NO. 3.

New Zealand Mail, Issue 1205, 5 April 1895, Page 7

NO. 3.

New Zealand Department of Agriculture. John D. Ritchie, Secretary. SHOT-HOLE MOTH, DIAMOND-BACK MOTH, CABBAGE MOTH. fPlutella crucifer arum.) By T. W. Kirk, F.L.S., &c., London. In July, 1884, I read a short paper on this moth before the Wellington Gardeners’ Mutual Improvement Society, and subsequently, November, 1888, published the following in the Hawlcfs Bay Herald : This insect is found from August to May, but is most plentiful in the summer. It came under my notico in the Welling ton District about nine years ago (i.e., 1879), appearing first in a garden in the small farms at Pahautanui, whence it

rapidly spread £0 all the cultivations in the settlement, and thence over the whole of the Wellington Province. It is, however, very erratic, appearing in great numbers in a particular locality, then suddenly departing, to appear again perhaps toward the end of the season ; or it may remain all the season.

It was introduced from Europe, but is now a widely-distributed species, being found in North and South America, Australia, and throughout New Zealand ; indeed, probably wherever cabbages or turnips are cultivated. The damage is, of course, done by the larv®, which feed on the leaves of all crucifers, but especially of cabbages, cauliflowers, and turnips. The larvae are shaped something like a small spindle, are green, or sometimes yellowish-green colour, with a brown or greyish-brown head. They measure, when well fed, from |in to fin in length, and about l-16th in in diameter. They will be found in great numbers on the underside of the leaf, sometimes working beneath a delicate network. They are voracious feeders, but easily disturbed, and when alarmed can quickly lower themselves by a delicate thread, and thus reach the ground, or remain suspended until the danger is passed. Though so small, these grubs, by their numbers, do enormous damage to culinary crops. I have seen in more than one market-garden the whole of the stock of cabbages and cauliflowers quite destroyed and have counted as many as 170 grubs on a single leaf. When about to change from the chrysalis stage the caterpillar spins a spindleshaped cocoon, either on the ground or beneath a network on the underside pf the leaf. From this cocoon the moth emerges in about fifteen days. The complete insect is very variable in colour and markings, but the following may be taken as a fairly good general description: Brown, mottled with white, antennse white, when at rest they point straight forward ; crown of head and disc of thorax white. Superior wings long’and

narrow, with an indented white stripe along their inner margins, which, when the wings are closed, form diamonds along the back; inferior wings lance-shaped, ash-coloured, with long fringe. Length, about three lines ; expanse of wings, six to eight lines. In Europe there are two generations a year, but here there is a succession of broods from spring to well on in winter. Here, as almost everywhere, nature has happily provided a check to undue development of numbers. A small ichneumon, measuring about three lines by four to six lines across the wings, attacks a great many of the grubs, and deposits its eggs in them, so that from one-half to two-thirds of the pupae hatch out flies instead of moths. Any pupae showing brown colour should, if possible, be left, as they are sure to contain the parasites. Numerous remedies have been tried, such as an infusion of tomato and gum leaves, and many others.

* * >. -* As I have already mentioned, the grubs are very impatient of disturbance. They appear to have a much more decided aversion to lime, especially gas-lime, than most caterpillars, but it needs to be frequently and lightly applied. I have myself adopted the lime treatment with most satisfactory results, and have also found it a good plan, after a very hot day, to give the crop a thorough hosing, after which great numbers of the grubs will be found dead. The pest is usually much worse in dry seasons than in wet anes. The way in which I apply the lime is as follows: A long canister perforated at both ends is filled with lime. Taking this in both hands I pass between the rows of cabbages; holding the canister a short distance from the ground I shake vigorously, thus doing two rows at once. A better plan, and one which answers admirably, has since been suggested—namely, spraying, or if on a small scale

watering with a fine rose, with the follow* iftg i coal-tar boiled in one gallon of water, and while boiling dilute with fifty gallons of fresh water ; stir well for some time, and it is ready for use. All insects dislike tar and will get away if possible. Give the crop and ground about it a good dressing. If 011 a large scale, soot and lime applied with the strawsonizer are good ; the tarwater may be applied by means of the same machine. Stimulants such as nitrate of soda will also force on the crop, and so save a dead of damage. Seedlings should be placed in the tarwater for half an hour at least, then washed and planted; or weak tohaccawater will answer.