THE VEGETABLE GARDEN.

New Zealand Herald, Volume LXIII, Issue 19486, 16 November 1926, Page 20

THE VEGETABLE GARDEN.

COMMON INSECT PESTS. BY S.T.R. There are innumerable pests with which the vegetable grower has to contend in the culture of the various garden crops which he grows. Some of these crops lie brings to maturity safely and without much trouble. This is due mainly to the fact that predatory - insects and' injurious fungi are absent, or else those that are present have been controlled in an efficient manner. Many crops are lost however, through the negligence of the grower in not applying the remedies or preventatives for the pests at the correct time, or by failing to do so altogether. As several of the insect pests are very prevalent at present, heavy' losses are being sustained by some growers who are not aware of the most effective remedies. Therefore a deeper knowledge of these will be of great value to the gardener in combating his insect enemies. It is my intention to deal fully with the commonest pests of the most important crops. A knowledge of the life history of each pest will.serve a dual purpose—first, to enable him to know when to look for them, and secondly to serve as a guide to the time to apply the remedy when the insects are most readily destroyed. A description of each will also aid in the identification of the various pests, so that the correct remedies may be applied. The Diamond Back Moth. This moth has extensive damage to cruciferous vegetables (those of the cabbage family) and also attacks cruciferous weeds. It is a very common and most destructive moth, and if the gardener can check the ravages of this pest he will have accomplished something worth while. It is impossible to mistake the moth on account of the whitish markings on the wings, which, when folded, resemble dia-mond-shaped patches. The adult moth is slightly less than half an inch in length, and appears a greyish brown colour when in flight. These moths are plentiful during the four months from December to March. The adult female deposits her eggs on the under surface of the leaves of the host plant. They hatch in about ten days into greyish larvae which later turn green. The larvae, which have 16 feet and a characteristic black head, grow to a size of half nn inch. At the beginning of the season the eggs are laid on the leaves of cruciferous weeds until the vegetable" crucifers (turnips, cabbages, etc.), are coming on. The larvae eat the under surface of the leaves, .thus causing damage which will result in a lessened crop. This refers especially to cabbages as it is the leaf which is the " crop" part of this plant. If the larvae, which are caterpillars, should chance to 'become frightened they drop to the ground immediately spinning a silken thread; by means of which they regain access to the plant. In about four or five weeks' time they pass into the pupaj stage. They spin a loose silken chrysalis on the leaf and in about two or three weeks later the adult moths emerge. There may be several broods in one season. Control ol Pests.

The control of this pest is somewhat difficult. If the larvae are frightened to the ground and the silken threads then broken they are more or less helpless and have great difficulty in climbing bac-k on to the plants. For this purpose a bushy branch dragged through the rows of vegetable is most suitable. The eradication of cruciferous weeds will deprive the moths of & host plant and thereby check them to a certain extent. Nothing much in the way of spraying can bo done but an application of kerosene emulsion will be found to be helpful in keeping this pest checked. In apnlying this spray care should be taken" to spray the under sides of the leaves well to make it more effective. The best method of control for small gardens is the breaking of the threads. Birds will then come along and devour the larvae as they lie on the ground, whereas they do not always see them under the leaves. Another method which I find effective in checking the caterpillars is as follows and may be used by all who possess a garden hose. With a fairly strong pressure hose the plants on both sides of the rows, the water pattering on the leaves frightens them to the ground and the strong flow breaks the threads. If this is done every second day or so the catepillars will Have very little chance of survival. This method serves a double pose for, besides controlling the larvae, it also waters the ground during the dry months when the moths are about. The Potato Moth.

If it is at all' prevalent tjiis insect causes the potato-growers some anxiety. The anxiety is well founded for it will do considerable damage to the crop if'it once infests the tubers. This particular moth is smaller than the diamond-backed species, being about three-eighths of an inch in length, and is of a brown and grsy colour. As a rule there are two broods in a season. The moth-! of the first, or winter brood, deposit their eggs on the foliage of the crop. The pinkish larvae, which hatch from the eggs in froxn seven to ten days, burrow their way down the stem and thus they sometimes destroy the haulms. When the larvae are fully grown, being then , a little more than half an inch long, they pupate, usually in the dying leaves which ihey have destroyed. The eggs of the moths of the second brood are deposited on the tubers if the moths can get to them. The caterpillars when hatched burrow through the tubers, ruining them, and making what are known as " wormy " potatoes. They jiupate either in the tubers themselves or, as the first brood do, under the shelter of the haulms lying around on the ground. The moth gains access to the tubers through cracks in the soil, or if they become uncovered otherwise. Stored potatoes are just us liable to be infested, ,if they are Dot kept moth-proof. Controlling Potato Moth.

The control measures taken to guard against this pest are numerous. It is of prime importance that there is no source from which the crop could become infested, therefore destroy all haulms lying around and all cruciferous weeds, such as nightshade. Besides this all discarded tubers should be gathered and destroyed if not required for pig or fowl food, instead of allowing them to lie round ex-p-sed for the moths to get -et. If this be done there will be very few places that could possibly harbour the moths. That the chances of the crop being infested may be remote, rotation of crops should be practised, so that it is not grown on land that may have been infested. even though ever so slightlv, the previous year. The use of infested seed is one of the surest ways in which tho crop_ becomes infested and should certainly be discontinued. The moths of the second brood should be given no chances to gain access to the tubers. Cover the seed sufficiently \vhen planting to ensure this, and keep yell ridged during development, so that there are no cracks in the soil through which the moths could g»t to Pen dng, the tubers uld thin ; a to li® °n the ground ionger be t0 dry thfenl > but shouW Place «v\ d 7i. earth in a CGo1 ' draughty to freqacnt nn m ° ths aro "When moths account of the draught, the cron arfi noticed to be around Should ci r« aym2 ° £ arsenate of lead

The turnip fly, which, is really not a fly hut a flea beetle, does great damage to the turnip crop and, if very bad, will wipe the wholo crop out. The attacks of these insects are not confined to the turnip crop, for other cruciferous crops also suffer from their ravages. The beetle is most destructive in dry seasons, on account of the fact that it docs not thrive in wet weather. The adult insect is usually black in colour but there is sometimes a tinge of green. It has a yellow stripe on the wing. It has a length, when full-grown, of less than an eighth of an inch. The insects appear in early spring, after having passed the winter in sheltered places. The eggs are laid on the under surfaces of cruciferous crops or weeds. The eggs give rise to yellowish larvae about an eighth of an inch long. These larvae burrow into the leaves of the seedling plants and devour a great portion of them. As the larvae burrow into the leaves and are therefore invisible, the first sign of the presence of the insects that the grower usually rereives Is the dying of his seedlings. In about seven days the larvae emerge from the leaves and pupate in the ground. In about two weeks' time the adult beetles of a new generation appear and feed on the young turnips. These in turn lay eggs and a further generation appears, and so it goes on until there may be seven or more generations in a season. This turnip beetle is more or less'difficult to control. The beetles do the most damage while the plants are yet seedlings before developing any rough leaves. Therefore, the shorter this j stage is, the less will the crop suffer. To hasten the development of seedlings, use artificial manuros. Superphosphate has been found to bo one of the best fertilisers for this purpose. Destroying all cruciferous weeds is also helpful in controlling the pest. . To allow for the loss of a proportion of the seedlings it is better to sow thickly, using good quality seed. It has been found to be effective to soak the seed in some kerosene before sowing, as the smell is retained and is repulsive to the beetle. Turpentine may also be used for this purpose. Little can be done in the way of spraying, but an application of kerosene emulsion when the young seedlings firs appear above the ground is useful.