Spots first show 3 to 4 weeks following rain. Leaf death may occur if large numbers of spots build up. On clusters, spots similar to those that occur on leaves and shoots occur on the flower cluster stems. Lesions on leaves, shoots, and clusters become inactive during the summer heat but rain just before harvest can cause light brown spots on clean berries and spots quickly enlarge and become dark brown.
Infections generally occur when shoots begin to grow.
Spores are released in large quantities from the overwintering pycnidia on diseased canes and spurs. These are splashed by rain onto early developing shoots and infection occurs when free moisture remains on the unprotected green tissue for many hours. Reducing the source of the disease is important. Carefully prune out badly infected canes to reduce the carryover of spores. In all areas, spring foliar treatments may be advisable if rains occur after budbreak.