It's most likely powdery mildew. Here's some info about it and how to treat:
Powdery Mildew
Mildew spores can be brought into the grow room through air ventilation into your grow room, your cloths, pets and be carried by animals outdoors. and land on the plant infecting other parts of the plant, buds, stems, stalks and leaves, also spores can land on indoor grow room walls, tubes, growing equipment, hoods, ballast’s, cords and etc. Spores can remain dormant until environment factors trigger it, like high humidity and cool temperatures, poor air circulation. Powdery mildew in vegetative growth is much easier to rid than in the later stages of flowering. Night time temperatures and moisture triggers spores to be released. The mildew eventually covers and coats the plant thus reducing the process of photosynthesis. If left untreated powdery mildew will infect all plants in your garden and coat your plants in flour like substance and cause leaves to “suffocate” Yellow and die off. If your plants are in flowering, depending how far into flowering, your buds will eventually become infected and will not be able to be used. Buds will have a stale moist smell and will be coated with a white powdery substance that can’t be removed no matter what you do. Very early detection in flowering plants that have powdery mildew is extremely important, the longer you wait in flowering the more impossible it gets to eradicate this, due to this, bud size gets bigger in flowering and having high humidity temperatures over 65% can trigger active spores to start, not only powdery mildew, but triggers other problems from it, like bud rot. Not only will you have lower yield, but you won’t have any buds, due to the fact mold has crippled your harvest.
Strains vary in susceptibility to molds, just like other pathogens and nutrient requirements and care.
Prevent and Control
Symptoms of your plants having powdery mildew include: white blotches of furry stuff and white spots or splotches that you can wipe off, having humidity that is over 65%, also starts on darker areas of the plant and spreads to the top. Darker areas on your plant that do not get a lot of light will start to show this first, then when spores become active it spreads to everything. The longer you let it go the harder it will be to eradicate, late flowering plants that have this are extremely hard to get rid of, due to bud density thicker in late flowering plants, because of this the mildew attacks the buds which you can’t cure mildew once it affects the buds.(also known as Bud Rot)Plants that are stressed from environment factors, or fighting pest’s will be taken over more by this mold, due to the fact it’s already fighting problems. If you see your stressed plants getting it first, try to isolate the plant and bring down humidity, better air ventilation and or negative air pressure grow room. If you have mildew with your fans running, you will need to take them down and clean them as the fans can spread spores around the room. You will need to wash down everything in your indoor grow room, spores land on everything, so everything needs to be washed with mild hot water and bleach solution. Removing infected leaves from the grow room is critical, carefully removing them and trying to not knock spores into the air is a challenge. Applying a bag over infected leaves and tying it shut then removing it helps out with not knocking up spores in the air. Making sure you use h202 on stems that have open wounds from leaves that was removed. DO NOT water when lights are going to be going out, doing this keeps water on the plants soil and causes higher humidity levels, this goes for foliar feeding. Water plants when lights first come on or there is at least 5 hours left of lights on. You want to reduce the amount of humidity as possible if your levels of RH are high, you want to keep your humidity levels around 40 to 50%, and anything over 60% is going to trigger problems. Also keeping plants spaced apart allowing maximum air flow in between plants will help minimize plant to plant infection. Using a dehumidifier can greatly reduce humidity issues. Using a meter that tells your grow room conditions like temperature, RH and time can help combat your problems, by keeping track before and after you water can tell you how much if any your humidity can rise after changes made to the grow room. Sulphur Burner is another way to prevent and kill powdery mildew by vaporizing spores in the air. (Do not apply sulfur when air temperature is near or over 90°F) Controlling your mildew outdoors can be somewhat of a challenge, you can’t control outdoor temperatures, or environmental factors, Using Vapor Gard,Wilt Pruf sprayed over the leaves can prevent infection’s.
You will need to treat your plants with various organic and chemical controls. This list will work for indoor and outdoor growers in killing and preventing Powdery Mildew. Outdoor growers can use Organics List below to help prevent Powdery Mildew of starting, even after it has started using anything below will help kill it off. (Note: When using chemical and or organic control methods, do not spray the buds, and for health and safety reasons, stay away from spraying around the buds if all possible.)
AQ10
Serenade
Plant Shield
Garden Disease Control
Fungicide containing Lime, Sulphur
JMS Stylet Oil
Saf-T-Side Spray Oil
Sunspray Ultra-Fine Spray Oil
Neem Oil
Neem 2
Kaligreen
Safer Garden Fungicide
Concern Copper Soap Fungicide
Guardian Angel
Serenade Garden Disease Control OMRI
Safer 3-in1 Garden Spray OMRI
Sulfur Vaporizer
Organocide
SM-90
Malatox
Garden Sulphur
Sulphur Burner
Sodium Bicarbonate
Chi
Mother Nature's Karanja Oil
Concern Copper Soap Fungicide
