THE NEW TURNIP PEST. DIAMOND-BACK TURNIP MOTH—PLUTELLA

Otago Witness, Issue 1852, 20 May 1887, Page 6

THE NEW TURNIP PEST. DIAMOND-BACK TURNIP MOTH—PLUTELLA

CBUOIIEEAHUM.

The turnip, crops of 1886 and 1877 in Canterbury and elsewhere, but those of Canterbury in particular, have suffered to a very serious extent 'from, the ravages ,of a small greenish caterpillar— the caterpillar of an actrvje little greyish moth fcPlutella crucifercermi), which may be seen in countless thousands flitting-from leaf to. leaf, as one walks through a badly infested field during the months of 'March' and April.*". So great has been the ravages ' of- this i insect during the present -season '"that in some" instances | the turnip orop will be 75 per cent, of less

value than it otherwise" would" naVe^b'een The loss of the turnip crop is a most serioui matter to the farmer, fpr_on_.its_success,de pends the successful working 1 of his farm It has been" said' inlays gbn§ of ?r -£h!t|thre( successive failures ,of f .,the turnip crop ii Britain- would render bankrupt the? farniint interests of the country." JJp. Ngw^gealanc the ' culture or the turnip has i increase* enormously ; without it, it wouldjie difficul 'to profitably' carry 1 on the"^^©^'^^!)^^! into cultivation large areas of new Oand and, on the other h'anfi^tfie' fertility^ 6f !tha already under cultivation 'cbula riot '* be si well maintained.- Without the turnip thi trade in frozen- mutton- could not be carriw onto such W, extent asp bids fair to bi prosecuted bythe aid of ttiiß'crbp. sequently be readily admitted that the con tinuance of the pe9t would be a very seriou thing' indeed for thefarming interests. -iNb are its ravages confined to the turnip crop the gardens in 1 and around Gtiristchurch sho\ pretty clearly that the f pe'st' has - been ' s, work. The whole, of the cabbage tribe o plants have been more or less destroyed^ s much so that a whole plant can rarely no\ be seen. Vegetables of this description ar In consequence scarce and dear, and 'will b still scarcer as the winter advances.

Mr Fereday, our local entomologist, inform us that he has been aware of the presence c this insect in New Zealand- for' years pasi Its extraordinary increase within the pas two seasons is therefore difficult to v riders tanc Doubtless, the two dry warm- summers w have experienced may have" had somethin to do with their increase. ' We have bee informed by. Mr, Iveyj the 'director, of th School of Agriculture, that small 'birds ha* congregated in thousands in" his^infeste turnip crops, feeding on the caterpillars. ] is a significant fact that since the increase ( the small birds the periodical' raids, of catei pillars on the corn crops to which, we wei formerly subject have entirely ceased, an< no doubt they will largely <:curtail- the ii crease of the pest now under consideration so that it will be, admitted *that,iWh'ile th birds do much damage, they are not alto gether an unmixed evil... Of course, howeye everyone 'admits th^t unless tKey,. are kej within' reasonable limits .they would 800 become infinitely, pore, destructive than tr pests they now feed- upon. It ' is asserfce that it i costs the farmers of, New Zealan over-half a. million ,of money per annum 1 feed these birds. That is the estimate value of the grain destroyed by them. Tt following, is ,from> Miss "Or'merod'ss work, c "Injurious Insects":— - •'• ■ '

The caterpillar' of this 1 moth' (Diamom back Turnip Moth) seldom does inuc damage, but in 1851 it appearedjn enormoi quantities in England and Ireland, in k son cases almost clearing the attacked crop, feeds on the leaves of turnips and Swede and occasionally on cabbage. This cate pillar is about half an inch long and spindl shaped (that is, gradually tapering towar< the head and tail), of a pale' green colou with the head rather yellower, 1 or- grey ; has a pair of short- jointed feet on each of tl three rings next to the head, and the for most of these rings has a number of sme black spots; the two next" have each tv yellowish spots oil" the back. * As many as 240 of these caterpillars ha been 'counted on a single plant of inodera {size.' ■ They gnaw' the leave| ay/ay^own ,the veinsV'arid where f th'e attatekfis Md;*cle ,off these afterwards so' 'as utterly to destn the crop. -,'t. \ i>\ '''. vrSHW 1

When full fed they spin a cocoon of threa on the i remains: '.of; turnipileayes :or .on t] ground^ formed of such open net-work th the chrysalis can be seen through it. In t specimens observed, this light cocoon w left open at each end, so as to allow t' chrysalis to leave its old caterpillar-skin ov side at one end, and the moth (on comii out of the chrysalis) to escape at the othi

The chrysalis is' greyish white, wi several black streaks down the back at sides. The moth hatches from ib in abo 10 to 18 days, and to the naked eye appea not, unlike the clothes-moth. When ma nified it will be seen that the fore wings a long and narrow; with several pale spots < ,the fore edge, and a white or ochreousstri; along the hinder edge, this stripe beii waved. so th'atf when the -moth' is at- rest t two edges of the' wings laid flat ' along, t back ' form a " row of pale diamond-snap markings, whence thenam'e of " Diamond-ba Moth." , The,hinder wings have a very lo fringe. There appear to, be a^-sucpession broods, as the moth is observable from t end of June until October.

Prevention and Remedies.— This cat< pillar is too small to be conveniently got i of by hand-picking, and as it feeds' chic beneath the leaves, it is thereby protect from most' attempts to injure it ; , so that V lime soot, and salt have all been tried wil out more than partial success. Something more effective' might possij be' done (Jas with Turnip Sawfly) by taking scuffler between the, rows .with, a bough fir. or broom fixed so as , to sweep the grp off the leaves, " From the habit' of th< caterpillars of, throwing themselves ' do^ and' hanging by their threads on bei alarmed, many • would be 'so thordugl swept 'away that tKey could riot get ba again. In bad cases of attack it would worth while to try this plan rather th have the "whole crop destroyed ; or it naig answer to send a man and boy through t field, the 5 one" with ; a bough to sweep wi the other with soot' or (in; carefo} ham with gas-lime, .to throw, under the plants the fallen grubs. Again, a ( mixture of g. lime, lime,, and so'ot ' would', bY safe' in hands," 1 do good' to the plants/ and be v< bad for the caterpillars.^ „*• s ; , .-.

The growth/that this or any other %vita manure would cause would be very favo able!' In the, severe attack of this 'cat pillar ih^'lßsl; it was "observed that -I " g^owing'.rains "towards, tKe latter "part, July" saved 'some" of ttie crops ;' ajso thai those badly attacked the hoed and sing, portions perished, whilst' in 'the 'parts i hoed enough was. saved for "about half crop. • ! ' '.- *" ■ This caterpillar rarely occurs,' but when does'is- : apt— unless ' prompt" measures^ < taken-r-to t sweep ;fche crop fairly" '^away.-^N ZeaJandCountiyJourni^fbr wayiiyt- ',„"