I have one huge raised garden bed for all my annual vegetable plantings. it's built into the house from field stone. My garden has been plagued with verticillium wilt, and my tomatoes that I plant here keep getting infected towards mid July. I've read that the best way to kill verticillium wilt is through solarization (covering the garden bed with plastic in the heat of summer for 4-6 weeks), but this is not an option for me as I don't have anywhere else to plant.

Is there anything else I can do now in the later winter before growing season starts? Like mix in an organic fungicide. This is my vegetable garden so I wouldn't want to use anything toxic....
thought about replacing all the dirt, but I think I got verticillium wilt from delivered dirt in the first place...