Macadamia

Macadamia spp.

1. Identification and origin

Macadamias (Macadamia integrifolia Maiden & Betche, Macadamia tetraphylla L.A.S. Johnson and hybrids) belong to the Proteaceae family and are native to the humid forests of the east coast of Australia. Domestication began in the 19th century, with subsequent expansion to Hawaii, where the crop became commercially established. Today, it is one of the leading high-value nuts on the global market.

2. Economic importance

The macadamia is prized for its mild flavour and buttery texture, being consumed raw, roasted, caramelised or used in pastry, confectionery and the cosmetics industry. Macadamia oil is valued for its oxidative stability and lipid profile. The main producers include Australia, South Africa, Kenya, China, the United States (Hawaii), Guatemala and Brazil. Global demand has been rising owing to the consumption of premium nuts.

3. Botanical characterisation

Evergreen trees of medium size (6–15 m), with a dense canopy and coriaceous leaves, entire or serrated, arranged in whorls. The inflorescences are long, pendent racemes, with small, white or pink flowers. The fruits are globose drupes with an extremely hard shell, containing a single nut with a high oil content. The root system is deep, adapted to well-drained soils.

4. Soil and climate requirements

It prefers humid subtropical climates, with temperatures between 18–28 °C and well-distributed rainfall. It tolerates light frosts, but severe damage occurs below –3 °C. It develops best in deep, well-drained soils of medium texture, with a pH between 5.0 and 6.5. It is sensitive to waterlogging and to strong winds, which can cause fruit drop.

5. Main pests

• Macadamia nut borer (Cryptophlebia ombrodelta): perforations and significant fruit losses.
• Stink bugs (Nezara viridula, Piezodorus guildinii): damage to fruits and premature drop.
• Scale insects (Coccoidea): sap-sucking and sooty mould.
• Mites (Tetranychus spp.): chlorosis and reduction of photosynthesis.
• Nematodes (Meloidogyne spp., Pratylenchus spp.): root galls and decline in vigour.

6. Main diseases

• Flower and fruit rot (Botrytis cinerea): losses under humid conditions.
• Trunk canker (Phytophthora cinnamomi): wilting, necrosis and death of plants.
• Leaf spot (Cercospora spp.): irregular lesions and leaf drop.
• Anthracnose (Colletotrichum spp.): damage to leaves and fruits.
• Root rots (Armillaria spp.): progressive decline in infected soils.

7. General crop management

This includes choosing cultivars adapted to the local climate, planting in well-drained soils, balanced fertilisation, regular watering without waterlogging and formative pruning to improve air circulation. Monitoring of the macadamia nut borer and Phytophthora is essential. Harvesting should be carried out when the fruits fall naturally or reach physiological maturity, followed by adequate drying to preserve quality.

Bibliographic references

• EPPO Global Database. Macadamia integrifolia, M. tetraphylla – pests and diseases.
• CABI Invasive Species Compendium. Macadamia spp. – datasheets.
• Nagao, M. A., & Hirae, H. H. (1992). Macadamia. In: Nagy, S., & Shaw, P. E. (Eds.), Tropical and Subtropical Fruits. AVI Book.
• Stephenson, R. A. (2005). Macadamia: Domestication and Commercialisation. Rural Industries Research and Development Corporation.
• Hardner, C., et al. (2009). Genetic resources and breeding of macadamia. In: Jain, S. M., & Priyadarshan, P. M. (Eds.), Breeding Plantation Tree Crops: Tropical Species. Springer.