I have some small, purplish spots on the canes of my black raspberries. What is it and how can it be controlled?
The small, purplish spots are most likely due to anthracnose. Anthracnose is a serious fungal disease of raspberries, especially black raspberries. The disease is readily recognized by the small, purplish spots that develop on young canes. These spots enlarge and become somewhat oval-shaped and slightly sunken with buff-colored centers and purple borders. With late season infections, spots are generally larger, more numerous, and more buff or gray than purple. Berries on anthracnose infected canes are small, dry, and seedy.
If the raspberry planting is seriously infected, prune all canes back to ground level in late winter/early spring. Remove and destroy the pruned plant material. Then follow with several fungicide applications during the growing season. Use only those products labeled for control of anthracnose on raspberries. In following years, one application of liquid lime sulfur in early spring, just before the leaves emerge, will control the disease. Also, remove and destroy the old fruiting canes as soon as the harvest is competed.