CONTROL OF RAGWORT AND OTHER WEEDS BY SPRAYING.

New Zealand Journal of Agriculture, Volume XL, Issue 5, 20 May 1930, Page 291

CONTROL OF RAGWORT AND OTHER WEEDS BY SPRAYING.

REMARKABLE RESULTS WITH SODIUM AND CALCIUM CHLORATE.

J. W. Deem,

Director, Fields Division, . Department of Agriculture

For the last twenty years or more various sprays have been tried for the control of ragwort. Some have been a partial success, but owing to such difficulties , as poisoning of stock, excessive cost of material, cost of application, and failure to actually kill a large proportion of the ragwort-plants none have been sufficiently practicable to come into general use. - ' „

During the past six months the Fields Division has. been testing the merits of sodium chlorate and calcium chlorate for the control of ragwort, with very gratifying results. Where properly applied the chemicals mentioned completely destroy all the plants and stand out far above any other sprays for the control of ragwort that have come under the writer’s notice. In addition to the control of ragwort they appear equally effective for pennyroyal, St. John’s wort,. ox-eye daisy, and many other soft-leaved weeds, while there are indications that they will be valuable in the control of Californian. thistle and similar weeds. However, further work is necessary before reliable information will be available in respect to these latter plants.

Points of Investigation and Trial Results.

A start was made to experiment with chlorates on ragwort in October, 1929. The main points of investigation were : (1) The effect of the spray on weeds ; (2) the best time to apply it to secure . the greatest efficiency at the least cost; (3) the most suitable strength to use ; (4) the best method of applicationwhether as a spray or in dry form ; (5) the effect on pasture. Careful work was carried out under the several aspects, and the results may be summarized as follows : ’ ■ . ■ ' . (1) On ragwort, pennyroyal, St. John’s wort,. ox-eye daisy, and similar soft weeds a 100-per-cent. kill was obtained .where all plants

were properly sprayed. It may be mentioned - here that only a light wetting of the plant with the spray is necessary. (2) The best results were obtained when the plants were young, so long as there,, was sufficient, foliage to hold the spray. For instance, ragwort was /best treated when it was from 3 in. to 9 in. high. Areas at this stage treated in October have shown no signs of recovery Older ragwort right up to the flowering stage is equally well destroyed, but a great deal more time and material are required to cover the plants ; besides, where the plants are allowed to grow big a certain amount of suppression of pastures has taken place.

(3) The material was tried as a spray -at strengths varying from i to .10 per cent.—i lb. of material to io gallons of water up to io lb-, of material to io gallons of water. It was soon discovered that the stronger strengths were not desirable, and generally it has been found that 4to 5 per cent, gives the best all-round results. But 2| per cent, has given excellent results with ragwort, and even'i per cent, has given 6o per cent, of kill on tall ragwort in full flower. Until such time as definite strengths have been further tested our advice is to use from 3to 5 per cent., according to the . age of the. plants. In no case has the material at these strengths" failed to give ioo per cent. kill. The spray has . very little effect on the plant for the first twenty-four hours, but, after this it gradually changes colour, and is dead in about a week. Spraying should not be done while it is raining, but in the trials where rain came on an hour or . two after . spraying it did not appear to have any detrimental effect on the results.

(4) The calcium chlorate was applied as a spray, but the sodium chlorate was tested both as a spray and in the dry state. The latter method was equally effective where the crystals were applied direct to the weed,-but was a great deal more costly, both as regards time taken to apply and. cost of material. Therefore spraying is recommended for general work. - ’ •

... (5) .Spraying with .strengths up. to 5 per cent, had little detrimental effect on the grass, but stronger solutions caused considerable burning ; likewise the dry applications. It was also noted that any burning in the spring during the growing-period, and when rain was frequent, disappeared in a few days, whereas summer burning took a longer period for recovery. • • General Notes.

Both sodium and calcium chlorate are safe so far as stock, are concerned, and spraying may be done while the paddocks are being grazed. Mr. C. S. M. Hopkirk, Officer in Charge of the Wallaceville Veterinary Laboratory, has drawn .my attention to a statement in the Cornell Veterinarian that sodium chlorate in fairly large doses is claimed to be a tonic for cattle. While both chlorates have done excellent work here, it is considered that the sodium has given the better results. The question as to ' which chlorate to use will greatly depend ,on cost of material and convenience of transport. . The general question of costs of sodium and calcium chlorate is at present receiving attention. The material used up to the present has cost less than 3d. per pound f.o.b. London, and slightly lower quotations have now been received.

Sodium chlorate is supposed to be easily inflammable when dry on clothing. Users are therefore advised to wash any clothes that

may become saturated with this material during spraying operations before allowing them to dry. Calcium chlorate has the advantage that there is not the same danger from fire. Sodium chlorate, while quite safe to handle, forms explosive mixtures with a number of other substances —for . example, strong acids, sulphur, and sugar. It should therefore always be ' used alone '(as powder or dissolved in water as instructed above) and never mixed with other substances. From the farmer’s point of view these chlorates have the great advantage that they completely kill ragwort and similar weeds ; the work can be carried out without fear of poisoning stock ; what is really •of the greatest importance is that the weeds may be tackled as soon as they show above ground in the spring, and the work practically

completed before the busiest time of the year sets in ; and when the weeds are sprayed in the young stage the cost of material is not great. It must be remembered that all ragwort does not appear at the same time, so it is necessary to go over the farm several times in the year and spray what weeds are showing at the time. At the Stratford Demonstration Farm it was necessary to go over the field three times. The main crop was treated in November, and later in January and February, when certain plants that had been missed in the first spraying were killed.

' It is very difficult to arrive at the quantity of-material required to spray an acre of land infested with ragwort. For instance, on the Stratford Demonstration Farm, where only scattered plants were to be found, approximately lb. of material per acre was used, whereas on

another farm, where a fairly solid block of 5 acres of ragwort standing about 3 ft. high was treated, approximately 22 lb. of sodium chlorate per acre was used. Although most of the plants on this area were in bloom, the effect of the spray was such that all were killed and noseed ripened, as would have been the case had, the plants been cut and allowed to lie. This is important, preventing, as it does, reinfestation by seeds. The work carried out clearly indicates that spraying with chlorates is much faster than either cutting or pulling, and the expenditure in material is amply recovered in the lesser labour involved. In addition,, the chlorates definitely kill, and therefore give promise of providing the farmer with a method whereby the elimination of ragwort may become possible. The foregoing matter may be regarded as preliminary. More definite information and instructions will be given in a further article to be published shortly in the Journal.