Botrytis (gray mold)

What's happening

Botrytis blight takes hold when humidity is very high and air is stagnant, especially on leaves that stay wet or on dead and dying tissue left against the plant. Unlike the dry dusty patches of powdery mildew, botrytis appears as a fuzzy gray-brown mold over mushy, water-soaked spots, and it rots the leaf or stem it lands on rather than just coating it.

How to fix it

Remove every affected leaf and any decaying debris from the soil surface with sterilized snips and throw them away — don't compost them. Treat the remaining plant with neem oil and dramatically improve conditions: increase airflow with a small fan, ease off the humidity slightly, stop overhead watering, and never let cut or dead leaves sit against the rhizome. Botrytis spreads through still, damp air, so ventilation is the real cure.

This is general guidance based on common symptoms; individual plants vary.