Brassica - perhaps the most important agricultural and horticultural crops, but not without some effort

A few years ago, we were lucky enough to visit the vegetable plot at the Tasmanian Botanical Gardens, made famous by Peter Cundall on the ABC programme, Gardening Australia. Actually, we acted like groupies who had just scaled the walls of the home of their favourite rock star. We took turns posing for photographs beside each of the 6 vegetable beds. I can’t describe the level of our excitement when we located the compost pile! All I can say is that it was just as well we were travelling without our children as had they viewed our giggling behaviour we would have lost all credibility as parents!

The six bed crop rotation system of the vegetable plot is designed to fit into the average backyard. One of the beds is currently a brassica crop. Brassica is a genus of plants in the mustard family (Brassicaceae). It could be well argued that this genus contains more important agricultural and horticultural crops than any other genus.

Brassica is a native of western Europe, the Mediterranean and temperate regions of Asia. Cultivated species are grown worldwide but many of the wild species grow as weeds, especially in North America, South America, and Australia. Why, you ask?

Almost all parts of some species have been developed for food, including the root (rutabaga, turnips), stems (kohlrabi), leaves (cabbage, Brussels sprouts), flowers (cauliflower, broccoli), and seeds (including mustard seed, and oil-producing rapeseed). Versatile little plant isn’t it?

They provide high amounts of vitamin C and soluble fibre and contain multiple nutrients. There have been claims of anti-cancer properties also.

So growing any of the various Brassica plants can lead to the joy of harvesting your own  fresh salad greens, bunching or braising greens, as well as small and large

heads and root crops. Generous servings of pac choi, chinese cabbage, tatsoi, broccoli raab and mustard greens, can feed and amaze your family and friends!

Not all Good News

However, it is not a crop without some issues. It is susceptible to clubroot spore that lurks in our soils. Clubroot is caused by the pathogen Plasmodiophora Brassicae which can potentially persist in soil and water for up to 20 years even in the absence of host plants! Chinese cabbage is very sensitive to the disease. Cauliflower is less susceptible than Chinese cabbage; but more susceptible to the disease than broccoli and head cabbage.

How To Win the Fight

Avoid double cropping brassicas. It is best to rotate brassica crops with non-brassica crops (e.g: potatoes, carrots, sweet corn, pasture) to reduce the clubroot spore load in the soil. Affected plants produce large distorted roots and wilting is often the

first noticeable symptom. The galling or knots on the roots may not be obvious until affected plants are removed from the ground. Plants which are severely infected will be stunted, therefore producing poor quality crops which may not even live to harvest.

If you are watering from a dam near brassica plants or weeds, irrigation water

should be taken from the surface, as clubroot spores will settle to the bottom. Avoid taking the muddy water from near the bottom of a dam.

An acidic soil pH should be limed before planting the crop. The disease is less virulent when the soil pH is at least 7.0 as the germination of the spores is inhibited. Care must be taken not to increase the soil pH too high,  otherwise nutrient deficiencies may occur, or diseases of other crops may become more prominent (e.g: powdery scab on potatoes).

Liming is best done in partnership with the crop rotation, and calcium and boron application as this will maximise the potential to control the clubroot pathogen.