Bud rot is a destructive fungal disease that attacks the flowering parts of a plant. This infection starts internally, making it difficult to detect early, and it can spread quickly through a crop. If left unchecked, it can lead to the complete loss of a plant’s valuable flowers or even an entire cultivation cycle. Understanding the signs and the conditions that allow it to flourish is the first step in protecting your plants.
How to Identify Bud Rot
The initial signs of bud rot can be subtle because the fungus begins its growth deep within the dense flower structure. Growers should look for individual sugar leaves that begin to yellow, wilt, or turn brown in patches. A mushy, grayish discoloration on the stem just below the flower is another early indicator that the infection has begun to spread from the core. Once the infection progresses, the affected area will turn a dark gray or brown and take on a soft, slimy consistency.
The only reliable way to confirm the presence of this mold is to gently pull apart a suspect flower to examine its inner core. A rotten interior will appear dark gray or brown and may have a visible, wispy white or grayish-white fuzzy mold growth. Rotting buds may also emit an unpleasant, musty odor that contrasts sharply with the plant’s normal aroma. Since the mold works from the inside out, the infection is already well-established by the time external visual cues are obvious.
Understanding the Fungal Pathogen
Bud rot is caused by the fungus Botrytis cinerea, commonly known as gray mold. This fungus is opportunistic and can survive for extended periods on dead or decaying plant material, waiting for the right conditions to attack healthy tissue. Botrytis cinerea is an aggressive organism that produces vast numbers of microscopic, asexual spores called conidia, which are easily dispersed by air currents, water, and human activity.
The fungus requires specific environmental conditions to germinate and thrive, primarily focusing on moisture and temperature. Spores need free water or a relative humidity level above 90% to initiate an infection. Optimal temperatures for fungal growth fall between 64 and 75°F (18–24°C), though growth is possible as low as 32°F (0°C). The combination of high humidity, poor air circulation, and cooler temperatures during the late flowering stage creates the perfect environment for this disease to flourish.
Immediate Steps for Infected Plants
The discovery of bud rot requires immediate action to prevent the infection from spreading across the rest of the crop. The first step is to isolate the infected plant or branch to minimize spore dispersal. When handling the diseased material, extreme care must be taken to avoid shaking the plant, which can release a cloud of spores into the air.
Using sterilized pruning shears, growers must remove the entire affected bud and surrounding tissue, cutting several inches below any visible signs of infection into healthy material. The fungal mycelium often extends into adjacent tissues that appear healthy. All removed waste must be immediately placed into a sealed bag for disposal, never composted, as the spores can survive and reinfect future crops. Tools should be sterilized with 70% isopropyl alcohol or a bleach solution after every cut to prevent accidentally inoculating healthy parts of the plant.
Long-Term Environmental Prevention
Preventing Botrytis requires making the cultivation environment inhospitable to fungal growth. Maintaining appropriate humidity levels is the most important preventative measure, as the spores require moisture to germinate. During the flowering phase, relative humidity should be kept below 55%, decreasing to 40–45% in the final weeks before harvest.
To manage the environment:
- Indoor growers should utilize dehumidifiers to actively manage air moisture and keep the humidity stable.
- Increase air circulation with the strategic placement of oscillating fans to ensure air moves freely over and through the plant canopy.
- Proper plant spacing and regular pruning of non-essential inner leaves help prevent the formation of stagnant, humid microclimates within dense foliage.
- Outdoor plants benefit from covering them during heavy rain and gently shaking off any excess dew or moisture in the mornings to avoid prolonged wetness.