Pseudocercospora leaf spot of actinidia

The disease is caused by the fungus Pseudocercospora actinidiae, a serious pathogen that specifically targets plants of the genus Actinidia. This fungal pathogen primarily affects the foliage, leading to necrosis and premature defoliation. As a foliar disease, it directly interferes with the plant's ability to produce energy, impacting overall vigor.

The primary host for this pathogen is the kiwi plant (Actinidia deliciosa and A. chinensis). While it mostly impacts leaf tissue, severe cases can lead to reduced fruit set and smaller berry size due to the lack of sufficient energy production from the leaves. In commercial orchards, this disease can become a significant limiting factor for yield productivity.

Symptoms typically begin as small, chlorotic spots on the leaf surface that gradually enlarge and turn brown or grayish. In humid conditions, a characteristic olivaceous fungal growth (conidiophores and conidia) can be observed on the underside of these spots. If left untreated, the spots may coalesce, leading to extensive leaf dieback and premature abscission.

Environmental conditions play a critical role in the disease cycle. The pathogen thrives in warm, humid weather, with temperatures ranging between 20°C and 25°C being ideal for spore germination and infection. High rainfall or overhead irrigation systems promote the spread of spores from the soil and infected leaf litter to healthy foliage.

Management of this disease requires an integrated strategy to minimize the inoculum and protect the plant canopy:

• sanitation by removing and destroying fallen infected leaves at the end of the season;
• pruning to improve air circulation and canopy penetration, which helps leaves dry faster;
• application of protective copper-based fungicides or appropriate systemic chemicals during the growing season;
• maintaining balanced plant nutrition to ensure the vine can better withstand fungal pressure.