It has been particularly troublesome on rhododendrons lately. On rhododendron, look for brown to black sunken dead areas that girdle the stem. Leaves on infected branches wilt, die, and remain attached to the plant. Small, pimple-like fruiting bodies of the fungus can be seen in the cankers. Infection occurs through wounds, pruning cuts, and leaf scars.
Cankers develop slowly and can take four months to girdle a stem.
If pruning cuts or wounds near the soil line are invaded, large portions of the shrub can be killed. Infected fruit are brown, small, and very unsightly. Leaf spots are hard to find at this time of year, but the fruit infections are very noticeable. To control this disease, spray with a labeled fungicide in the spring and repeat until dry weather arrives or plant resistant cultivars such as 'Mojave', 'Shawnee' or'Teton'. This summer I conducted a fungicide trial to protect flowering dogwood against powdery mildew infection.