It sounds like a mushroom: odium ? That's really the first time I hear of odium and plants inside...there must be something I don't understand :-(
I'm sure someone having a better knowledge than I have of English will give you good advices or you'll find the right thing on the web (google -> odium). You can find chemical against it: we use " copper sulfate " here.
Anyway, viola does NOT live inside, it's definitively not a houseplant, it's gonna die man :'(
Do you know the kind of viola you have ? Pansy ? Violet ? viola sororia ? viola odorata ?

All the best.
Thierry.

Sounds like powdery mildew. Pansies are more prone to get it than violets, in my experience. Go look for images of 'powerdery mildew' on Google - to check and read-up on it; you should find advice on how to treat it, too.

While you're researching, check on 'downy mildew', too. It is different, but worth knowing about so you know what's what.

There are several types of both these diseases, but for violet/pansy purposes, one can just use those basic names.

Why not checking too for the botrytis track?
Good luck and keep us informed..

My co-worker had the same experience at work with her pansies. White mold on the leaves- probably podery mildew. We sprayed it with a little dish soap(ie dawn) and water combination. The mold cleared right up. however, they're leggy and miserable sitting on the windowsill. No blooms since the autumn. Sigh... I hope you have better luck with yours!

Karen :)

Thank you for the responses. These are 3rd or 4th generation plants from seeds originally labelled 'singing the blues violas' (viola odorata). They have self seeded everywhere ever since the first planting, and I let them, they are extremely hardy and a range of colors from near-black to light purple and yellow. My windowsill is totally sunny from sunup to sundown so they are doing quiet well, not leggy, and very rich green. The mildew persists, but when I water, it all rinses right off. It reforms by the next watering. It is having the effect of making the leaves curl a bit, but they are not dying, for the most part. All of the info online on downy mildew only deals with prevention, using copper products. But it's too late for prevention. I actually do expect to get blossoms. I had some coleus growing on this windowsill last winter, and some Nemesia had self seeded in the pots while they were spending the summer outdoors. Those flowers bloomed, so I am thinking these will too, with pots all to themselves. I will try the soapy spray. Has anyone heard of using milk to combat mildew? It seems I read that somewhere long ago.

"These are 3rd or 4th generation plants from seeds originally labelled 'singing the blues violas' (viola odorata)"
Sorry. They are not Viola odorata. T&M indicates Viola X williamsiana.
http://seeds.thompson-morgan.com/uk/en/product/3447/1
But i don't know if it's a true name.
Indeed they are in the genus Viola but they are pansies and not at all odorata.

--
Denis

V. X williamsii Wittrock (syn. V. X .stuartii Bergmans) = all crosses garden pansy X V. cornuta.

Depending how well T&M know the origin if their plant, they might or might not be correct in calling it Viola X williamsii. But I believe they are wrong to call it Viola X williamsiana - that does not exist, as far as I know.

Treatment of mildews: I use a rape seed oil insecticide that happens to also contain sulphur; works very well.

thompson-morgan ? @#!!&£?%$*$ ! Such a shame !!! Just wonder what they do with seeds ? None of them I had bought there germinated (In a way, it's better not to seed a pansy adorota germinating, GOD, even in nightmares such things can't happen ;-)) I could give you so many examples of the bad words I know in English, moreover some in French, but Xmas is coming and wouldn't like Santa Klaus to forget my home so I'll be a nice boy 'n' shut up my nausty mouth (fingers).
thompson-morgan ? ANYTHING, definitively !

sorry: "...not to SEE a pansy Odorata germinating..." !!! Sorry for the small mind ;-)
Odorata is adorata, but not in English lol
It's so much getting on my nerves :-/

Take care and get ready...HE's on the way ;-)
Thierry.

Many thanks Mike for your explanations on Viola X williamsii.
Relating to T&M, it seems they have a lot of misnamed plants on their catalogue ( i remember an old discuss on Viola sororia 'famecheck apricot' ??? ), and in France T&M's seeds are often very difficult to germinate. But, years ago, i started cultivate violets with the most incredible seeds i had never seen before : Viola sororia 'freckless'T&M sold in a marvellous old plants shop in Paris. Unfortunately, this shop has been closed since the owner has been retired.

--
Denis

An old discuss about sororia "famecheck apricot" ? Don't tell me Denis that T&M missnamed that viola ? Would it mean that in fact it's viola suphurea ??!!!!!!

It is shame that the discussions we have had on T&M mis-naming have been removed from GardenWeb - just because of being too long ago. Newer recruits to this forum, like you Thierry, don't have the benefit of being able to catch-up.

Also note that T&M call it Viola sororaria 'Famecheck Apricot'!
See http://seeds.thompson-morgan.com/uk/en/product/6985/1
They mean, of course, sororia not sororaria, but even that is suspect - we think it is probably V. odorata.

See also the link below.

Here is a link that might be useful: earlier discussion re 'Famecheck Apricot'

I have had very good luck controling mold/mildew with a strong brew of chamomile tea applied after it has cooled. I have never noticed any adverse effect to any of the plants or seedlings to which I have applied it. I usually spray with the tea when I see mold, then I water the plants with the tea for a while. It won't hurt your violets, so it might be worth a try!