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FUNDAMENTALS OF AGRICULTURE. 



Fungicides are chemical substances which destroy 

 the spores or mycelium of fungi. To be efficient the 

 fungicide must destroy the fungus effectively, but must 

 not injure the host plant; it must be reasonably cheap 

 and easy to prepare and apply. To kill a fungus the 

 fungicide must come in contact with it. Most para- 

 sitic fungi are buried within the bodies of their hosts 

 and cannot be reached by an external application, and 



HAND-POWER TANK, USED IN SPRAYING. 



hence it is seldom that fungicides can be used to effect 

 a cure by direct destruction of the entire fungus. The 

 usual use of fungicides is to form a protective coating 

 over a plant to prevent spores from germinating upon 

 its surface, and mycelium from penetrating to its in- 

 terior. To be effective this covering, like a coat of 

 armor, must be complete and constantly maintained 

 during the period of exposure. 



Spraying. In spraying, as in all other procedures 

 for the control of fungus diseases, success depends 



