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Bud Rot or Mold

Extreme Case of Cannabis Bud Rot 🙁

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.”

Table of Contents

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.”

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.”

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

  • Wind
  • Rain Water

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

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.

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?

  • 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.

Bud rot is a mold that develops in the thickest parts of cannabis buds. Read for more information on how to prevent and solve bud rot before spreading!

How to Stop Botrytis on Cannabis (Bud Rot, Gray Mold)

Get rid of Botrytis (bud rot, gray mold) on marijuana. The best ways to stop gray mold fast and prevent it from spreading.

What is gray mold (Botrytis cinerea)?

Botrytis blight, aka bud rot or gray mold, is a fungal disease that affects over 200 plant species. In cannabis, the disease causes a soft rot that damages buds during growth and after harvest.

The agent of gray mold is the asexual fungus Botrytis cinerea. Its name roughly translates to “grape disease” in Greek. Botrytis cinerea is an airborne plant pathogen with a necrotrophic lifestyle. The ability to induce programmed cell death plays a key role in the success of the fungi. [1]

What does gray mold look like?

Gray mold appears as a thick carpet of velvety spore mass. Affected plant areas gain a fuzzy web of gray/blue mycelium, visible to the human eye.

As bud rot progresses, the damaged, water soaked plant material collapses into black mush.

Where is gray mold found on cannabis?

Gray mold occurs in both growing plants and harvested marijuana buds. The disease often starts inside of the bud before spreading outwards. The risk of gray mold infection increases as cannabis matures and its buds grow denser.

Early signs of gray mold

The earliest symptoms of gray mold on cannabis typically appear as small bruises or discoloring of the bud. The bruises collapse into rot, followed by formation of the mycelium, gray mold.

Other symptoms include yellowing and damping off of leaves close to the infection. Regular inspection for gray mold can be done by carefully opening buds and checking inside, where gray mold tends to hide.

How fast does bud rot spread?

Once established, gray mold spreads quickly throughout the plant. The rate of infection is increased in favorable conditions .

Many times, cannabis plants are nearly destroyed at only a couple of days post-infection.

How to Stop Gray Mold Fast

The disease can be controlled by removing moldy buds, cleaning plants and adjusting the environment.

Discard Infected Buds

Tools: A knife or scissors dipped in a jar of high purity alcohol (USP grade isopropyl or Everclear), Q-tips and a garbage bag.

1. Cut out around the damaged area using scissors or a knife dipped in rubbing alcohol.

2. Put the moldy bud in the garbage bag.

3. Clean any freshly exposed damage on the plant with alcohol using the Q-tip.

4. Repeat as necessary. Dip blades in alcohol between cuts.

It’s good practice to solarize the garbage bags full of moldy buds (put them out in the hot sun) to kill any fungi before being disposed of.

Remove Dead/Dying Leaves

Botrytis can survive as sclerotia (a mass of hyphal threads) or mycelium on dead plant material such as leaf litter. [3] By remaining dormant, the fungi can wait until it has the chance to attack a living host plant.

Removing dead and dying leaves on the plant is helpful because, if you don’t do this, Botrytis may reside there. Eliminating the habitat is key to preventing another mold infection.

Pluck Fan Leaves

Stripping a plant of its leaves is a highly debated topic among growers, but one thing agreed upon is that during late bloom cycle, removing fan leaves will help prevent mold problems.

By cutting off large fan and sucker leaves, more light and air are able to penetrate the plant canopy.

Fan leaves can be plucked off by hand, although you may have to use a blade if they don’t pop off clean. Make sure to remove all of the petioles (the stem part of leaves) that tend to remain by the stalk of the plant.

Tidy Up

Botrytis is frustratingly difficult to eliminate due to the numerous ways it attacks plants. Inoculum sources are not species-specific, and the fungi can survive long times as mycelia and conidia (a type of spore) hiding in debris or around the grow room. [1]

🌞 Outdoors, remove any brush or mulch around plants.

🏠 Indoors, quarantine plants and scrub the grow room top to bottom with diluted bleach solution.

Gray mold is prevalent in high humidity environments with moderately warm temperatures.

Lower Humidity

Moisture often is more of a limiting factor to gray mold than temperature [4] , which is why lowering the relative humidity (RH) of the grow room works well to stop mold fast.

🌞 Gray mold thrives in humid, dark areas. Hence the benefit of opening plants up to allow for more sunshine and wind to come through. Outdoors, consider cutting back whatever is blocking the sun.

🏠 Indoors, aim to maintain RH under 45% towards the end of bloom cycle. RH can be lowered with techniques like increasing the air exchange in the room (cool air in, strong exhaust out), using dehumidifiers and circulation fans.

Protect Buds

Protecting buds from getting wet is an important step in gray mold prevention. Botrytis fungi germinate on damp/wet plant tissue before they spread throughout the plant.

🌞 Dew formation and unexpected rainfall can be avoided by putting a tent or greenhouse cover over plants. You could also move them inside.

💦 Maximizing the length of time between waterings reduces the moisture in proximity of the plant. Soil can be watered early in the day so that the ground will be dry all night. Avoid foliar sprays.

Increase Airflow

🌞 Moving potted plants to a hot, windy hillside is an ideal solution when growing outdoors. If the plants are rooted in the ground, surrounding vegetation may need to be cut back to allow for more airflow.

🏠 Increasing horizontal airflow helps to create a more uniform climate in the grow room, and reduces the likelihood of cool spots that may turn into condensation problems. [5] Oscillating fans can be mounted to the sides of the grow room for better air displacement into the plant canopy.

For hoop house style greenhouses, try rolling up the sides of the covering to get more horizontal airflow to plants during late bloom cycle.

Finish Flowering

An early harvest is better than a moldy harvest. Keep a close eye on buds in late bloom and be ready to pull early if you need to.

Bud Rot After Harvest

Equally important in preventing mold is the room used for drying buds once they are harvested. Think about this: In 2015, the HHE program visited an outdoor cannabis farm in Washington State during harvest to evaluate any potential hazards. They found that Botrytis cinerea was the main fungal species in the air. [6]

Causes

More often than not, the problem is humidity related.

Drying room issues

Buds that are drying in a room that’s too humid, or in a polluted airspace, are an easy target for mold.

Buds were put away wet

Big buds take longer to dry than popcorn nuggets. Getting the batch evenly dried will help prevent moisture release in storage, which leads to mold infection.

Bad storage containers

The usual suspects are zip baggies and pickle jars, both of which are not airtight.

Quick Drying

Traditional slow drying and curing methods are great for bud quality. That all goes out the window once mold appears. It’s better to take a hit in quality by quick drying than to lose it all to mold.

The fastest way to dry buds is to break them all down off of the branches and put them on drying racks or screens in a warm, dry location. You’ll lose the shape of the bud you would have had if they were hang dried.

💧 Dry out the air to dry out the buds. Relative humidity should be less than 45%

Dehumidifiers can lower the humidity of a room fast. However, overuse is known to make buds burn unevenly.

🌡️ Turning up the heat will speed up the drying process as well. Although too much heat will degrade cannabinoids and terpenes. Keep it under 80°F for minimal degradation.

Most hygrometers for sale have built in thermometers like this one on Amazon , so you can measure the temperature and humidity of the drying room on the same device.

💨 Fans can be used to create a gentle breeze for drying buds. Mold should be picked out of buds before using fans to prevent spores from spreading.

Salvage Buds: Desperation Methods

If the steps taken above are still not enough to control your gray mold problem, here are some last resort desperation methods for salvaging buds—to be used with caution.

  • Drying buds in the sun
  • Drying buds with high temps
  • Cooked in edibles, oils
  • Ice water extraction followed by an alcohol extraction
  • Make quick-wash iso hash (QWISO)

Exposing cannabis to solar radiation is known to cause THC loss and other cannabinoid degradation [12] , still it is a common practice for many growers in tropical areas around the world without access to power. A DIY method to circumvent the loss in bud quality is to make a wood stove that doesn’t need to burn hot to create a draft and drastically reduce the humidity of the room.

Is smoking gray mold harmful to humans?

Although no mycotoxins have been reported from Botrytis, it is still not recommended to smoke affected marijuana or concentrates. Precautions should be taken when handling moldy cannabis buds, such as wearing face protection. When a bag of moldy buds is opened up, a cloud filled with innumerable mold spores is released.

A medical condition known as Winegrower’s lung is known to be caused by inhalation of Botrytis fungi. [2]

On the other hand, Botrytis cinerea is regularly consumed in wines. “Noble rot” is what Botrytis is called by winemakers, and there are highly-valued dessert wines made with the fungus. [7]

How do buds get ruined by mold?

Bud density

Cannabis buds bulk up in density during the end of their life cycle. The loss of intra-floral ventilation due to buds increasing in size combined with high humidity makes them prime candidates for Botrytis cinerea spores in search of a host.

The hypersensitive response

Plants have evolved natural responses to combat pathogen attacks. One of the primary responses to pathogen attack is the process of an oxidative burst that triggers hypersensitive cell death in and around the attacked area. [7] This is referred to as the hypersensitive response and is done in order to cut off the food supply and keep pathogens at bay confined to that part of the plant. However, Botrytis works as a necrotrophic pathogen to utilize the dead tissue created and multiply on it. [8]

In other words, the fungi can exploit a cannabis plant’s defense mechanism for its pathogenic growth.

Chemical attack

Botrytis cinerea facilitates the formation of powerful chemicals that destroy buds and cause necrosis in plants. This includes various low molecular weight metabolites such as botrydial, oxalic acid, and HSTs. [1]

The fungi produce small RNA (sRNA) molecules that cause gene silencing to suppress host immunity. [9]

Spread

The fungi spread rapidly. When disturbed, they release a cloud of infectious spores, further spreading the disease. Damage occurs not just on buds but also on stems at pruning wounds where it can rot through the entire stem.

The stigmatic fluid present in buds serves as a nutrient medium for airborne conidia to germinate on. [10]

How does Botrytis infection start?

The infection starts with a fungal spore landing on a plant tissue. Plants may be attacked at any stage but freshly-injured areas and aging or dead tissue are preferred. The spores germinate in suitable conditions of temperatures approximately 60–77°F with high relative humidity. [11]

The fungus is capable of maintaining growth in a range of temperatures from 28–90°F, although growth is halted at the extremes. [4]

❄️ Cool temperatures may slow the disease down, but as long as it is moist the disease continues to infect and spread.

🏜️ Hot, dry weather with plenty of direct sunlight is perhaps the best solution to shut the disease down.

Bud Rot Sprays

Due to the nature of cannabis use (smoking), we do not recommend foliar spraying mature buds with fungicides or other solutions. However, if the outbreak is caught early on, an organic fungicide such as Trifecta Crop Control may prove effective.

Cannabis Strains Resistant to Mold

Tropical sativa strains are highly resistant to gray mold. These mold resistant strains have often developed the resistance naturally, through many generations of growing in wet, humid climates. Their airy buds allow air to flow within, and damaged buds tend to only turn brown and rot instead of harboring gray mold.

Landrace strains from Thailand, Laos, Cambodia, Vietnam are very resistant to gray mold. These long flowering sativa strains are fun to try if you’re growing in a tropical area, but are difficult to manage indoors or outdoors in temperate climates.

Read our list— 8 Resilient Mold Resistant Strains for sativas and hybrids that perform well grown outdoors on the Big Island of Hawaii.

References

You may enjoy further learning about Botrytis cinerea though these links.

Get rid of Botrytis (bud rot, gray mold) on marijuana. The best ways to stop gray mold fast and prevent it from spreading.