Diaporthe twig blight

Causative agent and type of disease. Diaporthe twig blight is a fungal disease caused by Diaporthe strumella (anamorph Phomopsis strumella). This pathogen acts as a necrotrophic parasite, invading the cortical tissues and phloem of woody plants, which leads to the formation of localized necrotic areas and subsequent dieback of twigs and branches.

Host range. The pathogen primarily targets members of the Grossulariaceae family. Black, red, and golden currants, as well as gooseberries, are the most susceptible hosts. The fungus is widely distributed in regions with temperate climates, where it survives as saprophytic structures on dead twigs or as dormant mycelium within the host tissue.

Symptoms and signs. Initial signs include the appearance of discolored, sunken areas on the bark of shoots or branches. As the disease progresses, the bark cracks, and numerous tiny black fruiting bodies (pycnidia) emerge through the epidermis. Affected branches show poor growth, chlorotic leaves, and eventually wither as the vascular system is girdled by the necrotic lesions.

Environmental conditions and impact. The development of the disease is heavily favored by prolonged wet weather, high relative humidity, and mild temperatures. The fungus typically enters the host through wounds, such as pruning cuts, cracks, or frost damage. The economic impact includes reduced berry yield, structural damage to the shrubs, and long-term decline in the productivity of the affected planting.

Protection and prevention measures. Effective management of the disease relies on an integrated approach focusing on sanitation and cultural practices:

• Pruning and destroying infected branches well below the site of infection.
• Disinfecting pruning tools with alcohol or bleach solutions between different bushes.
• Applying wound sealants to large cuts to prevent spore entry.
• Implementing preventative fungicide sprays based on copper or systemic agents during the dormant and early growth stages.
• Promoting vigorous plant growth through balanced fertilization and adequate spacing for better airflow.