Husk spot
Pseudocercospora macadamiae
Causal Agent:
- Fungal Pathogen: Pseudocercospora macadamiae is a fungal pathogen that causes leaf and nut spot disease in macadamia trees (Macadamia integrifolia and Macadamia tetraphylla).
2. Symptoms:
- Leaf Spots: The most common symptoms include the development of small, dark brown to black spots on the leaves.
- Lesion Enlargement: Lesions may enlarge, coalesce, and result in extensive blighting of the leaves.
- Nut Spotting: In severe cases, the fungus can also cause spotting on the nuts, affecting the quality of the macadamia harvest.
3. Disease Cycle:
- Overwintering: The fungus may survive in infected plant debris, serving as a source of inoculum for new infections.
- Infection: Spores (conidia) produced on infected tissues are spread by wind, rain, or physical contact, initiating new infections.
- Favorable Conditions: Warm and humid conditions, along with rain or high humidity, create favorable conditions for disease development.
4. Identification:
- Leaf Lesions: Identification involves recognizing the characteristic dark brown to black spots on macadamia leaves.
- Nut Symptoms: When present, spotting on the nuts may further confirm the presence of Pseudocercospora macadamiae.
- Microscopic Features: Microscopic examination may reveal the presence of conidia and other fungal structures.
5. Management:
- Cultural Practices: Good orchard hygiene, including the removal and destruction of infected plant material, can help reduce the inoculum.
- Fungicide Applications: Fungicides may be applied during periods of high disease pressure, following recommended guidelines.
- Pruning: Proper pruning to enhance air circulation can reduce humidity levels and limit the spread of the fungus.
- Resistant Varieties: If available, planting macadamia varieties with some level of resistance to the disease can be beneficial.
6. Importance:
- Economic Impact: Leaf and nut spot caused by Pseudocercospora macadamiae can lead to reduced yields and affect the quality of macadamia nuts.
- Global Distribution: The pathogen is of concern in regions where macadamia trees are cultivated.






