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African Violet Disease or Pest #925722

Asked March 09, 2026, 4:57 PM EDT

I inherited three African violets from departing co-workers over the years. They come from a large office environment, low humidity, good air circulation and lots of thrips, other pests and plant diseases. The leaves on all three are beautiful and not affected, but as the blossoms age they get covered with a grayish or whitish powder, particularly on the underside of the petals. Can this be powdery mildew even though the plants don't seem to match the environmental risk criteria? This has been a problem for as long as I've had them, probably ten years at work and another five here at home now that I'm retired. I keep them under a commercial grow light during the winter, give them Superthrive and Schultz' liquid fertilizer and water them each 1/4 cup every other day (six inch pot). I cut them back and repotted them this morning. The roots look fine and the soil was nicely moist but not water-logged. Can you suggest a treatment? Sorry, I don't have an iPhone so I can't send a picture, but I'll be glad to drop off a sample next time I'm in Anchorage if you would like. Thank you!

Anchorage County Alaska

Expert Response

Hi Jan,

Thanks for asking. You are probably right that you are seeing powdery mildew on the flower petals. The general recommendation for controlling powdery mildew is to increase air circulation, reduce humidity and maintain a consistent warm temperature. It sounds like you are already doing all of that.

Although we usually expect low humidity to limit the development, variations with maybe lower humidity during the day and higher at night could promote the development of powdery mildew. Relatively large temperature variations between night and day can also enhance the development. Depending on your light source, the leaves and flowers may get significantly warmer under the lights.

Removing inflected flowers as soon as you possible may help and spraying plants (including undersides of petals and leaves) with a mixture of baking soda (1 teaspoon in quart of water + a couple of drops dish washing soap) or 1 teaspoon of bleach in one quart of water. Plant protection products with neem oil may also work. If needed, the treatment can be repeated after 7-10 days.

Hope this gives you a couple of ideas for managing your African violets.

Thanks,

Meriam Karlsson

An Ask Extension Expert Replied March 10, 2026, 1:54 PM EDT

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