Brassica plants are already bolting or going to seed problems this year.
Now an even worse situation has occured. Two community gardens in the Eugene, Oregon area now have very bad clubroot; which affects most of the Brassica family, especially cabbage and broccoli.
The micro organisms can last up to 18 years and this is a big deal where we grow a LOT of Brassicas's here summer and winter.
The web site has cultural methods to help slow down the micro organism.
Lime the soil heavily.
Do NOT remove or move ANY soil.
Do not place the diseased plants into any compost piles.
Don't till the soil, which would move the infected soil around the garden.
If found, lay carpet or cardboard down so to not track ANY soil from the infected plot.
For the next few years, just use a garden fork to get the soil ready for planting.
Concentrate or grow Brassicas in one area so the disease, when and if found can be limited to one area, rather than the the whole garden plot.