University of Illinois Extension

University of Illinois Extension

Hort Answers

Fungal Disease

Phlox diseases
Phlox sp.

5 (1 = rare 5 = annual)
3 (1 = very little damage 5 = plants killed)
Phlox and many other plants

Plants Affected

Phlox sp. (Phlox) has several foliar diseases but the most common is powdery mildew.

Mildew causes a powdery white to grayish white growth on the leaves and stems. When the fungal mycelium becomes dense enough, the affected plant tissue turns brown and dies. Frequently the powdery mildew fungus is already growing on the plants by the time the phlox plants begin to bloom.

Life Cycle
This powdery mildew fungus needs three consecutive days that are warm and dry and nights that are cool and humid. The fungus over winters on dead plant material and mildew spores can be blown for miles.

Buy resistant varieties There are reports in isolated areas that the resistant phlox varieties have become susceptible to a powdery mildew fungus. Improve sunlight and air circulation. Fungicides and sanitation are helpful.

Related Resources
Home, Yard & Garden Pest Guide
Illinois Commercial Landscape and Turfgrass Pest Management Handbook
U of IL - Distance Diagnosis through Digital Imaging
U of IL - Plant Clinic