Septoria leaf spot is a fungal disease that can affect blackberry, boysenberry, dewberry, and olallieberry. The similar raspberry leaf spot that formerly was thought to also be caused by Mycosphaerella rubi is now known to be caused by the fungus Sphaerulina (=Cylindrosporium) rubi and is not common in California. The damage and methods for controlling these two diseases are very similar.
Identification
Septoria leaf spot lesions are circular and may have a brown or purple margin with a pale brown to tan center. The spots are generally 1/8 to 1/6 inch in diameter. Lesions on canes and petioles are similar to those on leaves but are more elongate. Small, black fungus fruiting bodies (pycnidia) of the Septoria (anamorph, or asexual) stage can be seen in the pale center area of mature lesions.
Life Cycle
The pathogen overwinters as mycelium and pycnidia in dead leaves and stems. The fungal spores (conidia) are spread by splashing water and wind. Infection and spots can occur throughout the growing season if plants are watered by overhead sprinklers or conditions are otherwise frequently wet.
Solutions
Plant caneberries in a sunny, open location and on a berm or mound of raised soil. Avoid crowding plants and keep canes pruned between rows. Control nearby weeds. These practices will increase air circulation around plants, which reduces surface wetness and helps to control the disease. Training systems for canes (e.g., trellising) also help improve air movement. Growing caneberries inside macrotunnels (hoop houses covered with clear plastic) helps greatly in controlling leaf spot because this environment keeps moisture off the leaves and flowers of the plants.
To keep foliage drier, use drip or furrow irrigation instead of overhead sprinkling. Direct any hand watering to soil around plants and avoid wetting the foliage. Irrigate in the morning instead of late during the day or at night so foliage dries more quickly.
After harvest and before the fall rains begin, prune out and destroy old fruiting canes and dispose of them away from caneberries. Where Septoria leaf spot has been a problem, prune out old canes and then spray plants with Bordeaux mixture or another copper fungicide before the first fall rain. Where the problem has been serious, spray plants again in spring when new canes are leafing out and again when flowers begin to open.
References
Adapted from Pest Management Guidelines: Caneberries, University of California Statewide Integrated Pest Management Program (UC IPM).
