For farmers
Olive Tree Diseases and Pests: How to Spot and Prevent Them
Contents
Olive tree diseases and pests rarely kill a tree outright: more often they damage the fruit, cut the yield and turn extra virgin oil into oil with high acidity. A grove can look healthy in August and lose half its value by October. Below are the problems olive growers meet most often in Albania and across the Mediterranean, how to spot them in time and what you can do.
In short
- Olive fruit fly: hang traps from July and act when catches rise and the first stings appear on the fruit.
- Peacock spot: copper sprays in autumn, before the rains, and in spring.
- Olive knot: never prune in the rain, disinfect tools and spray copper after hail.
- Timely harvesting and milling are the last line of defence for oil quality.
Olive fruit fly
The olive fruit fly (Bactrocera oleae) is the most important olive pest in Albania and much of the Mediterranean. The female lays her eggs inside the fruit; the larva feeds on the flesh and leaves the olive pierced, so it drops early or oxidises. Oil from damaged olives has higher acidity and off-flavours, so it cannot be classed as extra virgin.
- When: there are several generations a year; the critical period runs from July to October, especially in cool, humid summers.
- How to spot it: tiny dots (stings) on the skin of the fruit, later exit holes and darkened flesh.
- Monitoring: yellow sticky traps with pheromone, checked weekly, plus a sample of fruit.
- Control: mass trapping with traps or bait bottles; kaolin clay, which leaves a protective white film on the fruit; bait sprays (protein plus an approved insecticide) applied to part of the canopy only. Organic growers use spinosad-based baits and kaolin.
- In years of heavy attack, picking a little earlier saves the quality of the oil.
Peacock spot
Peacock spot (Spilocaea oleagina) is a fungus that shows up as round, dark brown spots with a yellow halo on the upper side of the leaves. Infected leaves drop, the tree weakens and flowers less the following year.
- Conditions: high humidity and mild temperatures, around 12–20 °C, so autumn, mild winters and rainy springs.
- Prevention: pruning that opens the canopy, and copper sprays (copper oxychloride, copper hydroxide or Bordeaux mixture) in autumn, after the harvest or before the rains, and in spring, before flowering.
Olive knot
Olive knot (Pseudomonas savastanoi) is a bacterial disease that forms galls, or knots, on branches, shoots and the trunk. The bacterium enters through wounds: pruning cuts, hail, frost and blows from sticks during the harvest.
- Don't prune, or beat the branches at harvest, when the tree is wet.
- Cut out and remove knotted branches; disinfect your tools after each infected tree.
- After hail, frost or pruning, a copper spray closes the “doors” to infection.
Olive moth
The olive moth (Prays oleae) has three generations a year: one feeds on the leaves, one on the flowers and one on the young fruit, which then drops in June–July. It is monitored with pheromone traps. At flowering, Bacillus thuringiensis products are a targeted option that is also accepted in organic farming.
Black scale and sooty mould
Black scale (Saissetia oleae) sucks the tree's sap and excretes honeydew, on which a black fungus, sooty mould, grows. Leaves covered in sooty mould photosynthesise less. It is controlled with pruning that opens the canopy, with paraffinic (mineral) oil used according to the label, and by protecting its natural enemies.
Verticillium wilt
Verticillium wilt (Verticillium dahliae) shows up as the sudden wilting of branches or part of the tree, often in spring. The fungus lives in the soil and spreads more when host crops such as tomato, potato or aubergine are grown between the olives. There is no effective chemical treatment; prevention relies on healthy young trees, avoiding host crops between the rows and removing dead branches.
Olive tree diseases and pests at a glance
| Problem | Signs | Critical period | What to do |
|---|---|---|---|
| Olive fruit fly | Stings and holes in the fruit | July – October | Traps, kaolin, bait sprays |
| Peacock spot | Round spots on leaves, leaf drop | Autumn – spring | Copper, pruning for air |
| Olive knot | Galls on branches and trunk | After wounds (hail, pruning) | Hygiene, copper after wounds |
| Olive moth | Damaged flowers, small fruit dropping | April – July | Pheromones, Bacillus thuringiensis |
| Black scale and sooty mould | Insects on twigs, blackened leaves | Spring – summer | Pruning, paraffinic oil |
| Verticillium wilt | Sudden wilting of branches | Spring | Prevention, no host crops |
Rules for treatments
- Use only products registered for olives in your country and follow the doses on the label.
- Respect the pre-harvest interval, the number of days that must pass between treatment and harvest. It matters for the safety of the oil and for the olives being accepted at the mill.
- Do not spray insecticides during flowering, to protect bees.
- For doubtful cases, especially sudden dieback of trees, ask a local agronomist or the plant protection service.
Why it matters for the oil
At the mill, olives damaged by the fly or picked up from the ground are recognised immediately: their oil has higher acidity and a weaker aroma. A well-protected grove therefore gives not only more kilos but oil that is worth more. Read what olive oil acidity means and how fruit health affects olive oil yield. Protection starts with olive tree pruning, which keeps the canopy airy.
Frequently asked questions
When should olive trees be sprayed for olive fly?
When traps show rising catches and the first stings appear in the fruit sample, usually from late July to September. Bait sprays are repeated according to the label and the catches.
How do you treat peacock spot?
With copper sprays in autumn, before the rains, and in spring, before flowering, together with pruning that opens up the canopy.
Can an olive tree with olive knot be saved?
Yes. Cut out the knotted branches, disinfect your tools and protect the wounds with copper. The disease is kept under control with constant hygiene during pruning and harvesting.
How can I protect an olive grove without strong chemicals?
Combine traps and mass trapping for the olive fly, kaolin, copper within the permitted limits, Bacillus thuringiensis for the olive moth and regular pruning. These are also the basic tools of organic olive growing.
This article gives general information. For specific products and doses, follow the label and the advice of your local agronomist.
