The olive moth: three generations, three kinds of damage

The olive moth (Prays oleae) is not an ordinary pest: it has three generations a year, and each attacks a different organ of the tree. It winters inside the leaf, eats the flower buds in spring, and enters the fruit in summer.

Control therefore is not a single calendar — it depends on knowing which generation you are dealing with.

Three generations, three kinds of damage

Leaf generation — where it overwinters

Moths from larvae that fed in the fruit lay their eggs from September to December on the upper surface of the leaves. Eggs hatch in 8-16 days depending on temperature; the young larva bores straight under the leaf epidermis, feeds in the fleshy tissue between the two epidermal layers, excavates a cavity 2-3 mm long and overwinters there.

From late February it leaves the chamber and feeds on tender shoot tips and leaves. On maturing it pupates — gluing two leaves together, folding a single leaf, or spinning a cocoon among the terminal leaves. Moths emerge from late March to early April.

Flower generation — one larva, 30-40 buds

In April and May the eggs go onto flower buds and bud stalks. They hatch in 8-10 days and the larva enters the bud.

Over 10-15 days of development a single larva can damage 30-40 buds. On completing development the larvae bind buds and flowers together in a web of their own silk and pupate inside it. Moths emerge within 7-10 days.

Fruit generation — the serious one

When the fruit reaches the size of a large peppercorn (late May to early June), eggs are laid on the sepals of the fruit. Usually one egg per fruit.

Hatching within a week, the larva enters at the base of the fruit stalk and works towards the stone. On the way in it breaks the connection between stalk and fruit — the fruit shrivels, blackens and drops. This is called "peppercorn drop". Such fruit has not yet formed oil and is a total loss.

A second wave of shedding comes at exit: the larva matures in 2.5-3.5 months and leaves the fruit to pupate, cutting a visible hole near the stalk. That hole usually severs stalk from fruit, and the fruit drops within days.

Larvae leaving the fruit pupate under bark on trunk and branches, in cracks and crevices, or in the soil. Pupation takes 10 days; moths emerge from September to December and the cycle begins again in the leaves.

Why heavy in some groves and absent in others?

The instruction's answer is striking. The olive moth becomes a problem particularly in:

• Isolated olive areas
• Certain microclimates
• Areas sprayed heavily in previous years, where the natural balance has been broken

That last point matters: over-spraying manufactures this pest. Studies in Türkiye have identified 12 parasitoids and 8 predators of the olive moth — Chrysoperla carnea, Orius species, Scymnus ladybirds and a series of parasitoid wasps. Full-cover spraying kills them too, and the moth is left with a free run.

Control

Biotechnical: pheromone traps

When the olive buds begin to swell, in late March to early April, mass trapping is carried out with one delta-type pheromone trap per three trees.

Chemical: do not spray the flower generation

The instruction's advice here is clear and runs against instinct:

t; The flower generation carries abundant predators and parasitoids. For this reason spraying in this period is not recommended.

The exception: in years of light crop, if damage to leaves and new shoots exceeds 10% at the start of the season, a treatment may be applied 7-10 days after the first moths are caught in the flower generation.

The preference is to treat only the fruit generation. Its threshold:

⚠ No product names or doses are given in this article. Plant protection products and doses appear in Annex 4 of the Ministry's instruction and registrations change. Consult the current licensed product list and your Provincial or District Directorate of Agriculture and Forestry before treating.

Hosts

Besides the cultivated and wild olive, its hosts include mock privet (Phillyrea), jasmine (Jasminum) and privet (Ligustrum). Hedge plants along the grove boundary therefore matter.

How to recognise it

Summary

• The olive moth has three generations a year: leaf, flower, fruit.
• It overwinters in a 2-3 mm cavity it excavates inside the leaf.
• In the flower generation one larva consumes 30-40 buds.
• The fruit generation causes two waves of drop: "peppercorn drop" on entry, and the stalk-base hole on exit.
• ⚠ Spraying the flower generation is not recommended — natural enemies are abundant then.
• Fruit generation threshold: live egg + larva in 10% of lentil-sized fruit.
• Biotechnical: late March to early April, one delta pheromone trap per three trees.
• ⚠ Heavy spraying multiplies this pest: it has 12 parasitoids and 8 predators, and they die too.

Source

t; Republic of Türkiye, Ministry of Agriculture and Forestry, General Directorate of Agricultural Research and Policies, Department of Plant Health Research. Olive Integrated Pest Management Technical Instruction. Ankara, 2022.

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