New Zealand Department of Agriculture.

Manawatu Herald, 9 July 1895, Page 3

New Zealand Department of Agriculture.

JOHN D. RITCHIE, Secretary. LEAFLETS FOB FARMERS, No. 16.

By T. W. Kibk, F.L.S., &c., London.

Fig. 1. Potato in state of putrefaction after being bored by the grub. Fig. 2. Grub, abovlt average size. Fig. 3. Head and first three segments, upper side, enlarged. Fig' 4. Ditto, under side. Fig. 5. Moth, natural size. Fig. 6. Ditto, magnified : this cut show£ the body rather too pointed, and without the hairs on the last segment. Fig. 7. Fore : legß of moth magnified. Fig. 8. Hind ditto. Fig. 1 from nature ; Figs. 8-8 after French, the markings on Figs. 5 and 6 slightly altered.

The grub of this very destructive moth has long been known in many parts of the world, and for a very long period hai caused enormous loss in some districts in Australia. Nor is it a stranger in New Zealand — -some of the North Island growees have had a bitter experience of its destructive powers. The caterpillar or "grub ".is from fin. in length. The colour ia dirty- white, with a pinkish, or. sometimes greenish, tinge. The head ia dark, occasion* ally.ftltoodt black. Oti reaching the tuber it eats galleries in all directions, and so induces putre&qjipn. It attacks potatoes both intfieid and store. Afirivtd at maturity, the grub takeerup 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— of dirty- white silk. The chaysalis measures about three. tenths of an inch ; and the time spent in thil stage varies from eighteen to twenty-seven days. The moths

usually pairj within twanty-four hours after emerging, and eggs are laid ~%ithin the next forty»eight hours ; but it it probable that other layings take plact, for the moths live for Beveratan^ks ; and in one case, at least, t|9 moth took the male three times ia&ight days, and fresh eggs were deposited after each time within twenty -four 5. hours of the event. I am unable, at present, to say whether this il common with the species. I isolated two females, after impregnation, in order to ascertain how many eggs were laid. The first deposited 117, and the other 128. The first were all deposited in the eyes of the potato ' 'lying on the floor of the breeding-cage ; in the second case the potato had been carefully covered with earth, and young shoots had had developed to the length of about 2 Jin., and the moth, being; unable to get at the tuber, deposited her eggs on these shoots, quite close to the ground. Thes« and other results, obtained from examinations of specimens reared in confinement, agree well with the description given by Mr Tepper,' Mr French, and other writeri on the subject. The moth ii veryaotire both on foot tod wing, taking short, quick flights, and running rapidly ; it is a night-flier, and is attracted by light ; this I knp/W to my cost, as opening the breedinf-oagea one night to try the effect iw a strong light, some of my belt tpecimens. flew straight at the lamp, and, were spoilt. The*lWli^W ! tßeniothi vary, and I believe that the tracings on . those thai pupate in the stalks are

darker tbairon those that come from the tubera. '■ Farther experiments are, however, necessary before this can be stated positively. The tobacco crop in some parts of New South Wales, and lam informed in Queensland also, has been attacked by this pest. The fact that it feeds on othlr^lants 'besides those of the Solandcew cultivated for food, will increase the difficulty of dealing with it. . . - The. Measures adopted must be prevequve rather than curative. The infested districts it will be well, if possible, to abstain from

groring potatoes for a season or two ; failing this, take care that all sets are sound and free from eggs, and the ground thoroughly clear of weeds ; plant rather deeper Ehan 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 if any grubs have been gathered along with the crop ; if so, remove the affected tubers, otherwise the potatoes will soon become a mass of putrofaotion.

As stated above, the moth is a night flier, and attracted by light; therefore, cheap forms of lamps or fires may be used with advantage, and will destroy hundreds. A good plan is to place a light canvas Bcreen of convenient size on either side of the lamp. This screen should be sraered with grease, treacle, or other sticky substance. The number of moths thus captured will be surprising. r lhe lamp and screens may be removed from place to place. The lamps should also be used in the store 3or pits.

Never throw infested potatoes on the rubbish heap. This ia only increasing and spreading the pest— providing the very conditions it rejoices in. Always destroy all grubs by soaking the potatoes in water for some days before giving to the pigs, or, if not required for the pigs, soak in the same way before burying; or, better still, burn the lot. Mr Allan Wight has observed that grubs hatching in the stalk are frequently slow in eating their way to the tubers, and has proved that harrowing off the tops somewhat early and burning them in heaps is very beneficial — always provided that the potatoes have been kept well earthed up.

Mr French states that air-slaked lime, well harrowed in before planting, has been found of great advantage. He also suggests that potatoes should be so planted as to allow of the use of the strawsonizer to distribute tar-water or other fluid obnoxious to insects, and so largely prevent the laying of eggs.

Mr Allan Wight, of Paeroa, the well-known entomologist, considers Lita solanelh a native of this country, and states that it formerly fed largely on the bulrush or raupo (Typha angmtifolia), and that as this was used for thatching potato-houses, the insect soon discovered that the tubers were more to its liking.

It is quite certain, however, that the species has been known for many years as a potato-pest, even in this hemisphere, being reported from Tasmania in 1854, just about the date when Mr Wight first observed it on the raupo. Is it not likely that it was brought to New Zealand in some of the earliest importations of tubers, and took to other plants in consequence of the scarcity of potato ? I have proved by experiment that it will feed on Solatium avictilare, a native of this colony.

Tar water is prepared as follows : £lb coal-tar, boiled in 1 gallon of water, and, after boiling for some time, diluted with 50 gallons fresh water. This must be stirred till well mixed ; it is then ready for use.