CHAPTER XIX 



DISEASES 



It is difficult for the amateur to realize the many ills to which 

 apple trees are subject, but as the apple industry becomes older and 

 more specialized, the more apparent is the necessity of a thorough 

 investigation of the diseases of this fruit. 



Careful observation of all the characters of any disease, with a 

 full description of them on the part of the investigator, will aid 

 in determining just what particular trouble besets any tree. This 

 is especially true when the orchardist has a good, reliable guide 

 to compare with the written description of the disease. Often a 

 treatise may be most helpful if it is arranged in some logical order, 

 especially with reference to the parts of the tree affected. 



It is the purpose of this chapter to set forth in a practical 

 manner the diseases of the apple tree with special reference to 

 the parts affected. 



Diseases affecting the Woody Parts of the Tree 

 below Ground 



Root gall (Pseudomonas tumefaciens). Many times when young 

 apple trees are removed from the nursery rows a bacterial growth 

 in the form of a brown swelling or knot may be noticed on one 

 or more of the roots. Generally these knots are located near the 

 collar or crown of the roots, and therefore near the surface of 

 the soil ; but sometimes they are found to a considerable depth 

 beneath the soil, and occasionally aboveground on the trunk. 



When these knots, or galls, first develop, they may be whitish 

 in appearance ; or, if aboveground, greenish, owing to chlorophyll 

 formation. This color, however, is soon lost and the knot be- 

 comes brown and warty. In the north these galls generally decay 

 at the end of the season, but in the south and southwest they 

 sometimes may continue to grow for a much longer period. 



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