Entomosporium leaf spot

Taxonomy and nature of the pathogen: Entomosporium mespili is a plant pathogenic fungus belonging to the kingdom Fungi and the phylum Ascomycota. Its sexual state is identified as Diplocarpon mespili. This pathogen is a specialized parasite that targets various members of the Rosaceae family, causing significant aesthetic and physiological damage to plants.

Diseases and host plants: The primary disease caused by this fungus is known as Entomosporium leaf spot. Key host plants include pears, hawthorn, quince, amelanchier, and mountain ash. The infection manifests as small, reddish-brown to black spots on leaves, which often develop yellow halos. Severe infections lead to premature defoliation and can stunt the overall growth of the host.

Biology and life cycle: The pathogen overwinters primarily as mycelium or conidia on fallen, infected leaves on the ground. When spring temperatures rise and moisture becomes available, the fungus produces conidia, which are splashed by rain or wind-borne onto young foliage. Once the infection is established, secondary cycles occur throughout the summer, significantly increasing the fungal inoculum.

Environmental conditions and impact: Disease development is heavily favored by cool, wet spring weather and periods of high humidity. The economic impact includes reduced plant vigor, poor fruit quality, and increased susceptibility to secondary stressors. In nurseries, it can lead to complete defoliation, which inhibits the sale of stock and weakens the plants significantly before they enter dormancy.

Control and management: Effective management requires an integrated approach. Sanitation is crucial, involving the removal and destruction of all infected leaf litter to reduce the overwintering population. Promoting airflow through proper pruning and planting spacing helps minimize moisture on leaves. Chemical control involves the application of appropriate fungicides during the growing season, particularly before and during wet weather periods.

• Sanitation by removing and destroying fallen foliage.
• Pruning to improve canopy airflow and light penetration.
• Application of protective fungicides during early spring.
• Selecting resistant species or cultivars where possible.
• Monitoring plants regularly for the first signs of leaf spotting.