You basically have two alternatives - chemical or biologic treatments.

For the "chemical" way, you have two options; disinfectants or fungicides. Physan 20 is a great disinfectant, but Biosafe Systems Disease Control has less phytotoxicity. Cleary's 3336WP (generic: thiomyl) is likely the most effective fungicide. Copper-based treatments like Phyton 27 may work, but can be damaging to some plants.

For biological controls, Concentric Ag (formerly Inocucor) Garden Solution is the most broad-spectrum, curing and preventing diseases while boosting the plant's health in general, with other biological brands (EM-1, Quantum Orchid) being much narrower-scope treatments.