RAGWORT CONTROL

Evening Post, Volume CVII, Issue 28, 1 August 1929, Page 19

RAGWORT CONTROL

CINNABAR MOTHS

PROSPECTS OF SUCCESS

iWAMING- TO OPTIMISTS

: Farmers at the present stage must not be too optimistic concerning the control of .ragwort by the cinnabar moth, and must still actively continue to check the weed by cutting or by other, means at their disposal, until it can.be definitely shown that' the insect will act as an evident factor, points out Dr. D. Miller, chief entomologist and director of "Weeds Control Research at the Cawthron Institute, Nelson. He adds that it must be fully realised by .the farming community that the liberations of the cinnabar moth already made were merely preliminary, and only a phase of an experiment to deter .mine the behaviour of the insect in the Sold under its new environment. Dn fortunately, too much publicity has been given to the,possibilities of weed-con tail by means of insects; and any one believing that ragwort, or any other weed, will suddenly disappear "as soon as an insect is liberated will stand to .be deeply disappointed. : The most that can be expected of any practicable means of control is to sufficiently cheek but not,/exterminate.'

• In the-August number of the "New Zealand Journal of Science and Technology," Dr. Miller gives an interesting account of the present position of the researches into the control of ragwort ■through the agency of insects. It was ■';i"'.>1927 that investigations into the possibility of controlling noxious weeds in New Zealand by means of insects wa3 at the Cawthron Institute he writes. At the outset it was decided to concentrate upon the •four weeds of major importance—blackberry, ragwort, gorse, and piripiri. In the ease of blackberry, gorse, and pirit>iri~the investigations are still in the .:;p.«UiJninary stages,' but- the work on : ragwort has advanced, to such an ex- ■ tent tha.t field liberations of the cinnabar mbi. (Tyria jaeobaeae), imported for the control of the weed, were made last autumn.

. The utilisation of plant-feeding insects in the control of weeds, especially of weeds closely related to economic •plants, is fraught with many dangers, •in that there is always a possibility of ;.«io insects in question extending their tood range beyond weeds to include ; agricultural crops. Under the noxiousweeds control scheme, and in order to guard as far as possible against this possibility, only insects that are known to be restricted to the weeds in question, or to plants of no great economic ■value in their natural haunts, are selected for importation to New Zealand -Ue insects are then kept under strict quarantine in special insectaries until ...the.possibility of economic plants bein^ . attacked by them under New Zealand conditions has been thoroughly tested. „It this proves negative the insects may I'M liberated in the field;' as has been doi 3 m the case of the cinnabar moth.

V TAKING EVERY PRECAUTION. ,;•.••.: Of the several insects found attacking ; -ragwort in Europe and Great Britain '■the caterpillar of the cinnabar -moth ,:..ivas selected as giving most promise as a means of controlling the weed in ■ iiew Zealand; its- normal food plants :, are groundsel and ragwort, and in its .;. vatural haunts it sometimes occurs in epidemic' form, when it clears lar^o areas of the host plants. . '.Furthermore ythq insect, isjiorinally attacked by some ; nfine or ten whieK^'teh'3 ' to" Keep it from developing abnormally . but before it is liberated in the Dominion these parasites aro eliminated, so that the insect should have every op,:portunityof. increasing to a far greater ;■ extent in its new environment than, it would in its country of origin. ;• ■ : Although the cinnabar-moth, caterpillars are not known to attack plants of economic valuo in • Europe o Britain, it was nevertheless necessary to submit ;; the insect to a series of starvation tests :.- in IXew Zealand-before considering the 'question of liberation. Except in the ; case of ragwort, groundsel, and cine-. •xaria, these tests proved negative,- and : ..an official permit from the Government was given authorising liberation: How-

ever, owing to later reports receivod from England, somo douot existed as to whether the larvae would attack potatoes, although the tests already made in Nelson had proved negative. In view of this, liberation in New Zealand was postponed -until further and more detailed tests-with potatoes had been carried out bq'th at Nelson and at Rothamsted in England. These tests again showed that .the insect could not survive on potatoes, and liberation was proceeded with.

FIRST LIBERATIONS. On. the 11th February, 1929, field liberations of the cinnabar moth in New Zealand were commenced, it being found most convenient to distribute the insect in the egg.stage. In order to secure the supplies of eggs, fertilised moths v/ere placed in muslin cages enclosing ragwort growing in the Cawthron Institute grounds, and later the leaves upon which the eggs were deposited were removed and distributed in tin boxes. Altogether some 500,000 eggs have been distributed at the fol lowing points: Cawthron Institute grounds, and in the Te Puke, Hamilton. Stratford, and Invercargiil districts, It was not intended that these liberations should be made to all ragwort districts of the Dominion, but only to selected areas; in, order to ascertain the effect of-the insect upon ragwort, and its manner ■' of behaviour under field conditions .where it would be exposed to the influence of its new environment. However, it is intended to make more widespread, distribution of the insect during the'coming spring, and with this in .yiew a 'supply of several.thousand cinnabar moth pupae has been arranged for. ;.'■.• ;;:•-.•

. In New;-.. Zealand thero aro at least five species of insects that, :as larvae normally attack ragwort,' but. none of which actually serves as a, sufficiently permanent means' of control, though at times the weed;.may .be temporarily cheeked by one or more of them. These inseetsare the magpie moth, two species of moth stem-borers, a fly pith-borer ana aleafrminer. ''The magpie moth, with its black and hairy caterpillars, has been confused with the cinnabar moth, but the two' are totally distinct. PROSPECTS OF CONTROL. Discussing the prospects of ragwort control, Dr. Miller says that in the inseetaries the devastating effect of the cinnabar moth was extremely apparent, and if this condition could be maintained each year in the field one could safely say that ragwort would no longer rank as a major weed. But: under field conditions the insect enters a complex of factors any one or all of which might be so detrimentally influential as to prevent it from maintaining a standard sufficiently epidemic for effective control. Among such possible detrimental factors are climate, natural enemies, and disease. Regarding climate, one should expect that the meteorological conditions of the Dominion would be rather favourable than otherwise, especially in the North Island; in Southland, on the other 1 hand, the greater severity of the climate will probably have a- staying influence upon the insect. . • . / ■

Of possible natural enemies, predaceous and parasitic insects will certainly influence the problem; even at this early stage of establishing the insect it has be.en found that the two parasites attacknig the early stages of the magpie moth ■ are both parasitic upon the cinnabar moth. To what extent these parasites will affect the general issue is not yet known.

The disease factor is not to bo overlooked, since in the insectaries a polyhedral disease destroyed a very, great proportion of the caterpillars; in the insectary, however, conditions were favourable to the development of this disease owing to overcrowding and high temperature and humidity. It is hoped that similar epidemics will not destroy jtho cinnabar-moth caterpillars upon open field conditions.

Mr. Charles B. Cochran is likely to provide London theatre-goers with a novel kind of printed programme—printed in white on black paper, so that it can be read by holding it up to the light from the stage.

Blacksmiths and wheelwrights throughout the country are finding a revival in their trades, as more wagons arc iv use and local builders are going to blacksmiths for wrought iron and other materials. . - -

A Littauer Foundation has been founded with £200,000 by Mr. Lucian Littauer, an American 'glove manufacturer,. with the object of promoting "a better understanding among all mankind."