Transactions of RHASS Volume 1940 - Page 028
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| Year | 1940 |
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44 THE CONTROL OF PESTS OF FARM AND GARDEN CROPS. The strength at which a winter wash can be used most effectively varies for different species of insects and for different kinds of plants. Generally, a 5 per cent emulsion of either the tar oil or the mineral Oil preparation given above is used, except for plum trees and small fruit bushes, when a concentra- tion of 2 to 3 per cent is recommended. Time of application—Both washes should be applied during the winter months when the plants are dormant, generally from the end of November till the time shortly before the buds begin to open. In Scotland it is, generally speaking, necessary to apply these sprays before the end of February. Spraying should only be done on calm days when there is no likelihood of frost within about nine hours after treatment. Tam Oil-Mineral Oil Combined Wash—A combined tar oil- inineral oil wash is sometimes used to save labour costs, and a wash of this kind has been tried for several years at Aberdeen and found quite effective. This wash is easily prepared by mixing together equal parts of tar oil distillate and mineral oil. To three parts of this mixture is added one part of the emulsifying oil, Whitcol J. Whitcol J. is a proprietary emulsi- fying oil, and we have found in our trials that it is a most satisfactory substance for this purpose. This mixture should only be used during the dormant period as stated above. It is generally used at a concentration of 10 per cent—i.c., one gallon of the mixture to ten gallons of water, except for plum trees and Small fruits, when about half this strength is used. Precautions—All tar oils burn the skin, so that the eyes, face, and hands of the operator should be protected. The eyes should be covered with goggles, and the face and hands covered with grease. If the skin is burnt the affected area should be washed with one part of vinegar and four parts of water, and then treated with lanoline. Summer Sprays.—Summer sprays, being applied when the plants are in foliage, must be made of carefully selected materials to obviate the risk of damage to the plant. There are three important groups of summer sprays—namely, contact insecticides, stomach insecticides, and fungicides. Some materials, such as lime sulphur, act both as contact insecticides and as fungicides. CONTACT INSECTICIDES. Perhaps the" most important advances in insecticidal chemistry during the last ten years have been made in contact insecticides. The most important members of this group are soaps, oil emulsions, nicotine, derris, and pyrethrum. THE CONTROL OF PESTS OF FARM AND GARDEN CROPS. 45 Soaps.—-Sof’t soap has long been used both as an insecticide and as a wetter. It is used at various strengths, generally from 5 to 15 lb. per 100 gallons of water. It is a cheap and fairly efficient spray for aphids, but to keep aphids in check the treatment must be repeated every week or two. It has the disadvantages that it is difficult to prepare, as the soap has to be dissolved in boiling water, and that it is unsuitable for use in hard water. The difliculty of preparation may be obviated by using a method introduced by Dr Martin at the South-Eastern Agricultural College, Kent, which has been extensively tried out by us and found very effective. To make 10 gallons of approximately a 1 per cent solution of soap, dissolve 3; lb. of flaked caustic soda in 1 gallon of cold water and add to the solution 12 fluid ounces of crude brown oleic,acid, stirring thoroughly with a stick. When thoroughly mixed make up to 10 gallons with water. This mixture has been used at Aberdeen for treating aphids, i‘Specially on rose bushes, and when applied at weekly intervals afforded a high degree of protection. Some years ago it was decided to combine this soap spray with a fungicide to combat mildew, so that both pests could be treated at the same time. Trials of various substances showed that crude cotton seed oil was a cheap and reasonably efficient fungicide for mildew. A combined spray which we have tried over several years and found efficient contains 2 per cent crude cotton seed oil and 0'4 per cent sodium oleate. To make 25 gallons of this mixture dissolve % lb. flaked caustic soda in about 2 gallons of cold water. In another vessel mix 4 pints of crude cotton seed oil and 12 fluid ounces of crude brown oleic acid and add this mixture to the caustic soda solution, stirring thoroughly with a stick. When properly mixed make up to 25 gallons with water. Precautions.—As caustic soda is dangerous to handle it should be bought packed in i-lb. fins to reduce handling to a minimum. If any caustic soda comes into contact with ihe hands or clothes the part affected should be washed immediately, first with vinegar and then with water. Hard Waters—Ordinary soaps are useless in hard waters, but the difficulty may be overcome, as stated already, by first dissolving in the water i lb. sodium hexa-meta-phosphate per 100 gallons of water. . OilEmulsiom—The introduction of oil emulsions as insecti- L‘liiQS is mainly due to American workers. They are principally employed for treating red spider. Mineral oils for use as insecticides must be of a high degree of purity, otherwise impurities present will burn the foliage. During the last few years the great oil companies have placed on the market special grades of oil for summer sprays. Kerosene has been used for many years as an insecticide, but it is far too impure |
| Title | Transactions of RHASS Volume 1940 - Page 028 |
