Willow leaf spot

Willow leaf spot typically presents in early summer as small, dark brown or black lesions appearing on the leaves.

These spots gradually expand and may merge, creating large, irregular necrotic areas that often have a distinct dark margin.

Small, shiny, disk-like fruiting bodies known as apothecia develop on the underside of infected leaves in late summer.

Severe infection leads to widespread premature chlorosis and heavy leaf drop, which significantly impacts the health of the host tree.

The fungus can also infect succulent new shoots, causing small, elongated lesions that may deform the branches.

The disease is caused by the ascomycete fungus Drepanopeziza salicis, which specializes in infecting willow species.

The pathogen overwinters primarily in fallen, decaying leaves, but can also survive in the tissues of infected woody twigs.

In spring, the fungus releases ascospores which are disseminated by wind currents and splashing raindrops onto new foliage.

Once infection is established, the fungus produces conidia throughout the growing season to promote secondary cycles.

The biology of the fungus is strictly tied to the development of the host, ensuring it can persist from season to season.

The development of Drepanopeziza salicis is highly dependent on periods of prolonged high humidity and moderate temperatures.

Frequent rainfall during spring and early summer facilitates the germination of spores and the successful penetration of leaf tissue.

Dense planting schemes that prevent airflow within the canopy create a moist microclimate that favors rapid disease spread.

Poorly drained soils or sites with excessive moisture retention around the base of the trees exacerbate the risk of infection.

Trees that are already under physiological stress from drought or nutrient deficiency are more susceptible to the initial attack.

The primary damage caused by willow leaf spot is the significant reduction of the plant's photosynthetic capacity.

Premature leaf abscission limits the tree's ability to store carbohydrates, causing it to enter dormancy in a weakened state.

Continuous infections over successive years lead to dieback of branches, stunted growth, and a general decline in tree vigor.

From a nursery perspective, the disease drastically reduces the marketability and quality of young willow saplings.

Increased susceptibility to opportunistic pests and secondary wood-decay fungi is a common consequence of long-term infection.

The most important cultural practice is the diligent removal and burning of all leaf litter during autumn to break the life cycle.

Regular pruning to remove infected branches and improve canopy aeration helps to reduce the local humidity around the leaves.

Fungicidal applications, such as copper-based sprays, should be applied at bud break to prevent primary infections during wet springs.

Ensuring trees have adequate space and are not crowded helps to reduce the incidence and severity of the disease in orchards.

Selecting and planting naturally resistant cultivars is the most sustainable approach to managing this fungal pathogen long-term.