Bud Rot (Botrytis): Prevention, Signs, and What to Do
By The Budometry TeamPublished Updated
Botrytis works from the inside of a cola outward, so by the time you see it on the surface it is well established. Prevention is the entire strategy.
Part of our pillar guide: Grow Room Climate: Temperature, Humidity, Airflow and Smell
What it looks like
A single sugar leaf in the middle of a cola that has gone yellow or grey and pulls out with no resistance. Underneath, the bud is brown, dusty grey, and mushy or dry-rotted.
Conditions that cause it
Relative humidity above 55-60% in flower, stagnant air inside dense colas, wide temperature swings at lights-off that condense moisture, and thick foliage that traps humidity.
Prevention
Hold late flower at 45-50% RH. Keep oscillating fans moving air through the canopy, not just above it. Defoliate enough that light and air reach interior buds. Keep the lights-off temperature drop under 10-15°F.
If you find it
Cut out the affected cola and several inches around it with clean shears, bag it immediately, and remove it from the room. Do not try to salvage or dry moldy flower. Then fix humidity before the rest goes.
Frequently asked questions
- Can I smoke bud that had rot cut out of it?
- No. Discard affected material — mold spores spread through the surrounding flower even where it looks clean.
The full guide on this topic
Grow Room Climate: Temperature, Humidity, Airflow and Smell
Stage-by-stage temperature and humidity targets, VPD explained simply, how to size an inline fan, and how a carbon filter keeps a flowering tent from being noticed.