Botrytis in Cannabis: Identifying and Managing Bud Rot

Botrytis cinerea, commonly known as gray mold or "bud rot," is a destructive fungal pathogen that affects cannabis plants. It grows well in certain conditions. These include high humidity, low airflow, and thick plant canopies. This makes it a big worry for growers.

Studies from different state universities show that Botrytis is a common and harmful plant disease in cannabis farming. Without proper management, it can lead to substantial crop losses.

Gray mold usually appears as small, water-soaked spots on leaves, stems, or buds. As the infection progresses, these areas become covered with a fuzzy gray or brownish mold. Infected plants often show signs of necrosis, with parts of the plant turning brown or black and dying off. Bud rot is a common problem caused by Botrytis. It makes cannabis flowers decay from the inside out. This often goes unnoticed until a lot of damage has happened. Regularly inspecting your crops, especially in dense plant canopies, is crucial to catch early symptoms of this plant disease.

What Causes Bud Rot?

Bud rot, or Botrytis cinerea, is caused by a fungal pathogen that thrives in certain environmental and cultivation conditions. Understanding the causes is key to preventing its devastating effects on cannabis crops. Here’s a breakdown of the main causes:

1. High Humidity

• Bud rot thrives in environments with high relative humidity (above 60%). Moisture in the air provides the perfect conditions for fungal spores to germinate and spread.
• Dense buds trap humidity inside, creating microclimates where moisture is high and air circulation is limited.

2. Poor Airflow

• Lack of ventilation in grow rooms, greenhouses, or even outdoor spaces can lead to stagnant air around the plants. This traps moisture within the plant canopy and creates ideal conditions for fungal growth.
• Overcrowded plants exacerbate the problem by limiting airflow between them.

3. Cool, Damp Conditions

• Cool temperatures combined with dampness increase the likelihood of fungal growth. Morning dew, fog, or rain that settles on plants can lead to bud rot, especially during flowering.
• Outdoor growers are particularly vulnerable to these conditions, especially in wet or coastal climates.

4. Plant Stress or Weakness

• Weak or stressed plants are more susceptible to infections. Stressors include nutrient deficiencies, overwatering, underwatering, or physical damage to plant tissues.
• Damaged plant tissue from pruning, pests, or mechanical injury can act as entry points for fungal spores.

5. Overcrowded Plant Canopies

• Dense foliage traps humidity and prevents light from penetrating lower branches and buds. This dark, moist environment is perfect for Botrytis to thrive.
• Improper pruning or lack of training techniques, like SCROG (Screen of Green), can exacerbate this issue.

6. Inadequate Sanitation

• Spores of Botrytis can linger on tools, grow spaces, or even in the air. If hygiene practices remain poor, these spores can easily infect plants.
• Cross-contamination during handling of infected and healthy plants is a common cause of spread.

7. Overwatering or Poor Drainage

• Wet soil or bad drainage can keep roots moist and raise humidity around the plant. This can promote fungal growth.
• Excess water can also weaken plants, making them more vulnerable to infections like Botrytis.

8. Late Flowering Stages

• Bud rot commonly affects cannabis during the flowering stage, as dense buds and sticky trichomes trap moisture.
• Plants close to harvest are more vulnerable. They may be under some stress as they focus energy on making flowers.

How Does Bud Rot Develop?

Once spores of Botrytis cinerea land on a suitable host, they need:

• Moisture to germinate.
• Plant tissue to feed on, often entering through wounds or natural openings.
• Favorable temperatures (typically between 59°F to 77°F or 15°C to 25°C). 

The fungus begins inside the bud and spreads outward, often unnoticed until the damage is severe. The infected tissue turns dark, dries out, and crumbles, releasing more spores to infect nearby plants. 

By knowing these causes, growers can change their environmental controls, spacing, and cleaning methods. This helps lower the risk of bud rot in their cannabis crops.

Dosatron pumps do not directly get rid of Botrytis. However, they are very helpful in delivering nutrients and applying treatments to protect plants.

Delivering Vital Nutrients

Healthy plants are more resistant to infections. Dosatron pumps allow for precise delivery of nutrients like calcium, silica, and potassium, which strengthen plant tissues and make it harder for fungal pathogens to penetrate.

Applying Preventative Treatments

Dosatron pumps can mix and distribute hydrogen peroxide solutions, beneficial microbes, or fungicides. These treatments help create an environment that inhibits fungal growth.

Disinfection of Irrigation Systems

Spores of gray mold can travel through irrigation water. A Dosatron system can dose sanitizing agents like chlorine or peracetic acid into irrigation lines, ensuring a clean and disease-free water supply.

Consistent Application

Dosatron’s precision ensures that all plants receive the same amount of treatment or nutrients, reducing inconsistencies that could leave some plants vulnerable to infection.

• Optimize Plant Spacing: Proper plant spacing improves airflow and reduces humidity within plant canopies. This simple adjustment minimizes the environmental conditions that Botrytis needs to thrive.
  
• Control Humidity and Temperature: Use dehumidifiers and fans to maintain optimal environmental conditions. Keeping relative humidity below 50% during flowering stages can significantly reduce the risk of gray mold.
  
• Prune and Train Plants: Regularly pruning lower branches and removing excess foliage improves air circulation and light penetration, reducing the likelihood of fungal growth. Techniques like SCROG (Screen of Green) or LST (Low-Stress Training) provide a more open plant canopy.
  
• Sanitize Tools and Equipment: Prevent cross-contamination by sterilizing tools between uses. This reduces the risk of spreading Botrytis cinerea from infected plants to healthy ones.
  
• Inspect Plants Regularly: Conduct routine inspections, especially during periods of high humidity or after rainfall. Early detection allows for targeted removal of infected plants or areas, preventing further spread.
  
• Choose Resistant Strains: Some cannabis strains are naturally more resistant to Botrytis. Consult resources like state university agricultural extensions for guidance on selecting resilient varieties.
  
• Use Biocontrol Agents: Beneficial microbes such as Trichoderma or Bacillus subtilis can help prevent gray mold by competing with Botrytis for resources and space on plant surfaces.
  
• Proper Drainage: Ensure your growing medium and pots have adequate drainage to prevent waterlogging. Excess water increases humidity and creates favorable conditions for fungal growth.

• Dehumidifiers: Keep relative humidity below 50% during the flowering stage by using a high-quality dehumidifier. Monitoring and controlling humidity levels are crucial in preventing fungal outbreaks.

• Oscillating Fans: Strategically place fans within the grow space to improve airflow through plant canopies. Good air movement prevents moisture buildup, which is essential for limiting fungal growth.
• Hygrometers and Sensors: Use digital hygrometers or advanced environmental sensors to track humidity and temperature levels in real-time. These tools help identify problem areas and ensure conditions remain within the ideal range.
• UV-C Light: Use UV-C light treatments as part of your integrated pest management (IPM) plan. UV-C light disrupts fungal spores and can significantly reduce the spread of gray mold.
• Biological Fungicides: Incorporate natural fungal controls like Trichoderma or Bacillus subtilis. These biocontrol agents compete with Botrytis cinerea and reduce its ability to establish colonies on cannabis plants.