Willow black spot

The causative agent of the disease is the fungus Physalospora miyabeana (anamorph: Colletotrichum gloeosporioides). This pathogen is a significant threat to various willow species (Salix), causing necrotic lesions on foliage and shoots. It is classified as an ascomycete fungus capable of causing severe damage to both ornamental and industrial willow plantations.

The disease primarily targets willow varieties, with nursery stock being particularly susceptible due to high planting density. Under favorable conditions, the infection can spread rapidly across a plantation, leading to stunted growth and reduced vigor in young trees, which often results in economic losses for growers.

Symptoms appear as dark, often black, spots on the leaves, which may coalesce as the infection advances. On annual shoots, the fungus creates distinct cankers or dark lesions. These areas restrict sap flow, causing the stems to curve, wilt, and die back from the tips down, often leading to a general decline in the health of the plant.

Disease development is heavily influenced by environmental conditions, particularly high humidity, rain, and moderate temperatures. Spores are disseminated by water splash during rainfall, air currents, and contaminated gardening tools. The fungus overwinters in infected fallen leaves and dormant twig cankers, allowing it to re-emerge as an active threat during the next growing season.

Management of Physalospora miyabeana requires an integrated approach to reduce the pathogen population. The following measures are recommended:

• Regular pruning and removal of all infected shoots and branches.
• Sanitation, including the collection and destruction of fallen leaves in autumn.
• Ensuring proper spacing to improve air circulation and reduce humidity within the canopy.
• Application of protective fungicides during wet spring weather to prevent initial spore germination.