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Powdery Mildew On Marijuana Plants

Powdery Mildew On Marijuana Plants

Powdery mildew, also known as white powdery mildew, comes from lots of different fungi. Powdery mildew looks like white or gray powdery growths on your marijuana plants’ leaves.

It appears on grow areas indoors and outdoors and is foreshadowed by small bumps on the topsides of leaves. Typical species of fungi that go after hops will also go after your marijuana plants.

What is powdery mildew

Powdery mildew spores can be transported to your plants on the wind, through air ventilation systems, from pets, and any other living thing that moves (including yourself). Until the surrounding environment is ideal, the spores from mildew will stay dormant, biding their time.

What is powdery mildew cannabis

Powdery mildew on cannabis leaf

This is why powdery mildew can be so tricky - you never know when it is lurking and waiting for the perfect time to strike. Powdery mildew is one of those conditions that is better to prevent from the get-go.

The main problem arises with powdery mildew when it is able to grow until it severely slows down photosynthesis and, therefore, ruins your harvest. It, therefore, needs to be taken care of as soon as you are able to identify it. Powdery mildew is not as uncommon as some other conditions, so it is something that you need to keep an eye out for.

Signs of powdery mildew

You will know you have powdery mildew when you notice fuzzy, flour-like circular patches on your marijuana plants’ leaves. You might see leaves that look spotted, mottled, and wilting. The powdery mildew infection will quickly spread to surrounding leaves and will “eat” everything in its path.

Powdery mildew is quite recognizable, given its stark white in contrast with the green leaves, and it can be removed if you use proper treatment in a timely manner. The problem with powdery mildew is the spores - often you can’t even see them as they are spreading throughout the air, making them extremely difficult to avoid and combat.

Signs of powdery mildew weed

Signs of powdery mildew

Powdery mildew is the most likely to occur when humidity levels are high (above 55%) when there is not much air ventilation happening in your grow area. It also occurs when there is overcrowding of your marijuana plants at the grow site or in the grow room. Leaves touching other leaves are more likely to spread powdery mildew to each other, making it even harder to eradicate when your setup looks like that.

Powdery mildew generally goes for the youngest plants first, spreading across the entire plant and ruining the stems, buds, and leaves of your plant. You will notice a damp sort of smell coming from your buds - this is how you will know which buds have been affected by the powdery mildew.

Once the fungus has invaded a bud, it cannot be taken away. If the powdery fungus continues its course of action, it will eventually make your marijuana plant turn yellow, which will become brown, and then the plant will simply die.

Tip: make sure to download my free Grow Bible for more information about how to get rid of powdery mildew

It is crucial that you never let your plants reach this point. Make sure you are constantly inspecting your plants and always keeping a close eye out for any unexpected changes in your plants.

Not sure if your marijuana plants suffer from a powdery mildew infection? Check the article Marijuana diseases for a list with pictures of all possible marijuana diseases

How to get rid of powdery mildew

If it’s possible, you should take certain steps to avoid an invasion of powdery mildew anyway. When you initially plant or transplant your plants into their mature location, make sure they have plenty of extra room. If they are planted closely together, the likelihood of powdery mildew popping up is significantly higher.

When you water your marijuana plants, you should make sure that you are doing it at a time of day when they will receive five hours or more of light after that. This can be artificial or natural light, depending on your growing situation.

You can also try using a UVC light if you are an indoor marijuana grower, which will keep any missed powdery mildew spores from going for your valuable plants. Some growers who have a few years’ experience under their belts might prune some of the fan leaves that don’t receive any direct light due to shading.

uv lights growing cannabis

UV lights

This makes it so there are less ideal spots for powdery mildew to land and begin growing. It also has the added benefit of your plant conserving its energy and using it more efficiently for other leaves and growths.

If you do end up having a powdery mildew problem, one way to solve the problem is at home. One home remedy is 2 teaspoons of organic apple cider vinegar mixed with one quart of water. Mist this mixture onto your plants to both kill the powdery mildew growth and prevent any more from cropping up.

It can also be used preventatively before any powdery mildew arises at all. Another option is to do the same thing with one-half teaspoon of baking soda mixed with a quart of water.

Ingredients to create your own Powdery Mildew spray

Ingredients to create your own Powdery Mildew spray

Other options for destroying or preventing the powdery mildew include oil sprays such as neem oil, sesame oil, or fish oil. These sprays can also work well for other fungal diseases. A final option at your disposal is a milk spray made from 40% milk and 60% water.

This works so well because the milk has protein in it which reacts to the sun and naturally forms an antiseptic. This antiseptic is what kills the mildew. You can use a milk spray preventatively by spraying it on your plants every ten days, but only when the sun (or artificial light) is shining brightly. This is a common method for all gardeners to use on their plants.

Milk & Water spray to threat Powdery Mildew

Milk & Water spray to threat Powdery Mildew

In order to take care of a plant that has been infected with powdery mildew, you should utilize a plastic bag to remove the leaves that have been affected. Seal the bag and then put it into a disposal container that has a tight lid.

The reason for using the plastic bag is to prevent the spores from being sprung into the air and infecting other plants nearby. After removal of the infected areas, treat your plant with fungicide on the stems that held the removed leaves.

Other Methods
There are a few alternative methods that you can use to heal your plants, including oil sprays such as cinnamon oil, garlic oil, coriander oil, clove oil, jojoba oil, or cottonseed oil sprays. A commercial product like Mold Control will always to the job. If you want to make sure to get rid of powdery mildew, buy something like Marijuana Mold Control.

mold control cannabis

Easiest way: use Mold control

There are also copper-based applications that you can purchase at any garden center. You can also try one tablespoon of hydrogen peroxide mixed in with water, which destroys the fungus by oxidizing its cell walls. Yet another solution is one teaspoon of limonene that is combined with one quart of water, offering fungicidal properties without actually killing the fungus altogether.

Finally, there are sulfur burners to control and contain the fungus. When using sulfur burners, make sure that you keep away from it when the treatment is taking place - in people, sulfur burners can cause respiratory inflammation. After the treatment, be sure to wipe off every window and wall completely so that you know any residue from the sulfur burner has been removed.

Marijuana plant symptoms

Leaf Color:
- Pale colors
- White patches on leaves

Leaf Symptoms:
- Upper leaves and newer growths are affected
- Lower leaves and older growths are affected
- Visible white powdery patches on the leaves
- Spots
- Mottled, mosaic on leaves
- Wilting and drooping of leaves

Plant Symptoms:
- Mold

If you are looking for an extremely simple way to get rid of the powdery mildew, you should give the tap water - paper towel method a try. Simply get the paper towels wet and gently wipe your infected leaves with them, therefore removing the mildew that is already there. When doing this, make sure you don’t bump your leaves too much, as that could cause spores to enter the air and spread.

remove Powdery mildew paper towel

Remove Powdery Mildew with paper towel

You can also incorporate at least two fans into your grow room to improve the conditions and lessen the chances of powdery mildew development. You should have one fan directing air through the leaves of your plants and the other fan facing out from your grow room. This is so the “used” warm air is dispelled from the room and replaced with fresh air.

Remember that plants with strong genetics have less change of getting sick and are less vulnerable for pests and diseases. So make sure to buy cannabis seeds from a trusted seed bank.

Thanks for reading. Please leave comments or questions below and don’t forget to download my free grow bible



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Comment Section

61 thoughts on “Powdery Mildew On Marijuana Plants

By Mike Giannini on 25 January 2013

Can I smoke buds that had white mold on leafs? Thak You

By jamison crevier on 19 September 2013

iam trying applecider vinegar on my babys. white powdery mold starting on leaves. I really hope this works.

By Deborah preciado on 14 September 2017

I just seen three leaves affected after humid rain and sprayed with apple cider

By Nanna on 15 September 2017

Gonna try the apple cider vinegar mix, should this be done when lights are on or will it burn them?
helping a friend, so don't want to piss him off by burning his baby's.

By latewood_ILGM on 20 September 2017


You are talking about spraying an acidic solution on the plants; I think during lights out would be best. You also need to fix the issue that allowed mold/mildew to develop in the 1st place. OK?

Good Luck, lw

By Nanna on 26 September 2017

Ty, xxx's very much !
did that it's gone !
Thank's again !

By juwn on 13 October 2017

hey did it actually work? because i am out of option 🙁

By George on 12 January 2014

I just want to say...Thank you for this Info, and your help 🙂

By Jett Thompson on 24 November 2014

Can I smoke buds that had power mildew. I've taken off fan leaves and sprayed plant with clear water,I'm flushing the plant to harvest them. Thanks Jett

By Larrie on 6 May 2017

You could get very sick from smoking mold in your buds. It doesn't go away with drying, it is compressed tight inside your buds. People with respitory issues or even a healthy person can be affected. When you smoke moldy buds, you're ingesting it, not good my friends.

By freeman on 6 February 2015

What is the scientific name for the Powdery Mildew I have someone that had an attack from the mold needs to know. Thank you ƒg

By josi on 21 April 2015

powdery mildew can be controlled by Cleanlight!!!!

By N on 2 May 2015

powdery mildew specifically does not contain or release harmful mycotoxins found in most mold/fungi species. In short, although disgusting to the palate and may cause a vomit reaction If smoked, powdery mildew unlike other molds, is safe. Don't take my word for it tho, at very least google what I said and confirm it. Prevention is the best cure. never vend pm covered meds., ever.

By Jennifer ILGM on 4 May 2015

Thanks for sharing!!

By Kyle Sacker on 24 June 2015

to always give myself the best chances of not getting powdery mildew I clean my whole grow room with this stuff called Grow Clean. had PM once before this stuff!! introduced grow clean and bam! never saw it again

By Bill Graves on 24 July 2015

One thing that worked for me in a greenhouse with squash plants is one tablespoon of baking soda in a gallon of water. For more extensive treatment try using potassium bicarbonate as potassium is a plant nutrient and does not have sodium in it. Sodium bicarbonate works because most fungi do not like an alkaline environment and the bicarbonate is just alkaline enough to inhibit the fungus.
Wish you luck.
Bill Graves
Agricultural and Horticultural Consultant
Homestead, Fl

By Jennifer ILGM on 27 July 2015

Thanks for the tip Bill.

By latewood on 24 September 2015

I too use this method of Baking Soda to combat Powdery Mildew, mold. Baking Soda is highly alkaline. Mildew cannot thrive in such an alkaline environment.

A friend of mine in the Carolina's likes to spray diluted milk to combat mildew; I tis gentler than Baking Soda; IN his opinion.


Pingback: Diseases on Marijuana Plants, and How to Treat Them

By kim on 22 September 2015

How often can i spray my plants with the Vinegar water/

By latewood on 24 September 2015

Can I ask why?

I would be wary of spraying vinegar water on my plants because, that is acidic, and could harm the plant if not done with the utmost of care.

Please join our ILGM Support Forum for more opinions and expert advice. 🙂

By Housewife Grower on 20 April 2016

ACV and Milk combo. 2tbls ACV and 1/4 cup of milk to one gallon tap water in Co. Basement grow. Sprayed with 5 hours of light as recommended for use with milk. I had bad PM covering 70% of 4week budings. I was afraid to treat so I let it go until I had no option. 3days after treatment all PM gone and buds unaffected, maybe even healthier than my last grow. Now I use it as a preventative measure on my veg and before cloning. Don't tell my husband though he thinks he knows it All, jking, lol.

By Jennifer ILGM on 20 April 2016

Thanks for sharing Housewife Grower

By hmgrower on 16 August 2016

What is ACV?

By deadleg on 18 May 2018

Apple Cider Vinegar

By thor on 30 September 2018

apple cider vinager

By Jimmy pot seed on 28 August 2016

Awsome info,hope it will do the same on out door grow

By weedsky on 27 December 2016

It had no affect on the taste either I am in week 6 flower totally devastated it's my 1st grow hoping I can wipe and clean

By VF on 11 September 2017

how often do you treat with this method?

By Stacy ILGM on 11 September 2017

Hi VF,

We discuss several methods in this article, to which method exactly are you referring?

By Sue on 20 July 2018

Hi Housewife Grower. Did this work? When you say 5 hours. Is that after the lights have been on for 5 hours or when they have 5 hours to go before they turn off? Thanks in advance!

By Cecilia on 24 September 2015

I used some garlic water early on and hit the PM right away at first tiny sign on my outdoor. Now...they are budding beautifully, and I noticed one tiny spot today. Is it ok to use the ACV or Garlic water while it's budding w/o affecting the buds?

Thank you!

By latewood on 24 September 2015

This is one of those judgement calls. You are the best one to make this decision. You are there, and used this solution already. As with anything added, especially home type remedies; One must exercise good judgement and caution.

Feel free to join our support forum. We have many growers from around the world will to help you grow successfully.

By Newbie grower.. on 9 October 2015

Great site! I don't really smoke the stuff but have enjoyed growing it a few times. I live in a small coastal town so fog has always been my enemy, and the dreaded nasty caterpillars!! UGG Since we no longer have an ozone layer to protect us, our summers have been much warmer. 3 girls did Fantastic! I picked bugs, never sprayed even though there are (Safe Caterpillar Killers I have read about. One plant finished beautifully but my last 2 Fab girls broke out with mildew even with ideal hot outdoor conditions. First I used a wet paper towel and wiped off what I could and pinched off where it was easy with latex gloves being careful not to spread spores. Then I used this sites recommended 2 tsp of Apple Cider Vinegar in a quart spray bottle. I sprayed only affected areas 2 hours before the sun went down last night. This morning 2 hours before the sun started blaring I sprayed the leaves and buds (only 1-2 weeks to finish line) and presto, magic, it is all gone! Timing was good. I don't think you should spray right before dark as bud rot may occur but this simple organic vinegar and water did the job! Good luck and thanks for this info, it was perfecto!

By Jennifer ILGM on 12 October 2015

Thanks for sharing Newbie grower!

By dale on 19 May 2016

I have been using a product called CU H2O this is been working real well for me better than anything else that I've tried it is a natural product and that's what I like about it.6 month now greater looking plants happy

By Dale on 4 October 2016

I left a post here a couple months back about powdery mildew and I found a product called CU H2O I have been using this as a preventative and for the first time in 6 years ago and I have had no issues with powdery mildew at all very happy I also used it on my outdoor Garden this year with tomatoes and squash and it worked excellent

By Jay on 12 July 2016

Hi, we have had a lot of success with the DragonJuice PM2 from Completely Organic. It's an organic, non-gmo, toxic plant extract blend and PM fall off immediately and no toxicity to plant or quality of bud. In fact, gets rid of mold right in front of your eyes with immediate spray. Controls mold in 2 days. Plants healthier, higher brix and THC. Great tasting bud!

By John H Carlson on 14 August 2016

I have never gone pot for myself or commercially but have serviced many growers.
With the issue of air born mold spores/and or mycotoxins I have developed an air scrubber with the ability to turn 660 cfm of purified air. Oxidizing any anaerobic organism along with the mycotoxins. Each unit large or small has this same ability. Many folks have purchased theses units not for growing but in the "cleaning the air" from pot smoke.
For growing you can also spray a colloidal solution or tio2 on any surface and the chemistry will also oxidize any organic odor or mold spore.

By Swampy on 26 September 2016

I've been growing for over 35 years. It's basically farming and you learn something new each and every year. The tips you have here are sensible and easily understood. Nobody knows it all and your guide sure helps...thanx.

By Mikee on 21 June 2017

Thanks everybody

By cory on 16 August 2017

IN MY OPINION THE MILK AND WATER DOESNT WORK iv did this last year and it went away for a couple days but came right back quick...but the slufer burners work awsome and so does the organic apple cider vinegar and water

By latewood_ILGM on 20 September 2017

Milk curtails the growth of the spores, and must be reapplied every few days as you proved here. You cannot just treat an issue once and hope that is all you need to do. This type issue requires diligence. I like the Sulfur burners myself as mentioned, also.

By Jim Heron on 30 August 2017

ACTINOVATE !!! It's all I use for mold, and fungus issues ! Root drench every 10 days, foliar spray once a week. It will control existing mold, but prevents it completely if used before flowering ever starts. Pricey, but nothing but the best for my girls !!

By latewood_ILGM on 20 September 2017

Thanks Jim 😀 I will have to check and see how safe this product is to use.

By Nancy on 30 September 2017

After apple cider spray do the plants need to be washed and how long til they can be harvested.

By Doug on 29 November 2017

We had limited success with sprays and home remedies at best. Nothing seems to really work so great.
We found a place to buy a couple of UVC lights and tried it on a small section of our grow. It worked better than expected, and plan to purchase more, but was wondering if anyone has ever heard of these ?

By latewood_ILGM on 7 December 2017


Yes, UVC lights are known to a lot of growers, especialyl growers that are always adapting to newer ideas and products.

By Trent Thiel on 19 December 2017

This is no different than what is seen on grapes and wheat. Powdery mildew is most prevalent on lower leaves but can cause blighting of the upper leaves, heads and awns of susceptible cultivars. Within a few days after they appear, the white powdery pustules produce large quantities of small asexually produced conidia (also called oidia) in long chains, which are easily dislodged by wind or rain. These spores are single-celled, oval (8 to 35 µm) and colorless. As lesions age, the mycelium becomes more dense and turns grey (Wiese, 1987). Dark round cleistothecia (135 to 280 µm in diameter) develop in the fungal mass as the pustules get older. Ascospores develop in the cleistothecia and serve as the long-term survival structures. Cleistothecia may be empty if examined when plants are harvested because ascospores often do not mature for several months.

I would venture to say that there is little to no particulate recirculation filtration in these rooms. Considering the spores are 8-35 um, a MERV 13A or 14A particulate would eliminate this problem completely.

By Trent Thiel on 19 December 2017

May have been obvious, but I should have clarified that a recirculated air filter solution is for indoor growing only.

By lorene miller on 13 June 2018

How often do you spray, using apple finger and water?

By latewood_ILGM on 15 June 2018

In general indoors or in greenhouse we treat plants once every week or 2 to be proactive

By michael on 20 June 2018

hi guys first time growing in a small hoop house .10 x 16 with only 6 plants.2 fans on the plants. just notice what i think is powdery mildew. how often do i spray with the ACV ? my girls are about 30 inches tall with just a couple of the lower leaves infected . how long will it take to see results

By latewood_ILGM on 21 June 2018

I suggest following the directions when using any product.

By Rita on 31 July 2018

First of all thanks for helping us out, I'm in my 6th week of indoor grow and now this pops up! Will my foliar spraying the leaves and buds with the vinegar solution take away from my final product this far along? I only have 2-3 weeks left or would I be better to just wipe the leaves down with the vinegar solution? Thanks, ahead of time!

By grobi43 on 19 September 2018

Just completed a outdoor grow with-mixed results, trending toward failure - Bud Rot due to a span of heavy rains, high heat and humidity, resulted in loss of half of plants. Salvaged what I could; noticed the bud is fluffy, not compact (I figure due to high heat, day and night). Next grow will be stealth, indoor

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