Hazelnut Weevil Control Guide: Identification, Spraying and Prevention

What Is the Hazelnut Weevil?

The hazelnut weevil (Curculio nucum, formerly known as Balaninus nucum) is a beetle species and the most important pest of hazelnuts. The adult beetle is brownish in color, roughly 6-9 mm long, and is recognized by its characteristic long rostrum (snout). Using its rostrum, the female bores a hole into the young hazelnut fruit and lays its egg inside. The larva that hatches from the egg develops by eating the kernel of the nut.

Left unchecked, the hazelnut weevil can push crop losses up to 30-50%. Timely control is therefore of vital importance.

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Life Cycle

The hazelnut weevil produces one generation per year. The adult beetles emerge from the soil in May-June, lay their eggs and die. The larvae feed inside the nut, fall to the ground in August and enter the soil, where they remain in the pupal stage for 1-2 years.

Damage Symptoms

Externally Visible Symptoms

Recognizing hazelnut weevil damage from the outside is not always easy. The signs to watch for:

Small hole in the shell: The pinhead-sized hole bored by the adult beetle to lay its egg (entry hole)
Larger exit hole: The round hole, 2-3 mm in diameter, that the mature larva makes when it leaves the nut
Premature drop: Infested nuts may fall from the branch early
Husk discoloration: On infested fruit the husk browns prematurely

Internal Damage

When the nut is cracked open, the signs of internal damage are clearly visible:

Presence of a larva: A whitish, legless larva curled into a C shape inside the nut
Larval frass: Brown, sawdust-like frass residue inside the nut
Eaten kernel: The kernel is partially or completely eaten, leaving an empty shell
Mold: Mold growth caused by the larval entry point

Life Cycle

Adult Stage (May-June)

Adult hazelnut weevils begin to emerge from the soil from the second half of May onward. The emergence date varies according to the region and soil temperature.

Mid-May: The first adults emerge from the soil
Feeding: They feed on young hazelnut fruit and leaves
Mating: Mating takes place in June
Egg laying: Using its rostrum, the female bores a hole into the young hazelnut fruit and generally lays one egg
Adult lifespan: Approximately 2-3 months

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Critical Timing

In spraying, timing is everything. The spray must be applied after the adult beetles have emerged from the soil and before they lay their eggs. Once the egg has been laid inside the nut, chemical control remains ineffective.

Larval Stage

The larva that hatches from the egg feeds and grows inside the nut:

Incubation: The egg hatches within 7-10 days
Feeding: The larva develops over 4-6 weeks by eating the kernel of the nut
Emergence: The mature larva bores a hole in the shell and leaves the nut (August-September)
Entry into the soil: The larva that falls to the ground immediately enters the soil

Overwintering (Pupal Stage in the Soil)

The most remarkable feature of the hazelnut weevil is that it can remain in the soil for a long time:

The larva pupates at a soil depth of 5-20 cm
The pupal stage generally lasts 1 year, but some individuals can remain in the soil for 2 years
For this reason, even if spraying was carried out in one year, beetles may still emerge from the soil the following year
Continuous control is required; spraying in a single season is not enough

Control Methods

Chemical Control

The most effective method against the hazelnut weevil is chemical spraying carried out at the right time.

1st spray (late May - early June):

Applied during the emergence period of the adult beetles
When the nuts in the orchard have reached nut size (chickpea size)
The entire canopy must be thoroughly wetted

2nd spray (if necessary, 15-20 days later):

Repeat application in heavily infested orchards
15-20 days after the first spray

For the detailed spray program, see our spray schedule.

Mechanical Control

Methods applied in support of chemical control:

Collecting prematurely dropped fruit: Collect and destroy nuts containing larvae before they reach the ground
Cleaning beneath the trees: Gather the infested nuts from the ground and remove them from the orchard
Shaking: Shake the trees during the period when the adults are active and collect the beetles that fall

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Mechanical Control Works

Collecting and destroying prematurely dropped nuts is a simple but effective method. If the larvae inside these nuts are destroyed before they pass into the soil, next year’s population is reduced.

Cultural Measures

Cultural measures must be taken for long-term population control:

Soil cultivation: Shallow soil cultivation beneath the trees after harvest (September-October) brings the pupae in the soil to the surface and exposes them to their natural enemies (birds)
Orchard hygiene: Collect the nuts left on the ground after harvest
Natural enemies: Birds, especially starlings and crows, take hazelnut weevil pupae out of the soil and eat them. Support the bird population
Regular pruning: An airy tree structure makes it easier to monitor the pest

Spray Timing and Dosage

Licensed products and their dosages for hazelnut weevil control:

Active Ingredient	Trade Name (example)	Dosage	Application Timing
Lambda-cyhalothrin	Karate, Ninja	30 ml / 100 l water	Late May - early June
Alpha-cypermethrin	Fastac	30-40 ml / 100 l water	Late May - early June
Deltamethrin	Decis	50 ml / 100 l water	During adult emergence
Thiacloprid	Calypso	20 ml / 100 l water	After flowering

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Spraying Safety

Always use a mask, gloves and protective goggles while spraying
Do not spray in windy weather
Strictly follow the dosages on the product label; more product is not more effective
Spray outside bee flight hours (early morning or evening)
Observe the pre-harvest intervals

Important: Product choice and dosages should be updated according to the recommendations of the provincial/district agricultural directorate. The list of licensed products may change from year to year.

Conclusion

The hazelnut weevil is an important pest that causes serious yield losses if it is not controlled in a timely and correct manner. Successful control requires correct timing, regular application and an integrated approach.

In summary: