OAK DISEASES 



239 



Leaf-Blistek 

 Caused by Taphrina ccerulescens (Mont, and Desm.) Tulasne 



Practically all species of oak seem to be affected by leaf- 

 blister. It is found throughout the United States and Europe. 

 Although occurring commonly in this range it does no par- 

 ticular damage except in southern United States, where it 

 is epiphytotic in 

 favorable seasons 

 and defoliation 

 results. It is re- 

 ported that the 

 growth of the tree 

 is seriously im- 

 paired and the 

 individual is 

 sometimes killed 

 by repeated de- 

 foliation. 



Symptoms. 



The blisters 

 make their ap- 

 pearance on the 

 leaves before they 

 are full grown. 

 The spots are at 

 first grayish or 

 bluish on the un- 

 der surface and 

 yellowish above. 

 A bulging of the leaf is soon apparent, the convex side of the 

 spot usually being on the upper side of the leaf (Fig. 45). The 

 blisters vary from a quarter to a half inch or more in diameter 



Fig. 45. — Leaf-blister of oak. 



