Shot hole disease

Shot hole disease, caused by the fungus Stigmina carpophila (formerly Coryneum beijerinckii) of the Coryneaceae family, is a significant fungal infection affecting stone fruit trees. It is characterized by the formation of circular lesions that eventually drop out, leaving behind a distinctive "shot hole" appearance on the foliage.

The disease primarily impacts stone fruits such as cherries, peaches, apricots, and plums. The fungus overwinters in infected buds, twigs, and old leaves, surviving as mycelium. When spring conditions become favorable, the fungus produces spores that are spread throughout the canopy via rain splash and wind, initiating new cycles of infection.

Early symptoms manifest as small, dark purple or reddish spots on leaves. As these lesions expand, the necrotic central tissue turns brown and falls away, creating holes. On fruit, the fungus causes small, raised, red-rimmed spots, which can lead to deformation. On twigs, the disease often results in sunken lesions and gummosis, where sap oozes from the infected sites.

The development and spread of the pathogen are heavily dependent on moisture. Prolonged wet weather in spring is the primary factor driving the severity of an outbreak. Warm temperatures, coupled with high humidity, accelerate the life cycle of the fungus, leading to rapid defoliation and potential weakening of the tree structure over consecutive seasons.

Effective management requires a multi-faceted approach:

• Regular pruning of infected branches to reduce inoculum sources.
• Sanitation by removing and destroying fallen leaves and diseased fruit.
• Application of copper-based fungicides during the dormant season.
• Use of protective fungicides during the bud-burst and petal-fall stages to prevent primary infection.