CONTROL OF RAGWORT

New Zealand Herald, Volume LXX, Issue 21555, 28 July 1933, Page 14

CONTROL OF RAGWORT

VUSE OF SODIUM CHLORATE ELIMINATING DANGERS IMPARTING FERTILISING VALUE The feasibility of combining sodium chlorate, as a weed-killer, with some other substance to eliminate tho danger of fire which arises from tho uso of chlorates at present, and to impart the growth-stimulating virtues of a pasture fertiliser, is discussed by Mr. B. C. Aston, chief chemist, and Mr. J. H. Bruce, inspector of fertilisers, of the Department of Agriculture, in the current issue of the Journal of Agriculture. They consider that by producing a weed destroyer which, after doing its work, becomes a pasture fertiliser, a great advance would be made in the improvement of pastures at present suffering from, or threatened by, ragwort invasion. "It is hardly probable that a single application of any weed-killer, however efficient, will eliminate all the ragwort plants in a paddock," the writers point out. "Further, there are the seeds of tho weed which remain unaffected by the weed-killer and which will germinate and mature in due course, necessitating further treatment. There is also the continual menace of infestation from neighbouring lands to be guarded against, so that the more one considers the question the more it becomes evident that ragwort treatment should be combined with other pasture operations, such as periodical top-dressing, until at least the weeds aro under control. Problem of Bare Patches "AH bare patches left by the dying ragwort rosettes should quickly bo stimulated to become covered with pasture in an attempt to stifle the young ragwort seedlings and cover up spots which may become sites for reinfestation. One of the suggestions made is that chlorate should be mixed with limo and applied at the samo time as liming is performed. The objection to this in the pumide areas—particularly that of the coarsest kind of pumice soil —is that lime is not required and does not produce any apparent improvement in the pasture, and in some cases has an injurious effect in hastening the onset of bush sickness in stock." Mention is made of a salt of ammonia which is both a weed-killer and a fertiliser —ammonium sulphocyanide, now usually called ammonium thiocyanate. It is often called ammonium sulphocyanate in the United States, where its uso as a potent weed-killer is now being advocated, according to a recent report received by one of tho writers. This compound has fertilising properties, being a concentrated source of nitrogen, of which it contains about 37 per cent. Small-scale Experiments Obtaining a small quantity of the pure compound, preliminary experiments were made on a farm infested in places with ragwort at Miramar, Wellington, in January last, and some tentative results were obtained which compared favourably with those obtained from sodium chlorate on the same farm. Further experiments were instituted at a farm in South Karori in February last. These experiments were also tentative, as they were conducted on a small scale, there being only a small quantity of the ammonium compound available. Sodium chlorate was again adopted as a standard to compare the results of the treatment with other compounds. As was to be expected, sodium chlorate proved to be 100 per cent effective so far as ragwort was concerned, but good results were obtained with ammonium sulphocyanide at the same volume strengths of solution (2J per cent), using a knapsack sprayer. Ammonium tliiocyanato appeared more effective in proportion to the strengths of solution used, which were tried out in 2J, 5 and 10 per cent concentrations. The yellowing effect on the grass was progressively greater, but the ultimate recovery of the pasture was more noticeable. Sodium chlorate in 21 and 0 per cent solutions had a moro prolonged scorching effect, but after some months the grass began to conic away well. Retreatment Recommended

The United States experience is that the stronger the solution (from 10 to 20 per cent) the better the kill in the case of the nioro resistant weeds. Retreatment is recommended to kill any surviving plants, in which case the forI tilising action of thioeyanate is more pronounced. "What it is desired to indicate in the present miniature experiments is tho groat need for further larger-scale trials with numbers of different compounds which can be economically applied, and which will, in addition to being • weed-killers, net as fertilisers either by their direct action 011 growing pasture-plants or by indirect action in notinp; as soil sterilisers or improvers," the writers continue. "So far as we arc aware, there have been no attempts to try the effects of many diflerent weed-killers on ragwort alone. Some work is essential to determine the most appropriate material to uso and the right conditions for using it. Extensive Use Anticipated 14 It is extremely probable, judging from experience in tho United States, that quantities of weed-killer, running into thousands of tons annually, will be required in New Zealand in the future. It is, of course, extremely desirable that this should bo an Empire product, and, if possible, that it should be produced in New Zealand. Ammonium thioeyanate has already been produced in tho Dominion and' it is likely that, as both sulphur and ammonia are required in its manufacture, the production of thioeyanate, if it eventually proves satisfactory, may help in the production of carbon disulphide, which pould. be mnnufnctuml electrolyticallv in New Zealand were there sufficient demand to warrant the installation of a plant. "Carbon disulphide is largely used in horticulture as a fumigant anil insecti. cide. but the quantity so used is not at present large enough to just if v tho expense of erecting n factory to make it locally. Ammonia is also produced m New Zealand as a by-product of gasworks, but it is more largely manufactured from air and imported in large quantities from Great Britain in the form of sulphate of ammonia. Sodium chlorate, on the other hand, is almost entirely derived from foreign sources."