White powder on cannabis leaves – powdery mildew help!

DON'T panic. Powdery mildew in week 3 of flower is treatable.

Immediate steps:

1. Remove the worst affected leaves (bag them, don't shake spores around)
2. Increase airflow immediately — add another fan
3. Drop humidity below 50%
4. Spray with potassium bicarbonate solution (1 tbsp per gallon) — safe in flower

DO NOT spray neem oil in flower — it affects taste.

Your crop is NOT ruined if you act fast. The buds that aren't affected will be fine.

Adding to Dave's advice: after harvest, do a bud wash. 3 buckets: hydrogen peroxide water, lemon juice water, plain water. Dip and swish. This removes any remaining PM spores and is totally safe. I do this for all outdoor harvests.

Prevention for next run: keep humidity under 55% in flower, ensure good air circulation, and defoliate properly so air can move through the canopy. PM thrives in stagnant, humid air.