Minnesota Plant Diseases. 209 



operations against disease epidemics. In connection with such 

 a department a museum of plant disease would be found to be 

 an excellent aid, where exhibitions of plant products, with the 

 important diseases and graphic descriptions and illustrations of 

 them, would assist visiting agriculturists in recognizing and un- 

 derstanding the diseases of his crops. Such a museum would 

 be of great value to the farmers of the state above all in the dis- 

 semination of knowledge. 



Other preventive aids. Many of the treatments described 

 below as curative are also used as preventives and are found 

 in very many cases to be of great service. Where the begin- 

 nings of disease are not yet demonstrated but may be strongly 

 suspected, or where the likeHhood for the occurrence of certain 

 diseases is strong, spraying is sometimes of use in prevention. 



Methods of cure. Methods of cure cannot always be sharply 

 distinguished from preventive methods. Indeed the same 

 method may sometimes be used with both objects in view. 

 Curative methods in general, however, are directed toward the 

 destruction of the parasite which has already established itself 

 upon its host plant or which threatens such an attack, by the 

 presence of the spores. Two courses are open in such cases. 

 The fungus, together with the infected plant parts, may often 

 be removed by mechanical means, or chemical poisons may 

 be used, as sprays, dusts, etc., to kill the parasite without 

 injuring the host plant. The first of these methods has al- 

 ready been considered in its important aspect of prevention, 

 for it is properly a method of prevention against the spread 

 of disease. The accumulation of refuse should be prevented, 

 diseased parts of trees and shrubs and perennial herbs cut ofif, 

 and burned, and the spore-producing organs of disease-forming 

 fungi cut of¥ and destroyed. Particular care should be taken 

 to destroy the plant parts in which certain diseases pass the 

 winter. Prompt action, so necessary on the first appearance 

 of a disease which is to be treated by these methods of cutting 

 and burning, and cleanliness in farm management are two im- 

 portant essentials of success. The second method of cure, viz. : 

 the poisoning of the fungus and its destruction by means of 

 chemicals which do not, when used in the proper proportions, 

 injure the host plant, is one to which much study has been 

 u 



