Horse chestnut powdery mildew

Taxonomic classification and type of pathogen: Uncinuliella flexuosa is a fungal pathogen belonging to the kingdom Fungi, phylum Ascomycota, and order Erysiphales. As an obligate parasite, it survives and reproduces exclusively on the tissues of living host plants.

Diseases and susceptible crops: This fungus is the primary causal agent of powdery mildew on horse chestnut trees (Aesculus hippocastanum). The disease manifests as a white, dusty mycelial coating that spreads across the surface of leaves, often leading to discoloration and deformation.

Biology and life cycle: The pathogen overwinters as chasmothecia (fruiting bodies) within fallen leaf litter. During the spring, these release ascospores, which trigger primary infections on developing foliage. Throughout the growing season, the fungus spreads rapidly via conidia, allowing for multiple secondary infection cycles.

Conditions for development and harmfulness: The disease thrives in warm, humid conditions with stagnant air. Harmfulness is significant: heavy infestations cause premature leaf senescence, reduced tree vitality, and diminished aesthetic value, which is particularly problematic for ornamental trees in urban landscapes.

Management and control measures: Controlling the disease requires both preventive and remedial actions:

• Removing and destroying infected fallen leaves to reduce the overwintering inoculum.
• Pruning to improve air circulation within the tree canopy.
• Applying systemic fungicides, such as triazoles, during the onset of the growing season.
• Maintaining tree health through proper fertilization and watering to improve natural resistance.