Betty- Unfortunately, once a plant has Powder Mildew, it will always have it within the plant. All you can do is treat the symptom, but it will be difficult to eradicate it. We carry several products that focus on fighting the mildew for the remaining weeks of flower.
One of these products is brand new, and so far, we have been hearing great results. The product is called Mac's Miracle Mildew Wash. It is organic, non toxic, and leaves no residue. It can also be used all the way up to harvest! It retails for $34.95 a gallon.
Other products that can be used would be PM Wash from NPK Industries ($40/Gallon) and Green Cure ($16/8 oz powder). Of these products, Mac's seems to be getting the best results these days.
After you have harvested, you should thoroughly clean your grow room, including floors, walls, fans, lights, etc. This will help kill and remove any remaining Powdery Mildew spores. New plant genetics will also ensure that you are not bringing the PM back into your room.
Hope this helps!Answered by Zoltar