CATERPILLAR PEST

Press, Volume LXIX, Issue 20986, 14 October 1933, Page 13

CATERPILLAR PEST

RESULT OF WARM DRY SEASON METHODS OF CONTROL POISON MOST EFFECTIVE [By L. Morrison, Entomologist, Canterbury College and Canterbury Agricultural College.] The outbreak of caterpillars, which is alarming the agricultural community in the Ashburton county, is being widely discussed at present. A few remarks on this and similar outbreaks and how they have been dealt with will probably be of general interest. The destruction of wheat and grass which is meantime taking place is due to the ravages of the caterpillars of a fairly large, brownish, night-flying moth, Persectania ewir i (P. composita or Melanchra composita). This moth belongs to the family Noctuidae, a family which comprises more species than any other family of moth, and is well represented in all parts of the world. All the adults are dullcoloured, at least with regard to the front wings, greys or browns predominating. The posterior wings may be brightly coloured, as, for example, in the British "yellow underwing." Nocturnal moths frequently escape observation during the day, owing to the way in which the colourings blend with their surroundings. They nearly always fly at night or at dusk, hence the name Owlets or Noctuids, and they are readily attracted to lights. On a mild summer night these moths may often be seen, their huge eyes flashing like rubies, as they flutter in vast numbers round a street lamp or any brilliant electric light.

Widespread Destructiveness. The caterpillars are smooth and as a rule not hairy. They are often difficult to identify owing to the great similarity which exists between the species. Many species are enemies of agricultural crops, devouring wheat, oats, barley, grasses, turnips, potatoes, etc. Cabbage and other seed beds may suffer, including nurseries of young forest trees. Many species are known as "cutworms" from their habit of coming out to feed at night and cutting through the stems of plants, so that the plant looks as if it had been cut across with shears. Since the majority feed on the surface of ihe ground they have frequently been termed "surface caterpillars." The popular term, "Army Worm," first applied to the American Cirphis unipuncta (also present in New Zealand), has been applied to those species, e.g., Chareas graminis—antler moth, Persectania ewingi—New Zealand army worm, which, when they have exhausted the food near their breeding place, mass together and march in hordes in search of new fields.- It is usually in this stage that they are first discovered.

The Varied Groups. The cutworms fall into three groups, according to habit:— (1) Climbing cutworms, which actually climb up the plant and eat the foliage rather than the stem. The best known example of this type in New Zealand is Persectania steropastis, which cuts v-shaped incisions in the leaves of native flax (Phormium tenax) and shortens the length of the fibre obtainable. (2) Surface cutworms, which feed at or just above the surface of the ground and cut off the stems of plants ine great majority, including Persectania ewuigi, belong to this group. (6) bub-surface cutworms, which w?p?2 tI Sf ly ? el ? w the soil surface fn.l, cut , P ] ants from one to two inches below the ground. This is ai comparatively uncommon habit, but fe shown m particular by the Dale *ont?V Ut r r - m < P °rosa y grotis orthc! goma), a notorious nest of thp north W wS it ate % of When the cutworm is full fed it sopi down into the surface soil and change! to a beautiful reddish-brown chTysalfs £?«£££ thG adult *n T , he " umber of generations a year clfma J° V o y wi & the species a "d the climate Our New Zealand armv rj m H cp - ewingi) has two broods The first brood, of caterpillars is active at the present time, while the second wh o P °n w T ll grown harvest «me when binder-canvases and threshins? ma , c v. hm s s often toome cloggedl uf with their bodies. tiu ssi.a up

Experience in Britain, Noctuid larvae are particularly destructive m Britain to grass, cereals turmps, and potatoes. Thl species most commonly met with there are the turnip moth (Agrotis segetum), the heart and dart moth, the yellow under! wing, and the antler moth. In Canada frequent outbreaks of the variegated cutworm occur, while in the {jilted ?k u S ,, of Amerj ca the cotton worm the boll worm, the black cutworm, the fall army worm, in addition to those already referred to, are amongst the insect pests of that country. Although cutworms are always fairly numerous it is seldom that they appear in such enormous proportions as to become a real menace to the farmer in New Zealand or in Britain There are well authenticated stories told in New Zealand of their having held up railway trains in the early days, owing to making the rails slippery with their crushed bodies. Dr. Hilgendorf records a case in South Canterbury, when referring to the usefulness of birds, where he says, "Inspection disclosed an army of caterpillars on the march blocked by the water-race, and the sea-birds taking full advantage of the blockage. They were eating their fill, vomiting it up, and eating their fill again." The last serious outbreak, in Britain,' an outbreak similar to the one that is I meantime in progress in Ashburton; county, occurred in the Peak district ; of Derbyshire in 1917, when the, antler moth multiplied and cater-1 pillars commenced marching in I armies. • i In Canada and the United States the ' cutworm is a much more formidable' enemy, and destructive outbreaks are! far more frequent than in New Zea-! land. An extensive outbreak of the black cutworm (Agrotis ypsilon) occurred in Arkansas State (U.S.A.), in 1927-1928, when huge inundations of j caterpillars affected thousands of acres j of corn land.

Reason for Outbreaks. It is difficult to understand the reasons for sudden outbreaks like the' present Ashburton one. Insects are normally held in check by birds, ad-| verse climatic conditions, parasitic insects, etc. There does not seem to have | been recent violent fluctuations in the! bird population, while there is no' rea-1 son to suppose that the parasites of. the caterpillars have suddenly l diminished in numbers or become less effective. One is inclined to the be- | lief that the exceptionally dry con- 1 ditions of late must have been par-1 ticularly favourable for the multiplies-' tion and development of the army worm. Huge mortalities are liable to occur at times among insect larvae due i to the ravages of fungoid and protozoic i diseases. It is probable that the dry season tended to check the develop- i ] merit of these diseases. •

Various Control Mcthcu-. In countries where cutworms a.c regarded as being among the most serious insect pests the farm has to contend with, much labour and money have been spent in evolving means whereby they may be controlled. Running fire through old grass where an army is marching is a most effective means of destroying the caterpillars. Ploughing a deep furrow will alter the line of march and may even confine the caterpillars, at least for a time, to a restricted area. Such methods as driving mobs of sheep and the use of heavy rollers may have some limited use when the caterpillars are marching on hard, bare ground or on a roadway, but could not be recommended when a wheat crop, for example, is affected. By far the most effective method of dealing with cutworms to-day, and a method which has received worldwide recognition, is the use of poisoned bait. This is usually prepared bv thoroughly mixing 301b of bran and lib of Paris green (if whi J : arsenic is used a smaller quantity is necessary, say. I to 31b). To this is added molasses, say, 1 quart, and sufficient water, about two to three gallons, to moisten. A few drops of amyl acetate or nitrobenzine makes the bait much more attractive to the caterpillars. This bait may be scattered along furrows if these have been ploughed to break the line of march, or spread evenly over the ground. This bail, and there are many others of a similar nature, may be applied at the rate of 6 to 101b an acre. On occasion it has been applied in much greater quantities. Where this bait has been extensively used there is no evidence to prpve that birds have been poisoned either through eating the bait or the poisoned caterpillars. When used on wheat crops the danger to stock does not arise. When used on grass there is no danger of poisoning stock if they are kept off until rain has fallen, when any trace of arsenic left will be washed into the ground. Referring to the variegated cutworm in the Ontario Department of Agriculture Bulletin 359, April, 1931, it is stated: "Usually any outbreak can be controlled completely by the combination of the furrow and of the poison bait, but it is seldom that the furrow will be needed." Against cutworms in a garden a useful formula is: Bran 1 quart, Paris green 1 teaspoonful, molasses 1 tablespoonful, amyl acetate a few drops, sufficient water to moisten. The mixture should be scattered thinly between rows of vegetables as soon as cutworm injury is noticed. The bait is best scattered or placed round, but not touching, flower plants, after sunset, so that it will be in the best condition to attract cutworms when they come out to feed at night.

FORMER VISITATION COLD WINTER NECESSARY ■ "If these caterpillars are anything like those we had to deal with in 1865, it will take a very severe winter to exterminate them," said Mr John Nairn, a retired farmer, now living in St. Albans, v/hen discussing the plague of caterpillars in the Ashburton district yesterday. "At that time I was working for Messrs Wright and Murray, where Lincoln College is now and in the late autumn of 1365 we discovered in a grass paddock a mass of caterpillars an inch and a quarter long and all colours. Unless you saw them you could not imagine what they looked like. The movement of the mass was just like the sea on a fairly calm day." At that time the sod walls were all ' new, and in good condition, said Mr Nairn. A gap was made near the top of the wall so that when the caterpillars climbed up through it they toppled over into the ditch on the other side and were drowned. Soon, however, the ditch became blocked, and it was evident that the pests would reach a neighbouring paddock of late barley, nearly ripe. The gap was blocked, and the grass paddock was rolled with the wooden roller which was used in those days, until the ground was covered with slush. Even this failed to stop the progress ■ of the plague, and it completely destroyed the crop of barley. Mr Nairn does not approve of the suggestion to 'scatter poisoned bran, because it might be dangerous to stock. He believes that by driving sheep very slowly over the grubs their progress in a certain direction might be checked, but he does not think that this method would be successful in wiping out the plague. In the attack of 1865 the grubs were able to shelter in the tussocks during the winter, and he thinks that the last winter having been mild, they were able to shelter in the wealth of long grass from the previous season. "We noticed that whenever there was a cold blast of wind in the evening all the wriggling ceased temporarily," said Mr Nairn. "I do not think > we shall get rid of these caterpillars until we have a very severe winter."

KILLING OF BIRDS FARMERS CONCERNED (SI'BCXAi TO THE PRESS.) TIMARU, October 13. Members of the committee of the Timaru Agricultural and Pastoral As- ! sociation, fearing that the destruction of bird life might be responsible for the recent increase of blights and other pests, discussed the matter to-day and decided to take action which, it was hoped, would lead to an improvement in the position. Mr B. E. H. Tripp said that while I birds were disappearing in different I parts of the Dominion blights were increasing, and he. instanced the plague of caterpillars near Ashburton. He would like persons to refrain from killing birds, which were useful in dealing with such pests. "You would still want to see the little owls killed?" enquired Mr W. H. Orbell. "Oh, yes," answered Mr Tripp. Mr Orbell stated that about his property at Levels he was unable at present to see many sparrows, nor were there any larks to be found. On the contrary, there were numbers of dead birds lying round which had possibly been killed by little owls. He did not think the birds had been poisoned. Mr P. R. Claremont: There are plenty of birds at Claremont. Mr H. B. S. Johnstone suggested that one way to deal with the problem, would be to stop payment for birds' heads. He was convinced, he said, that the little grey owls were responsible for the disappearance of bird life in South Canterbury. The owls were difficult to deal with for the reason that it was hard to see them. He suggested that the association write to the various county councils recommending them to cease payment for birds' heads and to stop the sale of poison for birds. It was decided, on the motion of Mr Tripp, seconded by Mr W. H. Orbell, to write to county councils on the lines suggested, but to except German owls from any action to be taken.