Leaf spot—Mycosphaerella (Septoria) rubi
Leaf spot can cause symptoms on leaves and canes of blackberries and boysenberries. The disease is named
for the 0.12-inch circular lesions on the leaves. They have a brown or purple margin and, typically,
a whitish center. Lesions on canes and petioles are similar to those on leaves but more elongate. Small,
black pycnidia can be seen in the whitened area of the mature lesions.
The fungus that causes leaf spot survives on infected canes and leaves. Spores are dispersed by splashing
water. Avoid overhead sprinklers. Prune to provide good air circulation. Control weeds to reduce humidity.
After harvest and before fall rains, prune out and destroy old wood and apply a Bordeaux or a fixed
copper fungicide. Spray again in spring when new laterals are leafing out, and again when flowers begin to open.
Avoid susceptible varieties. Use an alternate-year fruiting program where canes are trained up as they
Lesions on canes