SODIUM CHLORATE

Timaru Herald, Volume CXXXVII, Issue 19803, 19 May 1934, Page 15

SODIUM CHLORATE

I USE AS A WEED KILLER CHANGES IN THE SOIL Sodium chlorate, when applied to j weeds, does not persist as such in the i soil, but gradually changes to common salt, which is relatively harmless. These changes depend on the poisoning effect on plants whose roots go to different depths, and also the effect of poison on subsequent crops. The chlorate changes into salt more rapidly when the soil temperature is high. Where the soil is fairly cool and dry the poison retains its strength ! unimpaired for at least ten weeks, j Where the soil is warm and wet the | poisonous effect is reduced at the end of three weeks and entirely disappears at the end of five. It would seem that poison which is effective for three or five weeks should be enough to kill any plant, but other factors now come into play, namely, the movement of the chlorate downwards in the soil, and the depths of the true roots of different plants. When the soil is dry the chlorate stays in the surface layers; when it is wet the chlorate sinks rapidly, and in some experiments it has been recovered in almost full poison strength from a depth of four feet, six months after it was applied to the surface. Instructions for Use For Californian Thistle:—Sodium chlorate costs just over 6d a lb., and at 2oz. a square yard this would cost £ls ian acre. It is, therefore, clear that j chlorate cannot be used on thistle j when there is an extensive area of it. I It can be profitably used only on small I patches. In dry climates like that of i Canterbury, the most effective way to j attack the Californian thistles is to ; poison them when they are growing in grass that will not be ploughed up for two years. Apply the poison in May, scattering It broadcast at the rate of 2oz. a square yard on all the ground occupied by the thistles, and well beyond their limits. Next summer (if stock can be kept off) rake and sow with white clover and ryegrass, but do not plough nor sow any deep rooted crop. Treatment of thistles in stubble, ! etc., depresses the weed, but is rarely followed by complete kills. Shallow-rooted Weeds Shallow-rooted weeds, such as old man twitch, should have the poison broadcast on them in dry weather. The quantity varies for different plants. Two ounces a square yard is usually enough for twitch, but more is required | for sorrel, which is one of the most re- | sistant weeds observed. Treatment |of such weeds is more applicable to I garden than to farm practice. Soft-leaved Weeds: —Most of these, including ragwort, are easily killed by very small quantities of chlorate, so small that they can hardly be applied undiluted. The chlorate, therefore, is usually dissolved in water. It is applied in a fine spray using enough to wet the leaves thoroughly. A recent trial has shown that a given quantity of chlorate applied to the crown is as effective as double the quantity applied to the leaves, and therefore, | special attention should be paid to the I crown of the plant if it is visible. The | spray is most effective on ragwort j when it is in flower, and during damp | weather. Instead of using water, the chlorate may be mixed with carbonate of lime, lib. of chlorate to 121 b. of lime. This is then dusted on the plants until each plant is about as white as grass when it is being top-dressed with 4cwt. of lime an acre. This dusting should be done when plants are in the rosette stage, both because the poison is more effective on the weeds when their crowns are exposed, and because the | grass surrounding them more quickly recovers from accidental injury. Caution While sodium chlorate is not dangerous when it is used reasonably, there are two conditions under which it may cause serious injury: 1. If it is mixed with organic matter such as charcoal or sugar, it may explode violently when struck with a steel or wooden implement. It will, however, not explode if struck when it is not so mixed. 2. Clothes which are saturated with chlorate spray and then dried will burn ! fiercely if a spark falls on them. ! Clothes so saturated and dried should be thoroughly rinsed to remove all the chlorate before they are used in any place where a spark from a fire, match or cigarette may fall on them.