PPDL Picture of the Week for
May 21, 2012

Powdery Mildew

Gail Ruhl, Sr. Plant Disease Diagnostician, Purdue University

Powdery mildew, a fungal disease, appears as a white, powdery fungal growth of mycelium and spores on the upper leaf surface.  Leaves and flowers may become infected, wither and die.

Conditions including high humidity, warm days, and cool nights favor powdery mildew development.  The disease is common in crowded plantings and in areas with restricted air movement. 

There is no cure for infected plants however powdery mildew can usually be managed with timely use of preventative fungicides coupled with the use of disease resistant varieties. Preventative fungicide sprays help protect healthy plant tissue from infection.  Products containing active ingredients such as triforine, chlorothalonil and sulfur are labeled for control of powdery mildew.  Be sure to follow label directions. Spraying won’t cure already-infected leaves, but it will prevent the disease from spreading to the rest of the plant.

For more information on resistant varieties and fungicides for management of powdery mildews, see BP-5-W: Powdery Mildew of Plants (pdf file).

Click image to enlarge

Powdery mildew shown on peony

Close up of powdery mildew on peony

Powdery mildew on peonies

Powdery mildew on phlox

White, powdery fungal growth typical of powdery mildew on the leaves of garden phlox.

Powdery mildew on phlox

Severe powdery mildew
infection progressing from lower to upper leaves on this phlox plant.


Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service