Gadenin日本語Get the appStart at the roots, not the leaves
Nine times out of ten, an olive that suddenly looks bad is a root problem showing up in the canopy weeks after the damage was done. Waterlogged compost through a cold wet spell suffocates the fine roots, and the tree cannot then take up water even though it is standing in it.
The tell is that the leaves dry and go gray-brown but stay attached, and the damage appears across the whole tree rather than in one branch. Slide the rootball out of the pot if you can. Healthy olive roots are pale and firm; drowned ones are dark, soft and smell sour. If that is what you find, cut back the worst of the dead roots, repot into gritty potting mix, reduce the canopy by about a third and water very sparingly until new growth appears.
| Symptom | Likely cause | First action |
|---|---|---|
| Gray-brown leaves that stay on the tree | Drowned roots | Check compost moisture, repot into gritty mix |
| Leaves curl and drop quickly | Genuine drought | Soak thoroughly, then let dry down |
| Whole canopy evenly pale | Nitrogen shortage | Balanced feed in spring only |
| One branch dies while the rest is fine | Dieback or trunk damage | Cut back into clean wood, sterilize the blade |
| Sooty black film on leaves | Scale insects above | Treat the scale; the film then washes off |
| Fruit with small holes, flesh brown inside | Olive fruit fly | Destroy affected fruit, do not compost |
Scale insects and the black film they cause
Soft brown scale is the pest you are most likely to meet on a garden olive, especially on a tree that has spent winter under cover. The insects look like small flat brown discs about an eighth of an inch (3 mm) across, sitting still along the undersides of shoots and the midribs of leaves. They do not move, so they are easily mistaken for part of the bark.
They excrete a sticky honeydew, and a black sooty mold grows on it. The mold itself does no direct harm but it blocks light from the leaf, and it is usually what makes a gardener notice the problem. Finding sticky leaves or a black film is your cue to turn the shoots over and look for the scales.
- Rub them off by hand On a small tree, wiping the shoots with a cloth dipped in soapy water removes most of the population in one pass. Repeat weekly for three weeks to catch the crawlers.
- Open the canopy up Scale builds up fastest in dense, still, shaded growth. Thinning the interior of the tree does more long-term good than any spray.
- Wash the sooty mold off afterwards Once the scale is gone, sponge the leaves with plain water. The black film lifts off and the leaves start working again.
- Check every tree you bring under cover Inspect shoots before a tree goes into a greenhouse or porch for winter. Scale that arrives on one plant spreads to everything sharing the space.
Olive fruit fly and other fruit damage
Where olive fruit fly is present, the female lays a single egg under the skin of a developing fruit and the larva tunnels through the flesh. From the outside you see a tiny puncture, sometimes with a slight brown halo, and later a small exit hole. Cut the fruit open and the flesh around the tunnel is brown and collapsed. Such fruit cannot be cured and will spoil the batch it goes into.
There is no cure for an infested olive, so the control is sanitation. Pick affected fruit off the tree as soon as you spot punctures, collect everything that falls, and destroy it rather than composting it, because larvae complete their development in dropped fruit and emerge the following season. Picking a little earlier, at the green or turning stage, also gets the crop off before most of the damage develops.
Not all early fruit drop is a pest. Olives routinely shed a large proportion of the fruit they set in early summer, keeping only what they can carry. A shower of tiny green fruitlets a few weeks after flowering is normal thinning, not damage.
Frost damage and how to read it in spring
Frost injury on an olive shows up late. A cold snap in midwinter may leave the tree looking untouched until growth restarts, when the affected shoots simply fail to break and the bark on them shrivels and turns dull. Resist the urge to cut anything in the depth of winter.
Wait until new growth is clearly underway in spring, then scratch the bark with a thumbnail. Green underneath means the wood is alive and will shoot. Brown and dry means it is dead, and you cut back to the first point where the scratch shows green. Olives regenerate strongly from old wood, so even a tree cut back hard after a bad winter usually rebuilds a canopy within two seasons.
Keeping a problem log
Record the date you first see each problem, which side of the tree it appeared on, and what you did. Olive pests are seasonal and repeat: scale showing up in late winter under cover, fruit fly punctures appearing as the fruit swells. Two years of dates tells you when to start looking rather than when to start reacting.
Photograph the affected shoot as well. Scale, sooty mold and simple sun scorch look very similar from memory a year later, and the picture settles the question in seconds.