Shot hole disease

Shot hole disease, caused by the fungus Clasterosporium carpophilum (also known as Stigmina carpophila), is a significant fungal infection affecting a wide range of stone fruit trees. This pathogen attacks leaves, buds, shoots, and fruits, causing necrotic lesions that significantly impair the plant's photosynthetic capacity and overall health.

The primary hosts of this disease include economically important species within the Prunus genus, such as peaches, apricots, nectarines, cherries, and plums. The disease is highly destructive in orchards with poor air circulation, as the pathogen exploits wet, humid conditions to germinate and invade host tissues, often leading to severe defoliation and fruit loss.

The disease is easily recognizable by its unique symptoms. On leaves, the fungus creates small, circular reddish-brown spots that eventually drop out, leaving behind distinct, hole-like perforations. On twigs and branches, the infection manifests as dark lesions that frequently ooze sap (gummosis). Fruit may also develop scabby, sunken lesions that render them unsalable for fresh market consumption.

The survival and spread of the fungus are closely tied to environmental conditions. Clasterosporium carpophilum overwinters primarily in infected buds, cankers on branches, and even fallen debris. As temperatures rise in early spring, the fungus produces conidia, which are disseminated by rain splash and wind to new growth. Prolonged periods of spring rainfall provide ideal conditions for the fungus to establish secondary infections throughout the growing season.

Effective management requires an integrated approach to minimize fungal inoculum and prevent new infections:

• Rigorous sanitation, including the pruning and removal of all symptomatic twigs and branches.
• Application of copper-based bactericides and fungicides during dormant stages (bud swell) and petal fall.
• Improving orchard airflow through regular pruning to ensure the canopy dries quickly after rain.
• Proper nutrition and irrigation management to maintain tree vigor and resistance to infection.