Damping off in greenhouse seedlings with known mold issues

We are having a real problem with damping off in a greenhouse here in Oklahoma. Mold spores are in our starter soil and probably also coming from water source which is pumped from a creek. Which fungicide is most effective for drenching soil, yet still soil friendly with no chemicals affecting plantings. Leaning towards copper. Also, if I treat seeds before planting, can I just coat with dry copper soap? Plus, tons of rain, high humidity, and daytime highs in the 80s.

Copper does work well for some things, but I’m not sure if it’s seed safe.
Baking your soil at 200°F or higher will definitely kill the mold. If you leave it in bags and set it in the sun it’ll do the same. @Micpot