All About Brassica Vegetables
The term ‘brassica’ is usually taken to refer to members of the botanic genus Brassica. Most of these brassica vegetables are grown for their leaves and flower heads: sprouting and winter broccoli, Brussels sprouts, cabbages and savoys; cauliflowers, and kale. Other members of the genus include swedes and turnips, which are grown for their fleshy roots, and kohl rabi, grown for its swollen stem.
The genus Brassica belongs to the family of plants known as the Cruciferae, which also includes another popular vegetable, the radish, as well as many familiar flowering plants. The vegetables are dealt with individually throughout this site, but this is a good place to have a word about some of the more common pests and diseases that attack most of the brassicas grown for their leaves and flower heads.
One of the most serious pests of this group of vegetables are the larvae of the cabbage-root fly, which are especially damaging to newly transplanted seedlings. The larvae tunnel into the roots of the young plants, causing them to wilt. The best way to control attacks is to sprinkle bromophos powder into the when the seedlings are transplanted.
Club root (also known as finger-and-toe) is a fungal disease that damages, and may destroy, the roots of brassica vegetables by causing them to swell. An outbreak of club root can be recognised by its effect on the stem and leaves, which become distorted and may turn a bluish colour. The disease may be controlled with thiophanate-methyl (available as Murphy Club Root Dip) and also by careful cultivation of the soil. Club root thrives chiefly in wet, add soils. Wetness can be prevented by improving soilby means of thorough digging and the addition of sharp sand and peat. Acidity can be reduced by digging in hydrated lime: about 1 kg per 2 m2 (1 lb per 10 sq ft) in the first year and about half as much in subsequent years. As an added precaution, dip the roots of the seedlings in a paste of calomel dust and water when you are transplanting them.
These nuisances are the best possible reasons for including brassicas in your rotation system. Both pests and diseases will build up if brassicas are planted in the same soil for several years in succession.
Caterpillars, mainly the larvae of the cabbage white butterflies, are a familiar pest of brassicas and can severely damage the leaves. They can be removed by hand, but a better method is to destroy the eggs (usually on the underside of leaves) before they hatch. Among chemical controls of both eggs and larvae, derris is the safest; it will also kill the flea beetle, which eats small holes in the leaves of brassica vegetables.