CHAPTER XX 

 HEMLOCK DISEASES 



Foxm species of hemlock or Tsuga occur in the forests of the 

 United States. The two eastern hemlocks are important trees, 

 especially in the northeastern states. The western species are 

 confined to the northwestern states and are large trees. All 

 four species are frequently used as ornamentals. 



Although several fungous diseases are occasionally found on 

 hemlock, it is less severely affected in general than pine, spruce 

 and fir. In the Northwest, the young trees are killed by a 

 root-rot and the older ones are often affected by the stringy 

 red-brown heartwood-rot. In the East, the leaf-blight, rusts 

 and wood-rots cause but little damage. 



Seedling Root-Rot 



Caused by Rhizina undulata Fries 



The roots of three- to five-year-old seedlings of species of 

 hemlock, pine, larch and fir are frequently attacked in the 

 forests of the Northwest by Rhizina undulata. The fungus 

 has been found in several eastern states attached to roots of 

 conifers but its connection with any root disease is not definitely 

 established. The same disease is common in Europe on seed- 

 lings of various conifers and has been known for many years. 



Symptoms. 



The fruiting-bodies of the fungus are formed annually and 

 grow on the surface of the ground. They are variable in size, 

 measuring often two or three inches across, irregular in shape, 

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