THE POTATO MOTH

Taranaki Daily News, Volume LIII, Issue 281, 20 April 1911, Page 7

THE POTATO MOTH

Messrs Webster Bros, have handed us the following communication from the Department of Agriculture, Fields and Experimental Farms Division, addressed by Mr. E. Clifton, Director of the Division, to the Fields Supervisor, Wanganui, on_the subject of the potato grub, of which we have lately had some experience:— The specimens were submitted to the 'Biologist, who reports as follows: The potatoes are attacked by the potato moth (gelechia operculella), a common pest of potatoes in many parts of the world. The potatoes often become affected while still in the ground, but a great deal of infection is liable to occur after they are dug. Any potatoes that are dug and left on the ground during the night are liable to have eggs deposited on them by the j moth, which is a night flier, and bags standing in the paddocks with the tops' covered witli potato haulms may have the potatoes badly infested before they are removed to the store or pit. Ail tubers which contain the grubs, the presence of which can be recognised by small masses of frass generally at or near the eyes, should be destroyed by soaking in water for some days or boiling. Theyi can then be fed to ni,"s, hut as nil the affected tubers must be dealt with at once only a certain amount can thus lie made use of. All apparently sound potatoes from an infested area should as soon after digging as possible be soaked in a solution of corrosive sublimate, loz. to Bgal. This will deposit a layer of poison on the skins, and if anv e<rgs are laid the young caterpillars will be poisoned before they can enter the tubers. It is probable that steeping in arsenate of lead. 21bs to 50 gals of water, would give.equally good results as corrosive sublimate. Both these mixtures are poisonous, especially the sublimate, and if the potatoes are to be used for food they should be well washed in water before being peeled or being fed to stock. In storing the potatoes, the stores should have all the crevices stopped to make them as moth-proof i as possible, and have tightly-fitting doors. For ventilation the doors can be opened during the daytime, but should always be closed at night, when the moths might be liable to enter. It is, of course, more than likely that, no matter how carefully the potatoes arc sorted over, tubers with the caterpillars inside will find their way into the store. The potatoes should be examined from time to time, and any infected should! be removed. If any moths or pupa cases are noted in the store, the room should be fumigated with carbon bisulphide, using 20 fluid ounces for every 1000 cubic feet involved. This operation may have to be repeated several times, at intervals of about a fortnight. The pitting of tubers likely to be affected is not recommended, as when once the pits are closed it is difficult to ascertain the amount of infection that has occurred. When the pits are opened all the affected potatoes should be burnt, and all refuse from the pit, especially the straw covering, which will jmrbor large numbers of the dormant insects, should be similarly dealt with. This is important and should help to lessen infection next year. For the same reason, all haulms in an infected paddock should be raked up after the potatoes are dug and burnt. The fires in the fields can be lighted at night, as they will then help to attract the moths that are flying about. The methods for dealing-' with the tubers are rather troublesome to adopt, but if no efforts are made it is likely that much ol the North Otaoo and South Canterbury crop will be ruined. ' Field treatment consists in using perfectly clean seed, not only on account of the pest, but because affected tubers, in having the majority of the eyes eaten out, do not develop. Potatoes having tunnels in thou, also allow the free entrance of putrefactive bacteria and fungi and often rot rapidly when planted. The use of air-slaked lime applied before the potatoes are planted is often recommended. The potatoes should be planted a little deeper than is customary and kept well moulded, never allowing any potatoes to become exnosed. For ease and efficiency of moulding, the rows should not, be too close together, 30in being little enousli to allow. Mr. Kirk has snjrjcstod spraying the tops with tarwater, but I cannot say whether this would be thoroughly efficacious in stopping the moths from laying their eg<»s on the foliage and stems. Early crops appear to escape infection to a great extent, so that it seems advisable to got the main crop in as early as possible and not delay planting.