CATERPILLAR PLAGUE

Bay of Plenty Beacon, Volume 7, Issue 77, 30 May 1944, Page 8

CATERPILLAR PLAGUE

MORE DETAILS ABOUT PEST

FIELDS DIVISION LETTER

In answer to further enquiries regarding 1 the destructive caterpillar pest on the Plains, the 1 secretary of the Primary Production Council has handed us J ihe following letter from the Plant Diseases Division, of the Department of Agriculture which sets out in full the habits and control of the visitation. Although the specimens were in a poor condition for identification, it would appear probable that the caterpillars (specimens A) are those of the cosmopolitan army-worm Cirphis unipuncta. I would like, to receive some more samples, however, sent to me direcit, for more accurate identification. A few clirysalidsfrom which the adult moth can be bred out Avould also be very useful. The seasonal cycle of the moth in New Zealand has not been worked out, but judging from overseas experience may be somewhat as following :— The winter is passed in the chrysalis stage or as the partly grown caterpillar just below the surface of the soil. Moths emerge in the spring (probably .November) and lay their eggs in clusters on the lower leaves of grasses. The leaf is generally folded lengthwise and fastened about the eggs with a sticky secretion. The young worms are pale green and have the. looping habit of crawling until about hall-grown. They may often be found by thousands in fields of grass, but because of their habit of feeding at night their presence is generally not suspected until the crop is nearly destroyed. When the food supply is exhausted in the fields where they have, hatchcd the caterpillars move in large numbers to near-by fields. When fully grown the caterpillars, enter the ground and pupate, emerging as moths in two or three weeks. There are probably several generations per year in this country, the caterpillars of the first brood being present about December and they may "possibly appear again as the. second brood in February and as a third in AprilMay. lit is to be understood that this is hypothetical as I have already .said above that the facts have not been worked out, but you may be able to tit this information in with your own observations. Mr G. V. Hudson of Wellington states that the adult moth first appears in the field in January and increases in numbers until the middle or .end of April. This information takes no account of broods or generations, but if the moths are abundant in the latter patft of. April that would account for the large numbers of caterpillars in May. The. moths themselves arc strong fliers, but remain hidden during the day, becoming act>*e at night. The < female is reputed to las' as many as 500 eggs. Control measures are as follows:

1. Poison baits.. This is one of the most effective, methods of dealing with the pest. The bait is spread in the tie Ids where the caterpillars are feeding or else across the. line of march when they are leaving pasture they have destroyed. A suitable bait is: Bran lOOlbs.; Paris green or white arsenic 4 to Gibs.: water sufficient to make a stiff mash, usually 7 to 8 gallons. If desired, 2 quarts of molasses may be added, but this is not strictly necessary. Mix the bran and poison dry, then add the water. If molasses is used, dissolve this in the water. ,If desired, hardwood sawdust may be substituted for half the bran. The bait should Jie spread in the late afternoon or early evening at the rate of about 201bs per acre. This may be done by hand from buckets or bags. According to one authority

"Spreading by hand from a horsedrawn wagon or motor truck is the common method ol application. One man scattering from a wagon can cover 10 acres" per hour; two men in a truck can covcr 20 acres." In this case the recommended dosage per acre was lOlbs. Ditches or furrows. Where the caterpillars are advancing from one field to another they may be stopped by ploughing a furrow at right angles to their line of march. The steep side of the furrow faces the. direction from which the armyworms are coming. They may be crushed by dragging a log up and down the furrow. A second furrow beyond the first may be cut to catch any caterpillars that pass the first barrier. If desired, the poison bait described above may be broadcast in the bottom of the furrow; in this case, of course, it would not do to drag the log up and down the furrow. We have stopped army-worms by ploughing 'deeply a strip four to live feet wide across, the line of march and broadcasting poison bait on the turned up soil. The face of the last furrow nu>t be left steep and unbroken. Every time that an outbreak of army caterpillars occurs, widespread damage is done either because the presence of the insects is not noticed until it is. too late, or because H,c)!:-imicii in next column)

it is believed that control measures are impracticable. In areas likely to be affected at this time of the year, it should be an annual practice. to search for the pest in the latter part of April. Early in the morning or late in the evening is the best time to search. MosJt of the caterpillars will be small and difficult to see, as they will tie concealed at the. base of plants, but a careful examination will always reveal their presence Where small infestr ed patches are discovered, especially in long grass? tins should be cut, straw scattered over the top and the. whole lot burned. Mr Dickson's specimens B are known as Lissopimpla semipunctata a parasite of Cirpliis unipuncta. This parasite occurs when large numbers of the caterpillar appear, but it is. usually not numerous enough to stop damage until too late. I. trust the. above information will prove useful.