Option 1: You know it's a fungus. Cleary's 3336 WP, generically known as thiomyl.

Option 2: Could be a fungus or bacterium. Phyton 27 It may take a toll on dendrobiums and some thinner-leaved genera. A "kinder, gentler" approach, yet just as effective, would be to use living beneficial bacteria and fungi, in the form of Concentric Ag Garden Solution.