Powdery mildew, bud rot and root rot

A survey of cannabis grows found several fungal problems again and again. All of them are easier to prevent than cure.

Problems to recognize

The risky moment

The hour after lights-off is when the air cools and humidity jumps. Keep fans running around the clock, and use a dehumidifier if needed.

Don’t use moldy flower

Don’t smoke, vape, eat or process moldy or suspicious flower. Isolate and discard affected material, and inspect the rest of the crop. Mold may extend beyond the spots you can see, so cutting off a margin, washing, curing, freezing or extraction doesn’t establish safety. Clean equipment and follow an appropriate disinfectant label or validated sanitation procedure. Never mix cleaning chemicals.

Starting clean

• Use pasteurized or fresh media where possible. Unpasteurized coco fiber was identified as a possible source of mold.
• If a plant dies of vascular wilt or root rot, throw out the plant and medium, and clean the pot.

Pythium is an oomycete (water mold), while Fusarium is a fungus, and they can cause overlapping symptoms. Brown roots alone don’t identify the pathogen. Get diagnostic help for persistent wilt or spreading disease. Humidity control helps, but powdery mildew can occur without free water on leaves, so a low room reading isn’t a cure.