How do I treat Powdery Mildew and leaf Hoppers

Hello everyone, it’s good to be here, I’m new to this forum and having a few problems. I am in southern Ontario and have my 4 big girls in the ground, they are flowering very well. Yesterday I noticed powdery mildew (PM) on some of the leaves, not very bad yet but very concerning. I have been pegging out stalks and thinning the leaves for airflow and light penetration but still with the rain we’ve been having I guess it’s inevitable. We have pulled additional leaves so that there is not any crossing over to touch others when dry, the colas are a different story not much to be done there. I have been reading about treatments, in that they are flowering most are not usable on the buds. Resin is not water soluble so I would say that my generic highly refined mineral oil is a no go and this has been confirmed a number of times elsewhere. Insecticidal soap was also suggested as forming a barrier between plant and mildew, this I would think would not mix with the resin and residue would rinse off. My two top contenders now are skim milk + water and H2o2 hydrogen peroxide + water, could anyone confirm that these (or one or the other) are safe to REPEATEDLY spray on buds that WILL be smoked. The leaf hoppers are not a major problem yet and with today’s rain they are absent, my interest in the soap though is in case they become a problem.

Thanks in advance


Hey @Mal25, welcome to the forum.
The grow guides provide some great info. Others will chime in too.
Check out this article in the mean time.
Several blogs on pests…

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The best trick for WPM is 3% peroxide. Use diluted down 4 to 1 at first. It should literally melt the WPM. Can you cover the plant when it rains? Get it out of the rain? Can you run a fan out to the plants? Can you bring them in at night? All things that are helpful.

Hoppers are gonna munch until they are killed. I use Captain Jack’s Deadbug Brew which contains Spinosad, a bacteria lethal to bugs but safe around pets and people.

Both of these products can be used right up to the day of harvest. Organic too.


Thanks for the links Norman, very interesting as far as toxicity though I’m leaning strongly toward milk and sun, would be nice to have a back-up though.

Hello myfriend,
Great to hear thanks, I don’t want to harvest early or throw any buds!

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Covering would be tricky, moving no, a fan maybe the best thing, or just repeat treatments. I read that water actually kills the spores? I don’t know if that’s true, meaning I guess that it’s humidity from trapped moisture that starts them growing and rain helps? In any case I have read that treatment must be repeated until conditions change. Spraying wet plants repeatedly is going to keep them very wet maybe creating another type mold problem

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Do some research on peroxide. Its very effective and the reactive molecule H2O2 degrades very fast. And it degrades into Water and Oxygen. Light accelerates this decomposition. Usually within 24 hrs its gone. So while high concentrations are dangerous, a simple 3% solution is safe and you can even dilute it further to treat mildew. I spray plants with full strength 3% to kill mites. Never harmed the plants at all.
And we all have some in our bodies as it occurs naturally in the earth.


Thanks for the additional info, I also do Bonsai, this is very useful!

Does the Peroxide spray damage the flowers?

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Peroxide can be used up to the day of harvest. It won’t hurt flower but may dry out some leaves if strong solution concentration.

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What mixture do you use?

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I think it depends on how bad the wpm. I’ve used straight 3% but some plants are sensitive to it and the leaves can get burned. I think I would start at a 25% solution of 3% (1/4 cup in a cup of distilled water). Distilled is important as there is nothing in it for the peroxide to react with. Foliar spray right at lights out and institute measures to lower RH because it’s telling you the humidity is too high.

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