Surviving infected buds develop small, weak, lateral shoots with stunted yellow leaves that wither and die early in the season. Yields are severely reduced because berries on weakened canes are dry, small, and seedy. On red raspberry leaves spur blight appears as small, chocolate brown lesions that rapidly enlarge along the midrib and larger veins to form angular or wedge-shaped areas. The widest part of the lesion is toward the margin or tip of the leaflet. Air currents and splashing rains carry these spores to young, tender canes and leaves, where they germinate and directly penetrate plant tissue.
Infections commonly occur where the leaf petiole is attached to the stem.
These spores are washed and splashed to other canes, where new infection occurs through wounded or unwounded tissue. Toward the end of the season, dark brown to purplish black cankers form where pruning, insect, and other wounds occurred on young canes. The cankers enlarge and encircle the cane causing the lateral shoots to wilt and die. On second-year canes, the side branches suddenly wilt and die between blossom time and fruit ripening. Close examination reveals the presence of cankers on the branches or the main cane where insect injury, pruning wound, or other type of wound has occurred.