Bud Rot: What It Is (+9 Ways To Treat & Prevent)

Bud rot (also known as gray mold, Botrytis Blight, or Botrytis cinerea) is a type of fungus that can affect many different plants, including cannabis.

It’s extremely common and can wreak havoc on the growth cycle of your plants.

It’s not just unsightly but can cause problems with water and nutrient absorption, which can kill your plant.

If you’re new to growing and less familiar with managing air circulation, then you may find yourself battling gray mold more than you’d like. Often, it’s more of a problem when growing outdoors because indoor growers have more control over environmental conditions:

• Temperature
• Light
• Ventilation
• Humidity

Along with powdery mildew, bud rot is one of the most common issues with plants worldwide in both agriculture and horticulture. These two separate diseases can go hand-in-hand, especially for cannabis plants.

What does bud rot look like?

The signs of bud rot can be tricky to spot early because rot usually starts from within before becoming visible on the outside.

The stem may appear mushy or gray, followed shortly by yellowing and wilted leaves. Affected buds usually have a soggy, browning core.

Sometimes a plant will look as though it’s coated in a gray mold. These are the spores produced by the fungus and they need to be eradicated as soon as possible. If you suspect a bud rot infection, check leaves, flowers, stems, and buds for signs of damage

What causes bud rot?

Bud rot is caused by fungus spores that thrive in stagnant air produced by poor air flow and characterized by excess moisture and damp soil. Bud rot takes hold in plants that may already be diseased, damaged, or vulnerable, so maintaining plant health is vital.

Dense buds and larger plants are more conducive to bud rot because they’re more likely to trap moisture. The closer you keep plants together, the harder it becomes to ventilate properly and the more susceptible they are to excess moisture and mold spores.

Growing outdoors is more likely to put your plants at risk of Botrytis because you can’t control the environment as easily. And, depending on your location, your environment may be extra prone to getting bud rot. Coastal areas, in particular, are susceptible due to challenges with high relative humidity.

Insects, splashing water, and human cross-contamination (using infected tools, for example) are a few other ways mold can be spread from plant to plant. They aren’t necessarily the cause of the initial problem, but they can be the cause of subsequent infections spreading through your space crops.

Is bud rot the same as Botrytis cinerea?

Botrytis cinerea is the scientific name for the fungus that causes bud rot. You’ll see it referred to as both of these names (along with other names like cannabis bud rot and gray mold).

Bud rot and powdery mildew are two different plant diseases, but they’re often confused with one another.

• Both are aggressive plant fungi that can affect the growth of cannabis buds
• Both are considered extremely problematic in the growing world.

Just like mildew, bud rot reproduces with fungal spores, which are transported through the wind and spread when they come into contact with the leaves or stems of the crop.

Bud rot can develop inside cannabis buds and then spread outwards, especially if your plants have denser buds. If your grow room or other grow space is on the smaller side, or if your plants are too close to each other, your harvest may be susceptible.

Some strains of cannabis are more mold resistant than others, so it’s worth researching the strains you want to grow before planting to ensure the strain you choose is suitable for your growing conditions.

How can I prevent bud rot?

Bud rot prevention is better than dealing with an infected bud, so it’s worth putting effort toward prevention. Here are nine ways you can help prevent bud rot mold from setting in from the start:

1. Choose healthy plants: Bud rot generally attacks plants that are unhealthy, damaged, or dying already. By choosing plants that are in good health—and by keeping them that way—they’ll be less likely to succumb to bud rot in the first place.
2. Be vigilant: It can be tricky to spot bud rot before it’s too late, so familiarize yourself with the way bud rot looks and catch it before it spreads. Check every plant, every bud, and all flowers for signs of the fungus.
3. Manage your environment: Mold grows well on old plant material that’s fallen to the ground, so make sure the areas around your grow space are kept clear. Pruning and training are great for your plants too.
4. Control humidity: The humidity level in your growing space is important for many reasons. Avoiding ideal conditions for mold to grow is a big one, so be careful to correct high humidity as it happens.
5. Space your plants out: You’re more likely to have mold growth problems if your plants are kept close to each other. Dense crops trap moisture and contaminants (such as mold spores). Keep air moving between your plants and ensure that air circulation is at optimum levels. Our guide to grow room ventilation can help.
6. Take precautions: If your plants develop early symptoms, remove and destroy all infected parts in order to save the rest of the plant, and separate the plant from the rest of your crop. Wear different clothes when handling any plants you suspect of being infected and don’t use infected plants for compost. You’ll just continue to spread the spores to new plants.
7. Grow indoors: Outdoor plants can be more suspeceptible to bud rot, especially if you live in a location with high humidity and low wind. Using a greenhouse, grow room, or grow tent reduces the risk of bud rot because you have complete control over your growing environment, which helps avoid temperature swings and improves humidity control. If you grow outdoors, use a leaf blower to use to remove any excess moisture from plants. This is especially essential after heavy rain or morning dew. Indoor plants can be kept dry with an inline fan.
8. Protect your buds from rain: If you grow outdoors and rain is in the forecast, cover your plants with a tarp to protect them. Avoid putting the tarp directly on your plants or leaves, as this could cause damage.
9. Research your varieties: Some strains of cannabis (such as Northern Lights or Royal Moby) have been designed to be more resistant to mold, making a perfect choice for the more mold-concerned cannabis grower.

Prevention is the best treatment, so take these precautions seriously, especially with regards to airflow, humidity levels, and infected buds. Once bud rot strikes it can be difficult to resolve. The invasive fungus is capable of causing significant crop damage, which sometimes goes beyond treatment if the infection gets to an advanced stage.

If you’ve confirmed a bud rot infection, it’s likely the infection will have spread across your grow space. As with prevention, all affected plants should be removed. Some cannabis growers choose to harvest immediately once they even suspect bud rot to protect the rest of their crop. Once a bud begins to mold, it’s no longer safe for consumption, so any buds showing signs of infection should be discarded.

It’s crucial to identify bud rot in its early stages to avoid issues with your harvest. At the first sign of and infection, it’s essential to take action to avoid further problems in your grow room or outdoor space.

• Don’t expose any healthy plants to any infected ones.
• Wear different clothes and use different gloves.
• Sanitizing or remove any equipment used in the treatment process.

Products, such as fungicides, can be used to treat infected buds. However, avoid using fungicides, neem oil, or sulfur if your plants have reached the flowering stage, and these products will change the taste, smell, and appearance of the buds from the inside. Make sure you read product labels and understand how to use any products used to combat a fungal infection.

Can rot happen after harvest?

Yes, so you need to be vigilant even as mold can appear during the drying process. Here’s how to avoid this from happening:

1. Check plants’ colas when picking and discard any affected areas.
2. Harvest after a dry spell so your buds have lower moisture content.
3. Pull off fan leaves and trim before drying.
4. Leave space between branches during drying.
5. Ensure the correct humidity, light, and temperature conditions for drying.
6. Adjust your drying speed if necessary. If you finding mold during this phase, increase the temperature of your drying room and decrease humidity.

Bud rot is the scourge of growers everywhere, and it’s important you learn to recognize the symptoms before you reach the stage where you actually get bud rot and fungus spores have begun to spread.

Of course, prevention is the best treatment, and the best way to prevent bud rot is to build a self-contained grow room with proper ventilation.

To learn more about airflow and circulation—including the equipment you need to keep bud rot at bay—check out our guide on choosing the best inline fan for your needs.