How to prevent club root in the Kitchen Garden
Many thanks for your recent enquiry regarding clubroot. This disease is extremely problematic and widespread, and once it takes hold in the soil there is very little the gardener can do to eradicate it. The vegetable plants most affected are members of the brassica family such as brussel sprouts, cauliflowers and cabbages, but swede and turnips can also be hit along with flowering plants like stocks and wallflowers. The disease causes the foliage of affected plants to wilt on hot days before recovering at night, stunting and the development of reddish purple tint on the leaves. Plants may also topple over and die and the roots of clubroot infected plants are swollen and distorted.
The bad news continues; clubroot can survive in the soil for up to 20 years as resting spores, which eventually germinate and invade roots through the root hairs. Different spores are produced within the root hair and then spread to other parts of the root, causing the tell-tale swelling and distortion. Treating clubroot once it is present in the soil is almost impossible, so it is impossible to state how important it is to prevent the disease appearing.
There are various techniques available to the gardener which will help keep beds free of this peril; sowing brassicas from seed in sterilised compost; applying lime (as you say) to raise the PH to 7 will help to lessen the problems; and strictly adhering to a 3 (4 if you can manage it) year crop rotation when planting brassicas is an excellent preventative practice. Chemical treatments are very hit and miss and certainly have no proven track record. Dazomet is a soil sterilant which may reduce the amount of spores present near the soil surface, but deep digging is likely to replace these. If you are unlucky enough to have a plot infected with clubroot, it may be worth trying some of the old wives’ cures – apply rhubarb, manure and soot or mothballs and egg-shells to planting holes amongst others. Alternatively, give up growing brassicas!
The key, then, is to prevent this disease from invading, and at the Kitchen Garden I follow a strict 3 year crop rotation plan and also raise all brassicas from seed.
Hopefully the above information will prove to be of some help. Many thanks once again for your enquiry and we hope to be of service to you in the future.