Plagiostoma salicellum

The disease is caused by the ascomycete fungus Plagiostoma salicellum. This pathogen is a leaf-inhabiting fungus that primarily affects various willow species (Salix spp.). It belongs to the group of fungi that cause foliar necrosis, leading to tissue death and potential stress for the host plant.

The primary hosts of this pathogen are various species and cultivars of willow. It is frequently observed on both wild-growing specimens and cultivated trees in nurseries or landscapes. In agricultural settings, such as short-rotation coppice plantations, heavy infestation can reduce the overall biomass production and growth rate of the trees.

Symptoms typically appear as small, brownish spots on the leaf surface. These spots may expand over time and coalesce, significantly reducing the functional photosynthetic area of the leaf. Close observation often reveals tiny, dark fungal structures, known as perithecia, within the necrotic spots, which are indicative of the fungus's reproductive phase.

The development and spread of Plagiostoma salicellum are heavily influenced by environmental factors, particularly high humidity and moderate temperatures. Rain splash and wind are the primary vectors for spore dispersal. The fungus overwinters in fallen leaves on the ground, serving as the primary source of inoculum for the following growing season.

Effective management requires a combination of sanitation and chemical controls to minimize the disease impact:

• Sanitation, which involves the removal and destruction of infected leaf litter to eliminate overwintering sites.
• Maintaining good airflow in plantations through proper spacing and pruning practices.
• Application of approved fungicides when environmental conditions are conducive to infection.
• Selecting resistant willow clones if such genetic materials are available for the specific region.