Transactions of RHASS Volume 1940 - Page 032
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| Year | 1940 |
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52 THE CONTROL OF PESTS OF FARM AND GARDEN CROPS. Bordeaux Mixture—For many fungoid diseases of plants Bordeaux mixture is the most widely used remedy. In this country, for instance, it is extensively used against potato blight and many other fungoid pests of vegetables, flowers, and fruit. When Bordeaux mixture is carefully made at home it is not excelled by any commercial brand. To achieve this result it is necessary to use materials of good quality. Bordeaux mixture consists of a gelatinous, colloidal suspen- sion of basic copper compounds, formed when a solution of copper Sulphate (bluestone) is mixed with milk of lime. Many different formulae are used in the preparation of Bordeaux mixture, but the most commonly used preparation contains 4 lb. copper sulphate and 4 lb. lime of good quality to 40 gallons of water. It is necessary to follow the directions carefully in order to make a Spray of good quality which will not injure the foliage of plants, but which will stick to the foliage. The quicklime should be as pure as possible. If the lime has been exposed to the air for some time so that a portion of it has become carbonated, a poor grade Bordeaux mixture will result. The quicklime should be Slaked and made into a milk with a few gallons of water. It should then be carefully strained through a fine sieve to remove grit which might cause trouble in the sprayer. In all caSes where lime is used in making sprays it should be treated in this way. The copper sulphate should be finely ground so that it goes into solution readily and should contain at least 98 per cent of crystallised copper Sulphate. Preparation—If only a small amount of Bordeaux mixture is required it may be prepared as follows :— l. Dissolve 4% lb. of copper sulphate in 2% gallons of water and be careful to see that all the copper sulphate has dissolved. If there is any insoluble residue it should be strained ofi. 2. Slake % lb. of quicklime and add water to make 2% gallons. This must be strained from all grit. 3. Pour these two preparations simultaneously into a third vessel and stir with a stick. This will make 5 gallons of 4 : 4 : 40 mixture. If large quantities of Bordeaux mixture are required it is advisable to make up strong stock preparations of copper sulphate and of milk of lime, each containing 1 lb. to a gallon of water. If stock preparations are covered to prevent evapora- tion they will keep for a long time. For use these stock preparations should be diluted with water before mixing. For example, to make 40 gallons of Bordeaux mixture from such stock preparations take 4 gallons of the stock solution of copper sulphate and dilute to 20 gallons, and in another vessel take 4 gallons of the milk of lime after mixing the stock preparation THE CONTROL OF PESTS OF FARM AND GARDEN CROPS. 53 thoroughly and dilute to 20 gallons, and then add the copper sulphate solution to the lime. The Bordeaux mixture is now ready for spraying and should be applied immediately and not allowed to stand. The freshly prepared gelatinous sus- pension of basic copper compounds, if applied to the plant immediately after mixing, will adhere to the sprayed surface in appreciable amount for several months. The effectiveness of most protective sprays depends to a large extent on the Spreading and adhering properties of the materials. Bordeaux mixture satisfies the requirements in these respects fairly well, but methods have been evolved for improving it. The spreading property may be increaSed by the addition of a wetting agent. The chief wetting agents used for this purpose are sulphite lye and lime casein. Sulphite lye is a waste product from the manufacture of paper and is comparatively cheap. For use 7 % 1b. of sulphite lye should be added to 100 gallons of Bordeaux mixture, or 3 lb. to 40 gallons. The lime casein spreader may be made by adding lb. skim milk powder to 100 gallons of Bordeaux mixture and mixing it in well, when the excess of lime in the Bordeaux mixture will act on the casein and form a calcium caseinate. The adhering properties may be increased by adding mineral oil or cotton seed oil made into an emulsion. Generally, 1 gallon of oil is added to 100 gallons of Bordeaux mixture. The oil emulsion is prepared by dissolving i lb. of copper sulphate in 95 gallon of water and mixing with it & lb. quick- lime after Slaking in 1; gallon water. These form a concentrated freshly prepared Bordeaux mixture. One gallon of oil is then poured slowly into this Bordeaux mixture and stirred rigorously until a smooth emulsion is formed. This emulsion is added to 100 gallons of Bordeaux mixture. It is very important that freshly prepared Bordeaux mixture be used for this purpose, or a poor emulsion will result. Preservation of Bordeaux Mixture—If it is not possible to use all the Bordeaux mixture within an hour or two after it is made, the mixture may be preserved by the addition of a small amount of Sugar. The sugar retards the breaking down of the gelatinous precipitate which is essential for good adherence to the plant. For each 1 lb. of copper sulphate in the mixture 3‘; ounce of sugar should be added. Prccautions.—Copper Sulphate solution should not be made or placed in iron, zinc or tinned vessels, because it corrodes these metals. The mixing should be done in copper or wooden Vessels: It is generally done in wooden tubs or barrels. In dissolvmg copper sulphate the powder Should be enclosed in a'bag and suSpended near the Surface of the water. This Will ensure that no undissolved particles will get into the solution and also that all the copper sulphate will be dis- solved. The milk of lime should always be strained to remove |
| Title | Transactions of RHASS Volume 1940 - Page 032 |
