"david taylor" wrote
I have an old book-Ernst Gaumann "Principles of Plant Infection" Crosby
Lockwood and Son London 1950.
It gives a good account of clubroot infection. Infection drops off rapidly
as the soil pH is increased in the case of a particular brassica falling
from 100 to 20% as pH is increased from 5.7 to 6.2, to virtually 0 at pH
7.
He also reported that clubroot was sustained in the soil by wild
brasiccas-charlock, lady smock,shepherds purse, garlick mustard etc.and
can be eridicated in 2 seasons if these weeds are removed.
I had a lot of trouble with club root when I lived in Cheshire and managed
to control it using this information.
Some brasiccas-Pak Choi, Cauliflower seemed to be sensitive, sprouting
brocolli spring cabbage wallflower were more resistant.
Apart from keeping the soil pH up and getting rid of shepherd's purse, I
used to surround the root balls of the plants with powdered chalk (my
neighbour was a salesman!) when planting out.
This with a pKa of about 8 would ensure an alkaline but non corrosive
start to growth.

Thank you David, interesting information, the pH of our new allotment is
about 5.5 and I realise that is potentially part of the problem. The
gardener with the worse clubroot problem told me he gets his soil to pH 7.5
on his brassica bed but rumour has it he also gets something from a farmer
friend to control it (?), his plot is 40 Sq Rods!!
Fist thing after liming is to plant some brassicas and see how they do and
with the plot not being used for over 10 years we might be concerned about
nothing.

--
Regards
Bob
In Runnymede, 17 miles West of London