152 



Elementary Principles of Agriculture 



Fig.91. The "brown rot" of plums and 

 peaches leaves "mummies" on the 



trees. 



Fig. 92. Black rot of grape may be pre- 

 vented by timely use of Bordeaux 



vitriol) known as Bor- 

 deaux mixture (given in 

 the Appendix) is most 

 often used. The plants are 

 sprayed with a very dilute 

 solution, so that a thin 

 film of the poison covers 

 the leaves, stems, buds, 

 and fruit of the plant. 

 Spores on the surface of 

 thoroughly sprayed plants 

 are killed, as likewise 

 others that fall on the 

 plants. It is often neces- 

 sary to make several ap- 

 plications, to replace the 

 film of spray washed 

 away by rains. Sulphur, 

 formaldehyde, and other 

 substances, are used for 

 special diseases. 



220. General Methods 

 in Using Sprays. Where 

 efforts are made to pre- 

 vent the attacks of fungi 

 by sprays, it is important 

 to know how and when 

 infection takes place. No 

 general rules can be given. 

 The time and manner of 

 applying the fungicide 

 must be suited to the 

 conditions peculiar to the 



