Phomopsis twig blight

Phomopsis twig blight, caused by the fungus Diaporthe vaccinii (formerly known as Phomopsis vaccinii), is a prevalent and destructive disease affecting commercial blueberry plantations. This pathogen specifically targets the vascular tissue of the canes, leading to wilting, branch dieback, and potentially severe crop loss if left unmanaged.

The disease primarily attacks highbush blueberries. The fungus typically enters the plant through wounds, such as those caused by winter injury, insect feeding, or pruning cuts. Once infection is established, the mycelium colonizes the vascular system, effectively blocking the flow of water and nutrients to the upper parts of the plant.

Key symptoms include the sudden wilting of terminal shoots, which often bend in a crook-like shape. As the disease progresses, the bark on infected canes develops reddish-brown lesions or cankers. Close inspection of the dead wood will reveal small, raised black structures known as pycnidia, which are the fungal fruiting bodies responsible for releasing infectious spores.

The development and spread of Diaporthe vaccinii are heavily influenced by environmental conditions, particularly high humidity and temperatures ranging from 15 to 25 degrees Celsius. Rain splashes and wind currents serve as the primary vectors for spore dissemination throughout the field, often leading to rapid outbreaks during wet growing seasons.

Effective management and prevention strategies include:

• Pruning and destroying infected branches, ensuring cuts are made well below the visible necrotic tissue.
• Sanitizing pruning tools with alcohol or appropriate disinfectants between every plant to prevent cross-contamination.
• Maintaining proper plant spacing to ensure adequate air circulation and reduce canopy humidity.
• Applying recommended fungicides, such as those containing copper or systemic triazoles, during critical infection windows like bud break and flowering.
• Promoting vigorous plant growth through balanced fertilization and stress management to help plants resist fungal invasion.