There are wettable ones that you can mix with water and there are ones that are more like insoluble granules that you apply directly to the root zone of the plant you want to treat. For what you need it will be a lot easier to work with one you can mix with water and spray.

The one I linked is wettable. I couldn't find the brand that I have been using on Amazon at first but I just found it now. It has a larger variety of fungal colonies, I can't tell you if that is a good thing or not though only been using it for a few months. It was really effective in stopping white fuzzy mold in take-away tek though.