Sulphur use for powdery mildew

QuestionWhat’s that yellow stuff that you keep brushing on your violets?

Answer:  The “yellow stuff” that this visitor to our shop was referring to was powdered sulfur.  It is our way of controlling powdery mildew, which seems to be a problem for us in spring and fall.  Powdered sulfur is our way of eliminating mildew on a violet without having to spray our entire collection with more toxic chemicals.  Since it’s our practice to regularly brush the leaves of our violets when we groom them, it’s not that much more work for us.  We keep a small jar of it at our side, and when we see a plant with powdery mildew, we dip the brush tip into the jar, getting just a very small amount of sulfur, gently tap the brush onto the leaves, then brush off.  It kills the mildew on contact, and keeps it from returning to the treated areas. 

We should mention that we’ve tried the method of simply placing containers of sulfur amongst the plants, but found this to be of no use.  It must be applied to the plants to be effective.  Where to get it?  As your local pharmacist.  A lifetime supply can usually be gotten for just a few dollars.


  • Powdery mildew is affecting the flowers of my African violets more often than the leaves. Will the sulfur be just as effective on flowers as leaves? Thank you.

    • Yes, but we’ve found that once the mildew is on the blooms, the damage has been done. We just remove the affected blooms–there will be more blooms soon on a healthy plant.

  • How long should we let the sulfur on the plant’s leaves before we brush it off? If I understood corectly, we have to dust with sulfur only the affected areas, not the whole plant and its neighbours? Is it necessary to repeat the treatment on the same areas?
    Thank you very much!

    • Very little is needed, just a few grains on the tip of brush. It only needs contact with the plant surface–brush it on, brush it off. If you can’t easily brush all of the sulfur off, you’re using too much. Mildew won’t reappear on the treated areas, but since the plant grows (producing new, untreated growth), mildew can always reappear on the plant if the environment is conducive to this. In such small quantities, unless you have a particular sensitivity to it, it should be safe to use in the home.

  • I have read about baking soda as a non-toxic treatment against powdery mildew and I was wondering if you have used it and if it has any positive results. Thank you very much, I am very impressed about what you are doing!

  • Have plant stand in room with overhead fun, running 24-7 and have had a terrible summer. Not new to violets or streps but this year has been unusually humid and warm here in SW MO. Most streps have mildew, tho it is not evident on the violets. Will definitely try sulfur.

    On another issue, I have had a terrible time with scale on both. Need some good advise as to where to go from here. Take leaves, chuck the worst, what ever it takes…..but do need to know best way to treat and prevent. I know circulation is needed….don’t really know what I could do to improve where the stand is, but want to have healthy plants….so help!

    • It is unusual to find scale on either violets or streps, though it does happen. You can go through your plants and get each scale with a q-tip and alcohol, but this will take some time and the effectiveness depends upon how good your are on finding each one. Better would be to restart plants from cuttings or crowns that have been thoroughly cleaned and are free of problems. Good practice to never bring plants in from the outside, since this is often the source of the original problem.

  • What is the difference between powdery mildew and mold . I`v had centers turn gray and limp in two days.

    • Splitting hairs, but mildew is a milder, more easily dealt with, kind of mold. Mildew will appear on surface of plant or blooms and is easily treated. Mold is more substantial, more visible and thicker, often appears on soil surface. Powdery mildew will appear when air is stagnant and temperature drops significantly (at night). Mold usually the result of damp conditions–usually when soil is kept very wet. This excess moisture collects in the plant center (like ‘dew’) and you can see the problems you describe, especially if air is stagnant and/or humidity is high.

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