Bacterial leaf spot and stem canker begins as light green, water soaked spots. These later turn brown or black with reddish margins. The leaf stalks become black and shriveled. A black decay extends from the tips of the twigs downward into old wood. The stems may be girdled by cankers and a bacterial ooze forms during warm, humid conditions. Avoid high temperatures, high humidity, and unnecessary syringing.
Several fungi cause leaf spots but infected leaves can by picked off and destroyed.