Hazelnut Nut Weevil: Why Are My Nuts Empty Inside?

Cracking open what looks like a ripe hazelnut only to find an empty shell or a plump white grub is the work of the hazelnut nut weevil (Curculio nucum). This beetle is one of the most damaging hazelnut pests in Europe and can destroy a significant percentage of the crop in a bad year. Fortunately, the life cycle has predictable stages that give you clear opportunities to reduce its impact.

Life Cycle of the Nut Weevil

The adult nut weevil is a small beetle, four to nine millimetres long, with a distinctive long curved snout (rostrum). Adults emerge from the soil in May and June and feed on developing hazelnut foliage before the females drill into immature nuts — usually in June and July while the shell is still soft enough to penetrate. Each female lays one or two eggs inside the developing nut. The larva hatches, feeds on the kernel throughout summer, then chews its way out through the shell in late summer or early autumn and drops to the soil where it pupates and overwinters. The following summer it emerges as a new adult to repeat the cycle. Some larvae spend two years in the soil before emerging.

Identifying Weevil Damage

Infested nuts often drop early — in July and August rather than at natural harvest time. If you collect some of these premature drops and break them open, you will either find a creamy white legless grub (the larva) or a hollow shell where the larva has already departed. Adults leave a small round exit hole in the shell. An external clue is a small brown dot or pit on the shell surface where the female drilled to lay her egg, though this is not always visible.

Management Without Insecticides

The most practical control for garden hazelnuts is sanitation. Collect all fallen nuts from the ground daily in July and August, especially the premature drops that occur before harvest. Destroy these immediately — do not compost them. This prevents larvae from exiting into the soil and breaks the breeding cycle year on year. Lightly cultivating the soil under the tree in late autumn and early spring brings overwintering pupae to the surface where birds and frost kill them. In small gardens, even two or three seasons of consistent collection can measurably reduce the weevil population.

Trapping Adult Weevils

Adults can be knocked from the tree by tapping branches over a collecting sheet on cool mornings in May and June when they are sluggish. Collecting and destroying these reduces the number of females that go on to lay eggs. This technique requires repeated effort but requires no chemicals and is practical for small numbers of plants.

Chemical Control

Approved insecticides for amateur hazelnut use are limited in most European countries. Any treatment would need to target the adult stage in May and June before egg-laying — spraying once the larva is inside the nut is ineffective. Always check current product approvals in your country before considering chemical options. For most garden growers, sanitation and physical controls are more practical and just as effective over several seasons.