SPRING SPRAYING

Sun (Auckland), Volume III, Issue 762, 7 September 1929, Page 30

SPRING SPRAYING

PREVENT POTATO BLIGHT Bordeaux mixture is a fungicide and gets its name from the district of France round Bordeaux where it is largely used as a spray against the fungus diseases of the grape vine. Its chief use in this country, but by no means its only use, is as a preventive against potato blight. It can be used against a large number of diseases and up to a few years ago was in fairly general use against the fungus diseases of the apple; but it is gradually being displaced by lime and sulphur, owing to the injury its application may cause to the foliage and the fruit. Susceptible varieties of apples are Cox’s Orange Pippin, Beauty of Bath and Lady Sudely. The injury is shown by burnt patches on the leaves and by yellowing. The damage to the fruit takes the form of russeting and in bad cases may cause the fruit to crack. The standard formula for Bordeaux mixture is: Copper sulphate, bluestone, 41b; quicklime (lumps), 41b; water, 50 gallons. To prepare, dissolve the copper sulphate in about one-fifth of the water by wrapping it in a piece of sacking and suspending it at the end of a pole just in contact with the surface of the water in a wooden tub and leaving overnight. The tub must be a wooden one. Place the quicklime in a wooden tub large enough to take the quantity of spray being made, and add the remaining water a little at a

time, with constant stirring. Pour the dissolved copper sulphate into the milk of lime, stirring the while. Strain through a strainer and use immediately. In spraying, it is essential to wet the surface of the leaves thoroughly on both sides, and the spray should

be used in the form of a fine mist or fog by spraying through a fine nozzle under high pressure. There are numbers of proprietary brands of Bordeaux mixture on the market, and if one of these is used it is best to follow the directions given with the particular brand. Hand sprayers may be used if the quantity of spray material required is small. For larger’ quantities a knapsack sprayer is recommended. There are several good sprayers on the market, but remember to procure one with a fine nozzle with considerable force to produce a fine mist, and be sure to wet both sides of the leaf surface. Bordeaux mixture owes its fungicidal properties to the presence of copper in solution. The copper is brought into solution either by the action of the carbon dioxide of the atmosphere on the mixture, or by the action of the fungus itself on the mixture.