aphids eat the tree sap, it can also leave the tree vulnerable to other pests, such as infection or fungus and frost damage.

SOLUTION – There are several easy solutions to rid olive trees of aphids. We recommend starting with soap & water:

  1. A simple mixture of dish soap and water can be sprayed on to remove the aphids which is harmless to the tree.
  2. Chemical treatments available at any nursery supply store, including safe, non-toxic varieties.

Here are a couple good videos on treating woolly aphids:  and

PREVENTION – Pre-spring rains and pre-autumn rains, spray with commercial applications of preventatives to keep pests from becoming a problem.

Scale Insects

SYMPTOMS – Yellow discoloring on the leaf, or a sticky residue on leaves, may be the first visible indicator of the presence of scales. These insects feed on the sap on the olive tree.

SOLUTION – To completely remove scale insects using a spray or oil, repeat the process as needed, especially in the egg-hatching period. Follow manufacturer’s instructions for these chemical treatments to eradicate scale insects.

Olive Peacock Spot

Olive Peacock Spot is a fungus affecting the leaves of olive trees. It’s only active and affecting trees during the growing season. But the time to prevent its infestation is during the dormant season with two oil applications (in the northern hemisphere) in November and February.

SYMPTOMS – Small black spots appear on the top surface of the leaves, which are lesions produced by the fungus. Unfortunately, the fungus is easily spread by windy weather and by insects, making it very difficult to control or contain.

For those growing olive trees for fruit production, Peacock spot can cause dramatic loss of fruit, reducing yields substantially. Worst case scenarios are complete defoliation, which can lead to twig death.

SOLUTION – This fungus is treatable with oil spray applications of copper mixture or fungicide. Follow the manufacturer’s instructions and document applications. If leaf spot is problematic for your orchard in California, please familiarize yourself with the University of California’s Agriculture Department’s report with the Olive Oil Commission on new methodologies for controlling this pest:

JEA Annual Report on Olive Peacock Spot

Scab Disease

SYMPTOMS – Purple or brown ring spots (often sooty) with a greenish center appear on leaves, followed by leaves turning yellow and defoliating. Premature leaf loss can be a serious problem. Scab disease may be prevalent during rainy weather in Spring and Summer and may result in aborted blossoming and shriveled or scabbed fruit.

SOLUTION – First, removed fallen and scab-affected leaves from the bottom of the plant during winter months. Next, prune out affected shoots and ensure overall pruning encourages good air circulation so that rapid drying of foliage will occur after rainstorms.

NOTE: You cannot use chemical treatments on scab disease for edible crops.

Powdery Mildew

Powdery mildew is a common fungus pest that is easily treatable with homemade or manufactured solutions.

SYMPTOMS – Looks like white flour or powder on tops or bottoms of leaves.

SOLUTIONS – Spray these solutions directly on mildewed areas to treat the plant and eradicate the pest:

  • Baking Soda Solution – 1 TBsp baking sodea, 1 TBsp dish soap, 1 gallon hot water – mix and apply.
  • Milk Solution – Use 1:2 ratio of milk to water (milk is good for health of an olive tree.) Mix and apply.
  • Neem Oil – This is a good, organic solution available at stores.
  • Apply every 2 weeks until the mildew is gone.

NOTE: Learn to spot the difference between powdery mildew and the white residue kicked up in nurseries from fertilizers. Though similar in appearance, the residue is harmless and can be wiped off leaves.

Verticuillium Wilt

This is a set of diseases affecting olive tree root.

SYMPTOMS – Leaf wilting, discoloration of leaves in yellow or even whole branches dying back. The difficulty is in the treatment: Root rot in any form is a result of poor drainage. If the olive tree is in a pot, it may be sitting in standing water in a saucer. If planted outdoors, are the roots bound up in heavy clay?

SOLUTION – Once root rot has set in, it is difficult for the tree to recover. There are no chemical sprays or treatments. Weeds can even spread these diseases. Test the soil for water absorption. Does it drain well? Can you aerate? Can you move any irrigation lines? If repotting or replanting the tree, ensure the soil is not infected with the fungus.

Olive Fruit Fly

Olive Fruit Flies pose serious problems for producers of edible olives and oil. Adult olive flies are rarely seen, depositing their larvae to burrow below the skin of the fruit. The larvae, in turn, then eat the flesh and create brown trails throughout the fruit as they eat their way out.

SYMPTOMS – Tan or brown entry holes can be seen on the fruit. Black, damaged areas of the fruit evolve. Maggots are seen inside the fruit.

SOLUTION – Olive fruit fly is controllable with aggressive treatment. But the fruit is unusable for production until free of the pest. We strongly recommend studying this publication from UC Davis’ Agriculture Department on treating this pest. Treatments offering in their comprehensive guide include organic insecticides, trapping and clay sprays. Here are two good references: from the University of California’s Statewide Integrated Pest Management Program and Olive Oil Source on Olive Fly Control.

These are the primary olive tree pest problems in California. New pests arrive on a regular basis, unfortunately. The key to good health for your trees remains regular inspection. Identifying anomalies, and seeking treatment immediately.


Resources for Olive Tree Pest Control

Want more help on treating olive tree pests? Just contact us.

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