SPRAYING FRUIT TREES, 339 



nately, however, it is possible to combat many pests and 

 diseases in one operation. Roughly, the enemies of fruit 

 trees and bushes may be divided into three classes, as 

 follows : 



(i) Leaf-biting insects, such as t'he various caterpillars. 



(ii) Pests which live by sucking the plant's juices, such 

 as the various aphides, psylla, etc. 



(iii) Fungoid diseases, such as Apple Scab, Brown 

 Rot, etc. 



Each of these three classes requires special treatment, 

 but by the use of combined washes or spray-fluids any 

 two or all three of them may be dealt with in one opera- 

 tion. 



The leaf-biting insects of the first class are destroyed 

 by poisoning their food. This may be done by spraying 

 with arsenate of lead. 



The sucking pests of the second class cannot be killed 

 by poisoning their food, because they pierce to the inner 

 tissues of the plant to obtain the juices on which they 

 live. They have to be destroyed by washes which either 

 block up their breathing pores (such as paraffin and soft 

 soap emulsion), or those that act directly on their skins 

 (such as nicotine or tobacco extract). 



The fungoid diseases, of the third class, are not touched 

 by the insecticides mentioned above. Against them we 

 have to use fungicides such as Bordeaux mixture or lime- 

 and-sulphur. 



Suppose we agree to employ arsenate of lead for the 

 leaf-biters, nicotine for the sucking pests, and Bordeaux 

 mixture for the fungoid diseases. We may thus be very 

 simply equipped against practically all our enemies. The 

 arsenate and Bordeaux mixture may both be obtained in 

 the form of paste, and the mixture in the form of extract. 

 Any of these may be used alone, and anj two or all three 

 may be combined, as required. With the quantities to 

 use we will deal later. Practically all we shall need in 



