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What Cause Bud Rot & How to Prevent It in 7 Sections

Finding bud rot in your cannabis plants before harvesting can be devastating. So much time, money, and labor you've spent to grow healthy plants. It can attack every part of your plant, and rot your buds from the inside out, leaving you wondering what cause bud rot.

It is most commonly found on the buds and colas, which are the most useful and precious part of your harvest. It is a well-known fact that almost every grower faces bud rot at least once in their career. Understanding what causes bud rot is crucial, but that shouldn't stop you from seeing your cannabis business success!

Whether you have already encountered bud rot on your plants or are proactively looking to prevent it, this article will provide you with all the information you need about what causes bud rot.

The article will discuss bud rot on cannabis plants, from identifying the early bud rot symptoms to understanding what causes bud rot and the best ways of bud rot prevention.

Let's start by defining what bud rot is and delve into the factors that cause it. You can also jump to a particular section that interests you in the content list.

What is Bud Rot

Bud rot is also commonly known as gray mold, it comes from a fungus known as Botrytis Cinerea, a necrotrophic fungus affecting many plant species.

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Someone called bud rot "Big Bud Disease" or "The Curse of the Successful Grower".

Bud rot can affect the flowers (buds) of various plants, the fungus infects the buds and spreads quickly, causing them to rot and become covered in mold.

When the environmental conditions become conducive, the mold rapidly rots the buds, leaves, and stems. Soon enough, it will increase from inside and spread out to the rest, ruining the buds and damaging your total yield.

That's why we always suggest bud rot prevention is much more important than treatment, as it can quickly spread and cause widespread damage.

Despite being admirably resilient, cannabis is still just that - a plant. Like all plants, cannabis can be affected by many diseases and harms, including viruses, fungi, bacteria, insects, and even some animals.


Does Bud Rot Have a Smell?

Bud rot often has a distinct, musty smell. This is due to the growth of mold and fungi on the infected buds. The odor can range from mild to strong, depending on the severity of the infection.

Bud Rot Life Cycle

The life cycle of Bud rot can be divided into several stages:


How Common Is Bud Rot?

Bud rot is a common issue faced by many cannabis growers, and it can be difficult to avoid in some cases.

Bud rot can be a devastating problem for cannabis growers, as it can destroy the plant's largest and most desirable buds.

Growers must be vigilant during the late flowering stage, as the risk of bud rot is the highest. The onset of summer and the transition into autumn also increase the likelihood of mold growth due to temperature fluctuations and high humidity levels, so growers should take extra precautions during these times.

Does Bud Rot Ruin the Whole Plant?

Bud rot can ruin the affected buds and can spread to the plant's other parts if left untreated. In addition, the infected buds will rot and become covered in mold, reducing the crop yield and lowering the quality of the remaining buds, making them unsaleable.

If the situation is severe, the infection can spread to the stems and leaves of the plant, causing them to rot and wilt. This can reduce the overall health and vigor of the plant, potentially leading to its death.

What Cause Bud Rot

Now that we understand the essential cause of bud rot is Botrytis Cinerea, let's consider why your plants could be suffering from it.

First, we need to understand what conditions the fungus or mold likes. It means if we know the conditions that allow bud rot to thrive, thus we can know the causes of bud rot, and how we could take the measure and prevent it effectively.

Below, we have summarized the conditions that could be promoting bud rot in your cannabis plants, including:

  1. Poor Air Ventilation
  2. High Relative Humidity Level
  3. Stagnant Air Temperature
  4. Dense and Fat Buds
  5. Extremely Dense Foliage
  6. Weak Immunity in the Harvest
  7. Plant Genetics
  8. Insect Wounds
  9. Wet and Rainy Conditions
  10. Inadequate HVAC for grow rooms

Identifying Bud Rot

Bud rot isn't specific to any geographic locations. Moreover, it can attack plants at any stage of life, most commonly found on the dense and fat buds before harvesting. It will develop and take on different appearances depending on what stage it is in.


Cannabis bud rot first appears as a white, wispy sheen over your buds. When left to grow and produce spores, it turns gray and then black (sometimes it is dark purple) while turning your once dense and supple buds into a mushy and slimy mess.

What Does Bud Rot Look Like During Different Stages?

Bud rot can also manifest at different stages of the plant's growth cycle. Here is a general description of what bud rot may look like during flowering, drying, and after harvest:

Different Stage


Bud rot during flowering

Discoloration and softening of buds and colas

Shriveled or distorted buds and colas

A foul smell, similar to mold or rotting vegetation

Brown or gray discoloration on the buds and colas

Bud rot during harvest

Soft or mushy buds or colas

A noticeable increase in mold or mildew growth on buds or colas

A foul smell, similar to mold or rotting vegetation

Brown or gray discoloration on the buds or colas

What does Bud Rot Look Like on Various Parts of the Plant

Bud rot can affect different parts of the plant in different ways. Here is a general description of what bud rot may look like on various parts of the plant:

Bud Rot on Stem: As it starts to occur and spread, the Botrytis bud rot will attack your plant's stem, making it first turn white and wispy, and then become a pale grey color and turn into a slimy mass. Finally, the stems start losing their rigidness and can no longer stand straight.

Bud Rot on Leaves: The infection will keep progressing, and you will notice your plants lose their color and start looking wilted and yellow with burnt leaves. This is because the fungus is smothering your plant and inhibiting chlorophyll production.

Bud Rot on Buds: Once it's done with the stems, Botrytis bud rot will make its way to the female plant's moist buds. The leaves will wither into a brown shade, and the pistils will soon follow. Eventually, the buds will be covered entirely in the gray mycelium, turning them into a gray-brown slime..

Bud Rot on Colas: It might just attack the biggest and fattest buds first, or it could form mold spots all over your marijuana plant. Additionally, you might be able to observe the cola turning into a darker color and getting dried out.

Look at the bud rot images (open full size on click).


Cannabis Bud Rot

When you notice your plant looks sick or shriveling. But you are not positive what the culprit is. "There must be something wrong" - it is your instincts. Since you found the leaves, stems, and pistils are pretty different from the plants in other areas, just like patches all over the plant.

The bud rot botrytis can attack every part of your plant, most commonly found on the buds. But the affected parts are usually noticeble and catch your attention easily. 

Early Signs of Bud Rot on Cannabis

What did bud rot do with your plants, and what are early signs of bud rot?

Bud rot can attack every part of the plant, and it goes through several stages before it matures and spreads. It is challenging to detect in its early stages since it rots your buds from the inside out.

But with the following list of bud rot signs, identifying but rot become easy.

Early signs



The first signs of bud rot may be the yellowing or browning of the buds


The buds may become soft and mushy, indicating they are beginning to rot


A white or gray mold may begin to form on the infected buds


A musty odor may emit from the infected buds


The leaves surrounding the infected buds may turn yellow or brown and begin to wilt

Later Stages of Bud Rot on Cannabis

In the later stages of bud rot, the following symptoms may become more pronounced:

Later signs



The mold on the infected buds may become more dense and visible, appearing as a cottony growth


The infected buds may continue to rot and become covered in mold, reducing the yield and quality of the crop


The disease may spread to the stems and leaves, causing them to rot and wilt


During the drying process, the infected buds may become brittle and break easily

Musty odor

The infected buds may emit a strong, musty odor

What Does Bud Rot Look Like Under a Microscope?

Under a microscope, bud rot can appear as a mass of branching, thread-like hyphae known as mycelium. The mycelium may appear white or gray and may have a cobweb-like appearance. The mycelium can also produce sporangiophores, which are structures that produce and release spores (spores) that can infect other parts of the plant.

How Does Bud Rot Spread

Botrytis fungus initially infects the plant from the inside, but as it grows, it spreads to the outside, making it vulnerable to air currents.

How can Bud Rot Spread

For bud rot to occur, mold needs to make contact with your plants first. It may seem like an unlikely occurrence, but the dusty spores of the mold are quite easily transported, reaching your plants through air, water, and other pollinators, like contamination by farm tools.

Once the spores get to your yield, they form a wound or tear in the external tissue and enter the buds. The Botrytis Cinerea then continues to break down the surrounding bud and spread out to other areas of the plant

How Fast does Bud Rot Spread

Bud rot spreads quickly and dangerously.

The white, wispy sheen (mold) may be seen only for a day or two before it becomes dark brown or gray. Therefore, it is difficult to spot when starting, since you’ll probably never notice this sign before it changes.

Then you see the colas (leaves around, buds and pistils) become dark, dried up, dying.

In less than a week, the bud rot can spread the whole grow room if the conditions becomes conducive, such as high humidity level, poor air ventilation, and stagnant air flow etc.

Can Bud Rot Happen Overnight?

Bud rot can occur relatively quickly, and sometimes, it can happen overnight. This is because the fungus that causes bud rot can overgrow under the right conditions, such as high humidity levels and poor air circulation.

However, it is important to note that the development of bud rot is usually the result of a combination of factors. In some cases, it may take several days or even weeks for the symptoms of bud rot to become apparent.

Where Does Bud Rot Start?

Bud rot typically starts on the buds of the plant. The buds are particularly susceptible to rot and mold because they are tightly packed and often have poor air circulation.

Once the infection has started on the buds, it can spread to the stems and leaves of the plant, causing them to rot and wilt.

Does Bud Rot Spread to Other Plants?

Bud rot can spread to other plants. The fungus that causes bud rot produces fragments that can be dispersed by wind, rain, or other means, infecting other parts of the same plant or other plants. Touching infected parts of the plant can also transfer the fragments to other parts of the plant or other plants, spreading the infection.

Is Bud Rot Harmful to Humans?

Bud rot can be harmful to humans if the infected buds are consumed or inhaled. Inhaling mold or fungal fragments can cause symptoms such as coughing, wheezing, nasal congestion, and difficulty breathing and trigger allergic reactions in some individuals. In severe cases, exposure to mold or fungal fragments can lead to more serious health problems, such as pneumonia or other respiratory infections.

How to Treat Bud Rot

To save a plant with bud rot, it is important to identify and remove all affected buds, cutting back to healthy tissue. If the infection is caught too late or is too severe, it may be difficult or impossible to save the plant.

How to Treat Bud Rot if it was Infected?


If the core is displaying the signs we mentioned above

  • Isolate and investigate: isolate by cutting it out and quarantine that area of your grow room. Sample and investigate all other plants nearby to determine if the botrytis cinerea has had time to spread out.
  • Remove the affected buds: cut off any affected buds with trimmers and store it in a sealed container to prevent any accidental spreading. Remove any healthy buds that are touching or in close proximity to the affected buds, as the spores can spread easily.
  • Consider pruning: if the infection is severe, you may need to prune back the plant to remove all affected parts. This can be a difficult decision, but it may be necessary to save the rest of the plant.
  • Dispose and sanitize: dispose of this container and sanitize all gardening equipment used as well as your clothes. Changing your clothes and wearing protective gear when moving from one grow room to the next.
  • Thorough assessment: before concluding your bud rot removal, do conduct a thorough assessment of the whole plant to ensure all the affected areas are removed quickly.
  • Keep the affected area dry: bud rot thrives in moist conditions, so it's important to keep the affected area as dry as possible. Use a dehumidifier to lower humidity levels if necessary.
  • Improve air circulation: good air circulation is important to prevent the growth of mold and mildew. Make sure your grow room is well-ventilated, and use fans to improve airflow.

During harversting

  • Make sure to leave space between hanging branches as your buds dry out or create an optimal environment for the drying process.
  • You can even try out various speed-drying techniques to limit the time that your buds spend in conditions that could promote Botrytis cinerea.


The differences in treating bud rot outdoors versus indoors are mainly due to environmental factors and the size of the growing area. Outdoor growers have to deal with the elements and weather conditions, which can make it more difficult to control the humidity and temperature levels in the growing area. Additionally, the larger size of outdoor grow areas can make it more challenging to isolate and treat infected plants, as well as to monitor the spread of the disease.

To treat bud rot outdoors, it is important to follow the same basic steps as when treating it indoors, such as removing infected areas, using fungicides, and providing proper ventilation.

However, outdoor growers may also need to take additional measures to protect their plants from the elements, such as constructing a temporary shelter or installing fans to increase airflow. In addition, outdoor growers may need to use larger quantities of fungicides to treat a larger growing area and to ensure that all parts of the plants are properly covered.

Can We

Stop Bud Rot?

It is a common tactic to spray fungicides at the flowering stage of your plant. Growers are also known to use Neem Oil or sulfur on affected buds. But the fact is, these practices do more damage than good.

Fungicides or oils have zero effect on bud rot. All they do is make your yield look, smell and taste horrible. Every grower needs to know that fungicides can only be used as preventative measures before the buds have formed.

Remember, if the infection has become widespread, you must cut down the whole plant in order to protect the rest of your plants. Don't risk your entire harvest in hopes of saving a single infected plant.

So, with bud rot, early detection and prevention is crutial. You should check your plants every day and perform a thorough assessment.

7 Tips of Prevention to Bud Rot

Again, prevention is always the best medicine when it comes to bud rot. Prevention is better than treatment for bud rot because it is easier, less expensive, better for the plants, and less stressful for the grower.

By taking preventive measures to avoid the occurrence of bud rot, growers can help to ensure healthy and vigorous plant growth and avoid the need for costly and time-consuming treatment measures.


Tips 1. Inspect and Assess Plants Daily

With bud rot, early detection can make all the difference for your cannabis plants. You should inspect your plants daily and perform a thorough assessment. Look between all the cracks and any crevices of suspect buds to find out if they have bud mold.

Tips 2. Isolating Infected Areas

If the core is displaying the signs we mentioned above, isolate it by cutting it out and quarantine that area of your grow room. Sample and investigate all other plants nearby to determine if the Botrytis cinerea has had time to spread out.

Tips 3. Wearing Protective Gear

Sometimes, a plant mold on bud will have grey-colored webbing or white, dusty spores, they can travel to infect the rest of the plants. Be vigilant when handling plants by changing clothes and wearing protective gear when moving from one grow room to the next.

Tips 4. Sanitize All Gardening Equipment

If your plants are already victim to bud rot, it is best to cut your losses and take down that part of the plant. Hopefully, you should be able to salvage the rest of your crop. Sanitize all gardening equipment used and your clothes.

Moreover, it would help if you didn’t think your plants are safe from bud rot after harvesting your buds. They can still catch the spores and become moldy.

Therefore, you need to be extra careful and ensure your buds don’t come in contact with the fungal spores.

Make sure to leave space between hanging branches as your buds dry out or create an optimal environment for the drying process. You can even try out various speed-drying techniques to limit the time that your buds spend in conditions that could promote Botrytis cinerea.

Tips 5. Prevent Bud Rot: Start with Humidity Control

We have gone over what is bud rot, factors that cause it, and prevention control. Now, we will discuss the best ways to stop bud rot from damaging your crops in the first place.

1) Inspect the Humidity Levels for Your Grow Room

The most important thing you need to do is carefully monitor the humidity levels in your grow room. Humidity should always be kept at a relative humidity (RH) of 40% to 50% to prevent bud rot.

Since Botrytis rarely exists in dry conditions, you should invest in an effective grow room hvac or dehumidifier to keep your crops healthy.

2) Let Your Air Circulate

Adequate air circulation will ensure your plants get cool, fresh air to breathe. It also reduces the chances of fungal spores existing in the air and settling on your crop.

Creating good air circulation pathways in your grow room is a must-do for preventing bud rot.

Tips 6. Consider Different Strains

Another critical component to consider is the strain of your plant. Some plants are more susceptible to developing bud rot than others.

Therefore, it is best to avoid planting those strains and instead opt for a mold-resistant cannabis plant. It will allow you to maximize profits from your yield and ensure a healthy harvest all year round.

We have compiled a list of various mold-resistant plants, categorized by indoor and outdoor strains, which you can look into for your subsequent yield.

Indoor Strains

Sweet Tooth

The Hawaiian roots give it excellent mold-resistant properties.

Moby Dick

Easy to grow with a bountiful yield.

Outdoor Strains

Holland’s Hope

Best to harvest in mid-September up to early October.

Jamaican Pearl

Should be harvested before its trichomes turn amber-colored.

Frisian Dew

Best in Northern climates that offer plenty of sunshine with cooler temperatures at night.

Important Note

Before picking out a strain to grow, be sure to consider all of its requirements. These will help you create the perfect environment for optimal growth and plays a vital role in preventing bud rot.

Tips 7. Determine the Dehumidification Size

Picking out the right dehumidifier will play an essential role in stopping bud rot. Your dehumidification size should be determined by how much moisture removal your grow room requires. Start by taking out an average reading of your humidity levels for a week, and then calculate how much moisture removal you need.

Your dehumidifier device capacity is usually measured in pints of moisture removal per 24-hours. Use this as a standard metric to pick out the right dehumidification size for your grow room.


At the End

Bud rot is often considered an inevitable phenomenon, a yield loss that every weed grower has to face. But, you can stop your plants from suffering the same fate. By growing the right strains of cannabis in the right environment, maintaining the relative humidity, ensuring sufficient airflow, and investing in a dehumidifier, you will be successful in preventing bud rot.

For further assistance on maintaining the correct humidity levels for your crop growth, reach out to our dehumidification system experts today.

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