P&PDL Picture of the Week for
July 26, 2004

Powdery Mildew

Gail Ruhl, Senior Plant Disease Diagnostician, Interim P&PDL Director, Botany & Plant Pathology

Powdery mildew is the name for the grayish white powdery coating of fungus mycelium and masses of spores growing on plant leaves, shoots and flowers. This disease is caused by a distinct group of similar fungi that attacks a wide variety of plants. Here it is seen infecting an ornamental honeysuckle.

Although plants infected with powdery mildew rarely die, the disease can diminish the beauty of landscape ornamentals.

Conditions including high humidity, overcast weather, warm days and cool nights favor powdery mildew development. The disease is common in crowded plantings and in areas with restricted air movement, thus to reduce infection, cultural control recommendations include adequate spacing between plants and in the landscape, choosing the right plant for the right location so as to make conditions less favorable for the disease.

There is no cure for infected plants, however preventative fungicide sprays will help protect healthy plant tissue from infection. Products containing active ingredients such as chlorothalonil, triademefon, triforine, and sulfur are labeled for control of powdery mildew. Hosts and diseases listed on specific product labels may differ between products containing the same active ingredient, thus be sure to read the label.

At the end of the growing season, destroy or discard powdery mildew-infected annuals and leaves of shrubs to reduce carryover of the mildew fungi into the next season.

Healthy Honeysuckle
Lonicera x brownii
'Dropmore Scarlet'
As per Mary Welch-Keesey, Purdue University Consumer Horticulture Specialist at White River Gardens, this is NOT an invasive honeysuckle. One of the parents is L. sempervivens, our native trumpet honeysuckle. Beloved of hummingbirds, too...

Click image to enlarge

Powdery mildew on honeysuckle flowers and leaves

Close-up of powdery mildew mycelia on leaves

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service