Blight causes brown or black spots which extend inward from the leaf edge and eventually cover the whole leaf. Space plants farther apart in subsequent plantings. Remove infected plants. No chemical control is listed.
Canker and dieback cause the shoot tip to become dark brown, wilt, and die back to the soil surface. The disease is most common during rainy weather. Infected plants should be discarded. No chemical control is listed.
Several fungi cause leaf spots on periwinkle. No chemical control is listed.
Root rots cause decay of roots and stems. In wet weather a cobwebby growth forms on the lower stems. The lower leaves rot and the upper part of the plant dies. No chemical control is listed.