DIAMOND BACK MOTH.

Dominion, Volume 2, Issue 503, 10 May 1909, Page 8

DIAMOND BACK MOTH.

Serious , ; .' • ~vTho'; diamond-back:motli;." which ';has'"serii--oiisly riddled : thb:'-leaves' of cabbage,, turnip, '.and,rapo in : .all.'parts of'.New .Zealand;'this: •year.'-is the subject'of some interesting ;hotba .in:;tno^"Journal;of the Canterbury A'.'-and P.;' Association." V -That;, journal says:—,:"; ;;,'.'"Pnr;oxpeVieii'ce.of farm'and/garden pests leads; us :.to the-co'netasion th'at ; tho larva of this/moth is"..without doubt the.roost*de'structiyo and thp,mos,t .difficult,of .all.pests. •;to:,control,: not/'eV4n>./excepting;ltho/'arnjy; caterpillar..;' ltVusually: /makes ;its} appear-" jance.;when! tho;!summer'.is->weH ; ./advanced.'' Fortunately; it,'cpn^mes',its : ;ravagos':tQj of ,■ the cabbage and turiiip; tribe, ''in.'-: other ;wbrds, ;.to: pod-bearing , or,; cruciferous plants. The tooth. - is ;grey : .in. about -, half an inch-:in,the spread'of .its, wings. .When.dis.turbed..; it flits', rapidly -from one .'plant'Y to" another/ ..-It -deposits, its.eggs:bh7''the, sur-.-face _ofy the .leaves. - Tho.Vcaterpiilqfs',■ hatch oiit' in-'a:short time, aad commenceVtoVfoed .voraciously: on ..the, substance' of tho -leaves, ■completely; denuding them till nothing but tho:mid ribs remains. The .caterpillars, when fully.grown, ..are about ono inch long,- of a delicate green'colour, with dark heads. When disturbed; they/.let tnernselves:down'towards /the: earth, /returning. to: their. feeding grounds when.'the danger is passed.,- The life of the caterpiUaV-is, about 'four. ..Wfieks.- ; It ••;•■ then, spins :a cbcoottv.of-.white,-'- silky' matter over itselfj:. .when, it' assumes .'the, chrysalis ';,form,--from ■ which .the. perfect insect /emerges in about 18 0r,20 daysj to,commence its round of ;egg-layihg; :It than probable that there are. more than/thr'ee'-Brobds'in a seaspii:'!:.,The late : ; Mr. '-.Peraday-..(a local entomologist) informed us'that;in his opinion- the insect ; is indigenous ; tb; .JNefr-.-Zealand. / The mbth.is present every season/in our.gardens [and. fields,-;';infesting .the turilip,''rape, '■' and /cabbage/crops in a greater'.or less; degree,. /it. bem'g: more 'prevalent hot, dry. .autumns;VSuch.j.unfpftunately^.is 1 the case this season,/ the ;absence,'p'f/rain..(up. to the time/of writing, March.B) beingrres'pbnsiblb for tho' tho attack, from which large -;■ areas;. of turnips' .'and ; rapo are suffering. Heports;aro : to..hand to the effect that farmers yhave^lost':'areas' 'varying'■ from 40, 60i and 80 acres and upwaYds—crops which aXfowiweeks/agb promised an abundance of autumn arid winter feed/ It is probable that early, and .copious rains would start a Becond ': growth, whichj however good, would fall very: far, short of-the original/'yield of feed. Should /|ho'_ infestation: bo .'general, it -will' ontail a serious loss, upon stock owners.'.ln thb year ,1851 this.'moth appeared in enormoußnunibers in United Kingdom/decimatingthe -turnip crops throughout Eng/and. Ireland..' fortunately Such -between. , In. :1866r87,iw0 had !ah';'attacks/which 'destroyed quite 75 per cent, of thb: total crop, of turnip '. and/ rapo in ' the Canterbury district'. Since"that ,'timoattabks of moro or. less virulence havo been intermittent. It is' true that small birds and starlings devour great -<iu'ftntities of- the/caterpillars, but tlioy are in. such'vast;quantities that their good office's _ avail,,little. .. "As/,regards proventivo mbas'Uros -hiyov-heen.:? suggested, we confess ;thatwe'have;:not j much faith in any of -|hem. The'-pest' may/bo kept. somewhere in check by, frequent with '.- soft soap and quassia water, kerosene emulsion, or tar /water,-" but/such' applications arc difficult and exporisivo when applied on a largo scale., _; Wo-have a.few rows of.cabbages and brocbli/ plants under experiment, and although .they ,/aro frequently ;sprayed with the aboTo 1 specifics, including scalding water," it is very questionable whether wo shall bo ablo f te save.them.'/ But oven if successful, ■tho cost: of/.application 'on a. .-largo; scale would bo veiy/ heavy., Spraying :is '.'utterly' ;usoless'unless appliod to tho under, sido of thb leaves. -, ... / : .- -"Keeping tho crops in a strong growing condition by tho _ application of nitrate of ; soda, lime, is recommended as a preventive / against thb attacks ■ of tlio larva of the diamond back moth.' Our oxporionco is totally at variance.with thig; suggestion. It matters little how strong tho plant,rtnay be crowinE, they are oaualli'. liable \>, '»ttaok,

and destruction Land upon -which a crop has'been destroyed as described should bo deeply ploughed as early: as possible in tho autumn. Im'this way multitudes of tho chrysalides will bo destroyed. Our experiments navo forced us-to 'tho conclusion that tho pest.will _never bo properlv controlled until, a machine is invented capablo of capturing the moth while on tho wing. Wo behove thar.it is quite possible to do so. Such a .contrivance would be worth hundreds, if not thousands, of pounds-annually to tho farmers of Canterbury alone."