The macadamia nut tree goes back to Australia and it was introduced in Kenya between 1945 to 1948. In Kenya, macadamia grows in the same climate suitable for growing coffee. The macadamia nut trees remained almost totally unknown in Kenya until after independence in 1964 when a Kenya farming family, Bob Harries and Peter Harries started multiplying the trees in a seedling nursery, planting them on their farms and selling some to other interested farmers.
The tree thrives best at 0-2000m attitude and grows to 9-20m a height and 45 cm diameter (dbh-diameter at breast height). The tree also grows best in areas with mean annual temperature of 15-29 Deg C. and mean annual rainfall of 700-2600 mm. It also requires well-drained soil which is fertile red loam or alluvial derived largely from basic igneous rock such as basalt with a pH of 5.5 to 6.5. Macadamia trees also don’t tolerate water and soil with high salt concentrations. They do well in drained loam and sandy loam with good organic matter content.
Here are some of the pest and diseases that affect macadamia trees,
Pests and Rodents.
Rattus rattus damages 5–10% of the developing macadamia (Macadamia integrifolia) nut crop each year. Extensive and persistent snap trapping significantly reduce rat populations and depredations on developing macadamia nuts. Also, many growers apply rodenticides to reduce rat populations in orchards.
Typical nut borer
They make holes by extensive tunneling through husk and shell and are visible when nut is cut open.
Remedy – Use resistance macadamia varieties.
– Application of appropriate insecticide.
Macadamia nut borer
They make holes in husk of the nuts. Infested nuts drop off the tree prematurely.
Remedy – Difficult to control with an insecticide once the larvae have entered the nuts. Appropriate insecticide should be applied if green fallen nuts exhibit damage or live unparasitized eggs are present on the tree.
Causative agent; fungi
Symptoms. Small brown spots on flower petals which spread to flower stalks.
Remedy. Application of copper based fungicides during wet weather.
Phytophthora trunk and stem canker
Causative agent; phytophthora cinnamomi
Symptoms. Stunted and chlorotic young trees. Lesions girdle the stem. In mature trees there is dark discoloration of wood is visible. Dark cankers may extend from trunk at the soil line to the lower branches of the tree.
It spreads by water flash as the fungi survive in plant debris in soil.
Remedy. Plant disease free stock. Soils should be well drained. Apply protective fungicides to tree trunks prior to wet season.
Causative agent; colletotrichum gloeosporiodes.
Symptoms; Black lesions on leaves and fruits. The lesions do not have clear, finite edges and often appear to merge with the green colour of the husk. These lesions can spread onto the nut. Husk rot can cause premature nut drop.
Remedy. Amistar Top (Syngenta) and Bellis (BASF) will both control the disease. Reduce inoculum by performing good orchard hygiene, for instance remove old nuts from the orchard floor and husks should be composted before using as mulch.
Chlorotic to yellow flecks on the husks which enlarge and develop tan brown centers’. Lesions may be covered in powdery gray spore masses during wet periods which mature into tough woody spots.
Remedy. Apply copper based fungicides. When planting go for varieties which are not susceptible to the disease.