Phomopsis twig blight

Systematic position and pathogen type. Diaporthe vaccinii (anamorph Phomopsis vaccinii) is an ascomycete fungus within the order Diaporthales. It is a significant phytopathogen known for causing serious dieback diseases in berry crops, particularly within the Vaccinium genus, impacting commercial agriculture globally.

Diseases and host crops. The fungus is the primary cause of Phomopsis twig blight. It mainly affects highbush blueberries and cranberries. The pathogen targets various parts of the plant, including stems, leaves, flowers, and fruit, leading to systemic damage and severe loss of plant vigor.

Biology and disease cycle. The pathogen overwinters as mycelium and pycnidia in infected stems or plant debris. During wet spring conditions, pycnidiospores are released and dispersed by splashing rain or wind. Infection typically occurs through wounds or natural openings, allowing the fungus to colonize internal plant tissues and eventually girdle stems.

Conditions for development and harmfulness. Disease development is favored by warm, humid environments, especially when heavy rainfall occurs during the bloom period. The damage caused includes terminal shoot dieback, stunted growth, and fruit rot. If left uncontrolled, the fungus can cause extensive mortality of canes and significantly reduce both fruit quality and shelf life.

Management and control measures. Successful control requires an integrated pest management (IPM) strategy:

• Rigorous pruning of infected shoots at least 15-20 cm below the visible lesion.
• Sanitation, ensuring that all pruned material is removed and destroyed.
• Application of appropriate fungicides during early bud break and bloom stages.
• Avoiding over-fertilization with nitrogen, which can lead to succulent growth susceptible to infection.
• Improving air circulation through proper plant spacing to decrease moisture accumulation in the canopy.