Powdery mildew on indoor plants
Powdery mildew, caused by various fungi, is a common problem on indoor plants during the fall and winter months. African violet, begonia, ivy, jade, and Kalanchoe are most commonly affected. Conditions that favor disease development are poor air circulation, low light, and cooler temperatures near 70° F. In contrast to powdery mildew species within the home landscape and home lawn, interior powdery mildew species are better adapted to drier conditions. These fungi tend to be most severe when relatively dry conditions exist.
The first sign of infection is white, thread-like fungal growth (mycelia) on infected plant parts. Columns of spores are produced on the mycelia, appearing as a white to gray powdery coating. This coating can be rubbed off with fingers. Spores produced on the powdery growth are blown or water splashed onto healthy plants, where new infections develop. The leaves, stems, buds, and flowers are susceptible to infection, with the majority of infections occurring on the leaves. However, individual powdery blotches also develop frequently on the stems. Severely infected leaves may eventually brown and die, while other leaves may show no sign of infection.
Chemical treatments are available for powdery mildew, but cultural controls are usually just as effective 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. Choose resistant varieties whenever possible. At the first sign of infection, isolate the plant. 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. There are many preventative fungicides available for powdery mildew. Read labels carefully for application instructions, as most fungicides cannot be sprayed inside the house. Make sure your host plant is listed on the label. Always check the label before applying a fungicide on edible plants, such as herbs. The following fungicides are currently labeled for powdery mildew on various hosts: thiophanate-methyl (Cleary's 3336), Funginex, sulfur, Bayleton, and Bonide Remedy (potassium bicarbonate).
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Revised by Chad Behrendt and Crystal Floyd 2000