White Powdery Mildew
by Sirius Fourside
Have you seen white spots on your leaves? Are your leaves dusted with round patches of powder that looks like flour?
If so, you’re most likely dealing with White Powdery Mildew, also known as White Powdery Mold or just “WPM” to cannabis growers.
White Powdery Mildew is usually a minor annoyance that can be easily fixed, but if you don’t catch it early, WPM can turn into a catastrophe that ruins an entire marijuana harvest!
For those who haven’t experienced WPM, imagine circular patches of a living, breathing, fuzzy, flour-looking substance showing up on your plant’s leaves without any warning. From there, the mildew can easily spread to other leaves and buds, rendering the buds unusable.
You’ll see “powder” on your leaves…
White Powdery Mildew has such an easy time spreading that even careful growers who take proper precautions can still experience it.
Luckily, the issue in the picture above was easily resolved because it was caught early and because White Powdery Mildew is completely reversible up to a point.
This article will arm you with the information to stop WPM’s proliferation before it even has a chance to take hold!
What IS White Powdery Mildew?
White Powdery Mildew is a rapidly reproducing (both sexually AND asexually) fungus who only knows how to do two things:
Eat your plants
Make more White Powdery Mildew
Fortunately, White Powdery Mildew is easy to spot since it creates white patches of fungal growth that stand out against the green leaves of a cannabis plant.
It can be removed from plants with proper treatment if spotted early on, but any buds with WPM should be discarded as they most likely contain many more spores than your eyes can see.
What causes White Powdery Mildew?
WPM needs moisture to thrive, but that doesn’t necessarily mean it needs water. Having a grow area with high humidity is all WPM needs to get started. This seems to be a bit problematic since young cannabis plants grow best in relatively humid environments (40% -60% RH). Luckily, high humidity usually only becomes an issue when it’s combined with the next cause (low/no airflow).
People who live in environments with extremely high humidity (such as the southern US or anywhere in the UK) can purchase a dehumidifier to control humidity in the grow area. This is especially important during the flowering phase when humidity needs to be much lower (45% rh) to prevent rampant growth of WPM and bud mold.
White Powdery Mildew has a hard time settling in a grow room where the air is being moved. High humidity will give WPM the conditions it needs to survive, but poor airflow is what gives it the ability to settle down in the first place. In fact, a small (preferably oscillating) fan moving air in a grow area will prevent the vast majority of White Powdery Mildew woes.
If you have WPM spores in your grow area and the air in grow area is never exchanged for fresh air, the spores get multiple chances to land on your plants and reproduce. This happens most often in conditions where cannabis is being grown in a closed, unventilated space – such as a closet – and precautions aren’t taken to exchange old stale air for new fresh air.
Leaves that are touching each other will form moisture between them, and thus they become more likely to contract WPM. Untrained bushy/leafy plants with lots of new vegetative growth are especially prone since they will often have their leaves mashed up against each other as they try to reach toward the light.
Advanced growers can defoliate some of the fan leaves that are completely shaded from the grow light to make fewer choice landing spots for White Powdery Mildew. Also, defoliation frees up energy for the plant to use when done correctly and increases yields! See our article on defoliation for more info.
How to Eliminate White Powdery Mildew
As I mentioned earlier, I recently had a battle with White Powdery Mildew. Rather, it might have been a battle if I noticed it later or waited to fix the problem. That’s the one good thing about WPM: in most cases when WPM is caught early, you can remove all traces of the mildew without harming your plants.
There are quite a few products and homemade concoctions people use to treat WPM. Among the effective treatments are:
Milk (1:9 ratio of milk to water)
Baking soda (2 tablespoons per gallon of water)
Neem Oil (4 teaspoons per gallon of water)
Hydrogen Peroxide (1 teaspoon of 35% H202 per gallon of water)
SM-90 (1:5 ratio of SM-90 to water)
Rather than go into these methods, I’m going to give you the simple strategy I use that gets rid of White Powdery Mildew on the first try, every time! Here’s my trusted 3-Step White Powdery Mold cure:
Remove White Powdery Mildew from leaves – Get some water (tap water works fine) and some paper towels. Wet the paper towels and use them to gently wipe the mildew off the affected leaves whilst being careful not to jostle any leaves with spores on them. Using a wet cloth will ensure that more spores stick to the cloth instead of becoming airborne. Note: While it isn’t necessary to use paper towels, their disposability helps to curb the spread of spores from one leaf to another.
Ensure plants have proper airflow and ventilation – Even if you have absolutely no airflow or ventilation in your grow room, having just two fans will drastically reduce your chances of encountering WPM while also benefitting your plant’s overall health. One fan should be oscillating if possible and should gently blow air over your plants. All the plants need is enough air to gently rustle their leaves which will make it hard for WPM to settle down. The second fan should be in your grow room pointing outward to exchange old air with fresh air. Having a fan pointing out of your grow room will force old air out of the room, and in turn, pull new air into the room. At this point, you’ll have new air coming in, being used and circulated, then kicked out. Keep in mind that two fans is a minimum .
Treat the infected plant with one of the options below to kill spores prevent future growth – Mix up your treatment of choice in a clean sprayer/mister. We recommend Lost Coast Plant Therapy (1oz/2btsp per gallon of water) or GrowSafe (2oz/4tbsp per gallon of water) as a safe second option . Make sure to consult the instructions on your treatment of choice to find the recommended dosage. Wait until just before your lights for off for the day and mist your (newly cleaned) plants. Get all the leaves even if you don’t see WPM on them!
There you have it! If you end up running into White Powdery Mildew, give this advice a shot and you won’t have to deal with it past that first day. If you do end up using these steps, feel free to let us know if it helped you or not, or how you did it differently. When growers know just a little bit about this plant disease, it doesn’t have a chance!
White Powdery Mildew Defense
What’s the easiest way to fight against White Powdery Mildew?
Have it completely outgunned!
Get the right stuff to let White Powdery Mildew know that your grow room is off limits!
Lost Coast Plant Therapy – Kills WPM as well as a bunch of other pests and it’s safe for flowers, pets and people!
GrowSafe – Another safe-for-buds pesticide that kills WPM and other pests. OMRI listed as organic!
Note: SM-90 is no longer available! Find out more here: What happened to SM-90?
Handheld Mister/Sprayer – A mister is awesome for applying treatment. Also, it’s the best way to foliar feed your plants!
Bonus! Papaya cannabis strain – The strain Papaya is potent, flowers early, and – most importantly – is disease resistant!
White Powdery Mildew (aka White Powdery Mold) can be the cause of white spots on your leaves that looks like patches of flour. Learn how to get rid of it!
Powdery Mildew fungus on marijuana plants
In recent years, the marijuana plant is becoming increasingly sensitive to the attack of the fungus called Powdery Mildew, also known as Oidium or White Mold.
It’s a parasitic fungus of the family of the erysiphales, which attacks the aerial parts of the plants.
Although this infection is relatively easy to cure, it can bring serious consequences, because it can cause damage to crops leaving them absolutely useless. In a first phase it develops on the leafs, to extend then to the petioles, stems and finally the buds, completely destroying the resin and leaving the marijuana plants totally unusable for smoking, since the spores of the fungus are solid matters that we would absorb during its inhalation.
Bud infected with Powdery Mildew
This pest affects both indoor cannabis as well as outdoor or greenhouse crops; for its propagation it needs strong humidity variations, a situation found very commonly in crops under artificial lights and in greenhouses. Outdoors the plague is more seasonal and usually appears more often in spring and autumn.
Powdery Mildew is a fungus that is easily diagnosed. It manifests as a typical white powdery that can be confused with dust on leafs and buds. In a second phase the attacked leafs become yellow and end up drying.
Powdery Mildew is an external fungus and its behaviour is very similar to that of sucking insects, since its small spores are carried by the wind and when they lay down on a leaf they put down rootlets that suck and absorb nutrients from the plant.
Powdery Mildew in indoor marijuana crops
Indoors, as we mentioned before, Powdery Mildew is an increasingly common disease and in some cases it’s necessary to take preventive measures from the beginning of the crop, but what will help us more to avoid this pest is to control the climate of our growing space. The aim is to prevent that the relative humidity of our growroom neither exceeds 65% nor goes down under 40%. To do this perhaps we will need a humidifier, to avoid that – with the lights turned on – the humidity doesn’t descend too much due to the effect of the heat from the bulbs. During the night hours of our plants, we should adjust the ventilation so that plants don’t produce condensation inside the growing room. In extreme cases we can use a de-humidifier. Another detail that can help to prevent the propagation of the fungus is to leave enough space between the marijuana plants, because shady areas are formed in the lower parts of the plants when they are too close, what favours the appearance of Powdery Mildew.
If you can’t avoid the ups and downs of your hygrometer, you can use preventive phytosanitary treatments.
Powdery Mildew in outdoor or greenhouse crops
Fungal infection of Powdery Mildew
In outdoor cannabis plants, the plague of Powdery Mildew appears with a certain seasonality, being Spring and especially Autumn the seasons with more propensity to get this disease. To prevent it, we should keep plants free of dried leafs and avoid planting them in areas with few hours of sunshine. If we grow in plant pots it’s convenient to turn the pot to make sure that all parts of the plants have a good exposure to sunlight. We also should avoid placing the plants too close to one another. It’s important that the air can circulate between them.
In greenhouses we should try to have a proper air circulation. For this, it’s recommendable to install some ventilators inside the greenhouse to force the air movement.
In autumn it’s recommended to realize preventive biological phytosanitary treatments, specially if we live in areas whit fog and mist.
Control of the Powdery Mildew
Within the biological treatments for the control of Powdery Mildew, we can find products like Propolix, Oidioprot from Ecoprotect or Ospo. They are two products of proven efficacy, but due to the high resistance of the fungus, we should make the treatment each 10/12 days until 10-15 days before harvesting our plants.
Macro of cannabis trichomes degraded by Powdery Mildew
There are also chemical synthesis products on the market like the Anti-Powdery Mildew from Compo, which can be used if we have exhausted the possibilities of biological origin, always taking into account that we have to respect the safety term that in this case is about 30 days.
Although in many books and gardening manuals it’s recommended the use of sulfur as a biological remedy to control powdery mildew, we do not recommend to use it with cannabis plants, given that even if we make it with great precocity, the smell of sulfur stays impregnated in the marijuana plant.
What is Mildew and how to combat it ?
When and how to move marijuana plants outdoors
Fungus gnats and cannabis plants
Caterpillars on Marijuana Plants
How to control Whiteflies on marijuana plants
How to combat aphids on marijuana plants
Comments in “Powdery Mildew fungus on marijuana plants” (42)
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 .
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
I watched a video from Jorge Cervantes, and he washes his buds in a H2O2 bath then rinses and hangs to dry.
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!
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
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!
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?
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!
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?
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!
[email protected] 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.
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!
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
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!
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
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!
Thanks for the quick response! I’ve got some 9% h202, at what ratio should i mix it? Thank you
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!
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
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!
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.
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!
do you know what the mix ratio would be using certified 35 food grade hydrogen Peroxide?
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!
Peroride to water ratio and will water milk mix work for indoor grow
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!
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!!
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!
Would buds lightly stricken with PM present a health problem if used for making oil/butter for edibles?
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.
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?
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!
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?
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!
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?
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?
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!
Can I wash my buds after harvesting to get rid of pm or can I make cannabis butter with it and use it? Ty
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
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
Great post. Thanks for sharing this detailed information about powdery mildew. Please share use of UV technology for treating powdery mildew.
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!
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.
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!
Thanks for sharing this information with us. Can we use UV technology for treating the powdery mildew.
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!
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.
susan gibson 2017-09-12
I used water and milk at a 60/40 ratio worked GREAT.
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!
Great Post. Thanks for sharing this post. powdery mildew is very common in plants. Can we use UV Techonlogy for treating powdery mildew?
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!
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.
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!
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.
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! 😀
Mixture of milk and water sprayed on plant works wonders
Dani Alchimia 2016-10-10
Hi JoeR, Thanks for the tip dude, I’ll try that for sure! 😉 All the best!
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
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!
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
Dani Alchimia 2016-04-26
Hi jack, Thanks for your comment, we’ll surely take a look at that product. Best vibes!
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
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.
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
big snapz 2016-03-23
Can I smoke my buds if they have a lil p.m on them
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!
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!
Dani Alchimia 2016-03-10
Hi Brendan, Thanks for your contribution! All the best! 😉
can you smoke white powder if on your marijuana plants?
Dani Alchimia 2015-11-27
Hi Steve, Fungus spores can really hurt your lungs if you smoke them. What you should do if you have plants with fungus is extracting the resin (dry sift, bho, etc.), mixing the resin with ethanol (Qwet) and then filtering with a 0.2 micron syringe filter. In this way you remove all spores and have a very nive cannabis concentrate. Hope it helped!
Excellent point Dani regarding prevention. Recently my grow became infected with powdery mildew and man is it hard to get rid of. I ended up using Green Cleaner. Worked get for me but sadly it was too late for a few of the ladies
Dani Alchimia 2015-10-15
Hi Glen, I had issues with powdery mildew for some years, although somehow it has vanished for the last 2 years. What worked best for me was penconazole, I used it twice during the pre-flowering stage and the plants were free from powdery mildew for all the bloom poeriod. Notice it is a systemic chemical. Still, I’ll always recommend preventive treatments with organic fungicides like Oidioprot. All the best!
Bert Shumaker 2015-09-17
u have to vaccinate while in vegging
Dani Alchimia 2015-09-17
Hi Bert, That’s something I always say to novice growers: it doesn’t matter if you don’t see molds or insects, always use some kind of preventive during vegging/pre-flowering and you’ll make sure to harvest your plants healthy. Thanks for your comment, Best vibes!
Chris Walters 2015-01-09
I’m trying a vinegar based spray and I still have sporadic mildew spots! Any suggestions?
Dani Alchimia 2015-01-12
Hello Chris, The first option would be raising a bit the concentration of vinegar. Another option is sublimated sulphur, or spraying your plants with natural orange juice. You can also try some of the products listed in this post, like Propolix or Oidioprot. As the last option, you can try systemic fungicides like penconazole, which are highly efficient. However, we don’t recommend using chemicals since they are dangerous and harmful for both our health and environment. If you have powdery mildew in your area, you will see it often. Get used to the idea of fighting against it, and treat your plants from seedlings regardless if you see powdery mildew traces on them. If you have a garden or backyard you’ll have to treat all plants too, since spores can easily enter your indoor growing space from the outside. The point is having clean plants so they can flower without the need to spray their flowers during the blooming period. Hope it helped, Best vibes!
Powdery Mildew is a fungus that is increasingly present in marijuana crops. If it isn’t done an appropriate treatment it can be very damaging to our