Use the search function, This question has been answered many times. Most people get tired of repeating themselves.
If you do a search you'll find what your looking for, since I'm a nice guy I did it for you.
I found several threads on it already.. I just clicked on a random thread and found:
Written by Finshenfool06.
Powdery mold is a form of pythia, i had it when i was trying to grow inside a cabinet. it is a air born spore and it can travel from your garden, into your house. their are a couple of things you can do.
option #1 first, go to your local tool rental place and see if they have a sulfur burner. if u treat the entire house you will have a better chance of getting rid of it completely. you are probably really careful but if you carie the plants threw the house to your garden and the powdery mold comes off and settles into the carpet. you have it in your carpet and it will keep spreading.
option #2 go to your local hydro store and get some neem oil and safer soap 1 oz of
oil and 1 oz of soap mix well in a sprayer with 1 gall water. spray entire plant top to bottom, stems and bottoms of leafs. treat again if mold reappears, more then likely the mold will be gone. but it can regrow on fresh sprouts/ new growth that has not been treated.