Hazel tree

Corylus avellana

1. Identification and origin

The hazel (Corylus avellana L.) is a shrub species of the Betulaceae family, widely distributed in Europe and Western Asia. It is considered one of the oldest fruit species in human use, with records of hazelnut consumption since the prehistoric period. Domestication and varietal selection intensified mainly in the Mediterranean region and Anatolia, where the crop acquired great economic importance.

2. Economic importance

The hazel is cultivated mainly for the production of hazelnut, intended for fresh consumption, the confectionery and pastry industry and processing (paste, oil, flour). Turkey, Italy and Spain are the main world producers. In Portugal, the crop is found mainly in the North and Centre, in traditional systems and some modern plantations. International demand has increased due to industrial use and interest in nutritionally rich nuts.

3. Botanical characterisation

The hazel is a shrub or small tree, generally with multiple trunks, reaching 3–6 m in height. The leaves are simple, rounded, with a serrated margin. Flowering is dioecious and occurs in late winter: the male catkins are pendent and conspicuous, while the female flowers are small, with red stigmas. The fruit is a nut enclosed by a leafy involucre (involucre or “husk”). The cultivars differ in vigour, habit, flowering time, hazelnut shape and ease of detachment from the involucre.

4. Soil and climate requirements

The hazel adapts well to temperate and humid climates, requiring chilling hours for adequate flowering. It is sensitive to late frosts during flowering. It prefers deep, cool, well-drained soils rich in organic matter, with a pH between 6 and 7. It tolerates slightly acidic soils and shows good resistance to moderate winds, although strong winds can affect pollination and fruiting.

5. Main pests

• Hazelnut weevil (Curculio nucum): perforation of the fruit and destruction of the kernel.
• Mites (Eriophyidae, Tetranychidae): leaf deformations and reduction of the photosynthetic area.
• Aphids (Aphididae): sap sucking and transmission of viruses.
• Hazelnut / chestnut moth (Cydia splendana): internal perforation of the fruit and significant losses.
• Stink bugs (Pentatomidae): fruit damage and premature drop.

6. Main diseases

• Eastern filbert blight (Anisogramma anomala): lesions on the branches and progressive decline (more relevant in North America).
• Root rots (Phytophthora spp.): death of young plants and decline in poorly drained soils.
• Powdery mildew (Erysiphe corylacearum): white mycelium on the leaves, reducing vigour.
• Bacterial diseases (Pseudomonas spp.): necrosis on buds and young branches.

7. General crop management

Management includes the choice of cultivars adapted to the local climate and compatible with each other to ensure effective cross-pollination. Pruning aims to maintain a vase or multi-stem structure, favouring light penetration and the renewal of the fruiting branches. Fertilisation must be balanced, with attention to nitrogen to avoid excessive vegetative growth. Weed control is important in the first years. Supplementary irrigation improves fruiting in regions with dry summers. Harvesting is carried out when the fruits detach easily from the involucre.

Bibliographic references

• EPPO Global Database – Corylus avellana.
• CABI – Crop Factsheets – Hazelnut (Corylus spp.).
• FAO – FAOSTAT and technical documents on nuts.
• Bassi, D., & Guerriero, R. (Eds.) (2020). The Hazelnut Genome. Springer.
• Molnar, T. J. (2011). Advances in hazelnut science and cultivation. Acta Horticulturae.