CHAPTER VI 

 ARBOR-VITiE DISEASES 



Two species of arbor-vitse (Thuja) are common forest-trees 

 in northeastern and northwestern United States. They occur 

 in moist river-bottom lands and along mountain streams. The 

 western arbor-vitse grows to a much larger tree than the eastern 

 species. Both species are extensively used as ornamentals. 



The eastern arbor-vitse is especially free from diseases. 

 The wood and roots of the living tree are seldom decayed 

 and no leaf or twig-diseases of any importance are known. 

 The western arbor-vitse, on the other hand, is destructively 

 attacked by a leaf-fungus. The younger trees may be killed 

 outright. In the nursery, arbor-vitse is subject to a common 

 blight which also affects juniper. Ornamental arbor-vitse 

 seldom suffer from fungous diseases but frequently are injured 

 by freezing-to-death, sun-scorch and other general troubles 

 (see index). 



Seedling-Blight 



Caused by Phoma sp. 



At least three species of Thuja, including the eastern and 

 western arbor-vitse, are affected by this seedling-blight. The 

 same disease is common on juniper. Young arbor-vitse trees 

 up to four years old are affected in the same manner as juniper 

 (see page 190). Cankers are formed which girdle the stem, 

 causing the plants to die. The disease often becomes epiphy- 

 totic and causes serious losses in nursery-beds. Control 

 measures have not been determined. 



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