Too late. Ideally, you need to start up a plot somewhere else. Do not
contaminate it with soil or compost from the infested area.
Perusing the Organic Method Primer...
This disease can remain in the soil for 15 years.
Keep the pH neutral to sweet, add lime if neccessary and the drainage
should be impeccably good. Start your own plants from seeds only
(DON'T bring in transplants). Don't use uncomposted manure.
Burn or trash the infected plants (DO NOT compost them). Have a
zero-tolerance for cruciferous weeds (shepherd's purse, wild mustards,
The disease organism thrives in warm, moist soil. Water crucifers very
lightly during periods of high heat--mist the leaves and barely wet the soil
surface (wait for cooler temps for full irrigation).
Put chopped rhubarb leaves in the bottom of your planting hole, cover with
2 inches of soil, then finish transplanting.