Two good looking fennel (finocchio) plants next to one another collapsed within days, with symptoms that I diagnose as root and crown rot. Symptoms are water soaked lesions at the base, dead root, and suddenness of collapse. The rest of the fennel plants (about 20, also good looking) show yellowing of small fronds, possibly a different disease, but are holding steady as we speak.

The other end of the bed is occupied by magnificent Brussels sprouts plants, clearly undiseased. I grouped them this way because they both want abundant water.

These are newish beds, in clay and part sun, and I have never seen these symptoms before. Given soil and exposure, what can I rotate in there, that will dissipate the crown rot fungus within two years? These clay-shade beds are mostly brassicas, because they grow well there and I eat them all winter long. I know well enough that brassicas are not what I want in there for a while.

Basically, what is unaffected by root and crown rot, that can be grown there?