SPRAYS FOR FRUIT TREES.

Otago Daily Times, Issue 20320, 31 January 1928, Page 15

SPRAYS FOR FRUIT TREES.

A NICOTINE SUBSTITUTE. CHEAP OIL EMULSIONS. In the report for 1926 of the Agricultural and Horticultural Research Station, Long Ashton. Bristol, Mr Staniland gives an account of oil sprays for spring and summer use. While these oil sprays are used very much in both. Canada and America (writes a correspondent of The Times) they have never become very popular in tais country, where, in. fact, only a few people have ever tried them, ana the vast majority have never heard of them. Ordinarily a mixture of nicotine and soft soap is used as a summer spray for killing aphides and other insect life, and though the nicotine sprays are very effective against pests they ar e very costly to the user. In small quantities nicotine costs 2s per ounce. The research station has undertaken this work in an endeavour to discover a cheaper spray of the same efficiency for killing pests. Oils of both mineral and vegetable origin have been used, including paraffin oil, liquid paraffin, several lubricating oils of varying heaviness, olive oil, sesame oil, linseed oil, cottonseed oil, rape oil, and castor oil. USE OF SOFT SOAP. These oils in the pure state must not be sprayed on to the summer foliage or the whole would be scorched ; and as they do not mix with water a diluted solution cannot be made by just pouring the otl into the water. But oil mixes with a watery solution of soft soap to form what is known as an emulsion. Thus each of the oils mentioned heretofore had to lv made into an emulsion with soft soap and water before being tested as a spray. Ordinary soft soap, preferably in the liquid form, such as is.commonly used in spraying operations, was found to be suitable for emulsification purposes. This liquid soap vvas diluted with water until onetwelfth of it was soap, then, oil, in quantity about the same as the soap solution, was poured into the soap solution, xne whole was then poured from one vessel to another several times until emulsification had been completed, and no oil rose to the top. Further quantities of water were then added to weaken the emulsion down to its desired strength. Some oils emulsified badly and others were costly, so only linseed oil and rape oil were deemed worthy of further trials ; these, when tested on the trees as a spray against insects, produced the following re suits: —The rape oil emulsion was found to possess rather higher killing power tnan the linseed oil, which was found to he quite unsuitable, as it “ varnished.” The rape oil proved satisfactory for killing pests and less damaging to the foliage than similar proprietary oil sprays now on the market. STRENGTH OF THE WASH. The report states that these rape-on sprays would seem to have a number of advantages of which the following may be mentioned: —(1) For spraying trees in the spring before growth has begun, in cases where the ordinary tar-distillate washes cannot be used. The strength of the wash for this puroose should be a 1 per cent, emulsion: (2) for spraying plants in the summer to kill ordinary green fly the strength to be used is £ per cent, emulsion, and this makes it a very cheap wash for the purpose; and (3) for spraying fruit trees in the summer to kill such pests as the apple capsid hugs, and the very common American blight or woolly aphis. The strength for this purpose should be from 1 to 2 per cent, emulsion. To grow sound, unblemished fruit seems impossible, unless much spraying is done to keep pests under control, and for use generally they must be cheap for purchasing and effective in action. Few sprays used to-day possess both nualities, and investigation work of this kind seems very desirable.