What Is Making My Macadamia Unhealthy?

Are there any black lesions on leaves and fruit, and soft black lesions on husks of nuts followed by the decay of nuts on the ground?

Are there any chlorotic to yellow flecks on the husks which enlarge and develop tan brown centers, lesions may be covered in powdery gray spore masses during periods of wet weather?

Are there any small brown spots on flower petals that spread to racemes (flower stalks)?

Are there a yellowing or browning of some leaves in the tree canopy, subtle change in color of tree canopy from dark to light green followed by entire tree turning brown?

Is the dark discoloration of wood visible by removing the bark from the trunk of the tree, dark cankers may extend from the trunk at the soil line to the lower branches of the tree?

Was there an extensive loss and damage of developing nuts or nuts that have dropped from the tree?

Are there any entry holes in husks of nuts, usually close to the panicle, holes usually have insect frass protruding from them and husks may have shallow, dimple-like depressions?

These symptoms indicate a fungal disease - Anthracnose. Avoid stressing trees by providing them with adequate irrigation and fertilization. Prune out dead or dying limbs from tree canopy to reduce levels of disease inoculum. Control insect pests to prevent stress to trees.

Husk spot is a fungal disease that may lead to severe yield losses in macadamia. Spores are spread by water splash from infected husks. Diseased husks may produce spores for up to 2 years following infection. Protective fungicide spray should be applied to the fruits when they are approximately the size of a match head. Remove any old and diseased husks from the tree to reduce inoculum levels.

Raceme blight is a fungal disease that is favored by wet weather and cool temperatures. Fungicide application is not usually warranted unless infection occurs during wet weather which can cause severe infections.

The fungal disease that causes these symptoms is called Slow and quick tree decline. Tree death may occur in a few months after initial symptoms have appeared. Remove any dead or diseased trees from the orchard and avoid wounding tree trunks.

Phytophthora trunk and stem canker is a fungal disease that can kill the macadamia tree. Plant only disease-free nursery stock in well-draining soils on a slight mound to promote drainage. Avoid wounding the trunk. Incorporate organic matter into the soil around the tree, and apply appropriate protective fungicides to tree trunks before the wet season.

Rodents like rats often attack macadamia nuts. Encourage predatory birds such as owls by providing nesting boxes in the trees. All food sources for rats should be removed from the orchard. Keep grass around trees mown short and, if possible, maintain a clear mown area around the orchard to deter rats from entering and to aid predators such as owls in detecting and hunting rats.

These symptoms indicate Macadamia nut borer. Control of macadamia nut borer can be difficult as insecticides are ineffective once the larvae have entered the nuts. Insecticides should be applied if green fallen nuts exhibit damage or live, unparasitized eggs are present on the tree. Old nuts should be removed from trees and the orchard ground at harvest.

If there are numerous round holes on husks and extensive tunneling through husk and shell is visible when the nut is cut open the culprits are Tropical nut borers. Cultural control methods include harvesting nuts at three-week intervals, and removing damaged nuts from the orchard. Applications of appropriate insecticides may be necessary if the infestation is severe.