CEDAR DISEASES 133 



Western Twig-Blight and Witches'-Broom 



Caused by Gymnosporangium Blasdaieanum (Diet, and Holw.) Kern 



The incense cedar is attacked by this rust disease and con- 

 siderable damage is caused in some regions. The other trees 

 attacked by the same rust, in the other stage of its Hfe history, 

 are cultivated apple, pear, quince, mountain ash and wild 

 species of apple, haw and service-berry. It is most destruc- 

 tive on the cultivated pear. The relation between the stages 

 of this fungus on the two types of hosts, one the incense cedar 

 and the other the plants of the apple family, is explained on 

 page 192, where the life history of these rusts is discussed. 



Symptoms. 



Two different effects are produced by this rust. When the 

 smaller twigs are infected, the first symptoms in early spring 

 are the small reddish brown spore-cushions which appear on 

 the surface of the scale-like leaves. During rainy weather 

 these cushions gelatinize and coalesce, forming yellowish masses 

 over the leaves. The leaves of the infected twig then turn 

 yellow and the twig dies. 



When larger branches are infected, dense clusters of upright 

 branches are produced. The fungus fruits in the manner 

 described above on the younger twigs of the brooms and the 

 twigs are killed. Most of the damage caused by this rust on 

 the incense cedar is due to the development of the witches'- 

 brooms which at times seriously deform the tree. 



Cause. 



The twig-blight and witches'-broom of incense cedar are 

 caused by the rust-fungus, , Gymnosporangium Blasdaieanum. 

 The teliospores formed on the spore-cushions on the cedar ger- 

 minate and produce basidiospores, which when blown to the 



