I would spray the affecte4d leaves and stems. If indoors, I would also water the pot or tray with dilute H2O2.
Spray on diseased leaves: 0.2% H2O2 :
Dilute "drugstore peroxide" 16:1, like 1 cup/gallon or 2 oz. per quart
Prolonged seed soaking or watering: 0.1% H2O2
Dilute "drugstore peroxide" 32:1, like 1/2 cup/gallon or 1 oz. per quart