Maple powdery mildew

The causative agent of this disease is the ascomycete fungus Erysiphe macrospora. It is an obligate parasite that specifically infects the foliage of various maple species, causing significant stress to the host tree by penetrating the epidermis and extracting nutrients directly from the cells.

The disease primarily affects maple trees, particularly species such as Acer platanoides. It is commonly observed in both natural habitats and ornamental landscapes, including parks and forest nurseries, where environmental conditions often favor the accumulation of fungal inoculum during the growing season.

Initial symptoms are characterized by white, cobweb-like patches on the leaves. As the disease progresses, these patches expand and become dense, flour-like white colonies. By late summer, tiny, dark-colored fruiting bodies called cleistothecia develop within the mycelium, which serves as the overwintering stage for the fungus.

The pathogen thrives in warm, humid weather, with optimal conditions typically ranging between 18°C and 25°C. Poor air circulation caused by dense planting, excessive shade, and high nitrogen fertilization can significantly accelerate the colonization of the canopy and the severity of the infection.

The economic and aesthetic impact of Erysiphe macrospora includes premature defoliation, stunted growth of twigs, and reduced cold hardiness of the trees. Effective management strategies involve strict sanitation, such as removing fallen leaves in autumn, thinning out crowns to improve airflow, and utilizing appropriate systemic fungicides during the early stages of the outbreak.