Powdery Mildew on Cannabis
Powdery mildew (PM) is a fungal disease that coats leaves in white powder. It spreads fast, weakens the plant, and makes buds unsellable.
What it looks like
- ●White powdery patches on leaf tops (like flour dusted on)
- ●Patches spread and merge over days
- ●Advanced: leaves yellow and die
- ●Can appear on buds in late flower (bud rot risk)
Quick diagnostic checks
Measure before you treat
Plant diagnostic essentials
These tools help confirm the cause of powdery mildew 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 AmazonGovee Bluetooth Hygrometer
Track temperature and humidity trends instead of guessing from one reading.
Check price on AmazonAC Infinity CLOUDLINE T4
Automate airflow to manage heat, humidity, and mold pressure.
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Causes ranked by likelihood
1. High humidity (above 60%)
Most commonSigns
- ●RH above 60% for extended periods
- ●Poor airflow
- ●Dense canopy
Fix
- ✓Drop humidity: 55-60% veg, 40-50% flower
- ✓Run oscillating fans at canopy level constantly
- ✓Defoliate dense inner growth
Recommended products
AC Infinity CLOUDRAY S6
Canopy-level oscillating fan — prevents PM
2. Poor airflow
CommonSigns
- ●Stagnant air inside the canopy
- ●Dense inner foliage
Fix
- ✓Prune inner leaves
- ✓Add clip-on fan at canopy level
⚠️When to worry
Always. Once established, PM is very hard to eradicate. Prevention > cure.
Gear that prevents this problem
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