6 Ways to Cure Powdery Mildew on Cannabis Organically


Any experienced cannabis grower has likely encountered one of the most common fungal diseases for plants – Powdery Mildew (PM).

Powdery mildew is a white, powder-like fungal disease that reproduces on the leaves of many different kinds of plant species. Thriving in high-humidity environments and moderate temperatures, PM can severely stunt your plant’s growth and yields by blocking your leaves ability to absorb sunlight and convert it to energy, a.k.a. photosynthesis.

Some facts about powdery mildew…

  • Powdery mildew reproduces sexually and asexually. It is a fast-growing fungi that is spread by spores. These spores most commonly infect susceptible plants via airborne transmission.
  • PM will quickly move throughout your plant, smothering it in white mildew – many instances in just a few days time. Left untreated, powdery mildew will effectively ruin your weed harvest.
  • This fungi can be spread through the wind, hitch-hike on your clothes or pets, and come through air-ventilation systems. Wooly aphids are also a known common transmitter of this infection.
  • Common plant hosts are cabbages, tomatoes, cucumbers and beans – even trees such as apple, pear and Japanese maple trees can carry PM. Make sure to eliminate ALL of your local powdery mildew, not just selectively your cannabis plants.
  • Powdery mildew will literally suck the life out of your marijuana – once identified you must take action ASAP. As PM takes over, you will see your whole plant yellowing and falling into slow, stunted growth.
  • If you grow indoors, be sure to clean all your grow room with a bleach-water solution, making sure to cover all surfaces and areas the fungi may be able to reside.
  • Getting rid of powdery mildew is not for the faint of heart. It is an arduous battle, often tending to go away for a few days to a few weeks, only to reappear later.

Those who have experienced massive outbreaks of powdery mildew outdoors or indoors will be the first to tell you – PM takes some real wizardry to cure.

There are many known remedies for powdery mildew available at-home and commercially. While bringing back a matured plant can be close to impossible if you want safe smoke, kicking the mildew out of younger plants can be done quite effectively.

Sunlight can be a lifesaver – if you have potted plants outside, ‘follow the sun’ with them. Make sure plants are in full sun for as many hours as possible, and also make sure the sun is not missing any sides of your marijuana, if possible. Hot sunny days combined with multiple foliar sprayings can be the KO punch to powdery mildew you need.

Stay away from sulfur and copper remedies, unless your plants are very young. Although these often work, they are toxic and not fit for smoking purposes. Once upon a time, a budding Blueberry Hash plant was sprayed down with a sulfur spray – it sure did get rid of the powdery mildew. A white sulfur residue was left behind that was impossible to remove, even after rinsing. Harvested, the resulting buds were completely unsmokeable – marijuana smelled and tasted precisely as if lighting a match – Fail.

A somewhat effective solution to PM is baking soda (sodium bicarbonate). Be wary though, case studies have shown baking soda to be only mildly successful. It requires quite a bit of baking soda to really get a good punch at powdery mildew, only seeming to knock out mildew growth for a short period of time. After a few days the powdery mildew usually sets back in – unless the mildew outbreak was minuscule, or the growing environment has been adjusted.

While foliar treating plants, make sure you cover up your topsoil. Although these remedies are ‘organic’, they still can be harmful to your soil’s microbiology. Simply cut pieces of slick cardboard to fit snug against the main stalk weed plants, effectively covering the topsoil and protecting from any dripping foliar spray.

Using a wetting agent, or spreader-sticker helps the spray stay on the foliage longer. There are many suitable kinds on the market, be sure to use one if possible. You can substitute 2 – 4 drops of Dr. Bronners soap per quart of spray soution as a spreader-sticker. Keep it out of your soil and don’t over do it, it’s easy to burn your plants up using this; 2 – 4 drops per quart is plenty.

 Organic Remedies

Potassium Bicarbonate

potassiumPotassium bicarbonate is the preferred alternative to sodium bicarbonate. In a study performed on gooseberries, an initial outbreak of over 90% infection rate throughout plants was reduced to approximately 10% affected plants due frequent foliar spraying of potassium bicarbonate – read the study here.

Well-known cannabis grower/activist Ed Rothenthol prefers to mix an ounce of sodium bicarbonate in a gallon of water together with 1.5 cups of milk.

Milk, has also been proven to help remedy powdery mildew – but beware, do not spray budding plants with milk, as the proteins will create an easy environment for blue/black mold or botrytis to grow. Furthermore, potassium bicarbonate is beneficial in fighting other mildews, rusts, and molds.

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Onyx Spider Mite and Powdery Mildew Killer

onyxxSpecifically designed for cannabis growers, ‘Onyx Killer’ contains a malady of different oils including neem oil, hemp oil, coconut oil and a few others designed to cure plants rid with powdery mildew, mites, or both. It has been proven to work effectively in the outdoor marijuana garden, as experienced personally by growers.

An elephantine South African sativa presented herself gargantuanly gorgeous, except for the unfortunate infection that swept over her quick. Always skeptical, who would think ‘Onyx Killer’ was going be that great, kind-of looking to like a ‘snake oil’ product – is even stated as “Can Use Through Harvest!”.

To much surprise, Onyx Killer effectively wiped out nearly all of the powdery mildew on that jumbo sativa, with the harvested flowers clean while reeking like a skunk.

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Apple Cider Vinegar

The uses and benefits of apple cider vinegar (ACV) are enough to write a book about. Many of us know people who drink, brush their teeth and bathe with the stuff. Relating to powdery mildew, the acetic acid contained in vinegar will help rid your plants of the infection. Spray two to three times a week for maximum effectiveness, making sure to cover the leaves fully.

It should be noted however, that although apple cider vinegar is strong enough to stop most moderate-level PM infections apple cider vinegar is not effective in eliminating a well-developed outbreak of powdery mildew.

Mix 2 teaspoons of organic apple cider vinegar into a quart of water – be careful not to overdo it, high concentrations of vinegar can burn plants.

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Actinovate (Streptomyces lydicus)

activStreptomyces lydicus (SL) is an organic microorganism that establishes itself on plants’ roots, stems and leaves. Once established the microorganism combats many diseases, blights and mildews (including powdery mildew, of course).

Beneficial for a wide range of plant species – from ganja, vegetable gardens, trees and lawns. Streptomyces lydicus is water soluble and can be applied with a foliar spray or root drench, helping with many possible problems in a plants’ life. Actinovate is stated as “SAFE for people, pets and the environment”.

Top growers in the field had tremendous results with microorganisms, being fond of Dipel bacillus thuringiensis (BT) for pests and Actinovate (SL) for plant diseases and mildews. Not widely known in throughout the general population – get your hands on this secret wonder-product!

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Neem Oil

neemoilNeem oil, produced from the seeds of the Indian neem tree, is a well known wonder product for plants. Naturally fungicidal, weekly application of neem oil will take care of most powdery mildew problems.

Professionals have had better results controlling powdery mildew with neem oil compared to baking soda (sodium bicarbonate) in controlled side-by-side studies. While normal doses won’t completely eradicate powdery mildew from mature infected plants, regular spraying will clean off the mildew, keeping it at bay. If neem oil is sprayed before plants have powdery mildew, you may rest assured they will not be easily infected with PM.

Being an organic insecticide and miticide as well, most gardeners should already have neem oil on hand. Some people complain about the smell, while others find it enjoyable, akin to a pine sol freshness.

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Green Cure

greencureOne of the most popular products of today’s generation, Green Cure is an effective potassium bicarbonate based product. Reputed to have performed as well or better than chemical fungicides in over 200 university studies.

Green Cure dehydrates mold and mildew spores instantly, critically damaging the life-force of the infection. For best results apply during a hot sunny day, and let your plants soak up the sun as the powdery mildew disappears.

Green Cure posseses the power to rejuvenate plants immersed in heavy powdery mildew infection. Proven to cure a large range of mildews and diseases, Green Cure is a safe and effective solution to your powdery mildew problems.

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Most remedies require more than one application to really be effective. Remember any moisture will likely wash the foliar spray off, even morning dew on plants can remove the coating off the leaves. Best time to spray is before noon on a dry, sunny day.

When trying to gain control over powdery mildew on cannabis, try to get your plants in a open, breathable spot. Fungi love closed humidity.

Good luck with the PM battle!

If you have any questions, experience, or comments about powdery mildew on cannabis please comment below.

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Disclaimer: We do not promote or undertake in illegal activities.


  1. // Reply

    I use Need tincture this year mixed with soap and all gone so quickly. I am an herbalist.

  2. // Reply

    Actinovate is monsanto.

    There is a product called “Forge” that’s even better and NOT Monsatan!

    1. // Reply

      Hey Jason,

      Yes, unfortunately Actinovate was bought out by monsanto, as much as I despise that it is still the same killer organic microorganism. Actinovate is just as organic and non-GMO as it has always been.

      Would you provide a link to this “Forge” product?

  3. // Reply

    I have an old secret recipe,
    5 gal bucket of water,
    2 cups earthworm casts,
    1 cup Grandmas UNsulphered molasses,

    Mix(i aireate with aquarium pump),
    For 24 hours, put in backpack sprayer,
    Soak down leaves , a cloudy day works best
    And thats it!!! 2-3 days not a spot of mold.
    Now thats organic!!! Its worked on the foggy Oregon Coast for decades where many a crop gets ruined, it qorks on 3 footers. And my 20′ “trees”…
    Your welcome, No charge

  4. // Reply

    Howzit! My plant is 6 weeks into flower. I’ve been noticing stem rot where a branch comes out of the main stalk. It’s happening in more than one spot.The branch would turn yellow and die off. It’s only on one plant. Have any experience with this? Genetic or some kind of bug? Mahalo for any manao.

    1. // Reply

      Hey brah,

      Sounds like you got stem borer problems. Common in Hawaii. Best bet is to inject Dipel [BT] (Bacillus thuringiensis) into the wound as soon as the ‘bruise’ is spotted. Keep a close eye on the main stalk and spray immature plants with BT as a preventative method.

  5. // Reply

    Thanks Bra! I think you are right! I see a little spot on or near where the rot is. Someone else from Hawaii on another site said it was a fungus problem. I’m growing the Kryptonite from Amsterdam seed co. Nice dense nugs. It’s suppose to be high in Thc and Cbd. 2-3 more weeks to go. I have 2 phenos of this strain and one is getting the stem borer. Thanks for your manao

    1. // Reply

      Hi Nugs808. Yes that stem borer is a prolific problem for tropical cannabis growing. So is that gruesome powdery mildew. I have seen more and more powdery mildew around the Islands decimate people’s crops, either by completely smothering the buds in white powder mold, or by the cultivator using harsh treatment in an effort to cure the mildew. How’s that Kryponite strain from Amsterdam seed co.?

  6. // Reply

    We use greencure and onyx to help our herb garden with powder mold, but only in the early stages before buds come.

    1. // Reply

      Agreed for sure Dino. Curing powdery mildew on cannabis should not be done while the buds are well developed. Best way to deal with powdery mildew is to take precautions from the very beginning. Spraying regularly with real deal organic neem oil works great for deterring pests, and keeping the wicked powdery mildew at bay. If things start developing, step it up. Neem oil will not eliminate well established white mildew on a cannabis plant. Try Onyx Spider Mite and Powdery Mildew Killer, Green Cure, and/or Actinovate (Streptomyces lydicus). Make sure to do this before the flowers have developed and with a little bit of luck you can be blessed with a clean, mold and mildew free harvest of the dank.

  7. // Reply

    Check out Mites & Mildew, not sure effectiveness against mites but 3-4 treatments about same amount of days apart will rid moderate outbreak of pm. Saved some very prized mothers and new cuts. Check it out. Otherwise look at oil fungicides is my opinion or combo both. I always continue process twice as long just to be sure. Cookie strains seemed to be most affected. Cured.

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