How to identify and avoid bud rot

Just like the satisfaction of a home-made cake can spur some to learn baking, a home-grown joint can tempt many cannabis aficionados into becoming growers. For beginner cultivators raising healthy plants can be one of the steepest learning curves. The rapidity at which a rogue fungus or mold can destroy a plant is breathtaking. Infected buds can be destroyed in as little as a week.

withered marijuana plant
The rapidity at which a rogue fungus or mold can destroy a plant is breathtaking. 
Photo by: Gina Coleman/Weedmaps

One of the most common diseases new growers encounter is bud rot, also known as botrytis cinerea, or gray mold. Bud rot can wreak havoc on crops if left unchecked, so the ability to detect its signs early and prevent it will help ensure healthy plants.

What is bud rot, and when does it occur?

Bud rot is a fungal pathogen or a type of mold that develops in the heart of cannabis buds. While the appearance of the fungus often occurs in the later stages of flower development, it usually permeates the bud tissue at an earlier stage in the crop development but remains dormant. When the environment becomes conducive, the mold rapidly rots the buds from the inside by crumbling the surrounding layers, spreading out in all directions. 

Usually, denser buds are affected, but in some cases, patches may become visible over the entire plant. As the mold spreads, it can produce and transmit spores to other plants. Mold can also become an issue after harvest during the drying process. 

How do you detect bud rot?

If you're new to growing cannabis and unsure of how to detect bud rod, here are some signs to look for:

Discoloration in and around the bud

According to Danny Danko, author of Cannabis: A Beginner's Guide to Growing Marijuana, there are several giveaways that indicate the onset of bud rot. ”The first sign of bud rot will be a discoloration of flowers and the short leaves protruding from them,” says Danko. “The buds will have pockets of brown, gray, or black (dark purple) chunks that look dry and crumbly.” Danko recommends using a magnifying glass or loupe to examine buds.

Bud rot initially appears as pale, powdery mildew on buds, but becomes darker in color as the bud assumes a slimy consistency. When the mold has fully taken hold, the infected bud will easily separate, showing a dark, dusty interior. The dust is mold spores.

Dark or dried-up colas

The colas, or central flower clusters that form in the upper portion of the main stems, may also hint at bud rot. Colas which appear dried up or darker in color can indicate the presence of mold. A diseased cola will stand out in contrast to the healthy tissue of the plant, making it relatively easy for even newbie growers to see that something is amiss.

dry marijuana plant
Colas which appear dried up or darker in color can indicate the presence of mold. 
Photo by: Gina Coleman/Weedmaps

Yellow leaves 

The sudden emergence of yellow leaves attached to colas can be a sign that there is mold at the base of the leaves. Yellow leaves with bud rot often fall out easily. Close inspection of the leaves may reveal mold spores close to the cola.

Can moldy buds be saved?

Once a bud begins to show signs of bud rot, it is unsafe for consumption and must be discarded. “In some cases, when discovered early, a grower can cut out the parts of the flowers affected by bud rot and reduce the spread,” explains Danko. “Use sanitized and sterile tools and clean them often to avoid spreading the spores.” 

After the infected bud or buds have been removed, the rest of the plant can be allowed to grow. However, if there is a widespread infection, destruction of the plant may be prudent to avoid infecting other plants nearby.

How do you prevent bud rot outside and inside?

According to Danko, bud rot tends to be more prevalent in outdoor plants, such as those in climates with humid fall weather like northern California or the Pacific Northwest.

One of the difficulties of plant mold is that it is such a pervasive pathogen. Bud rot can be caused by several different hosts and it can survive for extended periods of time in crop debris. Awareness of the microenvironments and climates in which the fungus thrives can help prevent bud rot.

Danko advises that the best way to keep outdoor plants dry is to protect them from rain and morning dew, and place them far enough apart that they aren't touching. “Cover the plants with a tarp, which doesn't touch the plant tops, or use a greenhouse enclosure to keep them dry. If they do get wet, shake them so that pockets of moisture don't form,” he says.

For those wondering does rain cause bud rot, the answer is that rainy weather fosters conditions conducive to bud rot. The problem is that high humidity and dampness accompany rain, supplying a source of moisture for mold growth on buds.

“Cultivators in areas prone to bud rot should consider growing plants that are more resistant to mold and powdery mildew,” states Danko. “Seeds can be purchased for plants that have acclimated to overly wet conditions.” Seeds that show mold-resistant properties or a higher tolerance to damp conditions include Durban Poison, Brazil Amazonia, and Colombian Gold.

Another option for wetter climates is timing your planting to avoid the onset of the rainy seasons. Auto-flowering cultivars, which start flowering when they reach a certain age, regardless of photoperiod, can be planted in the spring and harvested during the summer, before the wet fall season. 

Danko also recommends removing some of the lower leaves that fan out on bushy plants to promote airflow beneath the canopy -- this goes for both outdoor and indoor plants.

The best way to support indoor plants is by encouraging air circulation. An oscillating fan can efficiently keep air moving inside. “Use proper filtration for all air entering your room and seal off any places air can get in that isn't filtered, such as cracks under doors,” explains Danko.

“Keep your grow room on the warmer side, between 70-80 degrees F and maintain a relative humidity of 40-50 percent.”

Nighttime temperatures should be 10-15 degrees below daytime temperatures so the flowers have a chance to cool down internally. This helps the root system in the same manner. Humidity at night for preventing mold should be 40% or lower.

Neem oil, which is a non-toxic oil derived from the neem tree, is a natural fungicide. It can be diluted and sprayed onto the plant to help ward off the fungi that promote bud rot. 

It's also critical to avoid bud rot after you've harvested your buds. Leaving space between hanging branches as they dry, creating an optimal drying environment, or even speed-drying, can help prevent the conditions in which mold spores thrive.

Was this article helpful? Give Feedback

has been subscribed!

The information contained in this site is provided for informational purposes only, and should not be construed as medical or legal advice. This page was last updated on September 8, 2020.