CONTROL OF BUTTERFLY

New Zealand Herald, Volume LXXIII, Issue 22344, 15 February 1936, Page 8 (Supplement)

CONTROL OF BUTTERFLY

DEPARTMENT'S TRIALS The parasite imported to cope with the white butterfly continues to do good work, but it will bo necessary to assist in tho control by means of sprays for some time yet. Arsenical sprays are, no doubt, an effective means of controlling the caterpillars, but thefact remains that compounds of such a poisonous nature are not the best to recommend for use on green vegetables. Cabbages containing a percentage or arsenate of lead, if sent to market, may render the grower liablo to a penalty. With the object of discovering a nonpoisonous spray which would be cheap as well as effective, experiments have been carried out at the Plant Research Station. The results are published in the Journal of Agriculture. Leaving out the arsenical sprays, which are known to bo effective,* other tried were proprietary preparations containing derris, from which good results were obtained. Spraying Ratio Nicotine sulphate, at strengths of 1 in 800, 1 in 400 and 1 in 250, gave poor results. While nicotine is a noxious substance with which to spray cabbage when they are approaching maturity, the poor results from this well-known insecticide are surprising. Summer oil sprays also gave poor results, as also did trials with common salt solution, which it is reported stunted the growth of cabbage. The cabbage plant in a wild state—being native to the South of England, where it grows on the sea cliffs in saltimpregnated soil and is washed by salt spray—has always been regarded as a salt lover, so much so that the method in the South of England of coping with attacks of the cabbage root fly has been to place a handful of salt around the stem of the plant. It is of little value spraying with the salt solution, as cab-

bago is notoriously hard to wet, unless some sticking agent is added. What is required is a rosed watering-can, with which the plants can be drenched, thus forcing the solution into the folded leaves, and down tho holes in the heart made by the caterpillar. The solutions given in the experiments, namely, three to four per cent by weight, are evidently twice as strong as those generally usod, the usual rate being two ounces of salt to one gallon of water, or approximately 1.25 per cent. Spraying Ratios The efficacy of salt is known to every housewife who immerses the cabbage in salt water before cooking fh order to bring out any caterpillars or slugs whicii may be hidden in the leaves. It is only a slight step further to apply tho principle to the growing cabbage, in moderation of course. The sprayings at intervals of one month, irrespective of whether poison or contact sprays wore used, does not seem in accordance with modern spraying knowledge. The intervals between aro quite long enough for two broods of caterpillars to emerge. Two closo ratio sprayings have been found to give better results with contact sprays, than more at longer intervals. As tho experiments are being continued for another season tho results at present can only be regarded as inconclusive, except as regards tho arsenical and derris sprays.