Hazelnut Gall Midge (Mikomyia coryli): Symptoms and Spray Timing

What Is the Hazelnut Gall Midge?

The hazelnut gall midge (Mikomyia coryli) is a slender little fly about 2 mm long and bright red in colour. That vivid colour sets it apart from other small insects in the orchard, though its size still makes it easy to miss.

The damage is done not by the fly but by its larva. The larva forces the tissue it feeds on into abnormal growth, and the result is a gall — a swollen, misshapen piece of tissue.

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Do Not Confuse It With the Big Bud Mite — Both Make Galls

Two separate hazelnut pests produce galls, and their control differs:

Gall midge (this page): galls form along the leaf veins, on the husk cluster, on the green husk and at shoot tips. Spray late March to early April, repeated 20 days later
Big bud mite: the gall forms in the bud, which swells to the size of a pea and turns into a cone. Spray late April to early May, a single application, with an acaricide

Look at where the gall is: in the bud it is the mite; on a leaf vein or the husk cluster it is the midge.

Damage Symptoms

The larvae can form galls in four separate places:

Along the leaf veins: the most common appearance. Swellings running along the vein
On the husk cluster: the structure of the nut cluster is disrupted
On the green husk: galls on the covering around the nut
At shoot tips: shoot development is disturbed

Consequences

Leaves dry out and drop: as the number of galls on a leaf increases, the leaf dries and falls — the loss of leaf area weakens the bush
Misshapen nut development: galls on the cluster and husk prevent the nut from developing normally

Life Cycle

It has one generation per year.

Stage	Month	What happens
Overwintering	November – February	The larva overwinters in a white cocoon just 1 cm deep in the soil
Pupation	March	It pupates in the soil
Adult emergence	April	The great majority of adults emerge in this month
Egg laying	April	Eggs are laid at the tips of the buds of new shoots and in sheltered places
Gall formation	Spring – Summer	The larvae feed and the galls develop

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The Overwintering Site Is Very Close to the Surface

The gall midge overwinters just 1 cm deep in the soil. That means autumn and winter soil cultivation can directly affect the overwintering larvae. Unlike the cockchafer, whose eggs sit 15-25 cm down, this pest is right at the surface.

Economic Threshold

Spraying is applied in orchards where infestation exceeds 50%.

This threshold shows that the gall midge is more tolerable than most other pests: if less than half the orchard is infested, spraying is not advised.

Control

Chemical Control

The timing is phenological — it follows the state of the shoot, not a calendar date.

First application: when the majority of shoots carry two leaflets — in practice late March to early April
Second application: 20 days after the first
Why phenological: the adults emerge in April and lay eggs at the tips of new shoot buds. The aim is to meet the egg-laying period, and shoot development is the indicator of it

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Always Consult Before Choosing a Product or Dose

No trade name or dosage is given on this page, deliberately. Registered preparations and their dosages vary by region, pest and year. Do not apply any pesticide without consulting your provincial/district directorate of agriculture and forestry or an agricultural engineer. Always notify local beekeepers before spraying.

Cultural Measure

Because the larva overwinters in a cocoon very close to the soil surface, working the soil under the bushes in autumn and winter helps reduce the overwintering population.

Frequently Asked Questions

When should the spray be applied? When the majority of shoots carry two leaflets — in practice late March to early April — and again 20 days later. Rather than a fixed calendar date, go by the state of the shoot; orchards can differ by several weeks.

There are swellings on my leaves — gall midge or big bud mite? Look at where the swelling is. If a bud has swollen to the size of a pea and turned into a cone, it is the big bud mite. If the swelling is on a leaf vein, on the husk cluster or on the husk, it is the gall midge. The distinction matters because control timings and product types differ.

Should I spray if I am below the threshold? No. The Ministry sets the threshold at 50% infestation — one of the highest tolerances among hazelnut pests. If less than half the orchard is infested, the cost of spraying exceeds the benefit.

Are two applications essential? Yes, once the decision to spray has been made. Adult emergence and egg laying are not compressed into a single day, so one application misses part of the population. The second follows 20 days later.

This guide is based on data from the Hazelnut Research Institute of the Turkish Ministry of Agriculture and Forestry. Always make spraying decisions in consultation with an agricultural engineer.