
Bud rot is a pervasive fungal infection, scientifically known as Botrytis cinerea, that affects cannabis plants, particularly during the flowering stage. This disease thrives in environments where humidity is high and airflow is poor, making it a major threat to both outdoor and indoor growers. If left untreated, bud rot can decimate crops by causing buds to deteriorate from the inside out. This disease has a severe impact on your crops. By the time you notice the flower buds starting to rot, the interior of the buds has already been completely destroyed!
For cannabis growers, especially those applying organic farming, early identification and proactive management are crucial. Using a biological fungicide like FungiGuard provides a sustainable, chemical-free solution that prevents fungal spores from spreading, ensuring healthier harvests.
What is Bud Rot?

Bud rot is caused by the Botrytis cinerea fungus, which prefers damp and cool conditions to flourish. Cannabis plants are particularly susceptible due to the moisture that can accumulate within their dense buds, creating an ideal breeding ground for this fungus. The infection usually begins in the inner layers of the buds and spreads outward, causing the affected buds to turn grayish-brown and crumble when touched.
Outdoors, bud rot can strike after periods of rain, especially if plants don’t receive adequate airflow to dry quickly. Indoors, improper climate control—such as high humidity and poor ventilation—can increase the risk of fungal growth. Whether you’re cultivating cannabis in a greenhouse, indoor grow room, or open field, managing environmental factors like humidity and airflow is crucial to preventing bud rot.

The actual images of a cannabis plant afflicted with Bud Rot.
Symptoms of Bud Rot in Cannabis Plants

The actual images of a cannabis plant afflicted with Bud Rot.
Identifying bud rot early can mean the difference between saving your crop and losing a significant portion of it. The symptoms often start with subtle signs that can be easy to miss if you're not vigilant. Here are the key symptoms to look for at various stages of development:
- Bud-Level Symptoms: Bud rot typically starts in the interior of the buds, which makes early detection difficult. As the infection progresses, you'll notice discoloration—often a grayish-brown hue—along with a dry, crumbly texture in the infected area. Affected buds may also emit a musty, damp smell, a telltale sign of fungal activity.
- Leaf-Level Symptoms: Bud rot can also affect the leaves surrounding the infected buds. Infected leaves often turn yellow or brown, becoming brittle and more likely to fall off. Although leaf damage alone may not always indicate bud rot, when combined with the other symptoms, it can be a clear warning sign.
- Stem and Cola Symptoms: If left untreated, bud rot can spread from the buds to the stems and colas. You'll notice areas where the stems become soft and may start to break apart. This stage of the infection can cause entire colas to collapse, leading to.
By the time these symptoms become visible, the infection has often taken root deep within the plant, which is why regular monitoring is essential for early detection. Knowing how to recognize the signs early, especially during high-risk periods of high humidity, can save your crop from severe damage.
Common Causes of Bud Rot

1. High Humidity
Humidity plays a crucial role in the development of bud rot. When humidity levels rise above 50%, especially during the flowering stage of cannabis, moisture can easily accumulate within the dense buds. This creates the ideal environment for fungal spores to thrive and spread. Both indoor and outdoor growers must monitor and regulate humidity levels to minimize the risk of infection.
2. Poor Air Circulation
Inadequate airflow is another major contributor to bud rot. Cannabis plants, particularly in indoor grow rooms or greenhouses, can experience stagnant air, leading to high moisture pockets that encourage fungal growth. Outdoor plants that are spaced too closely can also suffer from poor air circulation, making them vulnerable to infection. Ensuring that air circulates freely around and through the plants is essential to keeping them healthy.
3. Cool Temperatures
Botrytis thrives in cool, damp conditions, which makes temperature control vital in preventing bud rot. When temperatures fall, especially at night, moisture within the buds and leaves doesn’t evaporate quickly, increasing the risk of mold. For indoor growers, maintaining a stable temperature between 60-77°F (15-25°C) can help reduce the likelihood of rot. Outdoor growers should be aware of sudden drops in temperature, particularly in humid environments.
4. Overcrowded Plants
Crowded plants can block airflow, creating small, high-humidity zones that are perfect for fungal spores to develop. Both indoor and outdoor growers should be mindful of plant spacing to ensure proper airflow and to prevent the dense canopy from trapping moisture. Regular pruning and plant training techniques, like defoliation or lollipopping, can also help by thinning out the plants and allowing better air movement.
How to Prevent Bud Rot
Prevention is the best defense against bud rot, and it involves a combination of environmental control and proactive plant care. Implementing these practices consistently can drastically reduce the chances of an outbreak in your grow area.
1. Control Humidity Levels
The key to preventing bud rot is maintaining optimal humidity. During the flowering stage, aim to keep the relative humidity between 40% and 50%. Indoor growers should use dehumidifiers to regulate the moisture in the air. Outdoor growers need to rely on natural ventilation, choose a suitable location to grow and good plant placement to avoid excess moisture. Proper humidity control is crucial to keeping fungal spores at bay.
2. Improve Air Circulation
Good air circulation is essential to preventing bud rot. Indoor growers should place oscillating fans around the grow room to keep air moving through the plants, especially in areas prone to moisture buildup. Outdoor growers should ensure plants are spaced far enough apart to allow natural breezes to flow through the foliage. Pruning large fan leaves and other excess vegetation helps promote airflow and keeps plants dry.
3. Maintain Stable Temperatures
Keep your grow room temperatures between 60°F and 77°F (15°C to 25°C) during the flowering stage to reduce the risk of mold growth. For outdoor growers, be mindful of cool, wet conditions, especially after rain. Installing temperature sensors can help monitor fluctuations, and making use of greenhouses or other shelters during wet weather can protect plants from sudden temperature drops.
4. Prune and Train Your Plants
Regular pruning and plant training techniques are vital for keeping plants healthy and preventing bud rot. Removing excess foliage, especially in the lower parts of the plant, helps reduce moisture retention. Methods like LST (Low-Stress Training) and SCROG (Screen of Green) can be used to ensure better light penetration and airflow throughout the canopy. Thinning out your plants also ensures that the dense areas where moisture tends to accumulate are more open, reducing the risk of fungal growth.
5. Water Plants Carefully
Overwatering is a leading cause of excess moisture, which can increase the risk of bud rot. Water your plants at the base and avoid getting the buds or leaves wet, as moisture trapped in the foliage can lead to fungal growth. Ensure the top inch of soil dries out between watering to prevent over-saturation. In outdoor growing, it's best to water early in the day so the plants have time to dry before the evening.
FungiGuard: The Organic Solution

1. Why FungiGuard is Essential
FungiGuard is a 100% organic solution designed for organic farming practices. It contains beneficial microorganisms that prevent bud rot and other fungal infections by targeting infected areas and stopping the spores from spreading. FungiGuard works particularly well in both indoor and outdoor growing, providing the protection needed in conditions where Botrytis cinerea thrives.
2. How to Apply FungiGuard
To use FungiGuard effectively, mix 2-2.5 ml of the product with 1 liter of water and adjust the pH level of the solution to between 5.5 and 6.5. Spray the solution evenly over the plant, ensuring it penetrates the buds and foliage thoroughly. Focus on any areas showing signs of infection to halt the spread of the fungus. FungiGuard can be used in both indoor and outdoor environments, making it a versatile tool for cannabis growers.
Combining FungiGuard with FungiShield for Maximum Protection
For severe fungal outbreaks or to provide extra protection, growers can combine FungiGuard with FungiShield. While FungiGuard works to kill existing spores, FungiShield forms a protective barrier around the plant to prevent further fungal development, particularly against threats like powdery mildew. This combination is ideal for growers facing persistent or high-risk fungal environments.
FAQs
What are the main causes of bud rot?
Bud rot is primarily caused by high humidity, poor air circulation, and cool temperatures. These environmental factors create ideal conditions for Botrytis cinerea to thrive.
How do I stop bud rot from spreading?
If bud rot is detected, prune the infected buds immediately and discard them carefully. Use organic fungicides like FungiGuard to treat affected areas and prevent further spread.
Can bud rot spread to other plants?
Yes, bud rot is contagious and can spread through airborne spores or physical contact between plants. Isolate infected plants and improve air circulation to minimize the risk of the disease spreading.