IF the disease is white rot (dramatic powdery white mildew around roots) the remedy is patience, chiefly, waiting at least four years before planting more alliums. Other vegetables are fine.
However I have found that the no dig approach is helpful by not moving soil around and keeping the fungal spores in one space, hopefully a small one. Also I find that building soil fertility with compost and manure has reduced my incidence of white rot.