RAGWORT

Evening Post, Volume CXXIII, Issue 70, 24 March 1937, Page 14

RAGWORT

A UNIVERSAL MENACE

METHODS OF ERADICATION

(Contributed by the Dominion museum.) New Zealand may be blessed with a wonderful growing climate for stock and crops; but this is not an unmixed blessing, since it applies also to troublesome.crops and fauna. We have) in consequence to wage a constant war against the vigorous increase of noxious weeds, and such damage-spread-ing imports as the white butterfly and deer. .-'• :

• The invasion of.this country by such unwelcome exotics has'been due to several causes —a purely accidental introduction, such as is common with insects and plants, or a planned introduction for the development of sport, as was anticipated with an increase o£ red and fallow deer. Stoats and weasels were brought in on a reasoned plant for rabbit control; but no one thought of the menace they might prove to native bird life. In a country such as this, introduction-. of exotic stock, whether plant or animal, is a risky proceeding, } although' in the march of progress both are necessary.

■i As far as weed plants are concerned, farmers in 'New Zealand are unlucky in that several of the worst weed introductions are some . of the most easily-propagated plants. Such a one is the prevalent ragwort—Senecio jacobaea—the ugly composite herb which now. is absent from few localities in the Dominion, and • whose presence stamps farmland or paddock with the insignia of incompetent or careless farming. There must be few people in the Dominion who do not recognise this unpleasant weed, with its coarse foliage and yellow ; flowers, which penetrates into even remote bush workings. The species belongs to the large family of composite or daisy-flowered plants. It. grows from two to four feet high, with a fleshy tap root. The foliage is coarse, with irregularly-cut leaf edges—hence the popular name "ragwort." The large, flat heads are composed of many flowers about an inch across, with long, strap-shaped, yellow petals; and these are- superseded in autumn by the browned heads bearing crowds of small fine seeds to which is attached a pappus of silky hairs. The seed of this plant was probably introduced accidentally to the South Island, amongst grass, seed, round about'lß74; and its prolific seed production, and the ease' with which the hairy achenes or fruits are dispersed by wind, is in great part the cause of its frequent occurrence, and of the difficulty in controlling its spread

Of recent years it often has become established in remote areas of bush, where its penetration may be followed along the access tracks —as it was introduced first by horses or on men's boots, and then quickly multiplied by its prolific seed production. If every farmer or inhabitant of New Zealand destroyed on. sight each newly-grown plant on his land, the pest would be capable of being controlled by the means employed at present. The trouble is that one good patriot cleans his land and his neighbour neglects to do so; and in the autumn the seed blows impartially on to the land of the just and the Unjust. In Britain and Europe, generally, this weed is seldom eaten by stock and causes practically no damage; in fact, sheep are put out to eat off the young plants to free the pastures of the weed; but in Canada and in New Zealand severe losses have been encountered through its means, and in South Africa a closely-allied plant—Senecio Burchelli causes a similar disease. Sheep seem to like the weed and can continue to thrive on it for long periods, provided that it does not entirely monopolise the grazing-land. Hence regulated use of sheep for nibbling down the young plants in spring, or the grazing of a few ewes with cattle on infected pastures, are excellent ways of controlling the pest. The chief noxious effect of ragwort occurs with ' horses and dairy cattle, which, after a few weeks grazing on badlyinfected-- country, are affected with an incurable disease: oi the liver. Bagwort does not spread' vegetatively, although it. will sprout, from rootstocks left in: the ground, and continuar cutting of the green tops before flowering is the most effective preventative. If this .is • done each year for three years.it'is usually effective in eradicating the weed. The same result on a large scale may be obtained by judicious stocking of infected land early in the season. The weed cannot persist on constantly-cultivated land; and the chief point, in eradication .is to prevent the plant from flowering and producing seed. Chemical weedkillers, such as sodium chlorate, or the improved, safer, commercial product, is utilised on a small area or to check the first appearance of the weed on land, while large-scale methods of control have been tried by the introduction of the. Cinnabar , moth, whose larvae feed on the , green parts; but on an area where the weed is rapidly increasing it is too difficult and slow to accomplish eradication with insect control alone. The work of clearing the land of this pest must be one of combined' effort of 'farmers, local bodies, and'the general public.