MAKCH. 1908 CIRCULAR. No 2 



CORNELL UNIVERSITY 



AGRICULTURAL EXPERIMENT STATION OF 



THE COLLEGE OF AGRICULTURE 



Department of Plant Pathology 



FUNGICIDES. 

 By H. H. Whetzel. 



Fungicides consist chiefly of chemical substances of a more or less 

 poisonous nature that are applied to plants in various ways to protect 

 them, or free them, from their fungous parasites. In far the greater 

 majority of cases, the fungicide is to be applied to healthy plants to pro- 

 tect them from the attacks of these parasites. The fungicide must be 

 of a kind or strength not injurious to the plant to be protected, but at 

 the same time it must be destructive, to the fungus spore that would 

 germinate and infect the unprotected fruit or leaf. Because certain 

 chemicals or certain strengths of these chemicals in solution are injurious 

 to some plants and not to others and because not all parasites are affected 

 alike by the poisons, different mixtures of different strengths must be 

 applied to different plants. The stajje of growth or development oi the 

 plant, the conditions of the weather, the life habits of the parasite to be 

 destroyed and other factors, are almost always to be taken into con- 

 sideration m applying fungicides to prevent diseases. We are rapidly 

 learning that Bordeaux is not a "cure all" for all diseases to which plants 

 are subject. We are also learning that the same strength of the mixture 

 cannot be used with safety on all crops. It constantly becomes more 

 apparent that other factors beside spraying play a very large part in the 

 control of fungous diseases, none perhaps more so than sanitation: i. e. 

 good and proper cultural methods; clean cultivation; thorough syste- 

 matic pruning; proper rotation; yards, waste lands and fence rows kept 

 free from weeds and volunteer plants These are really the things that 

 count most in the yearly fight against fungous pests. It is a significant- 

 fact that it is in the otherwise well-cared for orchard that sprajang 

 pays best. 



In the case of a few fungi, such as surface mildews, the fungicide may 

 be effectively applied after the parasite appears on the host plant. In 

 the vast majority of cases, however, the parasite works within the host 

 and the poison must be applied before infection takes place. 



423 



