Powdery mildew/mold 6 weeks into flower

Greetings All,
I have what I think is WPM…
I’m 46 days into flower and I don’t want to harm my girls so close to the end…
I’ve heard to use Perixode or baking soda…
Does anyone have experience with WPM this late in flower??

My attempt at pics using a flash…

The area I was concerned with is in the middle of the pic…
I see a row from top left to bottom right that looks like powder on the leaves.

Any help or suggestions greatly appreciated.

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@DirtBug what kind of air movement do you have on your grow space? Do you know your rh #’s? Definitely want to reduce them to save your harvest!!

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I’m using two 4" extractor fans (with filter) rated at 205 CFM each and have 5 other assorted fans including 2 oscillating fans. (grow space is 4x3.5)
My RH is 40-50% lights on and rises a bit to 65ish% with lights off.
My air movement has been adequate so far, but this grow I lost track of time and veg’d the girls about 3 weeks too long.
As a result my girls were over-crowded a bit. I’m pretty sure the overcrowding along with 65% RH was the problem that caused the WPM.
Thank You

First I’d recommend thinning out the plant canopy drastically. You will pay a small hit in yield but you’re risking losing everything now.

Next; mix a solution of 1/4 cup of 3% peroxide into 1 gallon of distilled water. Spray this generously over the entire plant and really soak down the flower. Make sure you have a lot of airflow and do this early enough in the ‘day’ for the plant to dry off. This will nuke your WPM but will make leaves look papery along the edges: plant ain’t gonna look happy no matter what you do. Baking soda leaves a residue and will clog the leaf stomata, ultimately suffocating it. Milk leaves a protein scale that looks like peeling sunburn.

You will likely have to dose plant weekly until it’s under control. A dehumidifier running at night would solve that: WPM can’t form below about 45% RH.

Plan on doing a bud wash in peroxide too: something most of us do as a matter of course.

After harvest it would be wise to spray down the grow space with straight peroxide (3%).


Was just about to suggest everything that @Myfriendis410 just recommended.

Good luck!

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Thank You @Myfriendis410 and @Newt for the assistance…
I already thinned the canopy :frowning_face: and I will be doing the peroxide spray this evening.
I will post my results…

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Do not spray when lights is on. Good way to cook your plant even more. The magnifying effect will take place aka the water droplets will burn the leaves with lights on.

I beg to differ. This has been disproved many times. The only way for this to happen is if the droplets can somehow be suspended above the leaves causing the light passing through to focus on the leaf, but the physics of gravity prevent it. Otherwise a rain and then some sun would fry the outdoor plants, and that doesn’t happen.


@Newt Even they said it could. Smooth surface very unlikely. But with hairs, it can. So you proved what I said is actually correct. As marijuana leaves has trichomes, this can play a key role of the plant getting sunburned.

If you don’t believe me, get in a pool for 8+ hours in sunlight. The water magnifies the sunlight and thus you will get fried. Learned this the hard way in Las Vegas. We was under the age limit to go into any Casino so me and my sister was in a pool 12 hours. We was fried. Blisters a 1’ plus.

Its never guaranteed it will happen. Just that it can happen. :+1:

So you do you and I will do me.

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Sorry. I didn’t intend to be confrontational. :hugs:

And certainly it takes me much less time to sunburn than 8 hours. I’ll get blistered in about the same time in or out of the pool, however. But I am very fair skinned, so it doesn’t take much for me. But I do spray CJDB in full light, mist my small clones and seedlings, and have foliar fed under the lights with no leaf burning. But sure I guess it could happen.

It just always struck me as odd, how pervasive this belief is, and I’ve never seen it outdoors under full sun, which is what prompted me to research it.

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You are fine. No offense taken. You have to take into consideration outside light isn’t 18 hours long. Which in a grow room this is a must if you want to Veg.

Theoretically if the leaves are completely horizontal, the water will be trapped on the leaf and will not drain off. This is when the problem may happen. No guarantee it will. I have seen leaves get burned. South Texas heat is brutal.

One can verify pretty easy. Put water drops with no nutrients on a horizontal leaf that won’t drain. I run only 12/12 so not long enough light but 18/6 would be a different story.

I think under the circumstances with the OP’s high RH at night that he’d be better off to spray during light on hours. His plant is going to suffer anyway and leaves are not going to be happy. Normally I’d agree with spraying just before night hours.

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