132 MANUAL OF TREE DISEASES 



are the most Important diseases of white cedar. As in the case 

 of the other rust-fimgi of cedar and juniper, an alternate host 

 is necessary for the completion of the life history of the fungus. 

 The witches'-brooms are never formed unless bayberry, sweet- 

 fern or wax myrtle shrubs (Myrica) are in close proximity to 

 the cedars. 



Symptoms. 



The infected branches of the cedar become slightly swollen 

 and produce many short laterals which form a compact broom- 

 like growth. In the early spring, orange spore-horns about an 

 eighth or a quarter of an inch long project from the bark of 

 the distorted branches. 



Cause. 



The witches'-brooms of white cedar are caused by the rust- 

 fungus, Gymnosporangium myrwatum. The life history of 

 this fungus is similar to that of the other cedar and juniper 

 rusts except that the alternate stage is developed on species 

 of Myrica. With this exception the life history described on 

 page 192 will apply in general to this species. 



Control. 



Since this rust-fimgus requires the presence of both the 

 white cedar and species of Myrica in close proximity in order 

 to carry out its life history, a simple means of protecting the 

 cedars is afforded by destroying the bayberry, sweet-fern or 

 wax myrtle shrubs. If these plants can be eliminated for a 

 distance of several hundred feet or a mile from the white cedars, 

 no further exchange of spores will be likely and the cedars will 

 be safe from infection. 



References 



Harshberger, J. W. Two fungous diseases of the white cedar. Proc. 



Acad. Nat. Sci. Phila. 1902 : 461-504. 1902. 

 Fromme, F. D. A new Gymnosporangial connection. Mycologia 



6 : 226-230. 1914. 



