PARASITIC CONTROL

Te Awamutu Courier, Volume 53, Issue 3829, 4 November 1936, Page 5

PARASITIC CONTROL

SCIENTIFIC ATTACKS ON NOXIOUS WEEDS. RAGWORT IN TARANAKI AND AUCKLAND. Steps taken to achieve parasitic control of noxious weeds were outlined in a review of the position by Dr David Miller, chief of the emtomological department and assistant director of Cawthron Institute. A noxious weed, he said, could be defined as an unwanted plant occupying too much valuable land. His job was a biological one—the use of insects not only to control other insect pests but to control weeds. The basis of weed control was sound farm management, but the trouble was that farmers could not afford to apply sound farm management, and all country was not suitable to sound farm management. The use of biological methods could be brought in and used in the fight against weeds. Prickly pear in Australia had been levelled to the ground by the use of insects. To-day farms were being established, and he understood the ground was invaluable for the growing of oats. The control of gorse, ragwort, and bidi-bidi were the jobs which were occupying their attention at the institute. They had started out with another Weed, blackberry, but had had to give that up. He had spent seven years on that particular research, combing the whole world for likely insects, but it was a difficult matter to find an insect which would confine its attention only to blackberry. They decided upon a flat-headed borer from the south of France. The grub of the insect did extensive damage to the blackberry, but the trouble was that when the beetle developed from that grub it had a weakness for defoliating apple trees. So far they had been unable to locate any other insect. They had to be very careful indeed that the insects were so specialised that they would confine themselves to that weed and nothing else. CONTROL OF GORSE. In gorse they had a legume. It was a risky business undertaking control of gorse by insects on account of the danger of parasites attacking other legumes, of which there were a number in New Zealand. They had discovered that there was a weevil existing in Great Britain the grubs of which attacked seeds of gorse. From studies in England and New Zealand (under strict quarantine) they had found that these weevils were so highly specialised that they could not lay eggs on any other legume. When the pods were soft the female bored a hole in the pod, put in the eggs, and blocked up the hole. When the pods burst the weevils were ejected, not the seeds. The first liberations were made near Alexandra, and in the area where these weevils were liberated they would not find a pod that was not infested with these insects. It would take a long time to get the weevil’s spread right throughout the country. His only regret was that this weevil did not destroy the flower. Gorse was an important plant from a hedge point of view, and before they started the above work they decided that they could not very well attack the plant. However, North Island farmers wanted to know if they could get an insect which would destroy the plant, and they were investigating the matter.

THE RAGWORT NUISANCE. The institute had been working on ragwort for some years. It liberated the cinnibar month about six years ago. Unfortunately, the moth produced only one. generation of caterpillars a year, which worked only six weeks before Christmas doing damage to the ragwort. A parasite turned its attention to this moth and destroyed it, so that it had died out after a few years. The institute had been blamed fdr introducing different insect pests, including the white butterfly, but as the cinnabar moth was black and the other was white, he did not know how they could be confused. The seeds of the ragwort were windborne, and they had now a fly which was attacking the seeds. Before the flower of the ragwort opened the fly was attracted by the smell. The fly would lay an egg in the disk of each flower, and a maggot was hatched, eating out every seed, and then boring out into the head of the flower, causing the whole flower to wither. Experiments had gone so far and they were so satisfied with it that they had commenced liberation in a small way. The position was very acute in the Auckland province and in Taranaki. Public bodies, certain banks, freezing companies, insurance companies, harbour boards (all those interested in land investment) had offered to put up finance to secure enough insects, the only stipulation being that they should be liberated in the Auckland province. The result had been that this year there were 490,000 of these insects on the way to New Zealand. When this supply had been established on a large scale they could draw supplies from the Auckland province for other places. THE BIDI-BIDI PEST. The bidi-bidi pest was a very serious matter with sheep-farmers, particularly in western parts. Some time ago he went to a wool store and estimated at that time that the value of the wool in that store was depreciated 33 per cent, through bidi-bidi. It was restricted in its range to New Zealand and one or two areas in Australia, but its main home was in Chile. In 1930 he went to Chile and found an insect which he thought would be ideal. He brought it to New Zealand, and carried out experiments which were so satisfactory that he went back last year and got a very large supply. The first liberations were made about three months ago, and the work done was most spectacular. Already they could find the grubs from these insects working in great style. He hoped it would do here what it did in Chile. St. >John’s wort was very prevalent in certain districts. It was not a weed of national importance, but it was of great importance locally. In 1928 the institute commenced working on it, but when they found that it was occupying the attention of the Austra-

lians because it was a weed of national importance they gave up working on it. Later on they would utilise the researches of Australia. In the North Island the variegated thistle was becoming a pest, and he had been asked to go into it. He did not know what could be done with the manuke from an insect point of view. It was a native weed. The Otago provincial council of the New Zealand Farmers’ Union, at a meeting in Dunedin passed the following motion unanimously:—“That this council views with alarm the spread of noxious weeds throughout New Zealand, particularly on Crown lands not previously infested, and requests the Government to convene a conference of representatives of State departments, mercantile companies, local bodies, farmers and sheep owners’ organisations, the Cawthron Institute, and Government research organisations, such conference to be i.eld in Dunedin to discuss possible avenues of action.”