834 



MANUAL OF TREE DISEASES 



States and in Califorma. The most severe damage occurs 

 where the twig-blight and canker types of the disease seriously 

 deform the trees. Although certain trees are more or less 

 affected every year, this blight occurs in epiphj-totic form in 

 seasons when weather conditions are favorable in early spring 

 for the development of the causal pathogene. The Oriental 

 plane and oaks in Europe, where they are extensively used as 



shade and omar 

 mental trees, are 

 attacked by the 

 same fungus. It 

 is probable that 

 the range of this 

 fungus is coexistent 

 with the distribu- 

 tion of the syca- 

 more and it may be 

 expected to cause 

 damage wherever 

 the tree is grown. 

 Owing to repeated 

 defoliation, several 



, Pig. 66. — Leaf-blight of sycamore. yg^pg -^ succession, 



and the twigs being killed back, the ultimate damage is con- 

 siderable. Cases have been rejMjrted in which trees were 

 killed outright. Generally, however, repeatedly affected trees 

 show great recuperative powers, and produce a second crop of 

 leaves year after year. 



Syirtptcrms. 



Leaf-blight becomes noticeable soon after or while the leaves 

 are expanding in the spring. Often some leaves and the grow- 

 ing tip of the twig are affected, turn brown and die as they 

 emerge from the bud. This symptom is often confused with 



