CONTROL OF WEEDS BY SODIUM AND CALCIUM CHLORATES.

New Zealand Journal of Agriculture, Volume 41, Issue 1, 21 July 1930, Page 1

CONTROL OF WEEDS BY SODIUM AND CALCIUM CHLORATES.

FURTHER INFORMATION AND ADVICE

J. W. Deem,

Director, Fields Division, Department of Agriculture.

An article by the writer on the use .of chlorates in weed control, especially in regard to ragwort, was published in the May issue of the Journal. 'Considerable interest in the subject has been created, and various statements and claims are being made in reference to the discovery and use of these chlorates for weed destruction. The position is that most of the chlorates have been under test for several years as agents for weed-control, and the general results, particularly in France and America, go to show that the most effective work is being done by sodium and calcium chlorates.

The attention of the Fields Division was z particularly directed to the use of these chlorates some eighteen months ago by reports of experiments carried out in the United States for the control of bindweed (convolvulus) by means of spraying with sodium chlorate. This suggested the possibilities of chlorates for the control of some New Zealand weeds, particularly ragwort and similar plants. We also learned that calcium chlorate was being tested in Australia by the Victorian Railway Department for the control of weeds on the railways. Inquiry was made from the authorities in Melbourne, and their report was so favourable that we decided to give both chlorates a trial. Half a ton of the sodium and a small drum of the calcium was secured, and experiments were started as related in the previous article.]

Ragwort being a weed that was causing farmers great trouble received most attention, although small experiments with other weeds were carried out, with the result that we found that most soft weeds were destroyed by one application, while the harder weeds, such as Californian thistle, blackberry, &c., were greatly weakened. At the present time there are indications that three sprayings have killed patches of Californian thistle ; but we shall require next season’s experience before making a definite statement regarding this weed. The same remarks apply to blackberry. Quite a number of experiments are under way this year with various weeds, and so soon as anything definite in regard to any particular weed is available the

information will be given due publicity. It may be mentioned here that Scotch thistle, which does a great deal of harm in good pastures by spreading out and smothering the grass, and which is costly to grub, is easily controlled when in the rosette stage by a spraying of sodium chlorate. ’ .

We do not look upon sodium chlorate as a “ kill-all,”, but apparently there are many people who have got the idea that if it will kill ragwort it will kill most things, and we have had inquiries from ah over New Zealand asking if the chlorate will kill couch, rushes, gorse, piripiri, &c. Up to the present we have not been able to thoroughly test the material on these plants, and cannot give any reliable information just now. We are carrying out tests, but it is suggested that farmers might also conduct small trials-themselves. We shall always be pleased to hear of results obtained by farmers.

In the last article the writer recommended the spraying of ragwort from early October onwards. Now, with the extra two or three months’ experience since the article was written, there can be no hesitation in advising farmers to start spraying so soon as the second growth appears in the autumn and to go right on throughout the winter .so long as the plants are appearing. This has the great advantage that the spraying may be done when the grass is short and the ragwort easily seen, and when more time is available for this class of work. Solutions of 2 to 2| per cent, are quite strong enough for winter work on ragwort. As already advised, a fine day should be chosen for the spraying.

In the previous notes it was pointed out that both sodium and calcium chlorate had been tested by the Fields Division and that both appeared efficient, but that we considered sodium the better. At the present time there are indications that ample supplies of sodium will be available at about sd. per pound for drums of 2 cwt., at 6d. to yd. per pound for smaller parcels, and with special quotations for |-ton lots.

Representations have been made to the Department of Agriculture that we should import the chlorates and sell to farmers at cost price, but it has been decided that so dong as merchants import sufficient and sell at a reasonable, profit over cost the Department will not interfere. Should any attempt be . made to impose an undue profit the Department certainly would reconsider the position. From the great interest merchants are showing in the matter this is not likely to happen, however.

Considerable discussion has taken place on the merits. of calcium chlorate as against sodium. chlorate, particularly in regard to the fire risk. The advantages of sodium chlorate are that it appears to do better work, is cheaper, better to handle, and ample supplies of it are available. Supplies of calcium chlorate, on the other hand, are not so plentiful, and, as already mentioned, it is at present more costly ; also, as it readily absorbs moisture it is not so easy to handle. It does not, however, present the same risk from fire. We have just landed a further half-ton of calcium chlorate, and its advantages and disadvantages will be thoroughly tested this year.

There does not appear to be. much risk with the dry sodium chlorate so long as it is not mixed with any other dry material, such as dry

earth ; but if mixed with the latter or similar material it is supposed to burn readily if it comes in contact with fire. The greatest danger ■appears to be when clothes become saturated "with the liquid spraying material and are allowed to get dry. They then burn rapidly if allowed to come in contact with fire. Persons using sodium chlorate as a spray should endeavour to keep their clothes dry, and if by chance the clothes get wet they should be rinsed with waterhot or cold —before drying. As a precaution, users are advised to wear oilskin leggings or gum boots when working with this spray. One of the Fields Division officers wore gum boots for several months when spraying 'with this material, and so far as can be seen it has not had any detrimental effect on the boots or his clothing.

Dealing with Blackberry

At a recent field-day gathering in Taranaki the writer mentioned in . reply to a question that there were indications that sodium chlorate would kill blackberry, but that we would not be in a position to give definite advice as to the proportion of kills or best method of application until experiments which were under way had been going long •enough to give conclusive results. This was miscontrued by some of the newspapers into statements that we were definitely recommending its use to kill blackberry. The position is that our trials show with blackberry, sprayed last December when in full bloom, a large percentage •of the plants killed, but some are still growing and will require further attention. This is in keeping with some of the experiments in Victoria, where the greater bulk of the blackberry was killed with a 15-per-cent. solution of sodium chlorate when sprayed in the summer, and a second spraying in the autumn cleaning up the remainder. There are also indications that applying the dry crystals round the roots of the blackberry might prove effective. However, as already indicated, we shall have reliable information on the subject later on. In the meantime farmers may test the matter for themselves.

Spraying Apparatus.

A knapsack sprayer will be found the most serviceable for general use, and it should always *be fitted with a trigger spray, which gives the person using it good control and prevents waste of material. The spray nozzle should also be fine so as to nicely wet the plants without using a great deal of material. A very good type of sprayer is now being made at Christchurch, and is retailed by dealers at £4 2s. 6d. Where only small quantities of weeds are to be sprayed a garden syringe may be used. Again, where only very scattered plants are to be treated it will probably be best to carry a small quantity of the crystals, and after bruising the plant with the heel, put two or three crystals on its crown.

It may be mentioned here that the Live-stock Division of the Department, which carries out the inspection of noxious weeds under the Act, is equipping its field officers with spray pumps and material to give small demonstrations in their districts in order to encourage farmers to adopt this means of weed control. All who are interested would do well to get in touch with the Stock Inspector for their district.