Guava Phomopsis blight

Phomopsis psidii is a pathogenic fungus responsible for the disease commonly known as Phomopsis blight or fruit rot in guava. As a member of the Diaporthales order, this fungus causes significant structural damage to the plant tissues, leading to necrosis and premature organ decay.

The primary host for this pathogen is the guava tree (Psidium guajava). The fungus targets various parts of the plant, primarily affecting young shoots, leaves, and maturing fruits, which are particularly susceptible to infection during periods of high humidity and rainfall.

Typical symptoms include the development of dark brown to black spots on the leaves and fruit surface. As the infection progresses, these spots often become sunken, and tiny, black, flask-shaped reproductive structures called pycnidia appear on the surface of the lesions, signaling the release of fungal spores.

Development and spread of the disease are highly dependent on environmental conditions, particularly high humidity and temperatures between 20°C and 30°C. Spores are disseminated primarily through wind-driven rain splashes and can also be carried mechanically by human activity or pruning equipment that has not been properly sterilized.

The economic impact of the disease is severe, as it reduces both the yield and the market value of the guava crop due to post-harvest decay and reduced tree vigor. To mitigate the risks, growers should adopt a comprehensive management strategy:

• Implement strict sanitation measures by pruning and removing infected branches and fallen fruits.
• Apply protective copper-based or systemic fungicides during the active growth and fruiting stages.
• Promote good orchard hygiene by ensuring proper spacing between trees to improve airflow.
• Regularly disinfect pruning tools to prevent the spread of the pathogen between trees.
• Select resistant cultivars if available to build long-term orchard resilience.