P&PDL Picture of the Week for
January 21, 2008

Powdery Mildew on Houseplants

Gail Ruhl, Sr. Plant Disease Diagnosticians, Department of Botany & Plant Pathology, Purdue University

During winter months, a fungal disease known as powdery mildew is often observed on indoor plants such as African violet, begonia, ivy, jade, and Kalanchoe. Fungal growth usually begins as discrete, usually circular, powdery white spots. As these spots expand they usually coalesce, producing a continuous matt of mildew, often mistaken for dirt or dust on indoor plants. Leaves, stems, buds, and flowers are susceptible to infection, with the majority of infections occurring on the leaves and flowers. Severely infected leaves and flowers may eventually brown and die.

Conditions that favor disease development indoors are poor air circulation, low light, and cooler temperatures near 70° F. The fungi which cause powdery mildew are spread by spores produced in the dusty, white patches on leaves and other plant parts.  Depending on the indoor environmental conditions, the fungus can continue to grow and spread during the entire year.

Although chemical treatments are available for powdery mildew, cultural controls are usually just as effective and preferable for managing powdery mildew within the home. Keep plants in well-ventilated areas and avoid overcrowding. Do not mist plants and avoid wetting the leaves when watering. At the first sign of infection, isolate the plant and remove and dispose of all infected plant parts. Severely infected plants may need to be discarded. It may be possible to start a new plant by taking a cutting from healthy tissue.

Powdery Mildew of Houseplants
Janna Beckerman, Extension Plant Pathologist

Click image to enlarge

Powdery Mildew on Sweet Pitcher Plant
Sarracenia rubra

Powdery mildew on rosemary
Photo by Janna Beckerman

Powdery mildew on african violet
Photo by www.steverd.com

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service