It’s essential to keep a cannabis plant healthy to increase the yield and give it the best chance of producing high-quality buds when it’s time to harvest. One issue that cannabis cultivators run into is the dreaded bud rot.

Also known as gray mold, this fungus can affect tomatoes, cucumbers, and roses, but we’re mainly interested in the issues it can cause cannabis plants. When mold occurs, humidity and poor airflow causes mold to increase. Unfortunately for growers, bud rot is super common. Here, we look at how to identify bud rot quickly and what to do about it to prevent crop loss.  

What is Bud Rot?

Botrytis cinerea, also known as gray mold or bud rot, is first identifiable on the plant stem as a gray coloration, but it'll eventually turn leaves yellow as well.

The leading causes of bud rot are environmental factors, including high humidity, poor air circulation, fluctuating temperature, and improper ventilation. It most commonly occurs in the late flowering phase, so be sure not to count your yield too early to avoid disappointment. 

Symptoms of Bud Rot in Cannabis Plants

Visual Indicators

The following visual indicators are a sign that your plant or plants have been affected by bud rot. 

Photo source: CDNSciencePub

1. Discoloration: Brown, gray, or blackened areas in buds.
2. Moldy appearance: Grayish, fuzzy or powdery growth.
3. Shriveling or wilting: Affected buds may look limp or dehydrated.
4. Deteriorating texture: Buds that feel soggy or mushy to the touch.

Smell

While the sweet smell of cannabis can indicate a good plant, it is also an indicator of whether a plant has bud rot. 

1. Unpleasant, musty odor that contrasts with the normal fragrant aroma of healthy cannabis.
2. Sharp, decaying scent indicating fungal infection.

Spread of Infection

Look out for whether or not the infection has spread before 

1. Early symptoms often appear at the core of the bud and spread outward.
2. Affected areas become soft and easily break apart.

How Bud Rot Develops

Botrytis cinerea affects more than 200 plant species, including the cannabis plant. The infection enters a plant through open wounds and then spreads spores across a whole crop in the wind, direct contact, or water. In cannabis plants, bud rot will start in a few damaged buds and quickly spread to the rest of the plant.

 Due to the fashion in which bud rot spreads, it’s essential to control humidity and ideally keep it between 50-70% in the cannabis growing area, ensure constant airflow, and prevent excessive moisture that can facilitate the growth and spread of bud rot. The following things should be avoided to prevent bud rot from sweeping through a crop:

• Overcrowding

• Overwatering

• Damaging plants

• Not leaving buds on too long

• Balancing nutrients

Identifying Bud Rot at Different Stages of Flowering

Here’s how to identify bud rot at different stages of flowering, so you can catch it quickly and resolve the issue. 

Early signs

Mild discoloration and a slight change in texture.

Mid-flowering

Greater spread of rot, more visible fuzz or mold.

Late-flowering

Total breakdown of buds, spreading across the plant.

Preventing Bud Rot in Cannabis Plants

In astudy by Canadian Science Publishing, bud rot was shown to affect as much as a quarter of the plants grown in greenhouse conditions. If you want to prevent it happening in your crop, follow these rules:

1. Implement proper environmental control by maintaining ideal temperatures between 65-80°F (18-26°C). This temperature may vary depending on the strains you are growing. Additionally, be sure to keep humidity levels between 50-70% in the cannabis growing area. 

2. Ensure adequate airflow and ventilation. This preventative measure can stop bud rot spreading as quickly through your crop and is a great way to prevent mold from starting. 

3. To keep your plants healthy, try these pruning techniques: 

• Lollipopping reduces the amount of branches lower down the plant and improves airflow to the buds at the top. 

• Defoliationremoves excess fan leaves to keep airflow to the plant. 

• Toppingremoves the top of the main stem to encourage horizontal growth that improves air circulation

4. Inspect your plant thoroughly and regularly to identify early signs of mold and bud rot quickly. 

5. Preventive natural treatments like neem oil spray can prevent growth, just avoid spraying it on mature buds. Fungicides like potassium bicarbonate can also be used to keep plants healthy and make an inhospitable area for fungus to develop. 

6. Never overwater and be sure to provide proper drainage for old water to prevent mold growth. 

How to Treat Bud Rot if Detected

Here’s how to treat bud rot if you detect it in your plants. 

Early Intervention

If you detect bud rot in your plant, remove the infected buds carefully with disposable gloves to prevent further spread. Additionally, you can isolate any affected plants quickly and remove them from the overall crop to prevent further spreading. 

Preventative Fungicides

Utilize preventative fungicides to ensure a healthy crop. Several options include neem oil or garlic spray in small amounts, which have antifungal and antibacterial properties. You can also use chemical fungicides like chlorothalonil, but you need to be careful when you administer them, as they are not advised during later stages of growth due to residue. 

Increased Air Circulation

One of the best ways to guarantee a great grow is to keep airflow around your crop. You can use humidifiers and fans to encourage good airflow and prevent bud rot spreading. 

The Importance of Harvesting Before Bud Rot Takes Over

Monitoring trichomes is one of the best ways to determine when to harvest a plant. Trichomes are the crystals on a bud that sparkle in the light. You can use a magnifying glass (like in a jeweler) to inspect trichomes. When the trichomes have become milky, it’s time to harvest.

While you can leave them on until they turn red or amber, this does increase the risk of bud rot. If you detect bud rot in a plant, it might be time to harvest early to prevent further spreading. Use sharp tools and act quickly, making sure you avoid shaking plants that could make the bud rot spread. 

Conclusion

Detecting Botrytis cinerea or bud rot in a plant can be disheartening, but it doesn’t mean you have to get rid of everything and start over again. Look out for grayish coloration during regular inspections to catch it early.

Implement preventative techniques and early intervention to protect the overall crop, even if you must isolate and dispose of some infected plants. Remember to maintain ideal temperatures and humidity, ensure adequate airflow and ventilation, prune well for airflow, inspect regularly, and never overwater.