NOXIOUS WEEDS

Nelson Evening Mail, Volume LXXIII, 13 June 1939, Page 8

NOXIOUS WEEDS

CONTROL OF GORSE, RAGWORT AND PIRI-PIRI BIOLOGICAL WORK OF CAWTHIOM INSTITUTE INVESTIGATIONS CONTINUED Investigations relating to the biologi* cal control of gorse. ragwort and pirU piri by means of insects have been continued during the past year by th® Cawthron Institute. The annual re« port of the Institute makes the follows ing reference to this work : GORSE Many requests were received for supplies of the gorse seed weevil »Apion ulids). There is every indication tha® the insect is exerting a pronounced influence in reducing the seeding oi gorse. A study of 1000 gorse pods taken last December from an area at Alexandra in Central Otago where the weevil was first liberated some years ago. showed that nearly 99 per cent, of the pod# were infested by the larvae of th® weevil. This result is all the more significant in view of the fact that th® drea from which the pods were collected had been burned over in recent yen.-. In another locality where a low weevils were liberated some seven years ago. propagation of the weevil has been so vigorous that it is now prevalent, at least half a mile away from the point of original liberation. In this case th® pod infestation was as high as 90 per | cent, and rapid re-infestation of area® where the gorse had been burnt wa® taking place Further observations ar® being made to determine the influence, if any. of the weevil upon the second I annual seeding of gorse and the percentage of viable seed produced during the full year. RAGWORT In previous reports mention has been i made of the introduction from England of a seed-flv which attacks the flowerI ing heads of ragwort. Liberations o t j this fly were made in ragwort area® j in different parts of the Auckland Pro* J v-ince during 1937. Owing to the lat® j emergence of the flies from imported J material, the main liberations were conI cent rated on a farm at Putaruru thd 1 only area where flowering ragwort cou’d be found at that time of th® Observations made during the yea® | after liberation showed that the seed* | fly had successfully passed the winte® I and had given rise to a new genera* | tion. the larvae of which were active in ragwort flowers In regard to thd Putaruru farm w here the main liberaj tion of the seed-fly had been made, tl was estimated that approximately 59 per cent of the flower-heads had been ! infested by the secd-flv. In the spring of 1938 it was evident I that the seed-fly had wintered successfully on the Putaruru farm and that detailed observations during the 1938* 39 summer would probably show th® ] practicability of controlling the seed* 1 ing of ragwort by means of the fly. Uni fortunately, at this stage of the investigations. the co-operation of the farme® l on whose property the seed-fly had been liberated was withdrawn and fur* ther observations could not be made Arrangements are now in hand fof ' the introduction of new’ consignment® of the ragwort seed-fly with a view to their liberation on Crown land outsid® the farming area PIRI-PIRI (Acaena *pp.i i Field observations this past season * have shown that the Chilean saw-fly (Antholcus varinervisi is maintaining itself and is increasing in numbers. During the winter liberations wer® made in Poverty Bay from supplie* bred at the Institute. Unfortunately the number of sawflies available for liberation has no< been so great as anticipated. Heavjf mortality was experienced in the prenupae held at the Institute owing t® fungus attack and no supplies were received from Chile during 1938 Arrangements have been made to alter the technique of breeding to elim* mate as far as possible fungus attack and negotiations are being conducted with Chile with a view to speeding up consignments of the saw-fly from th*| country.