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Spur blight (Didymella applanata) is a widespread fungal disease of raspberry, especially red raspberry. Cankers develop on canes just below leaf buds, usually near lower portions of stems. Purple cankers expand downward to cover the entire section between leaves. As cankers mature, bark inside cankers split lengthwise, and fruiting bodies can be visible as black specks inside canker centers. The following year, cankers continue to expand. As a result, emerging lateral shoots are weak, fruit production is reduced, and canes wilt. Leaves can become infected; brown wedge-shaped lesions develop. Infected leaves fall while petioles remain intact.  The fungus overwinters in infected canes, and spores infect new growth in spring. Secondary infections occur during summer if weather is rainy.

Early appearance of spur blight lesion on a cane.

(Photo: Thaddeus McCamant, Central Lakes College)

Characteristics of an older lesion.

(Photo: Mary Ann Hansen, Virginia Tech., Bugwood.org)

Splits in bark (circled) resulting from older lesion.

(Photo: Thaddeus McCamant, Central Lakes College)

Management:

• Practice proper sanitation (remove floricanes after harvest; remove all diseased canes; discard or destroy prunings away from plantings).
• Consider planting resistant cultivars.
• Increase air circulation to encourage drying of plant tissues (pruning, thinning, spacing, and managing weeds).
• Apply fungicides (especially dormant applications).

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