Bud rot (also known as gray mold or botrytis) is one of the most devastating fungal diseases to hit marijuana crops.  It thrives in cool temperate climates where a high level of humidity is present.

It is so harmful to your plants that it could destroy your whole garden of marijuana plants in less than one week! It will kill anything in its path, including seeds that are sitting in the soil and very young plants that have only just popped up.

It’s a marijuana grower’s absolute worst nightmare. You, therefore, need to do everything in your power to keep gray mold from infesting your precious plants.

What is bud rot

What is bud rot cannabis

Gray mold (bud rot) is a fungal disease that lives best in cool, humid, temperate climates. It is not location-specific and it attacks marijuana plants in all stages of life.

Gray mold comes from a fungus called Botrytis cinerea. This fungus can rot your buds from the inside out – thus gray mold’s nickname, “bud rot.” Botrytis can ruin other plants besides marijuana. Wine grapes, strawberries, and peonies also can be devastated from a gray mold infestation.

Download my free marijuana grow guide at this link for more growing tips

Gray mold can reach your plants any time through its dusty gray spores that are often transported through blowing in the wind as well as water. Plants need to have actual contact with gray mold spores in order to get bud rot – otherwise it is impossible. These spores are extremely easy to transport, unfortunately.

Once they have reached your site, they get inside your actual plants by entering through a “wound” or tear in the external plant tissue. If you train your plants, their stems might have cracks that mold could travel through. Any damage caused by caterpillars, snails, worms, mildew, or other pests can also create a “tunnel” of sorts for gray mold to get inside your plant.

Signs of bud rot

Signs bud rot cannabis

Gray mold bores into the youngest stems right where the soil sits and then turns these stems brown, making them soft and rotting. The stems then lose rigidity and fall over, or “damp off.” Gray mold also likes to attack the stems of older, more mature plants.

It first forms a brownish gray mycelium mass, which looks like a foundation of sorts. This then starts being covered by fungal spores. This sort of smothers the plant, making it turn yellow because it doesn’t have enough chlorophyll to remain its healthy green color.

If the gray mold circles all the way around the stem, it will weaken it until it has lots of cankers and is actually soft. There will be breakage where the cankers are, and any growth above this hub of disease on the stem will start wilting.

That is only part one of gray mold’s devastating behavior. After it’s attacked the stem, it will next move on to your female marijuana plants’ moist buds. The leaves will start turning brown and will wilt, and then the pistils will follow suit. The buds will eventually be totally covered in the gray mycelium and will turn into a grayish brown slime – making them totally useless when you harvest your plants.

Download my free marijuana grow guide at this link for more growing tips

Gray mold materializes in different ways. It can affect only the biggest and fattest buds of your plant, or (especially if conditions are particularly wet) it could form visible spots all over the plant. The cola might also be the only part of the plant that starts to turn darker and discolored, and maybe is even drying up.

The outside of the buds will look like it is drying in parts. The rest of the plant, on the other hand, may still appear to be thriving. Gray mold will always target the wettest spots on your plants first. If your plants have large colas, they have a large area inside that receives no air exposure and is therefore very moist. This means that this attacker is very likely to target these big colas first.

People generally start to notice a gray mold infestation once they notice deadened spots on their marijuana plant. It might also show up as white mold on the bud’s exterior at the beginning. If you catch it at this stage, you should take immediate action.

If it is indeed gray mold, you will be able to see that the inside of the bud is a dark gray or brown and appears to be dusty. Unfortunately, since gray mold moves so rapidly, it is unlikely that you will catch it when it is white and fluffy in its early stage.

You are most likely to find yourself with a gray mold problem if your plants are growing in a low-light environment. It is called gray mold because, although it starts out a powdery white color, it turns into brown or smoky gray color. Once you see these and other colors, you will know that the damage to your plant is already extensive.

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

How to get rid of bud rot

Get rid of but rot botrytis and grey mold weed

Now you probably understand the importance of avoiding gray mold from growing on your marijuana plants at all costs. If you are an indoor grower, there are certain steps you can take to decrease the chances of it ever becoming a problem. First and foremost, your plants need a warm, dry, breezy environment to live in.

For instance, you should always keep the grow room temperature higher than 70 degrees Fahrenheit, and don’t make the room so humid that your plants are visibly wet. The humidity should be kept below 50% at all times. These elements cannot be controlled in outdoor environments, of course.

Keeping your plants’ leaf density down is also a good way to increase air exposure and, therefore, decrease the likelihood of gray mold developing on your plant. Just be sure you don’t take away too many leaves because you still need as many as possible to keep pumping light energy into your plant for a successful flowering phase and harvest. Prioritize which leaves you remove by targeting ones that are covering other leaves or sites where buds grow.

Download my free marijuana grow guide at this link for more growing tips

If you are an outdoor marijuana grower, hopefully, you started your growing season off right by choosing a strain of marijuana that is well suited to your specific climate. If you live in a rainy and cool area, for instance, you should probably choose a strain that is specifically designed for cool, rainy climates. One such strain would be one that automatically enters the flowering phase, meaning its life is shorter than an average marijuana plant.

You can take some extra steps that you might not have thought about as well, such as changing your clothes before stepping into your grow room. This will limit the spores and pests that can be carried in via your clothes. If you have a house pet, keep it away! They can easily transport fungi and other living things you won’t want near your plants. You should also sanitize pruning shears every time you plan on using them so as not to transport any fungi or bacteria from the blades to the plants. Most of these precautions will work the same for outdoor grow areas as well.

If you water your marijuana plants during the day rather than at night, your plants will have an adequate amount of time to dry off before darkness falls again. This same principle can be applied to indoor gardens – just make sure you water your plants early enough so they can dry before you turn off the lights. Gray Mold loves moisture and darkness, so at least take away one of those elements to lower the chances of it infecting your plants.

One of the most important ways of keeping it from finding its way to your plants is to keep proper ventilation within your grow room. The moving air should go through every bit of every plant. Don’t be afraid of working hard during this tricky planning process.

You can also be more active in the prevention of gray mold. Try spraying bacillus subtilis or an oil spray with neem oil or sesame oil onto your plants to prevent it or form a barrier that doesn’t let mold germinate. You can also look into using Potassium Bicarbonate (KHCO3) to keep from molds and fungi from starting to grow. This is an organic product that comes from humans, animals, and plants – it is a sort of pre-existing self-defense system.

Download my free marijuana grow guide at this link for more growing tips

If gray mold has found its way to your plants despite taking all these precautions, all is not lost – at least not yet. If you spot a plant that is clearly diseased or dead from gray mold, remove it completely and destroy it. Do this to every plant you see that has the infestation. Obviously don’t add the destroyed plants to your compost pile, since it would cause even more problems. Simply put the whole plant into a sealable plastic bag and throw it away tightly sealed.

If you are absolutely dedicated to keeping your plants where they are instead of discarding them immediately, you can instead prune the affected leaves and buds. Once you have used pruners to remove the affected parts, clean them thoroughly with rubbing alcohol or peroxide.

Another method commonly used is the application of a bordeaux mixture made up of copper sulfate and slaked line. This is what most vineyard owners use to keep gray mold under control. Copper soap or copper spray is another option that can actually be used all the way until your plant’s day of harvest. This works best when it is sprayed onto your plants each week for ten days. Finally, you can either use sulfur burners or spray your plants with sulfur in order to make the treatment airborne. You can find these at a garden center or nursery.

In general, your best way of preventing it from getting out of hand is by always being aware and keeping a close eye of your plants. Inspect them regularly for signs of gray mold or any other potentially harmful conditions. Take note of any changes, especially when your plant is in the later stages of its flowering phase.

Keep an eye the weather, as well. It could tell you a lot about when to be the most suspicious of gray mold, such as just after cooler temperatures and rainy days. When you do know that rain is coming, you can simply cover all of your plants with a tarp to block the worst of it. Make sure you don’t actually put the tarp on top of the plants because it would risk damaging your buds. Instead, hang it above your plants for maximum protection. Make sure the tarp is held up by the middle rather than the sides so as not to allow the water to collect in the center. An alternative would be to simply go to your plants after a rain and shake them. This will keep water droplets from becoming a comfortable place for the mold to breed.

Marijuana plant sypmtoms

– Edges of leaves will look brown or burnt
– Leaves turn darker or purple in color
– Spots on the leaves
– Abnormal growing of the leaves
– Visible mold

Other Advice
It is never a good idea to use fungicides while your plant is in its flowering stage. You also shouldn’t spray the buds that have been affected with Neem oil or burn sulfur when your plants are in their flowering phase. It won’t provide an effective means of combating gray mold, and it will ruin the taste and smell (and appearance) of your buds, thus making all your hard work pointless anyway! Fungicides are only okay to use during your plant’s vegetative phase of life.

As a good rule of thumb, you should know once you have a gray mold problem that the environment that your plants are growing in too cool and too humid with not enough airflow. If you are growing indoors, once you have removed the original gray mold this is something you should change immediately so as to avoid future infestations of gray mold.

If, however, you are absolutely unable to change your environment (i.e. if you are growing outdoors), you need to be realistic with yourself. The climate isn’t going to change, and your plants have already been infected once. Do you really think that this will stop being a problem as soon as you discard the plants that have visible signs of bud rot? Probably not.

Download my free marijuana grow guide at this link for more growing tips

Instead of attempting to make it work somehow, it’s better to simply start an early harvest of all your unaffected buds. Having buds that were harvested early and therefore never reached their full size and potency potential is still far better than losing most of your buds to gray mold.

If you do harvest them early, you need to be especially careful during the drying process when mold can become an issue. While generally you would want to try and dry your buds through a slow-drying process, in this case, you should dry them as fast as realistically possible with lots of consistent air movement.

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

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

Robert

58 Comments

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  1. By Jerry

    ,02 Nov 2013
    If budrot attacks can I cut buds into som iso and save Hash?
    Was this comment helpful to you?
  2. By Kimberly

    ,17 Aug 2014
    Hi…I have one out of 15 plants that is displaying a bunch of grey mold on the stem. Is there anything I can treat this with before it effects the actual budding process? Im about a month or so from […]Read More
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    1. By Shawn krupa

      ,20 Aug 2018
      There’s a stuff called trifecta crop control this stuff is perfect you could use it all the way up to last week of flowering
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  3. By joe

    ,17 Oct 2014
    wont the copper sulfate on the buds combust when the weed is smoked? I heard the fumes are really toxic
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    1. By Calvin Hopkins

      ,02 Feb 2016
      I grow white widow outdoors. Bud rot is always a huge problem. Here in Florida in the summer it is neither damp or cool in the summer time. I have has fair success clipping off the rotten buds and saving […]Read More
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  4. By Symptom Checker – Identify Marijuana Plant Problems

    ,20 Jul 2015
    […] Bud rot […]
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  5. By larry

    ,03 Aug 2015
    Stating the obvious over and over does not kill grey mold.
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  6. By steve

    ,14 Aug 2015
    What about foliar feeding with peroxide to stop gray mold
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  7. By latewood

    ,19 Aug 2015
    It is so hard to suggest remedies for growers without proper input for our expert growers to consider. Please join our support forum, and post a topic with your plant issues. It will be much easier for our team of […]Read More
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    1. By Billy Rippe

      ,09 Oct 2017
      How can I do that?
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  8. By Diseases on Marijuana Plants, and How to Treat Them

    ,29 Aug 2015
    […] Another step can be to change clothes or wear protective gear before going into your grow room. The spores can attach themselves to clothing fibers and then release in the grow room if the environment feels appropriate. If all […]Read More
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  9. By Michael Cicchino

    ,30 Aug 2015
    Hey all, I just finished up a grow last week. my Jack Herer had 5 colas that had bud rot! All that work and I got about and ounce of weed. The colas were beautiful and I saw nothing until […]Read More
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    1. By Jennifer ILGM

      ,31 Aug 2015
      Hey Micheal, Thanks for sharing, So sorry that happened, but it adds to your growing experience, next time you’ll do much better!
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  10. By Tom

    ,06 Oct 2015
    Hi my plants are about 45 day in flowering,soil pots, one is 1 1/2 feet tall other is 2 1/2 and they look about done, most pistils are orange curling down, thick buds trichomes are hazy and dank smelling.I jus […]Read More
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  11. By latewood

    ,06 Oct 2015
    Tom, If it were me; I would harvest before any more damage occurs. Sounds like you were basically finished anyway. 🙂
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    1. By Tom

      ,16 Oct 2015
      Thanks i chopped dried n it came out good. My friends havein the same issue with a larger crop what’s the fastest way to dry!?
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      1. By latewood

        ,17 Oct 2015
        Tom, There is no shortcut, unless you want to sacrifice quality and taste. Make sure you have a lot of good air circulation, but do not have fans consistently pointing in one area of drying buds. If I feel that […]Read More
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  12. By K2

    ,11 Oct 2015
    So here is my take on grey mold. I live in the great north coast of California in the emerald triangle and every year I get accosted by the stuff. Just the other day I was clearing foliage from the […]Read More
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  13. By C

    ,12 Oct 2015
    You have a whole month more to go?? When did you plant? I planted May 1 and I think they’re almost ready.
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  14. By K2

    ,13 Oct 2015
    I got my starts in May. I have read that they take 9 to 12 weeks to flower, after 9 to 12 weeks of veg, and it looks like that is true for this strain..WW. I am getting big coloas […]Read More
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  15. By latewood

    ,16 Oct 2015
    Mold cannot exist in an alkaline environment. If the area you have infected with mold is at the stem base (nodes); You could use a baking soda and water mixture. TBS. peer gallon. The high PH, or alkaline environment will […]Read More
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  16. By Rjones

    ,22 Oct 2015
    I found bud rot in one of my plants. I carefully removed the infected buds, increased the air flow and I’m wondering if the other plants in the green house should be harvested asap, and will the smoke be safe? […]Read More
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  17. By latewood.ILGM

    ,22 Oct 2015
    It sound like your humidity is too high. Is it mold or bud rot? If you remove all damaged areas and dry in a cool dark DRY area, then you should be OK. I suggest you join our Support forum […]Read More
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  18. By Stop Diseases On Marijuana Plants Now!

    ,23 Oct 2015
    […] Another step can be to change clothes or wear protective gear before going into your grow room. The spores can attach themselves to clothing fibers and then release in the grow room if the environment feels appropriate. If all […]Read More
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  19. By Ann

    ,02 Nov 2015
    I also live in Northern CA, growing in a greenhouse. Planted late, early July, various strains but purchased “teens”. , was waiting to see 10% amber before taken down to dry. This is my first grow. There were two large […]Read More
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  20. By Terri

    ,08 Nov 2015
    Hello I really need some help. This is my first grow of medical plants and I have white spider web like stuff on some of the buds, I am now drying the buds and the white stuff seems to be […]Read More
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  21. By latewood.ILGM

    ,09 Nov 2015
    Terri , It sounds like you have a spider mite infestation. I would not smoke any of the bud affected by the webs. You are welcome to join our Support forum if you need help in the future, during your […]Read More
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  22. By Jon

    ,14 Nov 2015
    Thankyou for you concise thorough and honest advice, the author certainly seems a balanced individual Positive vibes coming your way
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  23. By Lucky

    ,29 Jan 2016
    botrytis need uv light to end life cyclus,some sorts are better against b.(read mostly sativas or fluffy indicas),if u sow that your leaves who growes from cola turn mysterius yellow is probably sign of botrytis in your buds,cut them 3-5 […]Read More
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    1. By Jennifer ILGM

      ,01 Feb 2016
      Thanks for the tip Lucky!
      Was this comment helpful to you?
  24. By Kronik801

    ,30 Jan 2016
    Robert has all the information a grower could ever need.Hes spread pretty thin these dayz ,with all the other projects he has going,Bergman lab to name one.im sure that project emptied the pocket real quick.so sell sell,sell to full back […]Read More
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  25. By Kronik801

    ,30 Jan 2016
    P.s. to those who are interested,Customs is on to most of the seed banks an their stealth shipping methods.Be patitent,an in contact with your supplier,daily if need be.that way when you or they are notified of the siezure..you can get […]Read More
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  26. By Tara

    ,03 Feb 2016
    I noticed in the article that Neem oil is suggested as one way to control the problem. I have had intermittent infestations of spider mite, but no fungal problems as far as I can see, however, after reading this I […]Read More
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  27. By Ben gittings

    ,04 Feb 2016
    Hi I have just harvest my crop a week early as I noticed bud rot I removed all Tht I could see of bud rot and left in dark tent with small fan do you think it will be ok […]Read More
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  28. By latewood.ILGM

    ,05 Feb 2016
    Ben, If you removed all the damaged matter from the bud, you should be alright if you can dry and cure it successfully with no further occurrence.
    Was this comment helpful to you?
  29. By Demetrius combs

    ,14 Apr 2016
    Thanks I always kan use advice.
    Was this comment helpful to you?
  30. By sonny

    ,19 Sep 2016
    so i am confused….you say you can use copper soap (aka copper octanoate) until the day of harvest, then a few paragraphs down you state that you should never use any fungicides during the flowering stage (?). I would really […]Read More
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    1. By latewood.ILGM

      ,21 Sep 2016
      sonny, I suggest you follow the directions on the bottle. Robert did say you could use this product until finish. From what you posted, it appears that the directions confirm what Robert stated in the “Get rid of…” section of […]Read More
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  31. By Growing Marijuana In A Greenhouse

    ,11 Jan 2017
    […] easily get trapped in your marijuana plants’ buds, causing a buildup and then the formation of mold over the course of several days or […]
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  32. By Veronika W

    ,23 Feb 2017
    Another option is getting a spray bottle and filling it with distilled water and about 2 tbsp. of apple cider vinegar. Give it a shake and spray that all over the plants (even the healthy ones… they seem to love […]Read More
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  33. By Rod

    ,06 Mar 2017
    I harvested some super nice Chocolope. It did have bud rot on the smaller stems. I tried to cut it all off and leave just the good stuff, but I am worried about smoking it or offering to friends to […]Read More
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  34. By Chad

    ,04 Sep 2017
    Courtney, the article was referring to cleaning your pruning tools with alcohol or hydrogen peroxide, not the budz themselves. Great info though, didn’t know that about the alcohol and bud oil. If the alcohol strips the thc from the budz, […]Read More
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  35. By Courtney B

    ,04 Sep 2017
    damn, wish I could delete my post. I suppose that’ll teach me to actually READ the ENTIRE paragraph before adding “my 2 cents”. Sorry, post is spot on, the alcohol was referring to cleaning the cutting tools, not the buds. […]Read More
    Was this comment helpful to you?
    1. By Stacy ILGM

      ,06 Sep 2017
      Hi Courtney, I will delete the comment you are referring to, no problem! 🙂 Stacy Ilovegrowingmarijuana
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  36. By EL BayBeBoi

    ,17 Sep 2017
    I know this is a old thread, but try wood ash, works well and non toxic!
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  37. By Mitchell

    ,25 Sep 2017
    *sigh*. In dire need of help here. Grew two plants this summer, both developed bud rot about a week apart. I pulled the first plant, dried it, & the buds are curing well. I pulled the second plant & it’s […]Read More
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    1. By latewood_ILGM

      ,28 Sep 2017
      Mitchell, I think I answered this question for you in another article… Break it up and let it dry. Pick out the rotten part, and hope for the best.
      Was this comment helpful to you?
      1. By Mitchell

        ,29 Sep 2017
        Thanks very much! Followed your advice & now it’s all drying & my fingers are cramped from being crossed 🙂
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      2. By sean looney

        ,03 Mar 2018
        Chuck H. Yes skunk is a demon for mould, but I wouldn’t grow anything else
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  38. By mike

    ,26 Sep 2017
    i’m growing outdoors and removed several caterpillars and cut a bud down since it looked like there was some bud rot in the middle. am in in big trouble? it’s been hot lately so that should slow any mold growth, […]Read More
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    1. By latewood_ILGM

      ,28 Sep 2017
      mke, I advise you to join our support forum. We will be glad to help you there. In order to give you informed advice si to discuss your grow environment, methods, and help you get back on track. support.ilovegrowingmarijuana.com
      Was this comment helpful to you?
  39. By Kygreen

    ,19 Oct 2017
    So if i cut the mold out is it still gonna b ok to smoke what wasnt molded on same plant
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    1. By latewood_ILGM

      ,29 Oct 2017
      I thought this blog article was about bud rot… Mold. Bad issue. If you can clearly remove all affected buds, you should be able to smoke what is left. However: If you have mold spores in the air; I would […]Read More
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  40. By Farmer

    ,29 Nov 2017
    It’s almost impossible in my area of the South to mature thick budded weed in October outdoors without fungicide sprays. I’ve grown early September maturing Indicas without them. I have pure Sativas still maturing in late November without fungicides. I […]Read More
    Was this comment helpful to you?
  41. By Chuck Hallas

    ,04 Jan 2018
    I’ve grown outdoors in a greenhouse (25′ X 50′) for the last 5 years. I have found anything with “Skunk” in the name molds quickly after flowers develop. I grow in the Northeast.
    Was this comment helpful to you?
  42. By Jeremy

    ,10 Jan 2019
    This happend to me and had no clue what it was Thank you for this
    Was this comment helpful to you?
  43. By Scott

    ,11 Feb 2019
    Ok got Springs #4 ph 5.8. Planting Out Doors again in pots 15 Gal.Useing Nous..Got really tough $/ $ any. Suggestions
    Was this comment helpful to you?
    1. By latewood

      ,13 Feb 2019
      Scott, I can not decipher what you are asking or commenting on. PLease just join our forum for guidance. support.ilovegrowingmarijuana.com Happy growing 🙂
      Was this comment helpful to you?

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