Question: Why do leaves of phlox plants turn white and die?

Answer: Perennial phlox plantings in Indiana are subject to powdery mildew disease, caused by the fungi Erysiphe cichoracearum and Sphaerotheca humuli. Signs of powdery mildew appear as a superficial white powdery growth on leaf and stem surfaces. Infected leaves may shrivel up and die. Although the disease does not kill plants, it reduces aesthetics and flower production. Where possible, choose varieties that have resistance to powdery mildew. Reduce humidity in phlox beds through wider spacing, full sun exposure and judicious watering. Fungicides are sometimes beneficial. Check the fungicide label for rates, timing and use for garden phlox. See Botany and Plant Pathology BP-5-W, for more information on powdery mildew on ornamentals.

--Dr. John Hartman, Extension Plant Pathologist, University of Kentucky, Lexington
Edited for Indiana by Gail Ruhl, Purdue University

Information listed is valid only for the state of Indiana.

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