Disease samples were collected on Graminaceous plants (Poaceae), animal feed grass (Panisetum purpurcum), spreading dayflower (Commelina diffusa), waterhyacinth (Eichhomia crassipes), Acerola (Malpighia glabra), Candle-nut oil tree (Aleurites moluccana), ornamental cactus, and wild cactus in the vicinity of Dragon fruit plantations. These samples were isolated to identify the fungus Neoscytalidium dimidiatum. Experimental results indicated that there was no Neoscytalidium dimidiatum fungus from isolate samples, except sample from ornamental cactus, based on the morphologically comparable spots caused by Neoscytalidium dimidiatum agent causal of Dragon fruit brown spot with 100 percent frequency. Pathogenicity verification of the isolates from ornamental cactus was conducted by Koch's rules again at 107 spore dilution, and the methods of inoculations were made with and without injury initiation. The ornamental cactus samples appeared yielded whitish spots in 5 days inoculation, orange and brown spots in 10 - 15 days inoculation, and then rotting of dragon fruit branches after 30 days inoculation. Therefore, the ornamental cactus is the main host of fungus Neoscytalidium dimidiatum.