Neopestalotiopsis macadamiae

Pathogen and disease type — Neopestalotiopsis macadamiae is a fungal pathogen within the family Amphisphaeriaceae. It is responsible for significant necrotic diseases in plants, categorized as a foliar and fruit pathogen. As an ascomycete fungus, it relies on the production of conidia for dissemination, which allows it to establish infections in various plant tissues, ultimately leading to significant structural and physiological damage to the host.

Host range — While named after its primary host, the macadamia tree (Macadamia integrifolia), this fungus has a broad host range. It has been observed affecting other subtropical species, nursery stock, and various ornamental plants. In commercial agriculture, it poses a recurring threat to orchards, particularly in regions where environmental conditions support the continuous life cycle of the pathogen throughout the growing season.

Symptoms and signs — The infection is visually characterized by the development of necrotic, brown-to-black lesions on leaves and fruit. As the infection progresses, these lesions can expand to cover significant portions of the foliage or result in fruit rot. Under high humidity, the pathogen produces black acervuli (spore-bearing structures) on the surface of the lesions, which release spores that can be spread by water splashes or wind-blown rain.

Conditions for development — The disease cycle is heavily dependent on moisture. Rainfall and overhead irrigation are the primary vectors for spore dispersal, carrying the fungus from upper branches to lower, healthy tissues. The ideal temperature range for rapid mycelial growth and sporulation is between 20°C and 28°C. Periods of persistent wet weather create a conducive environment for the fungus to transition from latent stages to active infection outbreaks.

Damage and control measures — Economic losses result from reduced photosynthesis due to foliage damage and direct spoilage of the macadamia nut crop. Effective control requires an integrated approach:

• Pruning and destroying infected branches to reduce the primary inoculum load.
• Applying systemic or contact fungicides during wet, warm periods of the season.
• Managing tree density and canopy structure to improve air circulation.
• Ensuring that only disease-free nursery stock is introduced into established orchards.