ROOT CROP PESTS.

Otago Witness, Issue 3102, 27 August 1913, Page 18

ROOT CROP PESTS.

INSECTS THAT DO DAMAGE—THE TURNIP FLY. Root crops are probably subject to more posts than any other crop the farmer grows. The plants are attacked by insects of various kinds both at the root and above the ground. They are liable to a considerable number of fungoid diseases, and both slugs and birds work considerable havoc among the young plants at times. The insect pests are particularly numerous, the most important of the whole of them, from the fact, that it often does the greatest amount of damage, is the turnip fly or turnip flea beetle (Haltica nemorum). This insect practically every farmer knows by sight, in spite of Us minute size. There are, however, two kinds, the most common being the one named, which has black wing-cases with a yellow stripe down each, and one that ;s black all over. Both are, however, exactly similar in their habits, and for practical purposes can be treated as one. The female beetle lays its eggs on the underside of leaves of turnips, but when turnips are not to be found it uses charlock, hedge mustard, and other plants of this kind. The grubs that hatch out from these eggs live upon the soft part of the inside of the loaves, whore they live for some six or seven days. At the end of this time they come out of the leaf and drop to the ground, and pupate just under the surface of the soil for about 10 days. As soon as the beetle emerges it starts to feed upon the leaves of any young cruciferous plant within reach. It is quite evident that the immense swarms of these beetles that suddenly appear after a few hot days at the end of May or beginning of June must have gone through their grub stage on charlock and such-like plants, so that there is no doubt that keeping the land thoroughly clean and the hedge-rows free from plants of the charlock class would reduce their breeding-grounds considerably, and very much decrease the intensity of an attack Unfortunately, there is NO VERY CERTAIN REMEDY when once the plants are attacked. The great thing seems to be to get the plants to grow as quickly as possible in their early stages. Soaking the seed in paraffin, and even in turpentine, has been found in some cases helpful where an attack is anticipated,because the flavour of the turpentine or paraffin seems to cling to the young leaves after the plants are up, and keeps the fly away to some extent. The practice of sowing a few pounds of common white turnip seed broadcast over the field after drilling swedes seems to have something to recommend it, for the beetles rather prefer the turnip to tho swede, and, at any rate, a considerably increased number of plants are provided for them to feed upon, so that tho damage to any particular plant is not so great, and, of course, the turnips arc cut up at the, first hoeing. Sowing broadcast a mixture -of lime and soot when tho dew is on tho plants also helps to some extent, although ths dressing hardly affects the underside of the leaves. Spraying with paraffin emulsions and with solutions of arsenic in the ' form of Paris-green have also been tried, but with only partial success. Those larmiers who possess a Strawsoniscr, or a spraying machine capable of giving a very fine misty spray, may use a spray of pure paraffin at the rate of one gallon and a-half to two gallons to the acre. To put on such a very small quantity requires a very powerful pump and ah exceedingly lino nozzle, for however quickly one goes over the ground a good deal more paraffin will be used, which may injure the plants if applied in too large a quantity. This fine spraying of paraffin has, however, been found useful. Roots of all kinds are subject to attacks of wireworm, but this is so well known in connection with other crops that no special mention of it need he made here, except to say that thorough cultivation does as much to prevent wireworms as anything that can bo recommended, while possibly one of tho soil fumigants might bn turned in at the last ploughing; but there is no remedy after tho attack shows itself. GREEN FLY ATTACKS MANGOLDS. Mangolds are also subject to'attacks of green fly, which usually shows by the curling of the young leaves soon after the plants .are singled. This, like most of the otWer pests, is exceedingly difficult to destroy. Were tho upper sides of tho leaves attacked spraying with paraffin emulsion or with one of tho proprietary insecticides would he beet, but ns tlie attack is always on the underside it is difficult to get at thorn. An attempt might bo made where the plants are a fair size to spray tho undersides of the leaves, using a hand spray with tho nozzle pointing nnwards. There is, however, no doubt that i praying, oven if it did not get at and kill many of tho insects, would to some extent prevent tho now leaves from being attacked by coating them with the insecticide. It may bo noted as an interesting fact that tho wasp is the greatest friend to the farmer in cases of swedes attacked by green fly, for the wasps collect these insects by thousands and carry them to their nests as food for tho grubs. Ladybirds and other aphis-eating insects also soon collect on the attacked crop, and appear eventually to clear the green flv off; but tho damage done by checked growth is often considerable. GRUBS OF VARIOUS MOTHS.

Tho next most common insect post amongst the swedes and mangolds is tho grub or caterpillar of various kinds of moths. This attack shows itself by the plants assuming a withered appearance wLoto the root Is about as thick as a load pencil, and if these plants are examined it will be found that they are oaten nearly or right through iust level with the surface of the ground. When tho plants are seen in this condition the caterpillars can usually he found by searching in the ground an inch or two below the surface round about the plant. Tho caterpillar is usually about long, of a greenish-brown colour, often with a few markings on it, and it curls

itself into a ring immediately it is disturbed. Quite a number gf moths have caterpillars of this kind, such ns the yellowunder wing, the heart-and-dart. moth, the silver-Y moth, and others. As these caterpillars lie in the ground all day, and only feed at night, they are very difficult to get at, and practically the only remedy seems to be thoroughly hoeing all round the plants, which turns out the grubs so that they can bo destroyed, and many of them arc cut by the hoe. It is as well to watch for any appearance of plants attacked in this way, so that this thorough hoeing may bo undertaken at once, for the grubs have a way of travelling from the plant they have destroyed to another sound one. Occasionally the leather-jackets, which are the grubs of the daddy-longlegs, will damage swedes and mangolds by eating them off below the ground in a somewhat similar manner to these surface caterpillars; but the leather-jacket, though causing the plants to wither and possibly die, only eats through the outside layers, and does not cut the plant right off in the way that the caterpillars do. Leather-jackets are particularly common in land that is manured with ni.ghtsoil and other town refuse, the smell of which possibly attracts the daddylonglegs. The same treatment as recommended for thg caterpillar is about the only remedy for the leather-jacket, though dressing with nitrate of soda along the rows seems to check the insects and helps on the plants. The turnip saw-fly grub occasionally dors a considerable amount of damage on turnips and swedes, but its attacks in any serious dimensions are not common. The grubs arc blackish-looking caterpillars from «Un to 2m long that ford upon the loaves. Spraying with paraffin emulsion or with some other insecticide would, of course, bo the remedy, as those can easily be got at.

THE MANGOLD FLY GRUB. The mangold is often seriously damaged by a email grub that feeds on the inner tissues of the leaves, making brown-look-ing channels all over the leaf. This grub is the larvae of the mangold fly (Anthomyia betas). The fly, which is something like a small house fly, lays its eggs on the undersides of the leaves, and the maggots as soon as they hatch cat their way into the middle of the leaf, producing scorchedlooking patches on the leaves. "When the maggots are numerous, the damage is often very considerable, and, unfortunately, it is very difficult to advise a remedy owing to the fact that the maggot is inside the i<-af. Spraying with paraffin emulsion may possibly do some good, but it cannot bo regarded as a certain cure. As there arc many generations in a season, it might lv? possible to prevent a serious attack later on by removing tho leaves containing the grubs as soon as they are seen in the early part of the season and burning them. Something may bo done, too, in preventing an attack in the next season by taking care to plough the land very deeply where a mangold crop that has boon attacked has been growing. The last batch of anMibs spend the winter under the surface of tho ground, ready to hatch out as soon as the weather becomes warm in the spring. If, therefore, the land is deeply ploughed they are turned in at such a depth that they cannot get out on to the surface, and arc destroyed. REMEDY DIFFICULT. This list, though not including all the insect pests to which root crops are subject, deals with the most important of them, though, unfortunately, I am unable to suggest any very definite remedies in most cases. The fact of the matter is that when a crop is once badly attacked, remedy is exceedingly difficult. Prevention is probably tho better course to attempt, and if preventive measures were more commonly carried out by farmers throughout the country these pests would probably become less injurious. Of course, tho intensity of any attack depends very largely upon tho weather, for in some seasons tho weather conditions are very favourable to some particular insect, while in another season the conditions may be such that it is reduced in numbers to such an extent as to do no particular harm. There is no doubt, however, that tho spraying machine, discreetly

used with the proper spray mixture, would in a great many cases prevent serious injury were the attack treated in. its early stages. Unfortunately, one is apt to allow an attack to escape observation until the damage is serious, and it is too late to do anything. This article is written with the intention of warning readers so that they may not be caught napping when any of the attacks occur.—W. M. T., in, the Farmer cind Stockbreeder. V