CHAPTER XV 



FUNGICIDES AND GERMICIDES FOR PLANT DISEASES 

 BY DONALD REDDICK 



PLANT diseases are caused by parasitic fungi or by bacteria, or 

 other vegetable parasites ; or by forms of physiological disturbance. 

 Each disease calls for special treatment. Most plant diseases must 

 be prevented, not cured. 



It should be understood that spraying is only one of the control 

 measures effective against plant diseases. Many diseases are not 

 affected by spraying, though perhaps more are susceptible to this 

 treatment than to any other. 



A satisfactory fungicide must be one that does not injure the plants 

 and at the same time is effective against the parasite. For spraying, ad- 

 ditional requirements are imposed; it should not dissolve readily in rain 

 water; it should adhere to foliage and fruit; in some cases it should 

 be colorless in order not to make ornamentals more unsightly than 

 when diseased. The fungicide which has been used most for general 

 purposes is bordeaux mixture. Lately some other preparations, par- 

 ticularly lime-sulfur combinations, have come into use, and in many 

 cases are supplanting bordeaux. There are in addition a large number 

 of other substances which have fungicidal value and are in more limited 

 use for specific cases. 



Practices 



Destroying affected parts. It is important that all affected parts 

 should be removed and burned, if possible. In the fall all leaves 

 and fruit that have been attacked by fungi should be raked up 

 and burned. Diseased branches should be severed at some dis- 

 tance below the lowest visible point of attack. Fungous dis- 

 eases often spread rapidly, and prompt action is usually necessary. 

 Practice clean and tidy culture. 



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