244 



MANUAL OF TREE DISEASES 



Twig-Blight 



Caused by SpJuBropsis malorum Berkeley ( = Physalospora cydonice 



Amaud) 



This twig-blight is common on chestnut oak in central 

 eastern United States. White oak and chestnut are also oc- 

 casionally affected by the same disease. The 

 W^S smaller branches and twigs of trees of all ages 

 ^/^H may be killed. 



Sym-ptoms. 



The leaves wither and timi brown. The 

 mycelium of the causal pathogene grows in the 

 bark and sapwood. The diseased bark becomes 

 sunken and wrinkled (Fig. 47). , Small black 

 fruiting-bodies break through the outer bark. ■ 

 Under the dead bark, the sapwood is dark 

 colored. The mycelium extends for several 

 inches in the sapwood above and below the 

 bark-lesion. This is evident to the unaided eye 

 as a black streak when the bark is peeled from 

 the twig. 



Cause. 



The fungus causing this twig-blight is known 

 as SphtBTopsis malorum. It occurs as a weak 

 parasite or saprophyte on the bark and twigs of 

 many kinds of woody plants. The New York 

 apple canker, black-rot and frog-eye leaf-spot of 

 apple are caused by this fimgus. Spores ooze 

 from the black fruiting-bodies produced on the dead bark and 

 may be washed by the rain to other parts of the tree. The 

 fimgus also rarely produces a perithecial stage which is known 

 as Physalospora cydomuB. 



Fig. 47.— 

 Twig-canker on 

 oak caused by 

 Sph(Bropsis ma- 

 lorum.. 



