CHAPTER IV. 



DISEASES INJURIOUS TO FRUITS. 



The diseases which the fruit grower has to combat are 

 numerous. No portion of the plant is exempt from their rav- 

 ages. Some diseases are perhaps not due to a special growth 

 in the tissues, but result from some physiological weakness of 

 the plant, due probably to unfavorable surroundings. Such trou- 

 bles can be stopped only by doing away with the cause, and 

 practically the only method of preventing them is by improved 

 cultural conditions, as is the case with Peach Yellows. 



The great majority of plant diseases are what are known as 

 fungus diseases. These are propagated by small bodies or spores, 

 given off in various ways, which act as seeds in starting new 

 growths. The life habits of these diseases are extremely vari- 

 able and often very complex. Some of them live one generation 

 on one plant and the next generation on some very different 

 plant. For instance, the Apple Rust (Gymnosporangium) lives 

 one stage on the foliage of the apple and the next on the Red 

 Cedar, where it develops the cedar apples that produce the 

 scarlet, gelatinous fruiting bodies commonly seen on Cedar trees 

 in early summer. This disease may be largely avoided by de- 

 stroying the Red Cedar in the vicinity of orchards. 



The remedies commonly used for plant diseases are to cover 

 the susceptible portions of the plant with some antiseptic cover- 

 ing. Such materials are generally termed fungicides. The ac- 

 tive fungicidal principle in most of those in common use is some 

 salt of copper, so combined as not to injure the foliage. The 

 most generally useful fungicide is Bordeaux mixture, which is 

 a combination of the salts of copper with lime and water. This 

 material* is adapted for use in diluted form when the tree is in 

 leaf, or when of increased strength, for use when the tree is bare 

 of foliage. Sulfate of copper solution is a valuable fungicide 

 for use when trees are dormant, but is very injurious to young 



*Formulas for insecticides and fungicides will be found In the Ap- 

 pendix. 



