CHAPTER XXI 



HICKORY DISEASES 



Several species of hickory (Caiya or Hicoria) occur as com- 

 mon trees in eastern United "States. Several fungi cause leaf- 

 spots of hickory (page 30). Besides these, the leaf-mildew, 

 witches'-broom and common white wood-rot are the only dis- 

 eases of importance of these trees. Although these diseases 

 and probably others are common on hickory practically no 

 mention of them is made in literature. 



Leaf-Mildew and Witches'-Broom 

 Caused by Microstroma juglandis (Bereng.) Sacc. 



The leaves of hickory and walnut in eastern United States are 

 often affected by this disease. Early in the summer the leaflets 

 show a white powdery mildew on the under side. The invaded 

 area of the leaflet is yellowish and defoliation may result. Re- 

 cently the formation of witches '-brooms on shag-bark hickory 

 has been shown to be another symptom of this disease. Brooms 

 are sometimes numerous on the trees and are as much as a yard 

 across. The leaves which appear on the brooms in the spring 

 are yeUowish green above and covered with the white pawdery 

 growth of the fungus below. The leaflets are smaller than nor- 

 mal and curled. They fall prematurely and leave the brooms 

 bare in midsummer. The fungus causing this disease is sup- 

 posed to be a simple basidiomycete forming nmnerous short 

 stalks bearing spores on the under sides of the leaf. 



188 



