Phyllosticta leaf spot of stone fruits

Phyllosticta circumscissa is a phytopathogenic fungus belonging to the kingdom Fungi and the class Dothideomycetes. It is widely recognized as the causal agent of phyllosticta leaf spot, or shot-hole disease, which significantly affects stone fruit crops, including cherries, plums, apricots, and almonds.

The disease is characterized by the formation of small, circular spots on the foliage that turn brown over time, often surrounded by a dark, distinct margin. As the lesion matures, the necrotic tissue dries and separates from the healthy leaf tissue, creating the signature shot-hole appearance that gives the disease its common name.

The life cycle of the pathogen is centered around its survival in infected plant debris. The fungus overwinter primarily as pycnidia on fallen leaves and within infected twigs. As environmental conditions become favorable during the spring, these pycnidia release conidia, which are disseminated by rain splash or wind currents to young, susceptible leaves.

Environmental conditions play a critical role in the epidemiology of the fungus. Optimal development occurs under conditions of high humidity and moderate temperatures ranging from 18°C to 25°C. Prolonged wet periods caused by rainfall are particularly conducive to the production and spread of secondary inoculum throughout the growing season.

To mitigate the impact of Phyllosticta circumscissa, it is essential to implement strict sanitation practices, including the removal and destruction of fallen leaves and infected woody parts. Chemical control is also necessary, typically involving the application of copper-based fungicides or appropriate systemic treatments during early spring and throughout the periods of peak infection risk to protect new growth.