My macadamia nut tree is turning yellow and is sparse on top.
Common Problems and Solutions for Growing Macadamia
Most modern varieties of macadamia are relatively disease and pest-resistant, but there are some issues you may face when growing macadamia nuts.
This fungal disease is often present in high humidity areas and when trees are stressed due to lack of water.
With husk spot, the lesions start out small and yellow before expanding. They’re often covered in white spores.
This fungal disease will affect your harvestable yield. Use a broad-spectrum fungicide to control.
Rats and Mice
With tasty, oily nuts littering the ground, rats and other nut-loving creatures will move in.
Remove all nuts regularly and don’t allow the nuts you won’t use to be left rotting on the ground.
Macadamia Nut Borer
These little insects bore into the husks of the nuts. Once they have entered, pesticides have minimal effects. The nuts will drop from the tree prematurely.
Apply pesticides the moment you see the first of the nuts on the ground affected by the borer. You should see a hole with debris surrounding the edge. There could also be scale-like eggs on the outside of the husk.
We would lean toward pruning any diseased or damaged branches, and any branches extending out too far.
Macadamias perform well in any soil provided it is loose and has a pH of at least 4.5 to 8.0. Side dressings of nitrogen and potassium are necessary for healthy plants but choose fertilizers with low levels of phosphorus. This is because the trees are native to Australia where soils are low in phosphorus. Fertilize the plant in spring. Pruning should be done at the end of winter, which I would consider doing now. These trees are a long-term project because they don’t fruit for years, but with careful macadamia plant care, you may get lucky and have a bearing plant from seed in half a decade or so and that would be something to crow about to your friends and neighbors.
Read more at Gardening Know How: Macadamia Plant Care: How to Grow Macadamia Trees
Here’s a couple of older articles on macadamia nut trees that you may find interesting.