Damage can become severe if infection occurs early in the spring. Under favourable conditions, the disease can completely girdle canes and laterals. We have noticed an alarming number of lesions on some raspberry plants this year. This disease is one to keep an eye on not only for this year but next year as well. Spur blight is another disease that has increased in incidence this summer.
Infections usually occur at the margin of leaves.
As the disease progress, the lesion expands down toward the petiole giving a yellow and brown wedge or V-shaped appearance. Eventually the disease travels down the leaf vein into the petiole and finally into the node of the priomcane. The infected leaves drop prematurely and the fungus produces a dark reddish brown or purplish lesion just below the node and around the auxiliary bud on the primocane. It is best to scout for spur blight lesions on primocanes during the summer. Spur blight is difficult to detect in the fall when the primocane develops a mature corky layer and turns brown in preparation for winter.