Gonatophragmium leaf spot

Gonatophragmium leaf spot is a fungal disease caused by the pathogen Gonatophragmium mori. This plant disease primarily affects the foliage of mulberry trees (Morus spp.), leading to premature defoliation and reduced plant vigor. As an agronomical threat, it is particularly significant in regions where mulberry leaves are cultivated as feed for silkworms.

The host range is centered on the genus Morus. Both white and black mulberry varieties are susceptible to this pathogen. The infection is observed globally in temperate and subtropical climates where mulberry trees are grown, often leading to significant losses in leaf biomass production if left unmanaged.

Symptoms typically manifest as necrotic lesions on the leaves. These spots start as small, discolored areas that eventually expand, turning brown or grayish-brown. Under humid conditions, the centers of these spots develop a fuzzy growth representing the conidiophores of the fungus. As the infection progresses, leaves yellow and drop prematurely, which disrupts the tree's photosynthetic capability.

The development and spread of Gonatophragmium mori are heavily influenced by environmental moisture. High relative humidity and frequent rainfall are the primary drivers for spore germination and infection. The pathogen overwinters on fallen debris and infected twigs, serving as the source of primary inoculum when warm spring weather returns.

Management strategies focus on reducing inoculum pressure and improving tree resilience:

• Strict sanitation measures, including the raking and removal of all fallen leaf litter during autumn.
• Pruning to ensure adequate airflow and sunlight penetration within the canopy.
• Application of appropriate fungicides during the early stages of disease development to protect new growth.
• Monitoring irrigation practices to avoid excessive leaf wetness, which encourages fungal proliferation.