White powder on buds and sugar leaves
Spreads from leaves to sugar leaves and bracts; trichomes look matted..
- Also called
- powdery mildew on buds
- PM on buds
- white powder buds
Likely causes, most likely first
Ranked for this sign on its own. Your stage, medium and readings change the order, so run the checker for your plant.
LikelyPowdery mildew
Fix: Treat early in veg: remove the worst leaves into a bag, improve airflow and stable humidity (avoid big day-night RH swings), and use least-toxic contact options (e.g. potassium bicarbonate, sulfur, or biological products, in veg only; never sulfur near oils or in flower). Once it reaches flowers there is no clean fix. Choose resistant genetics and clean clones.
Recovery: No new colonies on treated or new leaves within 7-10 days.
How to confirm it
- Wipe test for white coatings. Wipe a white spot gently with a damp finger or cotton bud and mark the leaf. Powdery mildew comes off as powder and reappears in 2-5 days on the same and nearby leaves; spray or hard-water residue wipes off and stays gone; trichomes and thrips scars do not wipe off. Wash hands afterwards: spores travel on fingers.
- Check temperature and RH at canopy height with a calibrated sensor. Put a calibrated sensor (salt test: a sealed bag with damp table salt reads 75% RH after 8-12 hours) at canopy height, out of direct light, and log for 24 hours including lights-off. Look for lights-off RH spikes and dew point.
Look for
Flat matte white patches on sugar leaves, unlike the sparkle of trichome heads..
The full guide: Powdery mildew in cannabis
Guidance, not a guarantee. The checker weighs common causes against what you tell it; confirm with the tests before you treat, change one thing at a time and watch the new growth.
