Phomopsis twig blight

Systematic position and pathogen type: Phomopsis vaccinii is an ascomycete fungus classified under the order Diaporthales. It is a specialized necrotrophic phytopathogen known to infect Ericaceous plants. The pathogen survives between growing seasons primarily as mycelium within infected stems and branches, and as pycnidia (fruiting bodies) embedded in the bark, ensuring its persistence in the orchard environment year after year.

Diseases and host plants: The primary host for this pathogen is the highbush blueberry (Vaccinium corymbosum), although it can also affect cranberry crops. The disease is known as Phomopsis twig blight. Symptoms are characterized by the sudden wilting and browning of current-season shoot tips, which later progress into dieback. As the disease advances, lesions may form around the stems, eventually girdling them and causing everything above the point of infection to wilt and die.

Biology and life cycle: The fungus enters the host through pruning wounds, winter injury, or insect feeding sites. Once inside, the mycelium colonizes the cortex and phloem, disrupting the vascular system. During spring and early summer, moisture triggers the release of conidia from pycnidia. These spores are spread throughout the canopy via splashing rain, irrigation water, and contaminated pruning tools, creating secondary infections during the active growth season.

Developmental conditions and impact: Disease development is favored by warm, humid weather and wet conditions. The damage caused by Phomopsis vaccinii is significant, particularly in young or stressed orchards. It causes serious canopy loss, reducing photosynthetic area and fruit yield. If left unmanaged, the pathogen can lead to systemic decline of the bushes, making the entire planting unproductive and requiring substantial economic investment for rehabilitation or replacement.

Protection and control measures: Effective management relies on a strict sanitation program and timely chemical intervention. Key strategies include:

• Pruning and destroying all infected branches, ensuring cuts are made well below the necrotic tissue.
• Sterilizing all pruning equipment with a disinfectant solution between each plant to prevent cross-contamination.
• Applying preventive fungicides during the critical windows of infection (e.g., bud break and early vegetative growth).
• Maintaining vigorous growth through proper irrigation and balanced fertilization to help the plants naturally resist initial infection.