Powdery Mildew on Cannabis: 11 Sure Fire Ways to Kill It

You walk into to your garden one day and notice some white spots and clumps on sections of your fan leaves on a couple marijuana plants.

On further inspection of a leaf, powder rubs off between your fingers.

If your wondering what it is? 

That's powdery mildew on cannabis.

You might have noticed this elsewhere on plants in your home or nature. 

If not found quickly and stopped in its tracks can ruin your whole garden if not careful.

Let alone be an issue with your health.

Some growers have found out the hard way, I have heard some bad stories especially when the left untreated.

Not to fear we will look at what powdery mildew is and how to prevent and stop it from infecting your cannabis plants.

What is Powdery Mildew?



A look into what Powdery Mildew is can be defined simply as a fungus disease of your marijuana plant.

The fungus will appear on the leaves and the stems of plants

More often the lower sections of the plant. 

But can appear on the upper part as well.

Plant mildew can start to infect the inside of the plant as well and can become systemic.

It not only infects cannabis plants but also affects all other species of plants from flowers to trees to fruit.

Powdery mildew reproduces on its own and will do forever.

Or until it is stopped, the fungus can be transmitted via wooly aphids in some cases.

If left untreated the plants will slowly break down with leaves turning yellow and curling up to slow deterioration, and eventually the leaves fall off.

With possible ingestion through edibles and or inhalation from smoking powdery mildew in your herb.

Its definitely harmful to your health.

Which is dangerous, especially if you are using marijuana as your medicine!

Cause of Powdery Mildew on Cannabis

Before we can look into preventing powdery mildew, we must look at the cause of the problem.

The fungus is made up of spores which can travel in the air, animals or pets, clothing, human transfer or wet leaves. According to Penn State University.

  • Clones can have mildew hidden, when growers spray the cuttings before selling, you will not notice until two weeks later when the spray wears off!
  • High Humidity can play a huge factor in developing mildew anything over 60 percent humidity can significantly increase your chances of getting mildew.
  • Crowded Plants when plants are confined in tight spaces (sea of green) the cannot breathe and increases the humidity level in grow room.
  • Air Flow lack of fans in the grow room or grow tent. With no air you get a higher chance of humidity.
  • Rain and Dew when growing outdoors can linger on your cannabis plants leaves or buds when flowering.
  • Watering plants at night can also a problem by not letting the water evaporate enough causing high humidity especially when using a grow tent a growing in soil.
  • Not properly pruning your plants and allowing the buildup of excessive foliage in the undergrowth area of the plant.
  • Fans can be an issue if there is mildew detected as it is a spore and can be blown around by the oscillating fans in the grow room. Best to turn these off until the outbreak is under control if you can.

Prevent mildew 

By knowing the cause of the problem, it becomes a lot easier on preventing mildew from occurring in the first place.

It all comes down to the environment, humidity and giving your marijuana plants some space and keeping moisture levels at a minimum.

It is always good to invest in a small pocket microscope to check on your plants from time to time.  

To make sure you do not see any white spots on the leaves or any other issue involving your cannabis plants.

What to look for when trying to find powdery mildew

  • White Spots
  • Appears in clumps of white
  • Has a flour consistency
  • Looks like white flour on the leaves
  • Can be yellow or gray from aphids

How to Kill Powdery Mildew on Marijuana

There a few different types of treatment you can use to get rid of mildew on marijuana for good before it's too late.

Some range from natural remedies used on house plants.

Others are from organic fungicides or foliar sprays.

One of the first steps to consider is just removing the leaves that are infected before moving on to other solutions.

Natural remedies are one to consider first over the commercial variety if you're into saving a little bit of money and the outbreak is not that severe.

Natural Remedies

These solutions can be found around the house and are safe for leaves and buds.

Baking soda:  one teaspoon per gallon of water

Spray solution on your leaves and buds. Check the next day, then spray twice on second day,wait one day if still around repeat

Apple Cider Vinegar 2-3 teaspoons per gallon of water

Spray solution on your infected leaves. Check the next day, then spray twice on second day,wait one day if still around repeat

Milk  mix 1 part milk to 3 - 5 parts water

Spray solution on your leaves and buds. Check the next day, then spray twice on second day,wait one day if still around repeat

I have not tried the milk natural remedy but I have heard from other growers this method works well in the first stages.

One grower has reported he tried a milk solution and was successful.

Mix 400 ml milk to 600 ml water.

Leave the solution in container in the Sun for about an hour. Then spray your plants

Check out the comments for the science behind it.

Hydrogen Peroxide for mildew:  Use 1 tablespoon per gallon

Spray solution on your leaves and buds. Check the next day, then spray twice on second day,wait one day if still around repeat.

Some of the natural remedies I use in the garden are baking soda or hydrogen peroxide solutions.

Once the outbreak is beyond manageable with natural remedies, then it means you must immediately move on to tested organic, safe foliar sprays to save your garden.

Potassium bicarbonate which is like baking soda but is much stronger and will kill the spores of the mildew very quickly.

Natural Organic Products

Neem Oil  a natural and organic oil that comes from a neem tree in India.

It's great for removing mildew. It also has additional benefits of being an insecticide and is great killing insects in the garden.

Four teaspoons per gallon of water.

Sm-90 for powdery mildew is  a natural product produced from plant oils is a great foliar spray to use to combat mildew and mold and can also enhance root growth.

Making this a great solution and can be used in multiple applications once the mildew is eliminated!

Green Cure Fungicide is for organic production and is made up of a Potassium bicarbonate that stops and prevents powdery mildew.

It's also beneficial for all other fungus infection on your plants.

Green Cure has been tested in over 200 universities and is registered with the EPA

Safergro Mildew Cure is natural fungicide that is safe for organic food production and long lasting to control and prevent powdery mildew. 

Banish the name says it all.  This will literally banish any powdery mildew on your plants.

What's really cool about his stuff is it works at the root of the fungicide.

Banish also creates a layer over the infected leaf to prevent mildew spots to germinate on contact with other leaves or plants.

This fungicide goes through a micronization process meaning it's oils are shrunk down to 1 micron.

So Banish can really get at the mildew in it's smallest form. You can use this funcide for treatment or even prevention. 

Safe for all fruits and vegetables also cannabis, made of all natural materiel it will also bio degrade from your plants and leaves over time as well.

Check out the short video on it,

UV Light

UV Clean Light is a new technology to treat plants with UV light as a preventative measure and also in treatment for powdery mildew and botrtis from plants.

You can also clean your grow room walls with this light.  

The downside is they are really expensive , especially for the home grower.

UV clean light can definitely be used in a commercial or licensed produced grow operation.

Final Thoughts

A good rule of thumb is to stop the mildew before it happens.

The main thing is to make sure your garden has a favorable environment. That is the key to preventing powdery mildew on cannabis.

Have you had mildew on your marijuana plants?

Did you try these solutions and did they help let me know in the comments

Grow on my Friends

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34 thoughts on “Powdery Mildew on Cannabis: 11 Sure Fire Ways to Kill It

  1. Hi Rachel,
    Thank you for reading the post.
    To answer your question , Yes you can use the special UV light to treat the mildew , but they are rather expensive for the home grower. I have put some info in post on UV light . check it out.

    • Hi E,
      Unfortunately you can still get mildew when using LED grow lights even if they have UV. The amount UV light they produce would not be enough to prevent it.

  2. I bought some clones from a reputable source and four days later powdery mildew showed up. I’m trying the SM-90 since I already had it. I caught it early on at least so I hope it does the trick. I wish I had seen this article first, however, as I should have removed the infected leaves before spraying it around… live and learn!

  3. Hi Holly ,
    It’s tricky when you get new clones sometimes because the PM is usually been quick treated and hidden only to appear days later again. I hope your clones make it.

  4. hi ive been using organic apple cider vinegar in a one gallon spray bottle on my inside grow, although it seems to be helping with the spread of the mildew it seems like its a battle with the same areas lower on the plants. ive decided to try some green cure do i apply this stuff with the lights on?

    • Hi Simmie
      Green Cure is best to use when lights are off, and let dry . So right before lights out you can apply it.

      Hope you get rid of the powdery mildew

  5. Hi like to know can you get powdery mildew out of the tissue of the plant. So you don’t have to worry about it coming out of the plant and have to keep treating the plant is there a way

    • Hi Daniel,

      I am not aware of a way to remove powdery mildew from the tissue itself, maybe with the further advancement of cannabis research it will be around the corner. Unless someone else knows anything let us know in the comments.

      • Yes, you can remove all pest and mildew, including diseases, using maristem propagation aka tissue culture done in a lab

  6. Hi all, just to add on the milk solution, I have had complete success in curing advanced powdery mildew with milk… the way to use it is as follows dilute 400ml milk to 600ml water allow solution to stand in an open container in the sun for about an hour than spray entire plant, the science behind this is that milk when exposed to direct sun and air builds up natural antifungal and antibacterial enzymes that kill the powdery mildew on contact.

    • Thanks for the info Daniel that’s really good to know. I will try the milk solution it if I ever get powdery mildew again.

    • Does the milk solution need to heat up in the sun or is the light the only thing that matters? I’m wondering because it’s like 40 degrees outside and the solution will be cold even though it’s in the sun. Thanks!

  7. I have been using a peroxide and water mix for a few years with good results on powdery mildew and gray mold as long as it is a mild case. For gray mold ( bud rot) removal of infected buds and a liberal covering of the surrounding area did not stop the rot but slowed the spread enough to make it to harvest with minimal yield loss. As for the powdery mildew it seems to stop it in its tracks.

  8. So I have had good success at eradicating powdery mildew that was determined early in the situation. Not a bad case just the insipiant stages of the disease by spraying with a solution of water and apple cider vinegar. Approximately 2 teaspoons of the vinegar to every litre of water. This will work on other plants thayvhlget the mildew as well. You need to treat well once and then repeat twice afterwards on the following days in order to actually kill the hook of the miceliam subcutaneous in the lead tissues. Regular suffocants will not kill the hook of the spores.

    • Thanks for sharing Paul , I always have bottle of apple cider kicking around. Will try it out next time , ( hoping there is not a next time! )

  9. Excellent article, thanks!
    My plants look great but I just noticed PM on some of them. They are growing outdoors and are in early bloom phase. It has been very hot here, so I have been watering everyday using drip irrigation.
    Considering all these factors, which remedy would be best? Should I cut back on the watering?
    Also thinking about prevention, as my garden is large and there is no way I can spray everything else…fortunately I haven’t seen it on other plants and trees…yet.
    Any suggestions?

    • Hi Norma,

      I would isolate the plants with PM and treat with banish. Or remove them completely. If you have a lot of humidity try spreading them apart if they are close together.
      Also are you getting run off on your plants? If so and watering every day is fine , if no run off wait about half a day more or a day longer to water.
      It’s tricky growing outdoors sometimes, Especially when it’s really hot, and you cannot control the environment.

  10. I run an outdoor farm in Humboldt, CA and we have been battling PM every year for the past 5 years. It never gets too bad but it definitely is a problem and is nearly impossible to eradicate once it sets in. We start our plants from seed and we feed compost tea weekly while using drip irrigation for watering every day around 4am. I am doing everything in my power this year to stop the PM from setting in. My preventative measures are; Spraying neem every 7-10 days starting in July and plan on stopping at week 6 of flower (end of September) to avoid harvesting neem covered buds, removing bottom branches and leaves that seem to be much more susceptible to PM also to support good air flow, and once a month I use wettable sulphur to spray the straw that we use to mulch our beds and cover our drip lines. I usually see the first signs of PM sometime in September depending on the weather that year. Do you have any suggestions of methods that could be used on top of what I have implemented already? I feel like PM is all about stopping it before it becomes an issue but its tricky.

    • Your right it is all about stopping it before it becomes a major issue , especially when you are growing outdoors. You seem to do everything on point. I am not familiar with growing outdoors and dealing with the different types of weather. I have big respect for you. The only thing I here good things about is the green cure and banish. Maybe cut the neem earlier on in flower.

    • If you had it in veg stage and kept it at bay and is not on your buds then yes. If your buds are infected then I would not consume it in any way.

  11. 1st time dealing with PM…Hoping its not completely advanced yet…Going to try the apple cider water mixture…would it hurt to also add baking soda?

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