MACADAMIA (Macadamia spp.)

Macadamia is a genus of nine species of flowering plants in the family Proteaceae. The nuts are native to south eastern Queensland, Australia. They are small to large evergreen trees growing to 2-12 m tall. The fruit is a very hard woody globose follicle with a pointed apex, containing one or two seeds. The kernel is the edible part and is enclosed in a hard shell surrounded by a green husk.

The nuts have the highest amount of beneficial mono-unsaturated fats (60-72%) of any known nut. They contain protein, carbohydrate, dietary fiber, as well as calcium, phosphorus, potassium, sodium, selenium, iron, thiamine, riboflavin and niacin.

Species

Only two species, Macadamia integrifolia and Macadamia tetraphylla, are of commercial importance, but there are many natural crosses. The remainder of the genus possesses poisonous and/or inedible nuts. The smooth-shell species are preferred in the market as they have higher oil content and are low in sugar. The main differences between the two species are:

Characteristics Macadamia intergrifolia Macadamia tetraphylla
Shell Smooth Rough
Nut Round or nearly round Slightly oval
Leaf margin Smooth Unevenly toothed
Full-grown leaf 3 leaves per node 4 leaves per node

 

The main growing areas are Kiambu, Muranga, Kirinyaga, Nyeri, Nyandarua, Embu and Meru

Recommended varieties

KMB-3 (hybrid), EMB-1, KRG-15, MRG-20

 

Ecological requirements

Altitude

The best growing altitudes are areas between 1500-2,000m asl. Mature trees can withstand mild frost periods, but above 1,600m asl the yield and nut quality may be low if there is little sunshine during the main production season.

Rainfall

The trees require moisture throughout the year with an annual rainfall of at least 1200mm.

Soils

The trees can grow in a wide variety of soils but do best in fertile and loose soils that allow good root development. They require soil pH of 5 to 6. Macadamia is sensitive to high salinity. Shallow and waterlogged areas should be avoided.

 

Temperature

Macadamia requires annual mean temperatures of 15 to 28°C.

 

Land Preparation

  • Establishment should be done mainly in the long rains.
  • Prepare land 2 -3 months before planting.
  • Establish wind breaks such as banana a year before planting.
  • Plant pollinator trees to ensure good fruit set as most varieties are self-incompatible
  • Dig planting holes 60 x 60 x 60cm. Spacing depends on topography and land use. Separate top soil and sub-soil and loosen the base of sub soil on reaching the required depth.
  • Refill the hole 1 month before planting using top soil mixed with fully decomposed manure at the rate of 20kg per hole.

Propagation

Macadamia seedlings can be raised from seeds that are picked up from the ground. Seeds should be mature but not more than 4 months old.

Raising seedlings

  • Select large seeds from healthy and high-yielding trees. Prepare selected seeds for planting immediately after picking:
  • Soak seeds in water for 24 hours before sowing.
  • Sow seeds with the white spot on the seed facing down.
  • Seeds can be sown in containers or directly in the field.
  • The seeds germinate in 1- 3 months.

Vegetative propagation

  • Graft the seedlings 12- 15 months after planting or when they are 1.0 – 1.5cm in diameter. Do not allow any side branches to develop before grafting.Wedge grafting is commonly used.

Wedge grafting:

 

Success in grafting macadamia is normally low because the stem is hardwood. Covering the seedlings with a polythene strip increases the success rate of grafting. The scion and the rootstock are tied firmly in position with a clear polythene strip. The scion is then wrapped with a clear polythene strip to ensure that it is well covered to prevent excessive wetting of the grafted portion should rain water flow into it. After the graft has healed and the terminal bud of the scion begins to sprout, loosen the polythene strip to allow the shoot to grow normally and to prevent girdling.

Spacing

  • Spreading varieties: 10m x 10m e.g. KMB-3
  • Upright varieties: 7.5m x 7.5m e.g. EMB-1, KRG-15, MRG-20

Transplanting

  • Seedlings are ready for transplanting 6- 10 months after grafting.
  • Water the seedlings before removing polybag to avoid roots injury.
  • Remove the polybag.
  • Scoop some soil from the earlier prepared planting hole and mix it with phosphate fertilizers at the rate of 50g per hole. Plant the seedlings and water immediately.

Field Management

  • Mulch the tree basins regularly to conserve moisture and suppress weeds; Mulch should not touch the stem due to risk of climbing pests.
  • Weeds should be controlled to avoid competition for water, nutrients, space and light.
  • Caging is done to protect the growing trees from herbivorous animals.
  • Water regularly, at least once per week during dry season. Avoid water logging.
  • Remove all side branches until the plant reaches a height of one meter
  • Prune to ensure there is a central leader with only wide-angled branches at various levels. Remove broken branches and shoots on the trunk below the graft.
  • Cut the central leader at 80-100cm to allow the first two side branches to develop; do not allow any lateral branches below this height.
  • Another framework is recommended at shoulder height. All the branches should be at an angle wider than 45°.
  • Remove all side shoots other than those at the levels described above.
  • Intercrop with crops such as coffee or beans to increase the gross margin per unit area and to maximize land utilization.

Manure and fertilizer Application

  • Apply 20-30kg of manure every year from the 2nd year onwards, before the onset of rains.
  • Apply Sulphate of ammonia fertilizer at the rate of 200g per plant per year.
  • Apply 200g of NPK 17.17.17 four times a year (April, May , November and December)

 

Major Pests

Pest Damage Control
Macadamia stink bug (Bathycoelia distincta) The bug attacks the nuts at pea size stage.

It feeds on the kernels which usually become spongy with or without brown pit-like depressions.

Destroy by burning premature nuts that drop

Use insecticides e.g.  Confidor, Lebaycid,

Stink bugs

(Nezara

viridula)

Attacks immature nuts leading to premature drop of nuts mainly in the dry season Use insecticides e.g. Confidor, Lebaycid etc. Destroy by burning premature nuts that drop.
Macadamia nut borer (Cryptophebia ombrodelta) The nut borer attacks the fruit from pea size to maturity and during storage.

It causes premature nut drop.

The bored holes on the shells give entry to water and micro-organisms.

The moth lays eggs on the nuts.

Hatching larvae eat and bore into the green husk.

The caterpillars feed either on a portion or entire kernel.

·    Control with insecticides e.g Dursban 24 ULV, Lorsban 4 EC.

·    Collect premature and damaged nuts that drop and burn to destroy the larvae.

Frequently collect nuts from the ground to avoid infestation.

Remove and destroy alternate hosts e.g. maize, citrus, guavas.

Remove nuts with visible holes on the surface and burn.

 

Major Diseases

Disease and causal agent Symptoms Control
Macadamia trunk canker (Phytophthora cinnamoni) Tree trunk becomes distorted, often exuding gum.

Affected plants look stunted, chlorotic and partially defoliated.

Graft M. integrifolia onto rootstocks of M. tetraphylla

Remove and destroy cankered branches

Anthracnose (Colletotrichum lindemuthianum) Drying of flower spikes.

The spores are visible on the nut surface, appearing black during the dry season and purplish during the rainy season.

Use recommended fungicides e.g. Milraz, Rindomil, Topsin M

Grafting M. integrifolia onto rootstocks of M. tetraphylla

Armillary root rot (Armillaria mellea) Cause trees to wilt and eventually die Control with fungicides e.g.  Ridomil, Topsin M, Milraz

Grafting M. integrifolia onto rootstocks of M. tetraphylla

 

Harvesting

  • Flowering to maturity takes 6-8 months.
  • Trees start producing nuts in the 5th Grafted trees come into bearing after 3 years. Mature nuts normally drop from the trees.
  • The main fruiting season is from May to September while harvest season lasts from October to March.

Macadamia nuts drop from trees when they are mature and they are collected from the ground

  • The area underneath the trees must be clear. Grass, old leaves, branches and other debris must be removed.
  •  The nuts must be collected regularly, at least once a week.
  • Nuts remaining under the trees for too long lose quality and are susceptible to damage by mould, rats and other rodents.

Post-harvest handling

  • Remove the husks within 1 to 2 days before storage to prevent deterioration from overheating or growth of moulds as shown in the photo below

Mouldy un-dehusked macadamia nuts

 

  • Remove any rocks, sticks or leaves before dehusking. If nuts cannot be dehusked immediately, they should be spread on trays or floors.
  • Inspect the nuts after dehusking and remove any foreign matter and nuts which are old, mouldy, germinated, cracked, excessively dark or bleached or damaged.
  • Avoid harvesting nuts directly from the tree or shaking their trees to make nuts fall.
  • Dry the nuts on wire mesh racks or spread on the floor to a moisture content of about 10% within two weeks to avoid mould growth.
  • Direct sun drying is not recommended for it causes cracks that exposes nuts to secondary infection and causes rancidity and browning of kernel.
  • Store in a cool, dry and well ventilated area free from objectionable odours as nuts pick up odours from the surrounding.
  • Use either jute or sisal bags for storage as synthetic bags encourage mould growth.

Yields

Nuts yields vary with tree varieties, spacing and orchard management. A 5-year-old tree can give 3 kg while a 15 year old tree can yield between 50-80 kg per year.

Utilization

The nuts are used in confectionery, cakes, ice cream and cookies or roasted and eaten as snack.

Marketing

Raw nuts are sold to local processors. Export of unprocessed nuts is prohibited