Maple leaf spot (Didymosporina aceris)

Didymosporina leaf spot is a fungal disease affecting various maple species, caused by the pathogen Didymosporina aceris. This disease manifests primarily as necrotic spotting on the foliage, which can diminish the decorative appearance of the trees and impact their long-term health if left unmanaged.

The disease targets various species within the Acer genus. While it is rarely fatal to mature trees, significant defoliation caused by Didymosporina aceris can severely stress young saplings and ornamental maples, making them more susceptible to secondary pests and environmental stressors.

Symptoms initially appear as small, brownish spots on the leaves, which gradually expand and darken. As the infection progresses, tiny black structures known as acervuli appear in the center of these lesions. These structures are crucial for the disease's lifecycle, producing spores that facilitate secondary spread during the growing season.

Environmental conditions play a vital role in disease progression. High humidity, frequent rainfall, and stagnant air allow the spores to germinate and infect new leaf tissues rapidly. The fungus overwinters primarily in the leaf litter, making the removal of debris a critical component of disease control.

• Practice proper sanitation by clearing leaf litter.
• Ensure adequate spacing between trees to improve air circulation.
• Apply fungicide sprays in early spring if the history of infection exists.
• Promote tree vigor through proper irrigation and soil management.

Management strategies focus on breaking the infection cycle. Removing the primary inoculum by raking and destroying fallen leaves during autumn is the most effective cultural control measure. In high-value landscapes, protective fungicidal sprays applied during the bud-break stage can significantly reduce the severity of the infection.