Powdery Mildew and cannabis

In recent years, the marijuana plant has become increasingly sensitive to the attack of the so-called powdery mildew fungus, also known as PM, white mold, ash, etc... It is a parasitic fungus of the erisifáceas family, which attacks the aerial parts of plants.

Although the infection is relatively easy to cure, it can have very serious consequences, since it can damage crops and make them 100% useless. In the first phase, it develops on leaves, to later move on to petioles, trunks and finally to the buds, completely destroying the resin and leaving the marijuana completely invalidated for smoking, since the spores of the fungus are solid matter that we would absorb when inhaling.

The characteristic white powder that forms powdery mildew
The characteristic white powder that forms powdery mildew

The pest affects both indoor cannabis plants and outdoor or greenhouse crops and for its propagation it needs strong hygrometric variations, suddenly going from low to high relative humidity, a situation that occurs very commonly in crops under artificial light. and in greenhouses. Outdoors, the plague is more seasonal and usually occurs more often in spring and autumn.

Powdery mildew is a fungus that is well-diagnosed. It manifests itself as a very typical white or ashy powder, which can be confused with powder on leaves and shoots. In the second phase, the attacked leaves turn yellowish in color and end up drying up.

Powdery mildew is an external fungus and its operation is very similar to that of sucking insects since its small spores are carried by the wind and when they land on a leaf they put out small roots that suck and absorb the plant's nutrients.

Powdery mildew-infected plants should be treated as soon as possible.
Powdery mildew-infected plants should be treated as soon as possible.

Powdery mildew in indoor cannabis crops

In indoor cultivation, as we have said before, powdery mildew is an increasingly common disease and in some cases, it is necessary to take preventive measures from the beginning of the cultivation, but what will help us the most to avoid contamination of the fungus is the Climate control of our growing space. It is about preventing the relative humidity of our growing room from exceeding 65% or falling below 40%. For this, perhaps we will need a humidifier, to avoid that with the bulbs on the humidity does not drop too much due to the effect of the heat of the bulb.

During the night rest of our plants, we should regulate the ventilation so that the breathing of the plants does not produce condensation inside the space. In extreme cases, we can resort to the use of a dehumidifier. Another detail that can help us prevent the spread of the fungus is not to put the marijuana plants too close together, since shady areas form in the lower parts of the plants that favor the appearance of powdery mildew.

If you find it impossible to avoid the ups and downs of your hygrometer, you can resort to preventive phytosanitary treatments.

Powdery mildew is a common problem in many areas
Powdery mildew or PM is a common problem in many areas

Powdery mildew in outdoor and greenhouse cultivation

In outdoor cannabis cultivation, the powdery mildew plague occurs with a certain seasonality, with spring and especially autumn being the seasons with the highest propensity to contract the disease. To try to avoid this, we must keep the plants clean of dry leaves and avoid planting them in areas with few hours of sun. If we grow in pots, it is convenient to rotate the pots so that all parts of the plants have good sun exposure. We should also avoid planting the plants too close together. It is important that air circulates between the plants.

In greenhouses, we must ensure proper air circulation inside the greenhouse. For this, it is highly recommended to install some fans inside the greenhouse that force air circulation.

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In autumn it is recommended to carry out biological preventive phytosanitary treatments, especially if we live in areas where abundant fog or mist occurs.

Control and management of powdery mildew

Within the biological treatments for powdery mildew control, we can find propolis, Oidioprot from Ecoprotect, or Fytosave from Flower. They are all products of proven efficacy, but due to the high resistance of the fungus, we must carry out the treatment every 10/12 days until 10-15 days before harvest. However, as we always tell you, it is better to be proactive and use these products during growth and until the end of pre-flowering; Let's try never to spray the buds with any substance!

Close up image of a cannabis leaf infected by powdery mildew
Close-up image of a cannabis leaf infected by powdery mildew

There are also other products on the market such as Oidio Killer from Agrobacterias or the anti-PM fungicide Flower, which we can also use. As always, we recommend that you keep in mind that you must respect the safety terms of any phytosanitary product that you use, if possible even increasing them.

Although the use of sulfur is recommended as a biological remedy for powdery mildew control in numerous books and garden manuals, it is highly discouraged to use it with flowering cannabis because even if we do it very early, the smell of sulfur can remain impregnated in the plant.

Happy harvest!


The articles published by Alchimiaweb, S.L. are reserved for adult clients only. We would like to remind our customers that cannabis seeds are not listed in the European Community catalogue. They are products intended for genetic conservation and collecting, in no case for cultivation. In some countries it is strictly forbidden to germinate cannabis seeds, other than those authorised by the European Union. We recommend our customers not to infringe the law in any way, we are not responsible for their use.

Comments in “Powdery Mildew and cannabis” (54)

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Justin 2023-11-20
Hi Dani, I noticed PM 3 weeks into flower, I have 6 plants that were too close together and extremely bushy, I cut the affected leaves off and lollypopped my plants, I introduced more air circulation and cut out the humidity, also doubled the space so no leaves on other plants touch, I'm now just over 4 weeks in and it hasn't come back. Can I assume that so long as I keep checking all plants everyday it might stay away? I have products at hand should I need them. I live in England and the local growshop said loads of people are having the same problem, we've had a couple of weeks of fog and humidity. Thanks in advance, I've learnt alot just reading the thread and other growers views.

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ajc 2023-08-29
just switched to flower 5 days ago noticed pm can I spray with hydrogen peroxide or is something else suggested!

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Kilgore trout 2022-09-23
Powdery mildew cannot be destroyed once you see if it’s over. None of those remedies witch. A blow torch kills it but ruined the buds! Also it kills the thx on the plant. It’s useless once detected.

Alchimia Staff

Tim Alchimia 2022-09-26
Hi and thanks for your comment. If a plant is already covered with PM then you're right, there's really no magical product or technique that can save it. However, if you see a small amount of PM appear on a few leaves, then it's not too late to halt its spread by improving cultivation conditions and spraying an organic fungicide or preventive product. Of course, outdoors growers have it a little more difficult as they can't simply reduce humidity and improve conditions, which is why it's so important to ensure they are in optimal health with adequate airflow. All the best and happy growing!

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Blazed 2022-09-10
I’ve got a manifolded plant 6 weeks into flowering. One top has a bit of white PM and some is turning black. It’s just on the sugar leaves mostly, not directly on any bud. I live in a tropical country and it’s the rainy season. I keep it sheltered during rain almost always and move it into the sun when not raining. Should I cut out the effected leaves? I have aloe growing too so I’d be happy to apply that. How do you recommend using it? Thanks for all the great advice given on here!

Alchimia Staff

Tim Alchimia 2022-09-12
Hi, thanks for your comment. It's always a good idea to remove any leaves or flowers affected by mould, followed by an application of an organic fungicide - which is where your aloe plant comes in. It has a fungicide, bactericide and anti-viral effect, and it also contains slycic acid, which activates the plant's "immune response" known ar systemic acquired resistance, enabling it to better fight pathogens and stress. To use it, take a small to medium-sized leaf, carefully remove the outer skin using a sharp knife, and then blend it with two cups of water (470ml). Dilute 1/2 to 1 cup of this with water to make a gallon of spraying mixture and use this to spray the entire plant or just the affected area. You can repeat applications as often as needed, but take care not to soak the buds too much as the excess moisture could lead to botrytis problems. Any leftover aloe mixture can be used to water your plant. I hope that helps. Best wishes and happy growing!

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Dakota (Oklahoma grower) 2022-08-29
I didn’t read every question because there was a ton, but what can I spray in flower to kill pm and what works as a preventative? So kill and prevent. However, I’m at the end of week 6. It’s very climate controlled now. I just bought more dehumidification so it should be easy to control from here on out.

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Tim Alchimia 2022-08-29
Hi, thanks for your comment and question. The issue with spraying plants 6 weeks into flowering is that you can't use anything that leaves a residue as this would remain on the flowers and could seriously affect the quality of the end product. There are various options available to you, however. Aptus Fungone is a residue-free fungicide based on hydrogen peroxide, which is quite effective at stopping PM and cleaning the leaves of spores. The manufacturer says it has preventive qualities too. Still, I'd be tempted to use another product like Oidioprot by Prot-Eco, which is safe to use up to 15 days before harvest (use with Milduprot for the best results). Ostroka Oidy is another product that fights PM without leaving a residue, although the makers don't specify how long before harvest it can be applied. Another, more homemade, method is to use a foliar spray of 1 cup aloe vera juice and 15ml Epsom Salts in 1 gallon of water, which can be used until the last week of flower. I hope that helps with the problem. Best wishes and happy growing!

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TMBoi407 2021-11-10
At harvest stage trichromes look good and milky with bout 20% amber and had a cold night so I figured I’d leave outside to try and shock it for a boost and was fixing to cut yesterday morning but noticed PM on just a lil of the top of plant and noticed more on the lil buds lower so I did what I could to cut them out and then after I mixed baking soda,dish soap,and water and sprayed it good but it’s trimmed all up pretty much so couldn’t leave it in sun all day didn’t want it to burn up but read where u use hydrogen peroxide even rite before u cut them to hang to kill off anything else and help with any PM I didn’t see,I guess what I’m asking is what should I do at this point can I spray it good with peroxide mix now and just leave it out one more night thanks for this site

Alchimia Staff

Tim Alchimia 2021-11-11
Hi, thanks for your comment. PM will often appear when at this time of year as a result of the swing in temperature between the day and night. At this stage, I would probably just spray them with hydrogen peroxide and directly harvest it rather than leaving it out for another night. This will act to kill any spores and stop the PM from spreading, and you can get the plant into a drying room where the conditions should prevent any further fungal growth. Of course, you can even decide to wash the plant once you've harvested it, either with a mix of water lemon juice and bicarbonate of soda or with diluted hydrogen peroxide. Simply dunk the plant into the first bucket with your cleaning solution (although I wouldn't recommend using dish soap or any other soap as this can degrade the resin), giving the flowers a good wash, then shaking off the excess liquid before rinsing in a second and third bucket of clean water. Then shake the remaining water off and hang to dry. This method is becoming very popular with outdoor growers, even just to rinse away any bugs or dust that may be on the flowers and give a higher quality end result. I hope that helps, best wishes and happy harvesting!

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Souramnesia 2021-10-30
Had pm early on during veg...used clarified hydrophobic extract of neem oil but only works if you catch it early. Cleared it right up..now I check my plants every day to make sure I catch it when it first starts..bonide rose rx 3 in 1 was the brand name..

Alchimia Staff

Tim Alchimia 2021-11-03
Hi, thanks for your comment. Yes, Neem Oil can be a very useful preventive agent against fungal pathogens as well as various insect pests and spider mites. As you say, it's important to catch any infestation early and to only use oil-based products while in veg, never during flowering. In fact, regular applications of Neem are an essential part of any good IPM (Integrated Pest Management) program and will ensure your vegging plants stay at optimal health levels! Thanks again, best wishes and happy growing!

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Jay A 2021-10-27
Hey. Im a new time grower. First grow i had wpm from outside so moving indoors to treat and get hit with a 2000 tsl mars hydro. Anyway, it never went away. I used apple cider , h2o2 , and baking soda. To me , definitely once its there. Its ALWAYS going to be. My question is , in my second attempt here , different spot in the house. Even two new lights , my clones which I got off of someone , have already in veg spots of wpm. Supposedly these strains , gdp , white widow, are resistant. However in my case I already see it . Like others , my grow room , I dont have a tent , is a 10x10 with a hygrometer stating I hit an average of 55% humidity and 66 low temp 77 high. What in the heck am I doing wrong. I use fox farm / mothers earth soil . I dont over water.Have three fans , one exhaust in the room going. Enough adequate lighting as well to a certainty as I have 2 , 2x2 1000 leds for side hits. So again , not to repeat myself , is it the clones/ the plant ? Or me ? Thanks

Alchimia Staff

Tim Alchimia 2021-10-29
Hi and thanks for your comment. I fear you're correct, once PM takes hold in a plant, it's almost impossible to get rid of, and the best we can hope for is to keep it at bay and avoid it spreading. I've seen the best results by using H2O2 or Potassium Bicarbonate. It's almost certain that the clones were already infected when you got them (your growing conditions look to be great). Personally, I managed to go a full year without any PM issues until I foolishly accepted clones from a friend who swore they were clean. Of course, within a few weeks, despite near-perfect growing conditions, they started to show white spots and I had to act very fast to prevent it from spreading to my other plants (ie. throwing the new clones out quick!). I've found that repeated treatment with wettable sulfur during vegetative growth to be the best way to protect plants against PM. Powdery Mildew is not systematic, so with adequate treatment it can be dealt with before switching to flower. Wettable sulfur cannot be used during flowering, as it will leave a nasty-smelling residue on the buds, completely ruining the flavour, but when used properly in veg there's nothing else organic that beats it. I hope that helps, best wishes and happy growing!

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Marcus 2021-10-14
Hi! Great thread! I have FM all over the plants, thinking about dipping the branches and buds in hydrogen peroxide and then hang to dry. I'll mainly make tinctures and infusions with the produce so should hopefully be fine. Question: how should I dilute a 3% hydrogen peroxide solution for the dipping? Thanks!

Alchimia Staff

Tim Alchimia 2021-10-19
Hi Marcus, thanks for your comment and question. The recommended ratio for bud washing is 1 cup/250ml of 3% Hydrogen Peroxide per 5 gallons of water. I hope that helps, best wishes and happy harvesting!

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Cartesearcher 2021-10-04
I was away and saw that I had PM on my plant when I just got back. It's all over and even a bit on the sugar leaves. Do you think it would be okay to consume after drying if I just vaped it?

Alchimia Staff

Tim Alchimia 2021-10-05
Hi, thanks for your comment and question. In your case, I would recommend you to wash your plants before hanging them to dry, to help rid the flowers and sugar leaves of any mould spores and other dust or dirt. You'll need 3 buckets, fill the first one with water and add 8 teaspoons of sodium bicarbonate per gallon, along with 40ml lemon juice per gallon. Fill the other two buckets with plain clean water. After you've trimmed away all the fan leaves and non-resinous material, dip the plants upside down into the first bucket and gently move them around in the liquid to help dislodge any dirt, bugs, etc. Remove the plant from the bucket and gently shake it to get rid of excess liquid and dirt, then dip it into the second bucket to rinse away any remaining lemon/bicarb mix before giving a final dip to rinse in the third bucket. Shake off the excess water and hang to dry, keeping a close eye on the plants as they go through the drying process. That should make your buds as safe as possible for consumption. I hope it helps, best wishes and happy harvests!

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OutdoorTom 2021-10-02
What if just the leaves of the lowest small buds have PM, is the whole thing shot? Do I need to wash everything. No visible PM on kola's or leaves. Just lower branches. If it is just the start of PM (very light , cloudy) on the leaves, is that very bad? I just cut them off. TIA

Alchimia Staff

Tim Alchimia 2021-10-04
Hi and thanks for your comment. Yes, you should remove the affected leaves and take some kind of remedial action. If the plant is flowering then that limits what can be sprayed on it but you can safely use Hydrogen Peroxide (3% strength) to help slow the mildew down. Another safe option would be diluted Aloe Vera juice, which will help wash away spores and strengthen the plant's defences against fungal attack. At the same time, do whatever you can to improve airflow in the affected area, such as removing the large lower leaves, and trimming away the lower buds that don't get enough light -- it's here where the PM starts and spreads from. I hope that helps. Best wishes and happy growing!

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Billy Budd 2021-01-04
Growing 5 Blue Dream feminized and had a little bit of PM here and there...heard about 3 parts water to 1 part Mouthwash and using small painters brush I meticulously applied only to the infected leaves...seems to stop the spread and kills PM after a few doses! My humidity level has consistently been around 35rh and temp around 72-76 with small fan during day so a little surprised I had any!.So far the best crop Ive ever had and Blue Dream taste great!

Alchimia Staff

Tim Alchimia 2021-01-05
Hey Billy, thanks for your comment. I'd never heard of using mouthwash for powdery mildew before, it's great to learn a new trick, thank you for sharing it with us. From what I can tell, the peppermint oil and Ethanol are the active ingredients in the fight against PM. I'm really glad it worked to solve the issue and that your harvest was a huge success, great work! Thanks again, best wishes and happy growing!

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Kamie kush 2020-10-11
I'm not sure if it's sugar leave or this pm your talking about . My first time growing I started in my garden outside along with everything else I grow . Thinking that they probably would not do anything . Well as time goes on I moved tomatoes by them sunflowers . I needed to hide them . Well I could not do that anymore so I got a greenhouse and put around them . So I'm not sure on anything much . I never feed them of spray with anything .. my garden is all natural I would say . My dirt all comes from the dairy farm behind me .. now it's not piles of cow shit . Lol they sell it .. anyway my garden is always big and beautiful .I had a pumpkin grow to be 101 lbs never grew them before. I have dealt with my share of pest . Mainly potato bug . Nothing killed them but fire . So I left potato out this year . So I'm thinking it's time to harvest mine ..??

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Debbi 2020-10-10
I got the PM exactly 1 week to harvest, just keep cleaning and clipping the leaves, 5 days toll Harvest, but, under control. It was my first grow and I must say, it's looking good, but, next year, where do I purchase the CU H20 so I have it on had? I did look on Amazon, and, I live in MI. Thanks in advance

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Jaxash 2020-10-05
I watched a video from Jorge Cervantes, and he washes his buds in a H2O2 bath then rinses and hangs to dry.

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Tim Alchimia 2020-10-06
Hi, thanks for your comment. Yes, that's a popular method for dealing with PM among US outdoor growers. I don't know anyone who's tried it here in Europe but there's no reason why it wouldn't work and indeed it seems a great way to save a harvest from potential disaster. Obviously, weed that has been dipped in Hydrogen Peroxide and water will never have the same quality as flowers that were harvested in perfect condition, but if it's a choice between washing the buds and throwing them away, I know which I'd choose! All the best and happy harvesting!

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JC 2020-09-29
Hi! my plants are just about ready to be harvested however I have been struggling with powdery mildew for a few weeks now. started as white dust on leaves and then the bigger fan leaves turned this black/brown colour. the colour has spread to some of the buds as well. I have been spraying the plants with a milk and water mixture and trimmed off all the black leaves. my question is, are my buds safe to harvest, dry and consume? i plan on washing them in hydrogen peroxide before drying to kill off the fungus

Alchimia Staff

Tim Alchimia 2020-09-29
Hi JC, thanks for your comment. Sorry to hear you've been having trouble with PM this season, for some reason I'm not seeing any in my garden this year, despite having suffered badly in previous years. The only thing I did differently this year was spraying wettable sulfur a couple of times in veg, so maybe try the same next year and see if you have any better luck! As for this year, I would trim away the very worst of the affected areas from the buds, wash/rinse what you intend to consume in 3% H2O2 before drying and you'll be fine to consume it. It's not the ideal way to treat cannabis flowers, but if we're talking about saving the harvest then I think it's fine. There's no evidence of PM negatively affecting the health unless there's some sort of allergy to it, which I believe is rather rare. I hope that helps, best wishes and happy harvesting!

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Starboy 2020-09-23
Hi guys, I have a question. Would it be safe to use mildew infevted plants for making infused oil to use in cooking and baking?

Alchimia Staff

Tim Alchimia 2020-09-24
Hi and thanks for your question. It's always best to use buds that are perfectly clean, although I realise it's hard to throw away your plants after so much hard work. So while using PM infested flowers isn't an ideal situation, it really depends on the seriousness of the infestation. If it's just on the leaves then you can just remove them and use the flowers as normal, but if it's made its way onto the flowers themselves I would recommend a couple of different approaches, as long as the mould isn't covering more than 30% of the flower. Any more than that and frankly it's probably not worth using anyway as the trichomes may not have developed properly as a result of such a serious infestation. Firstly, you could harvest the buds and wash them very gently (just a dip for a few minutes, really) in a 3% solution of Hydrogen Peroxide to kill the fungal spores before hanging them to dry. You can then safely use them to make oil for edibles. Making the oil without first washing the flowers, the spores will be extracted with the oil and it will need to go through a very fine filter to remove them. Alternatively, you can make bubble hash (aka ice water hash) from the flowers, which will wash away any spores in the process. The hash can then be used safely in edibles. I hope that helps. Best wishes and happy cooking!

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CALVINATOR 2020-08-31
Hey there. So two of my plants (Outdoor) about 3-4 weeks into flowering have PM. Is it early enough to foliar spray with a baking soda/hydrogen peroxide solution still?

Alchimia Staff

Tim Alchimia 2020-09-01
Hi, thanks for your comment and question. I'd say that you'll be fine spraying that kind of thing outdoors at this time, and probably for a couple of weeks more too. Personally I've used foliar sprays of Hydrogen Peroxide right up until harvest day! Best of luck and happy growing!

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kassperry@gmail.com 2020-08-21
I have a couple plants in pots outside. Ones in the 5 week of budding the second just started. I have pm in both of them been treating them with and organic fungal and pest spray. I trim the leafs with the pm on them and sprayed them. I've had to do this 3 times.☹️I'm always checking and triming . If i can't get ride if it if I keep it under control so it doesn't get to my buds will I be ok? First time grower.

Alchimia Staff

Tim Alchimia 2020-08-21
Hi Kass, thanks for your comment and question. Damn, I'm sorry to hear you're having PM problems. Are the plants in a damp area? If you can move them somewhere that they'll get better airflow and ventilation then PM nd other fungal pathogens will be less of a problem. Spraying can work to keep it at bay, although you'll probably need to rotate products to ensure efficacy. I would spray with H2O2 solution one day, then after a couple of days I might try some Potassium Bicarbonate. I would also be applying some kind of beneficial microbes to combat the pathogens, for example, Oidioprot which can be applied up to 15 days before harvesting. Personally I prefer to take preventive measures against PM, so I feed my plants plenty of Silica (Horsetail or Potassium Silicate), make sure the soil is inoculated with beneficial microbes (Trichoderma & Mycorrhizae), Spray a couple of times with wettable sulphur during the veg period (never to be used in flower) Powdery Mildew can be very ugly and will definitely affect the yield and vitality of the plants in a negative way, but unlike other fungal pathogens like Botrytis, the PM itself isn't toxic to humans and doesn't produce harmful mycotoxins, so while it's not ideal and not pretty and certainly not something we'd choose to do, it shouldn't be a health issue unless someone has specific allergies or is immunocompromised in some way. If you get to the harvest and there's some PM on the buds themselves, you should cut away the worst affected parts and then, depending on how bad it looks, you can wash the buds in Hydrogen Peroxide solution (3%) before hanging them to dry as normal. It's a bit of a pain but it's the safest way to ensure a cleaner harvest if PM has been an issue. I hope that helps, best wishes and good luck for the rest of the season!

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Joethenubie 2020-04-08
Thanks Tim for the quick response. I had sprayed them with the h202 mixture the day before I posted. As the plants dried, I still noticed it on them. I did notice that 3 plants of the same strain seemed to be effected more and my GG4 didn't seem to have much of any on it. I ended up harvesting last night and used the h202 bath mentioned before in the process. I also trimmed a little more than I normally would. This is only my 3rd crop so I'm kinda new to this and didn't have any PM problems before. I'm keeping my fingers crossed that I got rid of it because the buds look delicious. Thanks again for the help, a nubie ljke me can use all the help I can. I may even post how it turned out after the drying process. Take care

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Tim Alchimia 2020-04-09
Hey Joe, awesome, glad you got the plants harvested. Sounds like you did a thorough job with trimming away the infected parts, I'm sure it'll turn out fine! Hopefully, you can get the PM issue under control with your next crop. I grew outdoors in Spain for ten years before I saw any PM and now it's a real issue, I guess due to environmental factors because I also notice it on trees and bushes where it never appeared before. For this reason, I always select for resistance to PM over pretty much any other traits! Please let us know how the dried flowers turn out, I hope you enjoy them! Best wishes and happy harvesting!

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Joethenubie 2020-04-07
I have some PM on my flowering plants (7 weeks in. I notice it at about 4 weeks and treated them with a cider vinegar mixture. It seemed to help but it has came back. My humidity is not high and I do have a fan that runs while lights are on. My question isn't about prevention, I'll figure that out before the next crop, my question is, should i harvest early in an attempt to save the buds from being infected? My trichomes are mostly cloudy. What to do, what to do?....Thanks for having this discussion

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Tim Alchimia 2020-04-08
Hi Joe, thanks for your question and comment. Sorry to hear you're having PM issues. I know you said you'll figure out the prevention, but if your environment is dialled in then you can probably blame the genetics, my own personal experience over many years has shown me that some varieties are much more susceptible to PM than others. Skunk-based varieties and OG Kush/Diesel have been some of the hardest-hit in my garden. Now to your question... If I was in your position I would probably spray them down with a diluted Hydrogen Peroxide mix (1 cup of 3% H2O2 per gallon of water) to neutralize the mildew spores before harvesting and drying. Unlike Botrytis, smoking weed infected with powdery mildew isn't a health risk unless you have an allergy or are immunocompromised, but it's still recommended to cut away and dispose of any badly affected parts of the flowers. If your trichomes are mostly cloudy then I'd say it's a fair enough time to harvest anyway. I hope that helps some. All the best and happy harvesting!

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Budslinger420 2020-02-14
Thanks for the quick response! I've got some 9% h202, at what ratio should i mix it? Thank you

Alchimia Staff

Tim Alchimia 2020-02-14
No problem! I usually use 3% H2O2 but I had a quick search and found a recommendation for mixing 80ml of 9% H2O2 with 1 litre of water. If you find it doesn't do the trick then increase the dosage a little. Good luck!

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Budslinger420 2020-02-12
Hi there, Can i spray the bud directly with milk and water spray or any other spray? as iam in week 7 of flower and worried about damaging the bud? Thanks

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Tim Alchimia 2020-02-13
Hey, thanks for the question. I'll be honest, there aren't many things that I'd recommend spraying on buds at this late stage of flowering. Really the only option left that won't leave some kind of unwanted residue on your plants is a diluted solution of Hydrogen Peroxide (H2O2). Anything else will affect the flavour of your cannabis and could possibly be a health risk when combusted. I hope that clears up any doubts. Best wishes and good luck!

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Mauricio Machado 2020-01-31
great great post. most complete forum about the subject so far. i’ve been fighting pm for two years now. have tried sodium bicarbonate, milk and several oils without success. in my grow room pm shows up at week four of bloom and attacks just some strains (all of kush related). would like to try uv lights and h2o2. although the ac and the dehumidifier 24h a day, my humidity range (30-65%) should be the problem, as i understand from the comments. is that so? i use to trim pm infected plants cutting all the sugar leaves and throw away the material, keeping sore of half of buds to smoke (with very very little pm on them). so far without health problems. what is the risk of doing this? thank you.

Alchimia Staff

Tim Alchimia 2020-02-11
Hi Mauricio, thanks for your comment and question, apologies for taking so long to answer you. Yes, you're right, PM can be a real pain in the neck, and in my experience, it's mostly due to the genetics, with some varieties being much more prone than others, as you've noticed with your Kush varieties. I grow outdoors and I've spent a long time selecting varieties and phenotypes that are resistant to PM, often having to plant 2 packs of a variety to find a resistant plant. Selection is key! Having said that, I've seen PM prone plants grown without any problems, I think it's a case of combining the best plant health possible with the best conditions possible in terms of heat and humidity. If plants are very healthy they will be less likely to succumb to fungal issues, so I make sure I use a high-silica product to reinforce cell structure and resistance, GHE Silicate/Mineral Magic is a great option and should be used throughout the plants' life. A phyto-strengthener like Flower Fytosave will also help to keep your plants in optimal health and keep fungal attacks at bay. As for smoking buds with a little PM on them, I'm no doctor, but I'm led to believe that it's not a huge problem in itself. Botrytis and other fungal pathogens produce mycotoxins, which can cause serious health problems if inhaled, but Powdery Mildew does not produce these toxins, and can only cause health problems in case of allergy, meaning that while smoking buds with a little PM on them might not be ideal, it oughtn't to be a health risk as long as you're not allergic to it. I hope that helps, best wishes and happy growing!

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islandbob 2019-11-07
do you know what the mix ratio would be using certified 35 food grade hydrogen Peroxide?

Alchimia Staff

Tim Alchimia 2019-11-08
Hey Bob, thanks for the question. You can add 1 teaspoon of 35% Hydrogen Peroxide per litre of water as a start. If you see it's not working then increase the concentration a very small amount at a time, always with great caution. I hope that helps, all the best and happy growing!

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Wap 2019-08-26
Peroride to water ratio and will water milk mix work for indoor grow

Alchimia Staff

Tim Alchimia 2019-08-27
Thanks Wap, those are good tips. What ratio do you use in either case? For Hydrogen Peroxide I use 1 cup of 3% strength in a gallon of water, and up to 2 cups in severe cases. I've never tried milk, although I've heard it's important to use full-fat and that raw, unpasteurised milk is best. All the best and happy growing!

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brethren 2019-01-20
Hi there. How do you feel about green cure or just spraying a hydrogen peroxide/ h2o mix 2weeks before harvest? Started noticing some PM on fans creeping to sugars. I have been exfoliating those particular leaves and was ready to spray or even willing to meticulously wipe down the leaves/buds with the peroxide mix. Thanks for you help and input and site!!

Alchimia Staff

Tim Alchimia 2019-01-30
Hi brethren, thanks for the comment and question. Personally I have no problem using Hydrogen Peroxide right up till the day of harvest. I'm not so sure about Greencure though, as it's Potassium Bicarbonate which may leave some residue so soon before the end of the flowering period. I'd use it up to, let's say a week or ten days before harvest, and then use H2O2 during the rest of the time, which as well as helping with PM, will also go some way to removing any residue from Greencure. All the best and happy harvesting!

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Relampago 2018-11-03
Would buds lightly stricken with PM present a health problem if used for making oil/butter for edibles?

Alchimia Staff

Tim Alchimia 2018-11-05
Hi Relampago, thanks for your question. As unsightly as PM is, it doesn't normally represent a health risk in itself, so should be fine for edibles. You can filter the infused butter or oil through a 25 micron bubble bag, or even a coffee filter if you want to be extra-safe and remove any spores. As far as I understand it, the health risk from Powdery Mildew is very low even when it's on cannabis that's being smoked, but the micotoxins produced by the fungus can certainly cause problems in people with immune system problems. I hope that helps clear things up, all the best.

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Jon 2018-09-28
Tim...so I used 10 tsp Raw apple cider vinegar to one gal water...so I trimmed like a mad man ..and sprayed like crazy 2x +over.& over..I then took in a branch I broke and quick dried the buds at 160 degrees in a vacuum...The outside was laced with PM ...I broke it open the same on the inside...so did I ruin the high? the only way to know was to take a hit...I took a one small toke off off of 2 different kinds I had quick dried...surprisingly good taste (I had never dried in that method before) and definitely stony !! so I usually make "dabs" the 'vacuum with heat" is part of my dab system...so I read online that if I filter with a 45 micron filter (I use "ever-clear" booze to extract) they say it should remove the spores?? I ordered a system for filtering and I will post back my end results. with 10 plants I have a lot to lose. but now on another note, YOU have got me spooked about smoking it and my wife thinks I was nuts to test it..but I had to know ..you know?....so whats your prognosis.doc?

Alchimia Staff

Tim Alchimia 2018-10-01
Hi Jon, damn, I'm sorry to hear that the PM had got inside the buds too. Good for you for testing it though, you're not crazy, but all the same if it's really badly coated then I wouldn't smoke any more of it! I'm not sure about filtering out the spores etc with 45 microns, I'd definitely err on the smaller side myself and use 25 microns to be safe. Having said that, I have never tried a solvent extraction with PM infected material, so I can't really say. It ought to work though, and the alcohol is 100% sure to kill any spores too. I have, however, made ice water hash with material that had some PM, and I've spoken with a well-known US hash-maker about the subject too, and we're both in agreement that the water separates the mould from the resin. The mould spores float on the water where they can be scooped off with a spoon, while the trichomes fall to the bottom of the bag. This particular hash-maker has tried this multiple times and sent for lab tests run on the finished hash, where no trace of PM was found. Utmost care must be taken during drying to avoid re-appearance of mould. I think either method ought to work fine for you. Did you try using Hydrogen Peroxide to wash the plants down before harvest? That might be a good idea as a last step before hanging them to dry, it should kill off any spores so the problem doesn't extend while the plants are drying. Good luck and keep us posted!

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Jon 2018-09-26
Tim ...OOPS! I have an additional question...I was thinking I would cut down the buds and immediately "dip" them in "cleaner and then hang to dry..is this possible?

Alchimia Staff

Tim Alchimia 2018-09-27
Hi again Jon, no problem, we're here to help! Firstly, thanks for the info on the ACV treatment, I'd been researching but all the recipes I'd found were more diluted, like 2-3 teaspoons per gallon, have you noticed any ill effects from using a stronger solution so far? I'm definitely curious to try this myself. I think it's almost the only organic anti-pm treatment I haven't tested yet! The Aloe/Epsom method might be a good idea to try, yes, just simply for the reason of alternating treatments. Another option is Hydrogen Peroxide, I occasionally use it myself, the dilution I've used was 1 cup of 3% (10 volumes) in a gallon of water. This amount can be increased for more effective disinfection if you don't see any ill effects on the plants. This might be the best idea for a lats spray, to leave the plants really clean before hanging them to dry. As for dipping, it's definitely possible, I've seen it done, in fact Jorge Cervantes has some videos somewhere on YouTube with instructions about this. Personally I've never tried it because: A. I don't have a vessel large enough to dip my branches, and; B. I'm actually quite uncomfortable with the idea of dipping all my plants in the same, potentially pathogen-laden water. I'm much happier to thoroughly spray my plants down a day or even a few hours before harvest, to give them time to dry a little before I take them into the drying room. I think you're on the right track though, between throughly washing down plants and trimming away any visible PM, I imagine you'll get good results! All the best, good luck and happy harvesting!

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Jon 2018-09-26
Hi Tim...Thanks for getting back so soon...we do need quick answers and truly appreciate your help. we are right at harvest (I feel) for several plants PM has got the sun/sugar leaves and in some cases appear in some small locations in the bud (I dried a sample and took a look at it with 60x) ..i could only see a "wisp" of "web" mainly near the edges. Am I still OK? I am using "Raw Unfiltered Apple Cider Vinegar with Mother" 8 tsp to a gallon. I spray everything .....I try and "flood the bud". I want to be really aggressive at this late hour...I have trimmed the sun and some sugar leaves. Should increase the strength of cider? or should I use your Aloe/Epsom method?

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Jon 2018-09-24
Is the PM always visible? ,,,in other words if I see on the sun and sugar leaves and not on the bud ...viewed with a 60x loop...I do not see it in the bud center..I If I snip the contamination away (after several rinsing with "cider") the buds appear clean ..is that realistic thinking or only hopeful?

Alchimia Staff

Tim Alchimia 2018-09-26
Hi Jon, thanks for the question. In short, if you're not seeing it with a 60x loop, it's not there. I've had plenty of plants with PM spots on the shade and sugar leaves, but nothing on the buds. I think you'll be fine. May I ask how you're using cider to rinse the plants? Cider or cider vinegar? What dilution? Are you also spraying the buds to rinse them, or just the leaves? In previous seasons I've rinsed my outdoor plants down with a mix of Aloe Vera juice and Epsom Salts (1/2 to 1 cup aloe juice & 1 tbspn Epsom Salts per gallon) in the week previous to harvest, which seems to work really well to get rid of any contamination. All the best for your grow and happy harvesting!

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Justine 2018-04-05
Can I wash my buds after harvesting to get rid of pm or can I make cannabis butter with it and use it? Ty

Alchimia Staff

Tim Alchimia 2018-04-10
Hi Justine, thanks for your question, sorry for the delay in replying. We would never recommend consuming contaminated cannabis in any form, even though cooking may kill any fungus or spores, the mycotoxins produced by the mould will remain and can cause health problems, especially in anyone with increased sensitivity or a compromised immune system. Despite this, every year at harvest time you'll find growers washing their freshly-cut buds in a dilute solution of Hydrogen Peroxide solution in an attempt to clean them of powdery mildew, a technique made famous by Jorge Cervantes. We can't really recommend this approach, as it also seems unlikely to remove the mycotoxins. If in doubt, always think of your health first, it's just not worth taking the risk of making oneself unwell. All the best

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Brian 2018-02-12
Thanks everyone for all the helpful knowledge.. DALE and JACK..?? Was interested too in what you guys called “cuh2o”.. Didn’t see it anywhere online anywhere so was just wondering.. and everyone else that Named off a few I see and much appreciated.. happy growing

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stoppowderymildew 2017-11-21
Great post. Thanks for sharing this detailed information about powdery mildew. Please share use of UV technology for treating powdery mildew.

Alchimia Staff

Dani Alchimia 2017-11-21
Hi stoppowderymildew, Thanks for your input mate, I've read a lot about UV light to kill spores but never tried...luckily I don't see PM too often in my area!! Best!

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bill simmons 2017-09-24
I did not know about PM until today, and I finished harvesting and hanging my buds two days ago. The leaves were covered with the stuff. Must I trash it all?? Thanks...

Alchimia Staff

Dani Alchimia 2017-09-25
Hi bill, If the leaves were covered with pm, then it's possible that it also infected your buds. When I've been in your case, I've thrown everything away. Notice there are some methods to make extracts with plants infected by pm (you can dry sieve the resin, mix it with ethanol and filter the liquid mix with a 0,2 micron filter for syringes), although I've never seen a microbiological analysis demonstrating that this method really works. Hope it helped!

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stoppowderymildew 2017-09-21
Thanks for sharing this information with us. Can we use UV technology for treating the powdery mildew.

Alchimia Staff

Dani Alchimia 2017-09-21
Hi stoppowderymildew, From what I know, UV lights can be used against all fungi that grows from the outside in, being powdery mildew one of them. Best!

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susan gibson 2017-09-12
Good Luck!! The milk is supposed to act as an antibacterial when the sun hits it so use this method in the morning.

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susan gibson 2017-09-12
I used water and milk at a 60/40 ratio worked GREAT!!!!

Alchimia Staff

Dani Alchimia 2017-09-13
Hi susan, Thanks a lot for your tip! I've also heard orange juice works, although I've never tried... Best!

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stoppowderymildew 2017-08-18
Great Post. Thanks for sharing this post. powdery mildew is very common in plants. Can we use UV Techonlogy for treating powdery mildew?

Alchimia Staff

Dani Alchimia 2017-08-18
Hi stoppowderymildew, Yes, you can use UV lamps to treat several infections caused by fungi like powdery mildew or botrytis. Best!

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Nancy Peace 2017-04-25
We just got a few babies and have noticed some white spots of mold or mildew on the leaves.We want to stay as natural as possible and would appreciate the recipe for a vinegar solution.

Alchimia Staff

Tim 2017-04-25
Hi Nancy, to deal with powdery mildew in the most natural way possible, it's usually necessary to combine various methods. I haven't personally used vinegar, but I've read about people using 2-3 tablespoons of Apple Cider Vinegar per gallon of water, but be sure to get organic, unfiltered vinegar for maximum efficacy. Other tried and tested natural options are availaable, such as products like Propolix and Oidioprot. I've had good results using compost tea as a foliar spray or alternating spraying a weak solution of Potassium Bicarbonate with a 1.5% solution of H2O2. Some growers fight mildew by simply washing the spores off the leaves with a strong spray of water, while others use a diluted milk solution! There are plenty of different options and opinions, and the jury is still out on many of these homemade remedies, more research is needed. Good luck!

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Nancy Peace 2017-04-25
We just got a few babies and have noticed some spots of mold or mildew on the leaves. We want to stay as natural as possible and would like the vinegar solution remedy.

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Josh vandergaurd 2017-03-15
Hey! Dale! I tried out cuh2o after i seen you post something in here about it. Man o man, in about a week my pm problems were gone! I searched it on amazon and it popped right up, i figured i would try it cause well ive tried damn near everything else. Its natural, i can spray it on my crop litterally up untill the day of harvest. Doesnt mess with the taste or smell of my buds either. And plus it works as a micro nutrient! So i mean not only did i remove my pm issues i gave my plants some much needed nutrients in the process! :D

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JoeR 2016-10-08
Mixture of milk and water sprayed on plant works wonders

Alchimia Staff

Dani Alchimia 2016-10-10
Hi JoeR, Thanks for the tip dude, I'll try that for sure! ;) All the best!

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Terry Ayers 2016-09-11
i am in my 6 wk of flowerying og a 9 to 1o wk plant i got some pm how can i get rid of it

Alchimia Staff

Dani Alchimia 2016-09-12
Hi terry, Normally, we don't recommend spraying the plants in bloom, but if you think that the infection will cause problems you can spray your plants with some organic fungicide (not chemical, you're too close to harvest). I know it is a hard work, but the ideal would be cleaning the infected leaves manually with a cloth soaked in water and some hydrogen peroxide, and then spray the fungicide only on the leaves. Also, try to lower a little bit the humidity in your grow room (removing the lower parts of the plants and the largest, infected fan leaves can help). Best of luck!

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jack nickoleson 2016-04-26
Dang I didn't know there was a up to date forum out here I'm actually shocked. It looks like you had a little trouble getting that out there Dale lol but belive it or not I'm in central MI and I have too come across that powdery mildew evil $#%t lol took my whole crop in 2013 they really didn't have much at the time to get rid of the issue so I had to let it go any ways just the other day my buddy asked if I knew what the white powder on the plants was and I said yup u gotta find something fast he went and grabed cuh2o the next morning we took a peek and belive it or not it was gone

Alchimia Staff

Dani Alchimia 2016-04-26
Hi jack, Thanks for your comment, we'll surely take a look at that product. Best vibes!

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dale 2016-04-26
I come acrossed a product called CU H2O I have powdery mildew really bad and was about to lose my crop this stuff is amazing now I use it as a preventative I have been happy so far

Alchimia Staff

Dani Alchimia 2016-04-26
Hi dale, Glad to hear that, as you know powdery mildew can be devastating if not treated on time. Good for you! All the best.

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dale 2016-04-26
I come acrossed a product called CU H2O I have powdery w really bad and was about to lose my cRop this thing works really no I use it for preventative for 6 months I have been happy

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big snapz 2016-03-23
Can I smoke my buds if they have a lil p.m on them

Alchimia Staff

Dani Alchimia 2016-03-23
Hi big snapz, Smoking buds with fungi is never recommended. If you have a considerable amount of infected buds, I would suggest an extraction using ethanol and then filter it with a 0,2 micron syringe filter. In this way, you remove any trace of spores in your resin. We'll soon publish an article on this subject. Hope it helped!

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Brendan 2016-03-10
I'm just going to say one thing... for powder mildew to exist you need both high humidity and cool night time Temps... If you eliminate one of those problem solved!

Alchimia Staff

Dani Alchimia 2016-03-10
Hi Brendan, Thanks for your contribution! All the best! ;)

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