Climatic and soil requirements

Most soil types are suitable for the production of macadamias, provided they are well drained and have no restrictive layers in the top 1 m of the soil. Poorly-drained clay soils are not suitable.

 

The ideal temperature for macadamias is between 16 and 25 °C. Although the trees can survive when temperatures drop below 3 °C, they should not be regarded as frost resistant.

 

Height above sea level

Height above sea level influences nut quality and production. Production declines dramatically above 600 m. Above 640 m growth is slower and trees take longer to produce.  Cultivars suitable in areas between 600 and 640 m above sea level are Mauka, Kau and Keaau.  Cultivars recommended nearer to the coast, 90 to 300 m above sea level, are Purvis, Makai and Keaau.

 

Cultivars

The cultivars recommended are: Keaau, Kakea, Kau, Purvis, Pahala, Mauka and Makai.  They are regarded as superior to Nelmak 1 and Nelmak 2 for commercial processing and marketing. Their oil content is usually higher than 73 % and the sugar content is low enough to ensure an even, cream colour after the nuts have been baked. Under ideal circumstances the crack-out percentage will be higher than 40 %.

 

Soil preparation

If the physical properties of the soil, namely depth (0,8–1,0 m) and drainage are suitable for growing macadamias, the soil must be prepared carefully and well in advance.  The soil must be loosened as deeply as possible. It should then not be necessary to make large planting holes.  If the soil in the planting holes is compacted, the roots could become rootbound.

 

An investigation should be done after the planting of macadamia trees to ensure that root growth is not restricted.  Do not fertilise recently planted trees. They must first become well established and grow vigorously. It is wise to wait one year before applying fertiliser.

 

Fertilisation

Do not fertilise young, transplanted trees too soon. They must first become well established and start growing vigorously before any applications are made, preferably after at least 1year.  Never apply fertilisers against the stem of young trees.  Fertiliser must be broadcast evenly from about 0,2 m from the stem to about 0,5 m outside te drip area of the tree.

 

Macadamia trees are very sensitive to root damage, therefore each fertiliser application must be followed by a light, controlled irrigation.

 

Fertilisers must not be worked into the soil. When the trees are established and start growing, fertiliser must be applied regularly according to the table.

Quantity of fertiliser according to age (kg/tree/year):

 

- Trees younger than 2 years requires 0.3 kg of LAN 28% per tree, per year, 0.2 kg of Superphosphate per tree, per year and 0.2 kg of Potassium chloride per tree, per year.

- Trees between the ages of 3 and 8 years require 0.8 kg of LAN 28% per tree, per year, 0.4 kg of Superphosphate per tree, per year and 0.2 kg of Potassium chloride per tree, per year.

- Trees older than 8 years require 2.4 kg of LAN 28% per tree, per year, 1 kg of Superphosphate per tree, per year and 1 kg of Potassium chloride per tree, per year.

 

Zinc and boron sprays

Because most soils are naturally low in zinc, or the zinc is not available, this element must be applied every year. The following concentrations are recommended:

 

- Zinc oxide at 200 g/100 l water, or

- NZN at 150 ml/100 l water.

 

Many macadamia orchards are also low in boron and it is desirable to spray the trees every 2 years with 100 g borax or 75 g solubor/100 l water right from the start.

 

Irrigation

Water stress often limits tree growth, as well as the set, growth and quality of macadamia nuts. It is important to know how much water to apply and when to apply it if it does not rain.

 

- Trees 5 years and younger require 25 mm per month between January and March, 10 mm per month between April and July and 23 mm     per month between August and December

- Trees 10 years and older require 70 mm per month between January and March, 30 mm per month between April and July and 65 mm         per month between August and December

 

Diseases and pests

 

- Phytophthora root rot

This disease usually occurs as a result of mechanical damage causing injury. These areas usually become infected. Trees sufferin some kind of stress such as drought conditions may also get the disease.

 

- Nut borer

Nut borer is the common name for the larvae of 4 types of moths that can either burrow into the green husks of macadamia nuts or feed on the kernels. The damage can easily be recognised, but the moths are small and inconspicuous and seldom seen in an orchard.  Adult larvae are about 10 mm long and pale red or grey.  An infested nut can be recognised by a small hole in the husk which is surrounded by excreta. Affected nuts, especially young developing nuts, usually drop as a result of damage to the husks.  Susceptibility to attack by moth larvae differs among cultivars because of hardness and thickness of the shell.  No insecticide is at present registered against nut borer. It can, however, be limited by planting fairly resistant cultivars such as Nelmak 1, Nelmak 2 and the Hawaiian cultivars.  A natural enemy that plays a role in the control of false codling moth is the parasite Trichogrammatoidea lutea, which parasitises the eggs of the moth.

 

- Stinkbugs

Stinkbugs are the most important pest on macadamias in South Africa. Damage is caused by a stinkbug complex comprising at least 20 different types. The most important types are: two-spotted stinkbug, green vegetable stinkbug, coconut stinkbug, small green stinkbug, spotted stinkbug, yellow-edged stinkbug andyellow-spotted stinkbug.Stinkbugs can cause crop losses of up to 80 %.  Most stinkbugs have 4 generations per year and each generation causes a different type of damage to the nuts. The first generation is the spring generation (August to September), and occurs during or after flowering. This generation can cause extensive flower and/or fruit drop of small macadamia fruit.

The second generation is the summer generation (December). Damage occurs during fruit development or just before the fruit reaches mature size. Once the fruit has reached mature size, it remains on the tree even after stinkbugs have fed on it. Whenharvesting, these nuts will have large, sunken lesions on the kernels. The third generation, the autumn generation (February to March), is normally the largest.  This generation feeds on the nuts before and during harvest. Although it causes lesions on the nut kernel, no fruit drop occurs. The size of the lesions depends on the type of stinkbug. The coconut, two-spotted, yellow-spotted, and spotted stinkbugs are capable of inflicting damage late in the season because of their longer mouthparts. Less trouble is experienced from other stinkbugs during autumn. The fourth generation stinkbugs (winter) do not normally cause problems because most nuts have been harvested and stinkbugs are not very active during this season. The damage evident at the end of the season (stung nut kernels) is inflicted from December to harvest. The hardness of the shell does not limit stinkbug feeding. Nuts must therefore be protected against stinkbugs throughout the year from flowering until harvest.

 

Controlling diseases and pests

Stinkbugs can be controlled chemically.  There are signs which may indicate the presence of stinkbugs:

 

- An excessive number of fruit on the ground during spring and summer.

- Feeding marks (small brown or black sting marks) on the inside of the green shell.

- Egg masses on tree stems. Unparasitised eggs should be destroyed while those that have been parasitised should be left on the tree so that the parasites can hatch. Whenever chemical control is necessary pesticides should be applied judiciously. At present cypermethrin and endosulfan are the only active ingredients registered for use against stinkbugs.

- Cypermethrin is applied as a full cover spray at 20 ml/100 l water.

Endosulfan can be applied at 120 ml/100 l water when the shaking method of monitoring shows 0,7 stinkbugs per tree. It has a residual effect of a few days compared to cypermethrin which has relatively long residual effects. Endosulfan can therefore be used until the end of the production season for the control of stinkbugs.

 

Recommended guidelines:

 

- Monitor for stinkbugs before applying any pesticide.

- Spray cypermethrin after flowering to reduce the original population size.

- Follow up with an endosulfan treatment if the number of stinkbugs in the orchard warrants it.

 

Harvesting, storage and processing

Macadamia nuts drop from trees when they are mature and are then collected from the ground.  The main crop is usually collected from March to July.  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.  During the main harvesting period the branches may be shaken to loosen the nuts.

 

Never pick immature nuts.

 

The green husks around the nuts must be removed as soon as possible after harvesting.

 

Freshly harvested, dehusked nuts contain 25 % moisture and must be dried before they are stored in bulk.  Wire frames containing 3 layers of nuts are used for drying.  Air must circulate freely between the frames to prevent mould. A fan may be used.  The nuts could also be sundried, but if the freshly harvested nuts are exposed to the sun immediately, the shells may crack. These cracks provide access to insects when the nuts are stored.  If the nuts are not dried, but immediately stored in bags or other containers, fungal growth could occur.

 

Storage

The hard, undamaged shells offer adequate protection against insects during storage. The kernels of shelled nuts are,however, susceptible to infestation.  Because insects can infest stored nuts, the necessary preventive precautions should be taken.  A reasonable degree of insect control is possible if packhouses and storage areas are kept absolutely clean.  The shell offers total protection against insect damage and if nuts are to be stored for any length of time, it would be best to store them unshelled. Before they are stored, any cracked or broken nuts should be removed because cracks in the shell will provide access to insects.  Because shelled nuts are susceptible to insect damage, they can only be successfully kept in cold storage. The nuts should be packed into cartons as soon as possible after shelling. They can then immediately be placed in a cold store at 0 to –4 °C. Cold storage prevents fungal growth and rancidity. This method is also recommended for the long-term storage of unshelled nuts.

 

Shelling

For successful shelling, the nuts should be dried to a moisture content of about 1,5 % to ensure that kernels shrink away from the shells. Therefore, nuts should be dried before shelling. The final drying takes place in large containers through which hot air is circulated.  The macadamia nut has a very hard shell, but is easily cracked mechanically between rotating steel rollers. A nutcracker or shelling machine works on the principle that nuts are cracked between a rotating steel roller and a fixed plate. The distance between the roller and the plate is adjustable according to the grading size of the nuts. The kernels of the nuts that have been properly dried, drop from the shells when the nuts arecracked.