DISEASES OF CROPS 



203 



trees and more or less injurious to apple trees, dependent somewhat on the 

 varieties. They also occur on pears, quinces, cherries, plums, grapes, 

 roses and many other plants. The diseased tissues extend throughout a 



considerable part 

 of the plant which 

 makes cutting off 

 of these malforma- 

 tions a very uncer- 

 tain treatment. 



The hairy root 

 appears under- 

 ground as a mass 

 of fibrous roots and 

 above ground as 

 warty knots on 

 trunk and branch, 

 and is sometimes 

 mistaken for cank- 

 ers, due to other 

 causes. 



Treatment. 

 The organism w hich 

 causes this disease 

 lives in the soil for 

 several years, and 

 cannot be eradi- 

 cated except by a 

 long rotation of 

 crops. It is unwise 

 to set orchards, 

 especially peach 

 orchards, in old 

 berry fields or other 

 fields known to be 

 infected or to use 

 berries as inter-row 

 be infected should be de- 



YOUNG APPLE TREE FROM NURSERY. l 

 Showing the disease known as Root Gall. 



orchards. Nursery stock known to 



crops in 

 stroyed. 



PEAR 



Blight (Radlliis amylovorus [Burr], De Toni). This very familiar 

 disease causes the leaves and young twigs to die and blacken very much as 

 though injured by fire. These dead leaves hang on the trees during the 

 winter instead of falling in the autumn, as is the case with healthy leaves. 

 The disease also attacks the branches, causing black, sunken cankers from 



i Courtesy of The Field, New York. 



