Lesions may take up to a month or more to develop. The lesions on canes observed now were actually caused by infections a while ago. Infection and lesion development can occur on all tissue including leaves, flowers, fruit, and petioles but are most conspicuous on primocanes. The disease first appears as reddish purple, circular to elliptical spots that eventually become sunken with a grey or tan center. As the disease develops, summer spores are produced within the lesion and spread to other tissue the next time it rains.
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.