Preventing and Treating Bud Rot – Botrytis

Rambo December 12, 2011 46
Preventing and Treating Bud Rot – Botrytis

Sooner or later everyone growing marijuana indoor or outdoor will have to deal with the ravaging affects of a Botrytis cinerea outbreak.  This necrotrophic fungus is commonly referred to by marijuana growers as gray mold or bud rot, and once infected can destroy your entire garden in a matter of days.

Description and Identification

Botrytis usually first attacks marijuana plants from the inside of the thick buds a few weeks before harvest. Because the infection begins near the stem, it can be difficult to detect until it has become well established. Often the first telltale sign of Botrytis is a single leaf protruding from the kola beginning to wither and dry out. Botrytis can be spotted by bending larger kola slightly to reveal the interior of the bud and stem. If your buds are infected you will see either a gray, white, or blue-green mold with hairs growing on the inside of the bud. In wet and humid conditions this will turn the bud to slime. In dryer climates the affects of botrytis appear brown or rust colored and will crumple when touched.

Botrytis can also attack leaves, stems, and seedlings causing damping off. It should be noted that even dried and stored marijuana is not safe from botrytis and should be inspected regularly. If an outbreak is left unchecked, botrytis can spread to all of your plants and entirely destroy your garden in as little as a week.

There are many genetic varieties of Botrytis cinerea but all persist through the winter months in the form of sclerotia or mycelia.  In the spring, both the sclerotia and the myscelia produce conidiophores which grow millions of asexual spores (conidia) that are then spread by wind and rain.

Because of prevalence of Botrytis cinerea spores in nature, this fungus affects many species of plants besides marijuana.  Vineyards are often infested with Botrytis where it can either rot bunches of grapes or change the grape chemistry, making them actually more suitable for certain types of wine.  Botrytis also can cause significant damage to strawberry plants and tomatoes grown in greenhouses.

In dealing with Botrytis, nothing could be truer than “an ounce of prevention is worth a pound of cure”. While Botrytis is probably the most prolific mold found in marijuana buds, there are many different kinds of fungal outbreaks that could affect your garden. Luckily, most types of fungus thrive in the same environment, so in working to prevent one, you can effectively decrease the potential for other fungal outbreaks as well. Botrytis thrives in contaminated environments with humid air and poor circulations. A combination of cleanliness and climate control measures can be taken to decrease its prevalence.

Controlling Spores

Unfortunately botrytis spores are nearly impossible to completely eliminate from your grow room or garden. If you are growing marijuana indoors this begins with properly constructing your grow room.

If possible remove all carpet, curtains, fabric and trash from the grow room that could harbor botrytis spores. Cover wood or cement floors with linoleum that can be regularly mopped clean with at least 5% bleach and water solution. If you don’t glue the linoleum down, make sure that its edges are folded up around the baseboards of the room to prevent any spills from seeping under. Thoroughly wash the walls and ceiling with a bleach solution, and then repaint the room with a fungus resistant white paint. Covering floors with plastic or hanging plastic on the walls in not advised as this can trap moisture and create a fungus friendly environment.

Once all of your equipment is in place and wiped down with a bleach solution, treating the grow room with a high dose of ozone can help kill any remaining spores. When the room is filled with plants, you’ll need to make sure dead leaves and debris are never allowed to remain in the room. I’ve been in more than one grow room where the grower removed foliage but left it in the room’s garbage can to rot and spread mold spores.

For those growing marijuana outdoors, remove as much dead foliage from the garden as possible. Keep any grass or ground-cover as short as possible so that it does not trap moisture or prevent air circulation. If possible cover the ground around the plants with landscape cloth to prevent weeds and maximize airflow.

Humidity, Ventilation, and Circulation

In addition to keeping the grow room or garden as free of spores as possible, you must also maintain an environment healthy for marijuana plants, but inhospitable to botrytis. Fungi that affect marijuana plants thrive in conditions with overly wet and soggy soil, humid air, and poor air circulation. These problems can generally all be fixed through adjusting your watering schedule and proper ventilation.

It is very important to maintain a humidity level in your grow room under 50% and a temperature that is above 70 degrees F. To accomplish this, pay careful attention to your watering schedule and make sure you are not over watering your plants. Extra water in the room or pooling up in your garden will evaporate causing the humidity to increase. Warm air holds more water than cool air, so try to water only after the sun is up, or lights have come on and your room has reached its normal daytime temperature. This way the majority of the water evaporation takes place during the warm period which will not increase the humidity of the grow room nearly as much.

In addition to over watering, another common mistake for indoor gardens and greenhouses is using larger containers and more growing medium then necessary. While you certainly don’t want your plants to be root-bound, too much soil means extra expense on nutrients, extra water and extra humidity from evaporation.

CO2 generators produce more than just CO2, they also produce heat and water vapor. The heat will help keep the room above 70 degrees, but the water vapor increases humidity that must be dealt with. Make sure you are only running your CO2 generator during the daylight hours since this is the only time the plants benefit from CO2 anyway.

If you are running a sealed grow room or the air outside is above 50% humidity a dehumidifier can quickly and inexpensively remove extra moisture from the air while helping to heat the room. A 30 to 65 pint per day dehumidifier is capable of maintaining a grow room the size of a normal bedroom and is available for under $200. These dehumidifiers are easy to use but must be emptied daily, create some heat and generally draw between 400 and 700 watts.

If your grow room uses ventilation to keep it cool, make sure your fan is strong enough to quickly remove moist air sufficiently. If the air outside is above 50% humidity, you may need to stop drawing in outside air and use sealed light hoods and a small air conditioning unit to keep the rooms humidity low and the air within the correct temperature range. Make sure any outside air that is drawn into the room is filtered to remove as many outside contaminants as possible.

In addition to the airflow required to keep the room at the proper temperature and humidity levels, you must also maintain airflow through the plants themselves. Oscillating circulation fans will prevent pockets of moisture and help move air through the plants foliage and across the surface of the growing medium. An added benefit of circulation fans is that this airflow will also strengthen the plants stems so you won’t require as much staking towards harvest. Use selective pruning to remove any unnecessary foliage from the lower parts of the plant and avoid over crowding the plants.


As a preventative measure plants can be treated with foliar sprays. These can be either a non organic chemical based fungicide, an organic fungicide containing copper or sulfur, or they can be inoculated with foliar sprays containing beneficial fungi.

Chemical and copper or sulfur based fungicides can’t be used along with biological sprays because they kill fungi indiscriminately and will effectively wipe out your beneficial fungi along with the harmful parasite. While often effective, the drawback is that chemical or copper and sulfur bases sprays is they can only be used during a vegetative period. These  organic and non-organic chemical sprays can be extremely harmful if smoked, especially for medical marijuana patients, and should never be used after your plants begin to flower.

Biological based foliar sprays containing Gliocladium and Trichoderma, or products like Serenade that contain Bacillus subtilis can be used to both prevent and treat outbreaks of botrytis all the way up until harvest. These species are also fungi’s but colonize plants in a symbiotic relationship protecting them against fugal attacks.


Once an outbreak of Botrytis is discovered it is imperative that you take action immediately. If the conditions are right, an outbreak can spread and wipe out an entire garden of buds in a matter of days. Sterilize your pruning shears in alcohol and cut the bud at least one inch below the affected area. You must be very gentle while removing the bud to prevent spreading the spores. Make sure not to let the bud, your hands or the shears touch any other buds until they have been sterilized.

Once every kola has been inspected, and the damaged areas are removed, drop the humidity in the room as low as possible and make sure the temperature does not fall below 70 degrees. If the humidity can be maintained below 50%, continue to treat with biological foliar sprays all the way until harvest. If the outbreak is already widespread, consider cutting your losses and harvesting the garden early.

Health Problems

Botrytis cinerea may cause “winegrower’s lung”, which is a rare form of hypersensitivity pneumonitis. To a layperson this means an allergic reaction in the lung and airways that affects some who are predisposed. We can’t avoid mold spores, they are literally everywhere, and we smoke some in every joint without concern. Some medical marijuana patients however have compromised immune systems or respiratory problems and can become quite sick from smoking marijuana with high spore content. If your garden has had a severe outbreak of botrytis or any other fungus, it is imperative that you remove all infected bud and have your marijuana lab tested before offering it to patients.

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  1. mahayogi November 21, 2012 at 3:32 am -

    Hey there,

    I have been having issues with powdery mildew recently, and am wondering if it will ever be fully eradicated from my garden? I have lowered the humidity (I live in the Willamette Valley) to around 50% during the night, and 45% during the day hours using a dehumidifier/air conditioner and 6″ vent fan w/carbon filter. I have increased air circulation drastically, and have been treating my entire garden once a week with Neem oil concentrate, via root drench and foliar spraying. Despite my efforts it keeps rearing its ugly head. I feel like I’m making progress, but I want your opinion. Please help! Let me know if I will be rid of this plague soon/eventually, or if I need to start anew from seed. FYI: Mildew popped up during October when the rainey season started and the humidity spiked to around 80% at times for more than a week. Thanks for your help : )

    • Rambo November 21, 2012 at 4:11 pm -

      Powdery mildew can be very difficult to treat and even harder to get rid of completely. If possible drop the humidity in your room even lower. Neem oil can help but you may have more luck with a sulfur based product if the plant has not yet begun to flower. Burning sulfur always helps a lot. I have never heard of anyone using neem oil as a soil drench and I would advice against it. Your roots probably don’t have mildew and the plant won’t uptake the neem so all you are probably doing is damaging the roots. A few people I’ve talked to are having luck treating plants with UVC light. I haven’t tried it myself but will probably give it a shot this winter if PM becomes a issue for anyone I know. Even if all visible signs are gone, it can pop back up very quickly. This is why clones purchased from dispensaries are so often problems, they can look fine one day and like snowballs the next. Best of luck to you.

    • donwilshe December 25, 2013 at 7:16 am -

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  2. LE May 29, 2013 at 5:33 pm -

    HELP ! I need any info about Botrytis and lung infection.

    My husband is very sick with a fungal infection that can’t be identified. He got a bag of buds from a friend who traveled to Portland OR in February and again in March.
    It was grown indoors & looked really nice. perfectly uniform buds, red hairs, but not really mature looking. no seeds or sticks-just perfect little buds. No visible mold or powder. VERY PUNGENT. Practically skunk.
    One hit made me dizzy and light headed. I tried another time and same thing, so I didn’t smoke any.
    The taste/sensation was almost chemical.
    Husband smoked appx 2 oz. in 2months and is now very very ill, day 9 of hospitalzation.

    We live in northern Virginia (DC area) and everybody seems clueless about what it could be.
    He has asthma, so he may be affected by something that wouldn’t bother most people.

    Please…if anyone has any clue or theory please share. Thank you.

    • Rambo June 10, 2013 at 11:09 am -

      I’m sorry to hear about your husband. I have never heard about anything like this. I would doubt that it had to do with Botrytis but it’s not out of the question. If there is any coloration between smoking the cannabis and his illness, it more likely has to do with any number of pesticides or fungicides that may have been sprayed on the plant.

  3. Taylor August 23, 2013 at 4:10 pm -

    Some people told me to shred old leaves to pieces for feedind them to the plant (by mixing them to the soil at the bottom of the plant). After reading this article it might seem to me that this could be a bad idea, could you comment on that. Thanks!

    • Rambo August 23, 2013 at 11:17 pm -

      This is a bad idea. Feel free to throw them in the compost pile for outdoor gardens but there is a difference between compost and throwing dead leaves in your soil.

  4. Taylor August 23, 2013 at 4:17 pm -

    PS. I’m growing outdoor. Thx

  5. Sue August 27, 2013 at 8:35 am -

    I am growing outdoors in SoHum. this is the first time I have been hit with powdery mildew and I am scared to spray anything on my girls. they are starting to bloom. can I use Serenade? will it affect my status as organic? what about an aftertaste?

  6. JT August 31, 2013 at 8:06 am -

    Bud rot sucks. one minute you think you have a cannabis cup quality cola, then you get one little yellow bud leaf, look inside and its green toothpaste. There is hope though, 1. chop out bud rot, shed some tears and move on.2. chop up the bud that wasent affected. 3. take the bud and make bubble hash right away, you wont get much due to the bud being moist but it will be some of the best blonde hash this planet has to offer4.smoke it and enjoy being extrmely roasted thanks to your beautifull cannabis plant .5. bud rot solved in 5 steps

    • Rambo September 3, 2013 at 12:25 pm -

      I disagree with step three. Why not let it dry. Also making buble has from moldy pot does not mean you have removed the mold. Now you are just introducing water to an already moldy situation.

  7. carl September 11, 2013 at 11:19 am -

    I had what was believed to be a healhty , thriving, mature 24 plant crop until , thanks to your site, I discovered the gray plague. My 1st thought was it was some horrible insect etc.Then I found the gray death hiding in the buds. After multiple organic sprays, I have lost 50% or more of crop. I’ve grown for decades and have never seen anything like it.l live @6800′ 8n Colorado and have never had humidity isssues until this year.I grw in a green house and think my tomatoes could have been the sponser. I tried Seranade, Actovinox, baking soda solution, Ed Rosenthal’s, and ablend of Rosemary, Citronella, and Tamanu oil.The last combo seem the most effective, but once in buds, you’re pretty much screwed.

  8. Dr B ud September 19, 2013 at 5:46 am -

    Rambo, Any ideas for treating my greenhouse soil for mold/mildew spores? This years crop is getting hammered by bud mold although I’ve gotten the PM under control. Dropped my watering to when needed, have good air movement, and opened up the plants. This winter would like to address this problem during my down time when I’m doing my dormant soil amendment. May treat this year with copper fungicide worried about contaminating my colas. Cropped early those plants with severe bud mold problems. Your thoughts? Thanks

    • Rambo October 2, 2013 at 8:41 pm -

      You can buy bulk sulfur powder that is used for spraying grapes etc. That could be sprinkled on the ground but not sure if it would do any more good than harm. There are always going to be mold spoors present not matter what you do.

  9. steve C September 22, 2013 at 6:11 am -

    can I use a vaporizer after I sprayed my girls with sm90 when 2 weeks in,could that hurt me .

    • Rambo October 2, 2013 at 8:34 pm -

      I don’t know much about SM90 but it appears to be plant oil based so you should be fine. This product does not seem to be meant for best control though. I believe this is a surfactant made to reduce surface tension and encourage root growth. Probably made from yucca.

  10. steve C September 22, 2013 at 6:30 am -

    I am new at this so I asked a friend if I could spray my plants with sm90 to control pests,he said it shouldn’ t hurt them if they were marble size.was he wrong.have I ruined my crop ? what can I do with them now? thanks for any help you can give me.will I be able to salvage any of the crop? even a vaporizer?

    • Rambo October 2, 2013 at 8:23 pm -

      If what is marble sized? the Buds? I try to not spray anything on the plants while they are flowering. Any residue left behind can leave a fowl taste. That being said I doubt you harvest is ruined.

  11. Doug September 23, 2013 at 8:59 am -

    So can infected bud be salvaged in any way? To make tincture or butter? I’ve probably got it on close to a third of my small crop. The buds are looking so good, I really don’t want to composte them. What can I do?

    • Rambo October 2, 2013 at 8:19 pm -

      Cut out as much as humanly possible. Drop the humidity and harvest as soon as possible. Dry quickly and then cut out any further traces of mold. This won’t be good medicine for someone who is sick but won’t be dangerous for most people as long as you get the mold out. The parts that are moldy are garbage but the rest of the bud could make good and safe hash oil or tincture.

  12. Johnny September 29, 2013 at 10:52 am -

    So if you can’t make hash, what do you do? I heard of “flash drying” hear your room above 80, drop humidity, and that stops the mold from growing?

  13. Daniel September 29, 2013 at 2:33 pm -

    I have a large kola hanging up in my dry room. I have just noticed signs of botrytis on the bud. Is there any way to save the bud and safely kill the mold? Or should I cut my losses and throw it out?

    • Rambo October 2, 2013 at 8:01 pm -

      Cut the moldy area out of the mud and throw it away. The rest of the bud should be ok but try to dry it quickly then inspect for mold again once it is dry. Not a bad idea to isolate that bud from the others if possible.

  14. dre October 4, 2013 at 7:18 pm -

    I just found some brown mold on my outdoor plant . The Pacific North West brings a lot of rain this month. All the brown has been cut away, not too bad. Is there any advice how to finish the buds in this climate?

    • Rambo October 8, 2013 at 8:54 pm -

      All you can really do is keep them as dry as possible and harvest as soon as possible. In the past I have had some luck blowing the water off of plants with a leaf blower once the rain stopped but its easy to damage the plants this way as well.

  15. maximus October 7, 2013 at 8:18 pm -

    Tnx,very nice info!

  16. nappybutbald October 16, 2013 at 7:47 pm -

    I was hit with the Bud Rot crap this year out doors the one thing I found that really works and can be used up till harvest but I would not recommend. I let it dissipate for 15 to twenty days then started my slow harvest to test for taste of the product so far great. CAPTAN FUNGICIDE this stuff is used on strawberries, grapes, and most fruits and nuts. I found this at our local hydroponic store and was recommended by the staff.

  17. nappybutbald October 16, 2013 at 7:51 pm -

    It stopped the rot immediately !!! I used it twice within a 10 day period and stopped, last treatment was 20 days ago, harvest is within in two weeks.

  18. Mark S Jones October 31, 2013 at 3:50 pm -

    I haven’t seen using a dehydrator mentioned ?

    I’ve never had these problems before, and I’m learning so much for the future, but for now I’m determined to probably be stupid and smoke it anyway…

    Thank you for the best information I’ve found anywhere!

  19. Organic Toker January 4, 2014 at 3:01 am -

    Hey Rambo,

    A very good read with lots of info.

    I have one question, as Pseudomonas spp bacteria is a bio-control against fungal pathogens, will a foliar spraying schedule soon before flowering decrease the chances of bud mold?

    Thanks and keep up the good work!

    Peace out!

  20. Susan April 15, 2014 at 1:04 pm -

    Can I treat my soil with a safer fungicide sulfur to prevent mold before I clone. Or will clones root in soil treated this way?

  21. Sorelle May 17, 2014 at 2:30 pm -


  22. Sorelle May 17, 2014 at 2:43 pm -

    I live here in NorCal Humboldt area and bud rot or Mr. Bo as we call it is like a death sentence! It hits fast and is almost impossible to stop! The best way I’ve even saved 50% of a crop, once hit, was by putting on gloves, getting a jar of bleach or alcohol and carefully very carefully snipping out infected bud, put into a bag then dip scissors, dip hands and repeat! It spreads so fast by touching an infected bud bc the spours just explode! Everything mentioned above are great ways to prevent! Less humidity, air circulation, and not to over water plants! But under watering them can cause powder mildew too! Such crap! Sprays like Serenade can be helpful, and suffer bombs too but they can also burn plants! Stress them out! Growing in a greenhouse, on the coast, with a ton of moisture in the air via fog! Also doing them dep in the past causes all sorts of problems under the tarp at night! I’m amazed at how much we actually saved! Most ppl would of thrown in the towel!!!! It’s such a bummer when u spend so much $ and time on your girls just to have to literally throw them away in the end! Always hits the worst at the end too when everything is so beautiful and then boom! Ok vent over, but I’m pretty sure I’ve seen very few outdoor GH grows that at some point didn’t get spider mites, powder mildew, stem rot, or botritus!
    I hope by adding more fans, starting earlier in the year and not allowing plants to get so big (stems hold a ton of the moisture) and possibly getting a de hum for end that maybe, hopefully, fingers crossed we can avoid this plague!!!!

  23. Disgusted May 22, 2014 at 1:32 am -

    I bought some Girl Scout cookies at the local dispensary and it tastes so strongly of sulfur I do not want to smoke it. It taste like poison!
    is the sulfur actually harmful to my health…
    I’m so pissed off.. I asked a friend of mine who works at the dispensary occasionally and he said oh we don’t use that supplier anymore he sprayed all of this stuff with sulfur While he was curing. And so we’re just trying to get rid of it right now. I paid top dollar for what is supposed to be medical grade marijuana only to find out that they knew the whole time and it’s now clear to me that profits are more important than patients safety..
    Dispensaries like umpqua green cross are gonna ruin it for everyone… I’m considering calling the health department and the FDA and the AMA And maybe the DEA…
    Four hours ago I took two tokes off a bowl and had to throw it away. It was like smoking a bowl full of burnt match heads…
    And I have been suffering a pounding headache for the last three hours… Am I going to die???

  24. john daly June 9, 2014 at 6:29 pm -

    How bad is smoking unflushed weed for you iv flushed for 5 days 10 to 15 ltr of h2o but dry fast it was crap whats the best way to dry?i only have a small closet but it always smells funny

  25. Max June 10, 2014 at 7:02 am -

    Wow, superb blog layout! How long have you been blogging for?
    yyou made blogging look easy. The entire glance of your web sitee is fantastic, as neatly as the content!

  26. justjess June 26, 2014 at 3:23 am -

    H my pants have just sprouted and I move them inside to outbecause thenights get super chill. Anyways I left them outside one night and the best looking sprouter had looked like it snapped. But it actually had gotten super thin and fallen mid stem. And is now drooping severely but the leafs are still green with a noticeable dark underside. the other ones won’t leave the soil or seem to be dieing or the little leafs are curling up and turning yellow. I noticed the soil stays really wet. I’d this bud rot Did I mess up my plants. Please help Idk what to do this is my firs attempt growing was so looking forward to it. Also of out makes a difference I herniated my seeds in a paper towel

  27. David Anderson July 2, 2014 at 7:31 am -

    Rambo! I’m growing outside in Spokane Washington. First outdoor grow. I know that my plants will go into flower naturally on 7/21. Which has them finishing in late September. How do I ensure that in the later weeks im able to finish out flowery cycle without having to cut early because of mold. Would a covering help? Or should I force them week or two early with light deprivation do they finish early September? Please help!

  28. Brodie July 7, 2014 at 8:06 am -

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  29. Eloisa July 11, 2014 at 1:03 am -

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  30. Crownboy July 22, 2014 at 5:25 pm -

    At the first sign of mold, in northern climes, remove the offending mold and harvest immediately. I have to when growing outdoors on my deck.

  31. Maximus August 1, 2014 at 10:22 pm -

    Hi man,
    mold is one of the worst enemies of canabis.
    I would add that, even adding inert material in the cultivation medium such as perlite or expanded clay, helps oxygen to the roots and thus reduces risk oidio / botrytis.
    Its details are very useful, thanks for sharing!

  32. Adam August 19, 2014 at 7:21 am -

    Ok so my plants are 40 days into the flowering cycle and have looked amazing up until the other day….suddenly 3 out of the 4 plants fan leaves are turning yellow and this is happening very fast….the 4th plant does not seem to be affected thou. I know its probly to late for these but any help would be great!!! Thanks!

  33. Adam August 19, 2014 at 7:34 am -

    P.S Two of the 4 plants hairs that are affected haven’t even started to turn color. The other one is about 50% colors in the hairs as is the one that isn’t affected.