Macadamia is an ever-green tree whose origin of is Australia. The tree can grow up to a height of 20 m. Grafted variety start to produce fruits after3-4 years after planting and 6-7 years for the local varieties. The lifespan of these trees is approximately 20 years. The mature fruits consist of a cream to white seed, enclosed in a hard brown shell which is then enclosed in a green husk. Macadamia nuts are among the most expensive nuts in the world; hence their lucrative prices in the market. They can be eaten raw or fried or even processed to produce various products.
Kenya prides as being one of the leading producers and exporters of macadamia. Other than being a foreign exchange earner, macadamias are grown as cash crops in Kenya. There are various macadamia varieties including Kiambu 3 & 4, Embu 1, Meru 23 & 24, Taita Taveta 1 & 2, Kirinyaga 15 and Murang’a 20.
Ecological Conditions Suitable for Macadamia Farming
Macadamia production requires deep, well-drained soils, acidic to slightly acid with a pH level of 5-6.5.
Rainfall should be between 800 and 1200mm per year
The ideal range of temperature for macadamias is 16 °C and 25 °C.
Although different cultivars are suited to different heights above sea level, the maximum height should never be more than 600m. Any height above this affects the production of the nuts. Cultivars suitable in areas between 600m and 640 m above sea level are Mauka, Kau and Keaau while those recommended in areas between 90m to 300 m above sea level are Purvis, Makai and Keaa.
These trees are tropical, therefore ensure that the selected location receives full sun but sheltered from the wind. Sunlight greatly contributes to production of healthy fruits.
Cultivation and Maintenance of Macadamia
Different varieties do well in different regions. Therefore consider consulting an expert on the same. Propagation is done either through seeds or vegetative propagation. Several factors should be a guide in selecting the nursery trees including the leaves, soil mixture, shape of the tree, graft union, internodes among other factors. Freezing the nuts before planting extends their shelf life.
Prior to planting, the land should be tilled and soil loosened as possible in order to ensure that the tap roots sprout naturally. The recommended planting hole is 2ft by 2ft with spacing of 5m by 10m. An acre can accommodate 70 trees. Ensure that the trees are not congested as this cut off sunlight and other required conditions hence production decreases.
Fill the planting hole with manure and gently insert the seed with the bud end horizontally oriented to allow the taproots to grow properly. Plant it in same depth in which it was grown. Firm the soil around the roots to eliminate air spaces and water deeply after planting to help lessen the shock of transplanting. Other crops can be cultivated between the young trees. There are 3 main aspects to be considered before planting an intercrop. However, the intercropped plants shouldn’t be planted too close owing to the nature of the roots of the young macadamia nuts. Also eliminate the tall growing plants which could overshadow the young trees and cut off sunlight.
The soil should be slightly moist. Therefore water the young trees regularly, like three times a week. The frequency of watering should gradually reduce to once a week as the tree matures.
The young trees shouldn’t be fertilized too soon. Give the trees at least a year to become well established before application of fertilizers. When the trees are well established and start growing, fertilizer must be applied regularly. Apply fertilizer to the young trees at least once a year but for the cases where soil is rich in nutrients, do not fertilize often as this excess fertilization can easily damage the tree. Never apply fertilizer against the stem or the drip area of the young trees. Ensure that each time you apply fertilizer there is a light irrigation as the trees are very sensitive to root damage.
Mulching should be done frequently to preserve moisture and nutrients. Mulching also prevent growth of weeds.
Pruning aids in maintaining a good structure of the tree. Pruning is mainly done during the early stages of growth, before flowering and after completion of the harvest. Ensure that pruning is done in a slanting manner, keeping in mind the hygiene of the pruning shears to prevent pests and diseases. Also prune off the damages wood to reduce competition for nutrients. Pruning improves yield
Touch and color are the main aspects used to identify the ripe nuts. Unripe nuts are sticky and shouldn’t be harvested. Harvest the nuts when the skin begins to crack. The husk of unripe macadamia nuts is white and changes to chocolate brown when ripe. The nuts are very easy to harvest as they mostly drop off the trees when they are mature. For this reason the area underneath these trees must be clear to facilitate collection of these nuts.
Drying, shelling and storage of the nuts
The nuts should be dehusked immediately after harvesting as the husks are more difficult to remove once they have dried. The nuts are then dried to remove moisture which may cause formation of mildew and other fungal infections. In cases where the nuts are to be stored for longer lengths of time, it is always recommended to store them unshelled. The shell prevents insects and other pests from accessing the nuts. The shelled nuts should be packed in airtight containers and stored at very low temperatures of 0 °C to 4 °C to prevent damage by insects and fungal growths.
PESTS AND DISEASES AFFECTING MACADAMIA
These causes leathery scars on the leaves and nuts. They can be eliminated by use of horticultural oil. Organic mulch is also recommended to discourage the survival of these insects.
Mites cause brown spots on leaves and causes leaf defoliation. Ensure you maintain hygiene during all farm procedures. Pyrethrin could also be used in case of large infestation. Cut off and dispose the affected areas. Control them also pepper smoke.
- Macadamia nut borer
The borers burrow into the husks and feed on the nuts which results to the nuts falling off. Biological control measures can be adopted since there is no insecticide available against the borers. Ensure you choose a cultivar that is resistant to these pests such as Nelmak 1 and 2.
Caterpillars damage the flowers and leaves. Sprays can be used to control them, giving special attention to the folded leaves where the caterpillars tend to thrive.
Macadamia tree is disease-resistant. However various diseases may affect the tree on rare occasions.
- Root rot
Root rot is caused by fungus Phytophthora cinnamomi. This is the most common disease affecting the macadamia. This infection mostly occurs in moist, poorly drained areas. This disease causes sudden deaths of the plants. Some measures such as hot water treatment of seeds and grafting can help prevent root rots. Also ensure you dispose the affected plants immediately.
- Macadamia canker
This is a serious infection that affect the stem, leaves, fruits, branches, twigs, bark and other parts of the tree. This causes wilt and death of the young plants. Control is by spraying and raking up the affected parts. Ensure plant sanitation is maintained too.
Caused by pathogen Colletotrichum gloeosporioides, the disease affects the fruits, flowers and leaves, leaving dark spots and defoliation. Prevention of this disease involves pruning the dead branches of the affected tree before fungi produce spores and maintaining the correct conditions for the harvested fruits. It is controlled using copper-based fungicides.
- Powdery mildew
This appers as fungal growth on underside of leaves especially the new shoots. It is mostly common in poorly drained conditions. Well drained conditions should be maintained as a preventative measure. Adequate ventilation and air circulation in a nursery should also be maintained.
There are various challenges facing macadamia farming in Kenya including poor harvest management, availability of cheap imported nuts into the country, inadequate processing plants, lack of cultivars adapted to various zones and pests and diseases that affect nuts. However, despite all these challenges, there is a bright future for macadamia farming as its popularity increases among farmers due to their good prices in the market. Macadamia has many uses including making of beauty and confectionary products. Their fat is also a healthy option used for cooking. These oils are also nutrient densed and have a million health benefits.