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From the Pests of Ornamental Series
Description: During wet weather the leaves of common periwinkle (Vinca minor) may have brown or black spots that in most cases extend inward from the edges of the leaf. The spots may appear as circular areas up to 3/8 inch in diameter or may involve the whole leaf.
Vinca Canker and Dieback
Description: During rainy periods, shoot-tips of affected plants wilt, become dark brown, and die to the surface of the soil. Affected stems are nearly black in color. Tiny black fruiting bodies (black dots) are often found on the affected stems (seen with 10x magnifying lens).
Several species of fungi cause leaf spots on periwinkle.
Description: Leaves are streaked or mottled light and dark green and may curve downward. There is an increase in the number of secondary shoots. Flowers may be streaked with white. Plant and flowers are dwarfed.
Root and Sem Rots
Of the above mentioned diseases, the only disease of any consequence in West Virginia is Root and Stem Rot. It is widespread and evident throughout the growing season in most plantings.
Description: Shoot-tips of affected plants may wilt and die as the result of the rotting of the roots and lower stems. Both Vinca Canker and Dieback, and Root and Stem Rot occur in "patches" in a planting. The tiny black fruiting bodies, however, are not associated with Root and Stem Rot.
Cause: The fungus, Pellicularia filamentosa