"The spores were already in the mulch. About the only thing I know to do is to spray it all with fungicide and then repeat the spraying in 7 days."
DrDawg, those spores you're referencing are not something that will affect the plants. Those are perfectly normal in the decomposition of mulch and are actually beneficial. Spraying a fungicide will not only be an unnecessary expense but it will not be a preventative in protecting the plants from this type of fungus. I sure do understand your concern about putting a stop to plant fungus though, especially with all the tropicals and things you grow but this type shouldn't cause you any concern. Feel free to rest easy, you've got enough to deal with in your operation.
Petruske, I wouldn't be the least bit concerned about your hostas and this mold. As is the norm just be sure to not over-mulch as that is more detrimental than the fungus you see happening.
Shoe
