NOXIOUS WEEDS.

Press, Volume LXVIII, Issue 20621, 10 August 1932, Page 4

NOXIOUS WEEDS.

BIOLOGICAL CONTROL. (MOW. OU* OWH COWUESEOKDMT.)'. LONDON. July 8. Investigation into the biological control of noxious weeds in New Zealand has been jointly financed by the Empire marketing Board and the New Zealand Government. Mention is made of the progress of the work in the annual report of the Empire Marketing Board. This work has been carried out partly in New Zealand and partly at the Parasite Laboratory at Farnham Eoyal, Buckinghamshire. Blackberry, ragwort, gorse and piri-piri were selected for the main attack (says the report). The blackberry is closely related to economic plants such as the rose and the apple, and considerable difficulty, therefore, has been met'with in selecting insects which confine their activities strictly to the weed. The choice was eventually narrowed down to six insects, which were sont to New Zealand. Five of these were afterwards discarded as dangerous, and hopes ware pinned to the remaining one, a beetle called Coroebus rubi, collected in the south of Franco. Quantities of beetles have been bred at Farnham Eoyal and shipped to the Cawthron Institute for the last five seasons. Veity great caution has been exercised, and as it is not felt that absolute safety has been attained, the beetle has not yet been liberated. Kagwort, another troublesome weed. is not botanically related to agricultural crops, and there are several insects •which confine themselves to eating its foliage. Of these, the Cinnabar moth (Tyria jacobaeae) has been selected for the attack. Over 216,000 pupae were imported from England, and tests on economic plants were carried out for two years. The first liberation took place in the autumn of 1929, and, up* to the end of 1931, about 2,333,000 eggs had been distributed. Surveys of the insect unrler field conditions havo indicated that it is becoming established ani is beginning to control the ragwort. With regard to gorse, extensive studies have been made of a weevil (Apion ulicis), which bores its way inside the pods and eats the seeds. This insect has proved extremely difficult to rear in captivity. A number of individuals have, however, been raised in cages at Nelson, and last year the first releases were made in the field. The burrs of piri-piri have been estimated to reduco the value of wool in New Zealand by £250,000 annually. Thi3 weed also occupies large areas that would otherwise bo under pasture. It differs from tho other plants tackled in that it is a native of the Southern Hemisphere, and its natural enemies must, therefore, be sought outside Europe. A promising sawfly (Antholcus varinervis), whose larvae feed upon piri-piri foliage in winter and spring, was located in Chile. Dr Miller went oyer'to fetch supplies back & thf Cam

thron Institute, and the insect is now being established in the Dominion. The first five years of this investigation are now completed, and are considered by entomologists to be distinctly promising. Tho danger that these insects might do more harm than good by turning to economic plants under the stress, for instance, of starvation is being continually borne in mind. It will, however, take several years of further research before the efficacy of the method of biological control as applied to noxious weeds can be effectively assessed.