Cabbage’s Enemies

Press, Volume CIV, Issue 30936, 17 December 1965, Page 6

Cabbage’s Enemies

If you are looking for a path which will lead you from rags to riches, why not develop a cabbage which is resistant to the ravages of the white butterfly caterpillar. It is not often that one can harvest a cabbage that has not played host to this pest, especially if it has been neither dusted nor sprayed. Cauliflower, turnip, swede, kale and even some ornamentals which also belong to cruciferous family, such as nasturtium and mignonette, are also susceptible. In its early life the caterpillar tends to feed on the surface tissue of the leaf but as it ages, during which period its colour changes from a light green to a dull green with an orange stripe down its back and orange spots along its flank, it eats right through leaving nothing but perhaps a leaf vein behind. DROPS TO GROUND

It does not appear to become particularly perturbed when disturbed and in this way differs markedly from another caterpillar, that of the diamond-back moth, which can be equally destructive to a similar host range. This pest can be discerned from the white butterfly caterpillar by its great agility when touched or disturbed for it will immediately drop to the ground on a silken thread. Its mode of attack varies also during the early part of Its life as it burrows into the leaf centre, alongside the spot where it emerged from the egg, between the upper and lower epidermis, leaving a web of whitish irregular patches. These give the leaf a white, tissue-paper appearance. Subsequently they will feed by chewing out pieces. The caterpillar itself is quite distinctive, tapered at both ends and may be green, pink or yellow in - colour, though when mature it is usually light green. It attains a maximum site of threequarters of an inch and remains on its host when pupa-

ting—a feature of the dia-mond-back moth is that it rarely leaves the vicinity of its food plants. Its presence can be detected by disturbing a patch of infested cabbage, which sends them flying up only to settle almost immediately again. The main breeding season starts in September and reaches a maximum by the end of December or sometimes as late as February. Climatic conditions, particularly temperature, influence ‘.he cycle. EGGS IN CLUSTERS

The eggs are laid singly or in clusters beside the ribs or veins of the underside of the leaf. The moth is a small, slender, greyish nocturnal insect with a fringe of hairs on its hind pair of wings and a line of yellowish, triangular spots on the front wings. When at rest the wings are folded along the body, a characteristic of all moths, and if the insect is viewed from above the triangles on each wing appear to form a string of diamond shapes along its upper surface. SPOTTED WINGS

The white butterfly is so well known that a description is not warranted. It is quite easy to distinguish the male from the female for, although both possess a black spot on the hind wings, the female has two spots, to the male’s one on each forewing. The eggs are yellow, bullet-shaped and ribbed and are generally laid anywhere on the underside of the leaf. It takes little more than one week for the caterpillars to hatch out Although chemical control of these pests can be achieved by a variety of materials such is lindane, DJD.D. and carbryl D.D.T. applied as a dust or spray still predominates as the most accepted means of destroying them. As soon as adult insect activity is noticed it is advisable to put a protective application on whatever brassicas are growing In the garden at the time. In this way little or no damage will be done to the plants.