Botrytis (Bud Rot)
This guide is provided for educational purposes only and is intended for adults 21 years of age or older who are growing legally in their jurisdiction. Always follow product labels and local regulations.
Botrytis, commonly called bud rot, is a fungal disease that attacks dense flowers and damaged plant tissue. It often starts inside the bud where you cannot see it, then shows up as a sudden patch of dying material or a “soft” section of flower. When it appears, the priority is containment.
Start here if you are unsure what you are looking at:
If you suspect bud rot, handle buds gently and avoid shaking spores into the room.
Quick ID
- What you see: a section of bud that looks dull, brown, collapsing, or “dead” compared to healthy tissue
- Where it shows: dense colas, interior flower sites, and anywhere moisture stays trapped
- What confirms it: when you gently open the bud, the interior is brown or gray and may look fuzzy or dusty
- What it is often confused with: normal senescence, nutrient fade, mechanical damage, caterpillar damage
Simple confirmation method:
- Choose a suspect bud and open it carefully over a trash bag
- Look for brown or gray tissue in the interior where it should be bright and healthy
- Smell can be a clue. Rot often smells “off” compared to clean flower
Why Botrytis Shows Up
Botrytis thrives when moisture is trapped in dense flowers. It is most common late in flower, during humid stretches, or when airflow cannot reach the interior of large buds. Any tissue damage increases risk.
Common drivers
- High humidity and poor airflow through the canopy
- Dense flowers that hold moisture, especially late flower
- Condensation events, wet leaves, or irrigation splash
- Damage from caterpillars, pruning wounds, or mechanical breaks
First 24 Hours Plan
The goal is to contain spores, remove infected material, and stop the environment from favoring rot. This is one of the few problems where delaying action almost always makes things worse.
- Confirm it. Check a suspect bud carefully.
- Remove infected material. Cut out affected buds with margin and discard immediately.
- Bag and clean. Do not move infected material through clean areas uncovered.
- Increase airflow. Move air through the canopy and remove stagnant pockets.
- Stabilize humidity. Reduce humid periods and avoid moisture swings.
Do not do this:
- Do not shake infected buds
- Do not “try to save” visibly rotting flower
- Do not increase humidity to chase VPD while rot is active
Scouting and Monitoring
Botrytis is often invisible until it is established. You are scouting for subtle changes in bud texture and color, especially deep inside dense flowers.
Simple scouting routine
- Frequency: at least weekly in flower, increase to 2 to 3 times per week in late flower
- Where to look: densest colas, shaded interior sites, and any damaged tissue
- What to track: new suspect sites, humidity patterns, and which plants are most prone
- Tools: good lighting, gloves, clean scissors, notes
Control Options
Botrytis management is mostly prevention and containment. Once it is inside the bud, you do not “spray it away.” Your leverage is environmental control and clean removal of infected material.
Low-risk first moves
- Remove infected buds and dispose of them immediately
- Thin the canopy slightly to improve airflow and reduce trapped moisture
- Keep leaves dry and avoid water sitting in the canopy
If pressure is building
- Increase environmental discipline: airflow through buds and stable humidity
- Reduce overcrowding and remove weak interior sites that never fully dry
- Use only labeled options appropriate for your crop stage and jurisdiction, if applicable
Note: We intentionally do not list specific products, mixes, or rates here. Always follow product labels and local regulations.
Often Confused With
- Normal fade: leaf yellowing late in flower without rotten tissue inside buds
- Caterpillar damage: frass and chewing often precede rot in buds
- Mechanical damage: bruised tissue without fuzzy gray growth or spread pattern
If you are not sure, use the diagnostic tool: What Pest Is This?
Next Steps
Botrytis is best handled by staying ahead of humidity and not letting dense flowers stay wet. If you find it, focus on clean removal, containment, and tightening the environment immediately.
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