THE POTATO TROUBLE.

Ohinemuri Gazette, Volume XXII, Issue 2781, 24 April 1911, Page 3

THE POTATO TROUBLE.

WHAT WILJu THE OUTCOME

BE?

How serious is the loss which has been caused by the potato moth cannot be 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 these instances the tubers were irom the South Island. The trouble is attributed by experts to the particularly dry season. The pest is always' present to some extent, but a dry year is much to its liking, and consequently in such seasons—this season, for instance—it becomes really assertive. It need hardly be feared that it will be present in such a severe form next season. The action of the Department of Agriculture in causing the destruction ol some potatoes is supposed to have been taken with the object of preventing the introduction of the potato moth to clean and iairly clean districts., If the tubers are unfit for human consumption, the Health Officers have power to order their destruction. The grub of this destructive moth has long been known in various parts of the world. It was known in the North Island oi New Zealand half a century ago, and the Tasmanians were acquainted with it fifty-seven years back. Seventeen years ago a leaflet concerning it was circulated in New Zealand, and in 1907 a bulletin by Mr T. W. Kirk was printed. WHAT THE MOTH DOES. In the 1907 publication Mr Kirk says: " The caterpillar, or ' grub,' is from £in. to |in. in length. The colour is dirtywhite, with a pinkish, or sometimes greenish, tinge. The head is dark, occasionally almost black. On reaching the tuber it eats galleries in all directions, and so induces putrefaction. It attacks potatoes both in field and in store. Arrived at maturity, the grub takes up a position on the outside of a potato, piece of earth, or other convenient object, but usually near the mouth of its gallery, and spins a covering like a roof merely—not a true cocoon—oi ■ dirty-white silk. The chrysalis measures about three-tenths of an inch; and the time spent in this stage varies from eighteen to twenty-seven days. The moths usually pair within twenty-four hours alter emerging, and eggs are laid within the next forty-eight hours ; but it is probably that other layings take place, for the moths live for several weeics.'.. . I isolated two females, after impregnation, in order to ascertain how many eggs were laid. The first deposited 117, and the other 123. The first were all deposited in the eyes of a potato lying on the floor of the breeding-cage; in the second case the potato has been carefully covered with earth, and young shoots had developed to the length of about 2\ in., and the moth, being unable * to get at the tuber, deposited her eggs on these shoots, quite close to the ground. The markings of the moths vary, and I believe that the tracings on those that pupate in the stalks are . darker than on those that come from the tubers." WHAT THE GROWER SHOULD DO. Writing of what the growers should do, Mr Kirk says :—- " The measures adopted must be preventive rather than curative. In infested districts it will be well, if possible, to abstain from growing potatoes for a season or two. Failing this, take care that all sets are sound and free from eggs, and the ground thoroughly clear oi weeds ; plant rather deeper than usual, keep well earthed up, and bag as soon as possible after digging. Stow in a moth-proof room, and examine from time to time to ascertain it any grubs have been gathered along with the crop; if so, remove the ■ affected tubers, otherwise the potatoes wiP become amass oi putrefaction. The moth is a night flier and attracted •-.by light j therefore cheap forms oi lamps or fires may be used with advantage, will destroy hundreds. A good is to place a light canvas screen of convenient size on either side of the lamp. This screen should be smeared with grease, treacle, or other sticky substance. . . . The lamps should also be used in stores or pits. Never throw iniected potatoes on the rubbish heap. This is only increasing and spreading the pest—providing the very condition it rejoices in. Destroy all grubs by soaking the potatoes in water for some days before giving to the pigs, or, if not

required ior the pigs, soak in the same way before burying, or, better still, where practicable, bnra the lot." GROWERS' OBSERVATIONS. The observations of some othei gentlemen are worth noting. Mr R. Allan Wight, of Paeroa, observed that grubs hatched in the stalk were frequently slow in eating their way to^the tubers, and proved that harrowing off the tops somewhat early and burning them in heaps was very beneficial—always provided that the potatoes had been well earthed up.

Mr Wight considered the grub a native of this country, and stated that it formerly fed largely on the bulrush or raupo, and that, as this was used for thatching potato houses, the insect soon discovered that the tubers were more to its liking.

Mr French stated that air-slaked lime, well harrowed in before planting, had been found ol great advantage. He suggested that potatoes should be so planted as to allow) ot the use of the spray pump to distribute tar water or other fluid obnoxious to insects, ancj so largely prevent the laying of eggs. Tar water is prepared a3 follows :—Half a pound of coal-tar, boiled in one gallon of water, and, after boiling hard for 20 minutes, diluted with 50 gallons fresh water. This must be stirred until well mixed; it is then ready ior use, and should be kept covered till needed.