Dealing with clubroot

J.J. Strong
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The last weekend of September and first couple of days of October, I was in Musgravetown and also visited parts of the Bonavista Peninsula.

I visited an elderly couple’s garden where they said they had problems with clubroot affecting their turnips. That coincided with a phone call I had received from another reader in Conception Bay who was having trouble with his cabbage, not only those in the ground, but those in containers.

What could they do?

Clubroot (finger and toe)

Clubroot is a serious disease which damages brassicas (Cruciferae family).

Remember, brassicas include cabbage, cauliflower, Brussels sprouts, lettuce, swedes (rutabagas), turnips, radishes and others, so they all may be affected. It also affects some flowers and ornamentals, like stocks (Matthiola), candytuft (Iberis) and wallflowers (Cheiranthus).

Note: some common weeds are of the brassica family and can carry the disease.

Clubroot signs are the roots develop round swellings, the leaves become discoloured and the plants wilt in the sun. The plants may die, or grow slowly. The cause of clubroot is a slime mould, Plasmodiophra brassicae, which thrives in poorly drained soils, acid soils in manure and some plant debris. The spores can remain in the soil for up to 20 years, even when there are no host plants in the area.  

Treatment

There is no treatment, so lift the diseased plants and burn them.

Control

The soil clinging to your boots or tools can transport the disease from one area of the garden to another. It can be brought in from or taken to another garden. So either disinfect boots and tools or take care.

Likewise, purchased farm soil or other garden soil brought home may also contain the disease.

As for the soil in the containers, if it was just shovelled in from an infected area, then just being in the container will not prevent the disease. The only choice is to sterilize the containers and use new, clean, disease-free soil, brought in from an outside source.

Also try sowing brassica seed in trays or cells of sterilized seed compost, transplant in to potting compost and, as the plants grow, transplant up into pots, still with sterilized soil, until ready for outdoors, all of which means lots of work.

Old methods include applying extra lime, preferably in the fall. If not done for a few years, use at one pound per square foot (454 gm per 0.09 sq m).

Spread when the soil is damp and gthere is no wind, to prevent it blowing away.

Alternatively, mix a cupful into each hole at planting time and lightly fork in.

Another old, but still valid, recommendation is do not plant brassicas on the same site for three to seven years and in some cases it works. When growing, keep the area clear of weeds. Crop rotation is also important.

Some other precautions that can be taken include dipping the plant roots in a thick mixture of calomel dust, water and clay. Also before planting, drench the holes with a solution of Benomyl (1 ml to 11 ml of water).

A liquid clubroot control, by systemic insecticides and calomel dust, is available from some manufacturers, for use at the planting stage.

A few years ago, in the U.K., there was a liquid clubroot control containing Thiophanate-methyl, which I tried with only fair results. In Czechoslavakia, some greenhouse studies showed that growing summer savoury in infested soil can reduce the damage and that growing Chinese cabbage after the savoury will produce good crops.

Another alternative is sterilizing the soil.  Not an easy task.

Clubroot-resistant crops

There are still no cabbage varieties that are clubroot-resistant. However, several years ago Ken Proudfoot had developed some resistant varieties of purple top turnip — “Fortune,” “Kingston” and “Polycroft” and a white top “Brookfield” — but the  seed is not now available. Today the seed of clubroot-resistant turnip varieties “York” and “Marian” seed is available from Gaze Seed in

St. John’s. More on this subject next week.    

J.J,. Strong is a longtime member of the

Newfoundland Horticultural Society.

Organizations: Newfoundland Horticultural Society

Geographic location: Conception Bay, Brussels, Czechoslavakia Kingston York

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