pansy leaf brown spot on winter flowering violas

Jacqueline Williams

We used to grow winter flowering violas in a raised bed. They were attacked by pansy leaf brown spot the year before last.We chanced them again last winter but it was a disaster. We didn't plant them this year.

Does anyone have any experience of how many seasons to wait before trying again? Would changing the top layer of soil help? Or am I on a hiding to nothing?

Any help appreciated.