Only in recent years has Phomopsis twig blight and canker become an important disease of blueberries. Bushes that have been weakened by other factors are usually more prone to infection. In addition to twig blight and canker, the fungus causes a fruit rot.

Symptoms and Disease Development

Phomopsis canker is caused by the fungus Phomopsis vaccinii, which overwinters in infected plant parts. The primary symptom of twig infection is a blighting of one-year-old woody stems that have flower buds. The fungus enters the flower buds and eventually moves into the stem. Infected stems will wilt and die and young twigs will die back from elongated cankers produced by the fungus. Cankers on one-year-old stems become obvious by early summer and continue to progress downward, eventually encircling the entire shoot. In hot weather, leaves on infected twigs turn brown and remain attached to the stem. As canes mature, they become girdled by the diseased lesions. Fruiting structures of the fungus will form on dead twigs and leaves. These structures produce spores, which are spread primarily by rain splash. Infected fruit are soft, often split, and leak juice.

Disease Management

Recommendations include removing and burning all blighted or discolored wood during dormant pruning. When blighted tips appear in the summer, cut shoots back to a point where pith appears normal. No commercial cultivars show strong resistance to Phomopsis canker. A few blueberry cultivars vary in their resistance to the twig blight phase.