Leaf-rollers are easily controlled by the arsenical sprays used against codlin moth, but these sprays must be continued into the late summer after their need against codlin moth is past.
Diamond-backed Moth (Plutella maculipennis).—The caterpillars of this moth ([Fig. 10], 4) are commonly found attacking the leaves of cabbages, rape and other cruciferous crops and weeds. These caterpillars are small and greenish, and, if disturbed, suddenly drop suspended by a silken thread attached to the plant. The damage they do is very often extensive, considerable areas of the foliage being devoured. When fully developed, each caterpillar spins a silken cocoon on the under side of the leaf, and there transforms to the pupæ, from which a moth eventually emerges. The insect is small, narrow, and has a light-coloured, diamond-shaped marking along the back. The moth is nocturnal, and shelters amongst the denser foliage during the day; it emerges at night, and lays its eggs upon the leaves. The life-cycle from eggs to adult occupies some 36 days, more or less, according to the season, and there may be six or seven generations during the year.
In control, an important point to note is that the diamond-backed moth breeds upon cruciferous weeds—watercress, shepherd’s purse, and hedge-mustard—as well as on the old plants of a crop left in the ground; it is from such places that infestation of future crops arises, and the clearing up of such breeding places should be given close attention. Under garden conditions, control can be secured by spraying the plants with arsenate of lead (to which a spreader must be added in the case of cabbage), which should be done especially when the plants are young.
Kowhai Moth (Mecyna maorialis).—The caterpillar of this native moth sometimes becomes epidemic, when it does considerable damage to kowhai, broom, lupins, and sometimes clover. The caterpillar, which measures about an inch when mature, is of a greenish colour, having rows of black tubercles with white centres along the sides, and a double row of white spots along the back; from the black tubercles black bristle-like hairs arise. The caterpillar spins a silken cocoon, in which it pupates. The moth is comparatively small, the fore wings being yellowish-brown with darker markings, and the hind wings orange-yellow with a blackish border. There are at least two broods of caterpillars annually: the first in the spring, and the second during autumn. Arsenate of lead will give effective control on garden legumes.
Cut-worms.—This term is applied to the caterpillars of a number of night-flying noctuid moths; these caterpillars are smooth-bodied and rather worm-like, in some cases measuring from one and a-half to two inches in length when full grown. They feed at night, and their method of attack is characteristic in that they nip off young plants close to the ground ([Fig. 10], 5), so that the latter fall over, when they are devoured by the caterpillars; this habit has given rise to the name “cut-worms.” During the day the cut-worms are to be found curled up in the ground close to the plants they have been attacking. The moths of these caterpillars are rather stout-bodied, and measure about three-quarters of an inch long. One of the commonest species is the cosmopolitan greasy-cut-worm (Agrotis ypsilon).
FIG. 10.