This is bit of a gnarly one! There's some argument as to whether its the sticks or the leaves - some people say chopped up leaves dug in, others say a short length of rhubarb stick placed in the planting hole before you put the brassica in place. Both the sticks and the leaves contain oxalic acid, but the concentration in the leaves is much, much higher, which is why they're toxic if you eat them. Rhubarb leaves are often used to produce a brew that's used as an insecticide.
I can't find any scientific studies confirming or denying effectiveness, so maybe you could just try it and see what happens. Or take the safe option, lime, rotate crops, and grow club root resistant varieties.

Yes!

Although I thought it was the leaves...

I might be wrong!

Memory is not what it once was!

Edit; Sorry Bamboo must have been writing together

;-)

Also try dipping the roots of the seedlings in lime as you transplant them. Sounds drastic but it works. And be careful not to tread the infection round the plot in the soil on your boots.

And for those who do not have Club root in their soil, never, never, ever buy in any plants of the Brassica family (and that includes Wallflowers). The infection is soil borne, not seed and is always carried from one place to another on the soil round infected plants. Prevention is better than cure (if there was one).
The Rhubarb thing came up on the old Beeb site many years ago and despite requests the person who was going to try it never reported back.

You can always try this, but it won't work. Might make you feel better about your club root though!
Seriously though, clubroot (Plasmodiophora brassicae) it is a slime mould and it is very unlikely that it will be destroyed by oxalic acid or any other plant product. If this old remedy DID work then everybody would be using it, which of course they don't.
Sadly, the only thing you can do is to avoid growing brassicas and leaving weeds which are brassicas growing (including things like wallflowers) and then try cultivating them in large pots as they can usually outgrow the disease once they have an extensive root system.

Thanks very much to all for your answers,don't think i have club root but will keep these idea's in mind
norman45