Bud Rot (Botrytis) in Cannabis
Bud rot (Botrytis cinerea) is the worst disease in cannabis flowering. It rots buds from the inside out, turning flowers into gray mush.
What it looks like
- ●Gray/brown fuzzy growth inside buds
- ●Once-dense buds feel mushy or hollow
- ●Surrounding leaves yellow and curl
- ●A musty smell from affected buds
Quick diagnostic checks
Measure before you treat
Plant diagnostic essentials
These tools help confirm the cause of bud rot before you change nutrients, watering, or the environment.
Carson MicroBrite Pocket Microscope
Inspect leaf undersides for mites, eggs, mildew, and harvest-ready trichomes.
Check price on AmazonAC Infinity CLOUDLINE T4
Automate airflow to manage heat, humidity, and mold pressure.
Check price on AmazonVIVOSUN pH and TDS Meter Combo
Check root-zone pH and nutrient strength before changing a feeding plan.
Check price on AmazonSave the bud rot recovery plan
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Causes ranked by likelihood
1. High humidity in flower
Most commonSigns
- ●RH above 55% during flower
- ●Wet/cold nights (outdoor)
Fix
- ✓Keep flower humidity at 40-50% max
- ✓Bring outdoor plants inside for rainy days
- ✓Run dehumidifier at night when temps drop
Recommended products
AC Infinity CLOUDLINE T4 Inline Fan
Exhausts humid air on a thermostat/humidity trigger — the #1 bud-rot preventative
Govee Bluetooth Hygrometer
Alerts your phone the moment flower RH climbs past 55%
2. Stagnant air in dense colas
Most commonSigns
- ●Big dense buds with no airflow through them
- ●Foxtail growth trapping moisture
Fix
- ✓Canopy-level oscillating fans — air should move through every bud
- ✓Defoliate aggressively in flower (bottom ⅓)
3. Caterpillar damage leading to rot
CommonSigns
- ●Frass (worm poop) in buds
- ●Growing outdoors
Fix
- ✓Apply BT throughout flower to prevent caterpillar damage
⚠️When to worry
ALWAYS. Bud rot is the #1 cause of lost flower harvests. Act within hours of spotting.
Gear that prevents this problem
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