Sometimes the first sign of bud rot is a few leaves on the buds turn yellow seemingly overnight. The base of these leaves is where the bud is rotting
How to Prevent & Stop Bud Rot (quick summary)
Air circulation – It’s a really great idea to have an exhaust fan constantly venting out hot humid air and replacing your grow space with fresh air whenever possible. But no matter what, make sure there’s always plenty of
air moving over all the buds and leaves, and through the plant. This can take some planning.
Avoid wetness and especially high humidity – Don’t allow buds to sit in damp or overly humid conditions for long. Cover plants when
it rains, and otherwise shake them off when they’re wet. Bud rot is a fungus, and like all fungi, it needs a wet place to germinate.
Consider defoliating extremely bushy plants – If it’s extremely bushy and you can’t keep the humidity down, consider defoliating (removing leaves) on the middle and bottom of the plant. Each leaf is constantly adding
moisture, and removing leaves helps lower the humidity around the plant. Any leaves that aren’t getting light are only stealing energy away from your plant by the time buds are big enough to worry about bud rot. Those leaves are better off
gone especially if you need to lower the humidity!
Keep an extremely close eye on your longest, fattest and most dense colas. Almost like a cruel joke, bud rot usually attacks your biggest colas
Remove all affected buds immediately – Carefully remove and discard all buds with bud rot, as well as nearby buds – this is incredibly important if you don’t want to lose the whole harvest! Don’t let anything
any of the rot touch other parts of your plant, as it can further spread mold spores.
"When I had to throw away most of my plant due to bud rot, I cried a little, on the inside." ~ Cannabis Grower
Table of Contents
What Does Bud Rot Look Like?
What Causes Bud Rot?
How does the Botrytis fungus get to my plants?
How Do I Control Bud Rot?
What Does Bud Rot Look Like?
Usually, a bud rot infection becomes visible in just certain parts. Sometimes just the bigger and denser buds are affected, but other times you’ll get patches all over the plant, especially after a few rainy days.
You may see areas on the colas where everything (buds, pistils and/or leaves) are darkening, becoming discolored and/or drying up, unlike the rest of the plant.
The deadened spots usually stand out and catch people’s attention, even if growers don’t know what’s wrong, they often instinctively know that something is wrong since the spots don’t look like the rest of the buds on the plant.
In addition to the rot itself, you may see white mold on the outside of the bud at first – this is the first stage and it means plants need to be treated immediately! With advanced bud rot, the bud will easily separate so you can see inside. When the bud in question is inspected, it will be dark on the inside, usually gray or brown, and possibly dusty (this "dust" is fungus spores).
Depending on the life stage, bud rot can look...
white and fluffy
dark gray or brown (sometimes even dark purple)
the buds can be full of dark speckled dust which easily blows away (fungus spores)
"I lost half my plants last year to bud rot... After a couple of drizzly days, I noticed spots, and then I saw that it had spread to all my plants."
~ Cannabis Grower
Sometimes you might see a few yellow leaves appear suddenly on some of your biggest colas. It can feel like it happens overnight. That could be a sign that there’s mold at the base of these leaves. Always investigate any cola with yellowing leaves ASAP. If there’s mold you will be able to see the leaves are basically falling out, with mold or brown spots being revealed in the middle
Different Stages of Bud Rot – Catch it Early!
When plants are afflicted by cannabis bud rot, it starts as fluffy white growth in the middle or sides of buds, but the white mold quickly darkens into gray or brown and burrows deep into dense buds as the fungus takes hold. Sometimes you’ll see the initial stage on the sides of buds, giving you a possible chance to catch the infection early.
The Botrytis fungus looks white and fluffy in its initial stage, but you’ll probably never even see this stage before the mold quickly darkens and starts rotting the buds from the inside out
Once bud rot has taken hold over parts of a cannabis plant, the buds can sometimes look almost the same on the outside, at first, but they usually start looking like they’re dying in patches. Often the area will dry out and easily
pull apart. The inside of buds can turn brown, gray or even purple.
"I noticed one brown sugar leaf and it came out unfortunately easily, exposing what was inside."
~ Cannabis Grower
Some growers might think these drying spots mean that the plant is almost ready for harvest, but you know something is definitely wrong when just parts of the colas are being affected.
Here’s an example of advanced bud rot on an outdoor cannabis plant
What Causes Bud Rot?
Cannabis bud rot is caused by a type of fungus known as Botrytis cinerea.
In cannabis plants, Botrytis causes buds to rot out from the inside, hence the name "bud rot." If you crack open an infected bud, the inside will be a moldy dark gray or brown.
Bud rot can show up in many ways. For example, this cola here responded to bud rot by turning purple and mushy. with leaves that becoming crispy and dying. This is what the grower came back to find after a few days of rain.
Did you know? In addition to cannabis bud rot, Botrytis causes problems for many different types of plants, including wine grapes, strawberries and peonies.
Botrytis the fungus is sometimes referred to as "botrytis bunch rot," "botrytis blight," "bud rot," "grey mould" or "gray mold."
When it comes to cannabis, it is often only called "Bud Rot" since that’s the main symptom cannabis growers are worried about.
Any part of the cannabis plant affected by bud rot should be discarded immediately! This helps prevent further infection and all buds touched by this toxic fungus should never be smoked or used.
Throw Away All Buds with Any Sign of Bud Rot!
This is What Bud Rot Looks Like Ground Up
There are different stages of Botrytis as it matures and tries to release spores. An infection starts as fluffy white mold (or brown mold) and then spreads throughout the inside of vulnerable buds. The inside of those parts of the colas
darken to gray or brown. Once that has settled in, the mold tries to reproduce. The insides become filled with dark speckled dust that easily floats and spreads if the bud is cracked open. These are the spores of the fungus, so be careful
to avoid breathing in letting this speckled dust ever touch other parts of your plants.
Luckily, healthy cannabis plants will not develop bud rot unless exposed to stagnant air and wet conditions for an extended period of time. Your plants are more susceptible to bud rot, fungus, or mold when the temperature is hot or cold.
Aim for a temperature of 75°F (24°C) in the late flowering stage if possible.
How does the Botrytis fungus get to my plants?
Bud rot is spread to plants by dusty gray spores, usually in wind or water.
Most common ways Bud rot fungus spores get to plants
If your plants are never exposed to these spores, they will never get bud rot.
Unfortunately, the spores can easily be carried to your plant by a breeze, rain, from contact with animals, or even by clones from another grow room. Dormant spores can survive in many conditions only to affect your crops another time!
But... it’s not so bad. The fungus will never germinate if you take good care of your buds. And in any case, your plant needs a "wound" of some sort for the spores to take residence in your buds.
Possible wounds that can let Bud Rot fungus in include cracks in the stem from wind or over-training, damage from caterpillars, snails, worms, white powdery mildew, other pests, and larva, or any other type of injury or weak point can be
the point of entry for bud rot spores into the plant.
Luckily, even if your plant has been exposed to spores, Nothing will be able to survive and begin the cycle of a bud rot infection if you provide your cannabis with a cool, dry, breezy environment.
Bud Rot needs warm, humid conditions and stagnant air to thrive.
What triggers spores to grow into a full-blown case of bud rot?
Wetness or High Humidity <– MOST IMPORTANT FACTOR, DON’T IGNORE THIS!
This is the most important factor. If you’re suffering from bud rot or mold, even if you remove the affected buds, it will likely keep spreading until you fix the humidity and keep buds dry.
High humidity (above 55-60% RH) is the biggest contributor to mold growth and bud rot
Leaves should not be touching each other creating wet spots (defoliate plants that are too bushy)
Any situation where buds remain wet or in humid air for several continuous hours can be a trigger for bud rot
Bud rot is often triggered by rainy weather, especially if it lasts for days in a row
If outdoor plants collect dew during the night or get rained on, consider shaking plants to remove as much moisture as possible
Cool Temperatures Trigger Botrytis
Cool temperatures are ideal for spore germination of the Botrytis fungus. It’s most common outdoors in cool, wet or rainy conditions. However, as long as the relative humidity is high, Botrytis can attack at higher temperatures. Aim for
75°F or 24°C if possible in the flowering stage if you’re worried about bud rot.
Warm Temperatures Trigger Mold
Warm temperatures are ideal for mold growth, and different types of mold can strike thick buds with symptoms similar to Botrytis. Every degree above 70°F or 20°C increases the chance of mold especially in high humidity (mold typically won’t
grow below those temperatures). Since botrytis can strike at lower temperatures, it’s recommended to aim for a medium of about for 75°F or 24°C if possible if you’re worried about bud rot or mold in the flowering stage.
Bad Air circulation
Lack of wind or air circulation over the top, underneath and/or through the inside the plant
Leafy plants tend to collect water in between leaves and create humid pockets of air. This can cause wet spots and prevent air circulation through the plant, which makes a good environment for mold or fungus to grow.
"My fan could not circulate the air behind those colas. I thought it would be okay, but then I noticed super white fuzzy areas. Next thing I knew, half the colas had dead spots."
~ Cannabis Grower
Big, Fat, Dense Buds
Massive, dense colas have nice wet conditions on the inside which don’t get exposed to any air. This makes them a prime target for Botrytis bud rot or other types of mold.
It’s a cruel irony that you usually only get attacked by bud rot after producing lots of big buds.
Many types of stress, including bud rot, are more likely to hit your plant if it’s sick or suffering from nutrient deficiencies.
Certain strains are more susceptible than others
Some strains are very mold-resistant, while others get it easily.
Here’s a list of a few mold-resistant strains
How to Control Bud Rot (these are most important!)
The biggest thing you want to focus on is getting the humidity under 50% (most important!) and giving plants plenty of air movement.
How to Prevent Bud Rot
These are the most important points to remember...
Keep humidity under 50% RH (Most important!) – This is the most important thing you can do to prevent bud rot from growing. It’s rare to see Botrytis in dry conditions. Learn how to
control the humidity. If you don’t fix this, the bud rot may keep spreading even after you’ve removed all the affected buds.
Good air movement – Create good air circulation and make sure there’s always plenty of air moving over all the buds and leaves. Make
sure your plants are getting access to cool, fresh air.
Keep plant from big temperature swings between day and night – Controlling temperature and keeping the grow space from
experiencing big temperature changes can go a long way. Aim for 75°F or 24°C when you’re worried about bud rot, and avoid letting plants get hot or cool.
Avoid letting buds get exposed to wetness – Don’t allow buds to sit in damp or overly humid conditions for long. Protect your plants from rain and shake them if you notice they’re wet from rain or covered with dew.
Remove all affected buds immediately – Carefully remove and discard any and all buds that have possibly been affected by bud rot. Don’t let any rot touch other parts of your plant. This helps prevent bud rot from spreading,
but it’s not enough if you don’t take care of the environment. Remember, the spores are always around, and it’s just a matter of whether they get the right conditions to grow.
Other tips to help prevent bud rot...
Avoid plant wounds. Avoid injuring your plants, especially in the flowering stage. Don’t leave open wounds to seep out water and nutrients – cover any open injuries with tape or some other "cast" until injury closes up.
Avoid pests and keep plants healthy. A healthy plant is much less susceptible to all kinds of infections.
Keep some space between buds. Cramming a bunch of plants with a lot of buds in a small space can increase the chance of bud rot. Buds should never be touching each other. Try to make sure every big bud has at least a few
inches of "breathing room" to itself.
Defoliate leafy plants. Remove leaves on very leafy plants. If leaves are touching each other, they’re likely creating wet spots between them. R
emove big leaves that are covering or touching bud sites, as well as any leaves that are laying on top of each other. Your plant won’t "mind" if you only remove leaves from leafy areas, and this prevents moisture from collecting into damp
spots, while also improving air circulation around buds.
Watch out. Watch plants closely for signs of bud rot in the late flowering stage, especially on large or dense buds, and especially after humid or wet weather.
When growing outdoors...
Get a strain meant for your local climate. If you live in a place that has short summers and gets humid or rainy early in the fall, don’t get a strain that was developed near the equator!
There are fast-flowering, cold-resistant cannabis strains which are designed for growing outdoors in more rainy climates. For example, many
auto-flowering strains have quick lives – perfect for a short summer before the Autumn rain or frost.
A good outdoor strain for those worrying about bud rot might be Auto Frisian Dew, an
award-winning, mold-resistant strain made for outdoors. This strain goes from seed to harvest in about 12 weeks. Just plant seeds after the last frost in the Spring, then harvest 3 months later.
AutoFrisian Dew is resistant to fungus like bud rot. This strain is quick to harvest and will
grow in any climate which has (at least) 3 warm summer months before it starts getting cold or raining.
Breezy location – Try to plan your grow spot so your plants get a breeze, but not too much wind. This can be tricky, and it may mean visiting the grow spot a few times before planting.
Protect your buds from rain. If you know there will be drizzly conditions, cover your plants with a tarp to protect them from most of the rain. Don’t put tarp directly on plants or you’ll hurt your buds. Install the tarp up
above the plants, and make sure it’s held up by the center part, that makes it so rain runs off the sides of the tarp instead of collecting in the middle.
Shake plants. Some growers shake their plants on dewy mornings or after rain, so any water drops that form on the leaves don’t become breeding grounds for spores.
Fungicides, Neem Oil & Burning Sulfur
In the flowering stage, never use fungicides, spray affected buds with Neem oil, or burn sulfur.
These common tactics are not effective at stopping bud rot and will make your buds taste, smell and look terrible.
Some growers use fungicides made specifically for Botrytis in the vegetative stage. But when it comes to cannabis, fungicides can only be used as a preventative before any buds have formed.
If you already have bud rot and can’t fix your environment (which is the best way to kill Botrytis), I highly recommend cutting your losses and taking down the plant.
Most fungicides are not effective for bud rot. If you do plant to spray plants, it’s recommended to get one that’s specifically been developed to combat Botrytis.
Any treatments for Bud Rot should be applied in the vegetative stage as a preventative.
There’s nothing you can spray on your plants after bud rot has already formed. Unfortunately, there aren’t any effective fungicides or other treatments that are safe to use with cannabis in the flowering stage
How to Stop Bud Rot from Spreading
The inside of dense buds provide a great place for Bud Rot spores to grow, and that’s the main place you’ll find developed Bud Rot on cannabis plants. Once you’ve spotted bud rot, it’s important to act immediately.
As soon as even one part of a single bud starts showing signs of grey mold, the rot can spread to the rest of the cola and then to other buds on the plant. If triggering conditions (lack of airflow, wetness) have not improved, a single
point of infection can quickly ruin the harvest of an entire plant.
Never Spray Your Buds with Anything!
Bud Rot Removal
Immediately remove all rotted parts and nearby areas. The only way to stop the spread is to remove all signs of mold from the plant, then move plants to a cool, dry area with a nice breeze.
Be extremely careful not to let any rot touch any part of the rest of your plant.
What Happens Next?
You can either...
harvest the cannabis plant now
let it continue to ripen, but only if you fix the environment
If your plant has been affected by bud rot, it means they need less dampness and air that’s more dry. If you can improve the environment, you can allow the plant to continue ripening after you’ve removed the infected buds. However, if you
don’t fix the environment it will usually come right back, sometimes even attacking other buds overnight.
Here’s how to fix the environment:
add additional air circulation
lower the humidity (40-50% RH is optimal in the late flowering stage)
defoliate leafy plants (remove leaves covering bud sites, through the middle of the plant, and any leaves that aren’t getting light anyway)
prevent wet spots on plant
If you can’t fix the environment, I highly recommend cutting your losses at this point. If you know that it’s still going to be cool, humid or wet for your plants, it’s recommended you harvest immediately to prevent further
buds from becoming infected. Buds harvested early are better than moldy buds!
Whenever you do harvest your healthy buds, be extremely careful during the drying process. Normally growers want to slow dry buds, but if you’re worried about mold it’s better to dry them faster, with plenty of air circulation and movement.