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 later point has received much 

 study. It has always seemed 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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