White Powdery Substance - Knowledgebase Question

Roseville, MI
Question by sandyrodgers
July 23, 2006
I have a white powdery substance on some of my perennials. I have never had it before. It does not seem to be on my annuals (yet). It rubs off of the leaves and appears to wash off with water but is there the next day.
Can you tell me what it might be and how to get rid of it?

Answer from NGA
July 23, 2006


It sounds as though your plants have powdery mildew. Powdery mildew is a fungal disease that attacks plants when environmental conditions are right (warm days, cool nights, some humidity) and air circulation is poor. You can help avoid powdery mildew by giving plants the required exposure to sunshine, and plenty of elbow room so there's good air circulation all around them. Some plants are more resistant to powdery mildew, so choose carefully and avoid those that are mildew-prone. Unlike most other fungal diseases, powdery mildew can be held in check by strong sprays of water that simulate a downpour. Another effective treatment is regular sprays with compost tea solution. To make the spray, mix one part mature compost that contains some manure with five parts water. Let the mixture sit in the shade for two weeks, then filter through cheesecloth and spray on your plants. You can dilute it by half if you like. Repeat every two weeks. I hope you have some success with these methods. Good luck.

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