WILLOW DISEASES 343 



yellow pustules contain urediniospores which infect other willow 

 leaves. In this way the fungus spreads from willow to willow 

 diu-ing the summer. In the autumn teliospores are formed 

 under the epidermis in dark brown spots. These over-winter 

 and produce basidiospores which infect the larch needles in 

 early spring. Two other closely related species, Melampsora 

 confluens (Persoon) Cast, and M. cdpina Juel, occur on willows 

 in Colorado and Utah. The former species has its secial stage 

 on currants and gooseberries (Ribes) and the latter on species 

 of Saxifraga. 



Tar Leaf-Spot 



Caused by Rhytisma salicinum Fries 



Willow leaves are occasionally seen having thick tar-like spots 

 on them. The spots are usually about a quarter of an inch 

 across. The causal fungus is a close relative of that causing the 

 tar leaf-spot of maple. The discussion of the life history and 

 control of the maple fungus on page 223 applies in all respects 

 to this willow leaf-spot. 



Common White Wood-Rot 



Caused by Fames igniarius Fries 



Willows, among many other kinds of deciduous trees such as 

 poplar, beech, oak and maple, are attacked by the false-tinder 

 fungus. The wood is reduced to a white or yellowish punk 

 marked with numerous concentric narrow black lines. Enor- 

 mous losses in timber values are caused by this rot in the forest, 

 where it is much more common than in open stands or individual 

 ornamental trees. The symptoms and the sporophores are simi- 

 lar for all the kinds of trees affected and are described 

 under poplar diseases, page 305. The hoof-shaped type of 

 sporophore seems to be more common on willow than the 

 shelf-like form. 



