Ash rust

The causal agent of this disease is the rust fungus Macruropyxis fraxini. It is a specialized pathogen that infects the leaves of ash trees, causing systemic metabolic disturbances and interfering with the tree's vital photosynthetic processes throughout the growing season.

This pathogen strictly attacks species within the Fraxinus genus. While mature trees may tolerate light infections, the disease poses a significant threat to saplings in nurseries, ornamental ash plantations, and urban landscapes where environmental conditions often favor fungal development.

Symptoms are characterized by the emergence of chlorotic spots on the upper leaf surface, followed by the development of bright yellow or orange aecidia on the underside of the leaves. These structures represent the reproductive phase of the fungus, leading to severe leaf spotting, curling, and premature leaf drop.

The fungus thrives in conditions of high humidity and moderate temperatures, which are critical for the dispersal of spores via wind and rain splash. Once an infection is established, the pathogen can spread rapidly across a grove if the canopy remains wet for extended periods, facilitating secondary infection cycles.

Effective management requires a proactive approach centered on sanitation and chemical intervention. Growers should focus on removing and destroying infected leaf litter to reduce the primary inoculum load. During the active growing period, the application of registered fungicides is recommended if monitoring indicates high disease pressure or if trees show signs of decline.