There is no cucumber disease that goes by the name of Bacillium wilt. Might you instead be referring to Verticillium wilt or Fusarium wilt? In either case, there is no fungicide that will work as a treatment. These fungi grow inside the stems and there is no good way to get at them to eradicate them. The most common wilt disease in cucumbers is bacterial wilt, which is spread by striped cucumber beetles and spotted cucumber beetles. A good diagnostic tool for bacterial wilt is to cut a wilting stem, press the two cut ends together for a few seconds and then slowly pull the pieces apart. If bacterial wilt is present, stringy strands of bacteria will stretch between the cut ends. Fungal wilts will usually have faint brown streaks inside the stem when you scrape away the surface.