VIII 



DISEASES AND ENEMIES 241 



mixtures. - - Bordeaux mixture, though principally 

 valuable as a preventive, has also some importance as 

 a curative. Ifc is prepared as follows : 3 kilograms 

 (6^ Ibs.) of sulphate of copper (bluestone) are dissolved 

 in 100 litres (22 gallons) of water by hanging a bag 

 with the sulphate of copper in the water the day before 

 the application. Just before the application 3 kilograms 

 of quicklime are slaked with a little water and then 

 more water is added to make up 100 litres. The two 

 100 -litre solutions are now poured simultaneously 

 into a third barrel, or the bluestone solution is poured 

 slowly into the lime with continual stirring. The 

 resulting mixture must be used immediately, as it 

 spoils by standing. Only wooden barrels must be used, 

 and all contact with iron must be avoided. 



There are many different kinds of spraying machines, 

 which need not be described here. The present author 

 has used those of the following firms : the Deming 

 Company (Salem, Ohio, U.S. A. ),Gebr. Holder (Metzingen, 

 Germany), Besnard, and Vermorel, but many other firms 

 make equally good machines. It is only necessary to 

 point out that there is a great advantage in using a 

 machine in which the mixture is put under pressure 

 before spraying is begun, instead of being kept under 

 pressure by continual pumping while spraying. Such 

 a machine enables the workman to devote his attention 

 entirely to careful spraying, without having at the same 

 time to be busy pumping. 



Sulphate of copper (3 per cent solution) without 

 the addition of lime is much more effective, and has 

 much stronger fungicide properties, than Bordeaux 

 mixture, but it damages the foliage and can, therefore, 

 only be used for spraying leafless trees. It has proved 

 of great value in the fight against the Surinam witch- 

 broom disease, the spraying being performed after the 

 removal of the leaf-bearing branches. 



(d) By killing the insects by means of insecticide 

 mixtures. Of the insecticide mixtures three groups 

 may be distinguished : 



R 



