Chapter XV. 



Fungicides and Spraying Apparatus* 

 Jff 



Fungicides. By fungicides are understood those substances 

 which are capable of destroying or prohibiting the growth of 

 the spores or mycelium of fungi. Chemical solutions have 

 proved of great value when sprayed upon diseased plants. 

 Such a spray must not only not injure the plant, but must at 

 the same time destroy or hold in check the parasite. It becomes 

 evident, therefore, that such 

 sprays are of greatest benefit in 

 combating fungus parasites 

 which live on the surface of 

 the host plant, i. e., the epi- 

 phytic fungi, such as the pow- 

 dery mildews. These para- 

 sites can be reached directly 

 by the spray without the ne- 

 cessity of penetrating the leaf. 

 But the spray may be benefi- 

 cial in still other ways. For, 

 instance, where the fungus! 

 lives inside of the host plant, 

 and comes to the surface to 

 form its spores. Potato- 

 blight is such a form. The 

 use of the spray consists in the destruction of the spores and 

 the prevention of the spread in such cases. On the other hand, 

 a very large number of parasitic fungi produce their spores at 

 the surface of the host, but are not affected by sprays, e. g., 

 rusts of grains. In some cases, however, the spray is benefi- 

 cial against endophytic fungi and in these cases it is because of 

 the destruction of the spores and the prevention of the latter 

 from germination. The internal mycelium cannot be reached 



FIG. 102. A bucket pump. 

 Co.) 



(The Deming 



