Olive Tree Fungus: How to Tell Peacock Spot, Verticillium Wilt and Sooty Mould Apart

An olive tree that looks unwell gets one label from almost everybody: fungus. Spray something, hope for the best. The trouble is that three completely different problems produce three completely different stories on the same tree, and only one of them is treated by spraying a leaf.

Peacock spot sits on the leaf. Verticillium wilt sits in the wood and in the soil. Sooty mould is not really the problem at all, it is the residue of an insect that was there first. If you read the wrong story, you spend a season treating the wrong thing while the tree keeps declining.

Peacock spot: round marks on the upper leaf surface

Peacock spot is caused by the fungus Venturia oleaginea, which older literature and many product labels still list as Spilocaea oleagina or Fusicladium oleagineum. The EPPO Global Database keeps an entry with the accepted name and its synonyms, which is worth checking when you compare two sources that seem to disagree.

What you see: dark, roughly circular spots on the upper side of the leaf, often with a paler or yellowish ring around them, which is where the peacock eye name comes from. Affected leaves yellow and fall, usually starting low in the canopy and on the inside of the tree, where air moves least and leaves stay wet longest. A tree can shed a lot of foliage in the lower third while the top still looks acceptable.

What drives it: free water on the leaf and mild temperatures. Long dews, a shaded dense crown, overhead irrigation that wets the foliage, a wet spring. The pattern is the giveaway. Peacock spot is a leaf event tied to wetness, not a single branch collapsing in dry heat.

Verticillium wilt: one branch gives up while the rest looks fine

Verticillium wilt on olive is caused by the soil fungus Verticillium dahliae, which enters through the roots and moves in the vascular tissue. EPPO lists it as a pathogen with a very wide host range, and that matters for diagnosis, because a bed that previously carried susceptible vegetables or ornamentals can carry inoculum long after those plants are gone.

What you see: a sudden flag. One shoot or one whole scaffold branch wilts, the leaves curl inwards, turn dull grey green or brown, and very often stay attached instead of dropping. The branch next to it can look untouched. Cut into an affected shoot and the wood under the bark is frequently discoloured in streaks. Nothing you spray on a leaf reaches that.

This is also the point where honesty beats optimism. There is no leaf treatment that clears a vascular soil fungus out of a tree, and a badly affected olive can be beyond saving. Dr. Phyto is built to say that out loud when the evidence points there, rather than selling you a plan for a tree that has already lost.

One more reason not to guess here: a branch by branch dieback on olive is exactly the symptom picture people associate with Xylella fastidiosa, a bacterium listed as a Union quarantine pest in Annex II of Regulation (EU) 2019/2072. Suspicion is not diagnosis, and a suspected finding belongs with the competent national plant health authority, not in a bin bag and not on a trailer to another garden. Moving or disposing of suspect material yourself is not an option under that regulation.

Sooty mould: black film that wipes off

Sooty mould is the one that looks worst and worries people most. A black, dusty to greasy film covers leaves, sometimes twigs and fruit, and the tree takes on a sooty appearance. The fungi involved, commonly grouped under Capnodium and related genera, are not feeding on the plant tissue. They are growing on honeydew, the sugary excretion of sap feeding insects.

So the real question is who is producing the honeydew. On olive, black scale, Saissetia oleae, is the classic candidate, and EPPO holds an entry for it as well. Turn the leaves over, look along the twigs and at branch junctions for the dark domed scales, and look for ants running the trunk, because ants farm honeydew producers and defend them.

The test is physical. Peacock spot marks are in the leaf and will not rub away. Sooty mould sits on top and smears on your thumb. Treat the insect and the film stops being replenished, then weathers off over time. Treat the film and you have cleaned a symptom.

Before any spray: the authorisation question

Plant protection products are authorised country by country, for named crops, named pests and named application rates. A product that is legal on olive in one EU member state may not be authorised in Germany at all. In Germany the authoritative list is the online database of authorised plant protection products held by the BVL, and the label is the legally binding document, not a forum post.

Olive is also a food crop. That means pre harvest intervals and residue rules form part of the authorisation, and they are not optional extras. If the tree carries fruit you intend to use, settle that question with a qualified agronomist or ask us directly before anything goes into a sprayer. We will not improvise around a label.

What the diagnosis actually needs from you

A usable diagnosis on olive rests on a handful of observations: which part of the canopy is affected, whether leaves fall or hang on, whether the marks sit in the tissue or on it, what the wood looks like under the bark, how the tree is irrigated, and what the weather did in the weeks before the symptoms appeared. A general chatbot will happily name a fungus from a single blurry photo. The question is what it does with the three candidates it did not mention.

Dr. Phyto works from a curated knowledge base rather than free generation: 282 plants covered, 437 diseases and pests, and 957 treatment protocols, according to the figures published on the drphyto.app homepage. Look alike conditions are explicitly linked to each other, so a suspected peacock spot comes with the confusion partners attached, and every result carries a confidence level instead of a verdict. Recommendations are graded by climate zone and season, which is why a plan for a mild coastal spring does not read like a plan for a dry inland summer.

The European law part is built in rather than bolted on: 37 quarantine organisms from Annex II of Regulation (EU) 2019/2072 are held in the engine, with routing to 26 national plant protection authorities when a notifiable organism is suspected. To be clear about what that is and is not: Dr. Phyto is not an official diagnosis, not a plant passport and not a substitute for an official examination. It tells you who to call and why.

Getting a dated plan instead of a guess

Photograph the affected leaves from above and below, photograph the wilting branch and the cut surface of a shoot if there is one, and run the diagnostic conversation. You get a named diagnosis with its scientific name, the conditions it is most easily confused with, and a dated treatment calendar with reminders and a follow up check, including pollinator friendly timing where a product is involved.

The first diagnosis is free and you can start without signing up, in any of five languages: English, Deutsch, Greek, Italiano and Francais. Further diagnoses and the full treatment plans are paid, with the current terms set out on the pricing page and at the paywall. If your olive has been declining for weeks, the cheapest move you can make today is to stop guessing which of the three it is and let the tree tell you.