@blackthumbbetty
Just in case i’m going to give you this information. File it away for future
ew?
High Humidity
WPM needs moisture to thrive, but that doesn’t necessarily mean it needs water. Having a grow area with
high humidity is all WPM needs to grow. This seems to be a bit problematic since young cannabis plants
grow best in relatively humid environments (40% -60% RH). Luckily, high humidity usually only becomes an
issue when it’s combined with the next cause (low/no airflow).
People who live in environments with extremely high humidity (such as Florida and the UK) can purchase a
dehumidifier to control humidity in the grow area. This is especially important during the flowering phase
when humidity needs to be much lower (45% rh) to prevent rampant growth of WPM and bud mold.
Low/No Airflow
White Powdery Mildew has a hard time settling in a grow room where the air is being moved. High humidity
will give WPM the conditions it needs to survive, but poor airflow is what gives it the ability to settle
down in the first place. In fact, a small (preferably oscillating) fan moving air in a grow area will prevent
the vast majority of White Powdery Mildew woes.
Poor Ventilation
If you have WPM spores in your grow area and the air in grow area is never exchanged for fresh air, the
spores get multiple chances to land on your plants and reproduce. This happens most often in conditions
where cannabis is being grown in a closed, unventilated space - such as a closet - and precautions aren’t
taken to exchange old stale air for new fresh air.
Leaf-Leaf Contact
Leaf to leaf contact = moisture = White Powdery Mildew!Leaves that are touching each other will form
moisture between them, and thus they become more likely to contract WPM. Untrained bushy/leafy plants
with lots of new vegetative growth are especially prone since plants will often have leaves mashed up
against each other as they try to reach the light.
Advanced growers can defoliate some of the fan leaves that are completely shaded from the grow light
to make fewer choice landing spots for White Powdery Mildew. Also, defoliation frees up energy for the
plant to use when done correctly and increases yields! See our article on defoliation for more info.
White powdery mold on the stem of an outdoor plant - White powdery mold can grow nearly anywhere on the
plant that’s exposed to air.
How to Eliminate White Powdery Mildew
As I mentioned earlier, I recently had a battle with White Powdery Mildew. Rather, it might have been a
battle if I noticed it later or waited to fix the problem. That’s the one good thing about WPM: in most
cases when WPM is caught early, you can remove all traces of the mildew without harming your plants.
There are quite a few products and homemade concoctions people use to treat WPM. Among the effective treatments are:
Milk (1:9 ratio of milk to water)
Baking soda (2 tablespoons per gallon of water)
Neem Oil (4 teaspoons per gallon of water)
Hydrogen Peroxide (1 teaspoon per gallon of 35% H202)
SM-90 (1:5 ratio of SM-90 to water)
Rather than go into these methods, I’m going to give you the simple strategy I use that gets rid of White
Powdery Mildew on the first try, every time! Here’s my trusted 3-Step White Powdery Mold cure:
1.White Powdery Mold: Ruiner of beautiful plants.Remove White Powdery Mildew from leaves - Get some water
(tap water works fine) and some paper towels. Wet the paper towels and use them to gently wipe the mildew
off the affected leaves whilst being careful not to jostle any leaves with spores on them. Using a wet cloth
will ensure that more spores stick to the cloth instead of becoming airborne. Note: While it isn’t necessary
to use paper towels, their disposability helps to curb the spread of spores from one leaf to another.
2.Ensure plants have proper airflow and ventilation - Even if you have absolutely no airflow or ventilation
in your grow room, having even two fans will drastically reduce your chances of encountering WPM while also
benefitting your plants overall health. One fan should be oscillating if possible and should gently blow air
over your plants. All the plants need is enough air to gently rustle their leaves. The second fan should be
in your grow room pointing outward, pulling heat away from your plants (only needed if you have no ventilation).
Having a fan pointing out of your grow room will force old air out of the room, and in turn, pull new air into
the room. At this point, you’ll have new air coming in, being used and circulated, then kicked out. Keep in mind
that two fans is a minimum.
3.Treat plant with SM90 to kill spores prevent future growth - Mix 1 part SM90 to 5 parts water(I’ve found 7 parts
water to be equally effective) in a clean sprayer/mister. Wait until just before your lights for off for the day
and mist your (newly cleaned) plants. Get all the leaves! This diluted SM90 mixed will kill any spores it touches,
and anywhere it lands becomes uninhabitable for future spores. Plus, it’s safe to use - even during flowering - and
it smells awesome.
There you have it. If you end up running into White Powdery Mildew, give this advice a shot and you won’t have to
deal with it past that first day. If you do end up using these steps, feel free to let us know if it helped you or
not, or how you did it differently. When growers know just a little bit about this disease, it doesn’t have a chance!
