CHAPTER XII 

 DISEASES OF FRUIT TREES 



As in the case of insects, the writer makes no claim in the 

 present chapter to anything like a complete list of the fungous 

 troubles which may beset the orchard owner. He merely hopes 

 to give some suggestions, taken principally from personal ex- 

 perience, which may help the student and the orchardist in 

 recognizing the more common pests and in deciding what to do 

 for them. 



Importance of Knowing Why. — To the student, the fungous 

 diseases of fruit trees form an extremely interesting group of 

 organisms, one that he likes to examine and to study. To the 

 orchard owner they are a pestiferous collection of annoying 

 troubles against which he must be constantly on his guard. But 

 even with the practical orchard man it is very desirable that he 

 should give them sufficient study to know what methods are 

 best and why they are best. This latter point has received much 

 study. It has always seemed to the writer that almost anyone 

 ought to do better work if he knew why he did it in a certain 

 way rather than in some other way. If the man who sprays 

 understands that when he leaves live San Jose scales on the tips 

 of a lot of branches he is likely to have the entire tree reinfested 

 because the scales breed all through the season and crawl down 

 onto the part he sprayed ; if he understands this he is far more 

 likely to do good work than if he is merely told to spray 

 thoroughly. If in cutting out fire blight, he understands just 

 why he cuts as he does and why he disinfects his shears, he is 

 much more likely to do his work properly than if he is merely 

 "shown." So it seems worth while to understand something of 

 the life history of these fungous diseases that cause so much extra 

 work to the orchardist and to know just how the fungicides 

 affect them. 



Nature and Types of Fungus. — The fungus is merely a very 

 low form of plant life. It does not manufacture its own food, 



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