THE POTATO TROUBLE.

Dominion, Volume 4, Issue 1105, 19 April 1911, Page 8

THE POTATO TROUBLE.

: WHAT WILL. THE OUTCOME BE? I How serious is the loss which has been i caused by,'tho potato moth cannot bo stated at present, but it is -probably less . than ,is generally supposed. Potatoes ; have 'been destroyed in various places, and it is understood that in all theso instances the tubers were from the South i Island. . The trouble is attributed 'by exL perts to the particularly dry season. Tho ; pest is always present to somo ,extent, r but a dry year is much to its liking, and, consequently, in such eeasons—tliis sea- • Bon, for instance--'it becomes really asj sertive. It need hardly bo feared that it will'be present'in such a severe form next ! season.j. The action of the Department of Agri- ; culture in causing the destruction of ; some potatoes is supposed to have be£n i' taken with the object of preventing the f introduction of tho potato moth to clean and fairly clean districts. If the tubers are unfit for human' consumption, the , Health Officers havo power to order their ; destruction. None have been destroyed in Wellingi ton so far. > Tho grub of.this destructive moth .lias ; long been known in various parts of the ; world. It. was known in the North Island of New Zealand half a century ago, ; and the Tasmanians .were acquainted with j' it fifty-seven years back. Seventeen . years ago , a .leaflet concerning it was ciri ■ eulated in ■ New Zealand, and in 1907 a i bulletin by. Air. T. W. Kirk was issued. „ t j What-the Moth'. Don. -In the 1907. publication .Mr. Kirk'says': "The' caterpillar; ■or 'grub," .is" from "Jin. i to "i'in. 'in length. 'Hie colour is''dirtywhite, with a pinkish, or sometimes green- ; ish, tinge. The head is dark, occasionally almost black. On reaching the tuber ' it eats galleries in all directions, and ' bo induces putrefaction. It attacks potak toes'both-in.field alul in store.. Arrived at maturity, the grub takes up a position on ,ths outside of a potato,-pieco of earth, pr. other convenient objcct, but .usually ; near, the .mouth of .its'gallery,-'and spins a'covering like'a roof merely—not <i true { cocoon-~of-di'rty-wliitc. silk. . Tho cliry- • ,salis measures -about three-tenths of; an ; inch; and the 'time' spoilt- iii. this "stage ! varies from .': eighteen ' to. . twenty-seven ! -days. ;• Tho moths usually pair within r twenty-four .hours after emerging, and ; -eggs aro laid within the next-forty-eight : /hours; but it is probable that other "lny- | ; iiigs take, place, far the'moths .live-for' ;• .several weeks. . .-.-"I isolated two females, :■ in order to ascertain ; 'how-many eggs were laid.'- The first de- ' , posited 117,, and the other 123. The first' were:all deposited in the eye's of a potato i lying on the floor of the breeding-cage'; iii .the second esse' the potato, had been carefully, covered' with earth, , and young ; shoots had developed to the length lof ' .about'2Jiri:, and the moth, being unable i to get at the tuber, deposited her.egg's on j, these' shoots,. quite close to , the ground. The, markings of the moths-vary, and I believe : tliat- the. tracings on ,those that pupS.te' in -the 'stalks are "darker ' tlian : on i those that come from tho tubers."

What the Grower. Should, Do., „ .'. ; ; ,Wi;iting- should'do,'. ; Mr. Kirk' says:—''The'-measures adopted , must bo preventive rather than curative. : In "infested districts it will be. well,, if \ .'possible, to, abstain from.growing potatoes ! • lor ii season or two. Failing this, . take ; care that all sets are sound and freo from j' eggs, and tho ground thoroughly clear 6f i weeds; plant rather deeper than usual,' keep well earthed up, and bag as soon'as. '', ■ possible after digging. Stow.in a mothproof room, and examine from time to ' time to ascertain if any grubs, have .been •• -gathered along with tho crop; if.so,' re- ; . move the affected- tubers, otherwise the • potatoes will soon become a mass of putrc- ■ faction. . . . The moth is a night flier I and : attracted by light; therefore cheap i forms of:lamps.or. fires may bo used with ■ advantage, and will destroy hundreds. A ;.' good-plan is to place a light-canvass , screen of convenient size on either side ; of the lamt). This. screen should be ; .smeared with grease, treacle, or other ■ sticky, substance'.. ~ .....The ■ lamps should also be used in stores > or pits. ; Never' throw infected potatoes on the rub- :■ bish heap. This is'only increaisng and ', spreading tho pest—providing iho very , condition it. rejoices „ in.; Destroy-all I grubs, by soaking 1 .the potatoes in : water ; for-sdmo day's ; ,;bef ore giving to the. .Digs, : or, if not required for-the-pigs, soak'iii . the-, same way before, burying; or,' better etill, where practicable,' burnthe lot." '

i .Growers' Observations. ! The observations of some other gentlemen are worth noting. . Mr. , E. Allan ', Wight,' of Paeroa, observed that grubs hatched in the stalk were slow r ".in eating- their way to the tubers, and ! "proved that harrowing off the tops somc- : what, early and _ burning • them 'in heaps : was very beneficial—always provided-that ■the potatoes had been well earthed up. : Mr. Wight considered tho grub a native of this country, and stated that it forhie'r- ,' ly fed.largely on th'o bulrush or faupo, • -.and that, as this was used for thatching ; potato-houses, tho, insect' soon discovered : that the. tubers were move to' its- liking! : Mr. French "stated that air-slaked lime, well harrowed in beforq planting, had ; been found of great advantage. He s'u'g- ; jested that potatoes sKbiild "be so planted '.■ as to allow of the use of tho spray pump ; io distribute tar-water or other fluid obnoxious to insects, and so largely prevent ; 'the laying of' eggs. Tar-water "is proi .pared as," follows:—Half a" n>nind of co.-'-j . tar, boiled in one gallon of water,- and, I after, boiling hard for twenty.minutes, di- : luted with 50 gallons fresh water. This • must be stirred until well mixed; it is • then' ready for use, and should be kept . covered till needed.' ' •' .