302 MANUAL OF TREE DISEASES 



seriousness in the native poplar stands is yet to be determined. 

 The large number of trees killed in nurseries and the serious 

 effects produced on recently planted or old established trees 

 around the nurseries point to the possibility that this disease 

 may assume an epiphytotic nature. 



Symptoms. 



Trees recently transplanted and young nursery trees are 

 most seriously affected. Older and well-established trees 

 resist the disease to some extent and the cankers develop more 

 slowly. The cankers occiu* on the trunk, limbs and small 

 twigs. The diseased bark is slightly simken and somewhat 

 darker in color than the healthy bark. Cankers are commonly 

 found aroimd the base of twigs and limbs. The inner bark- 

 tissues and cambium are killed and these dead tissues are brown. 

 The canker enlarges rapidly and finally may girdle the trunk 

 or limb. Small raised pustules are formed on the diseased 

 bark. A hole is evident in the top of each pustule and from 

 this hole long twisted brown or cream-colored tendrils of 

 spores are pushed out. On the trunks and limbs of old trees, 

 the cankered area of bark falls away, leaving the bare wood 

 surrounded by callus. 



The general effect of the disease on the trees is the killing 

 of the twigs and smaller limbs and the disfiguring of the trunk 

 and large limbs by the formations of open wounds. Suckers 

 are developed from below the cankers, causing an ill-formed 

 tree. Thus, while only the younger trees are killed outright, 

 the older ones are made useless as ornamentals. In the forest 

 the continued activities of such a fungus might constitute a 

 menace to the successful production of conun^rcially valuable 

 trees, by interfering with the normal healthy development of 

 the older trees and preventing the natiu-al reproduction from 

 reaching matiu-ity. As yet, however, this disease has not been 

 reported in the forests on the timber poplars. 



