OAK DISEASES 245 



Control. 



The diseased twigs and branches should be pruned from the 

 tree. This may be done most eflSciently in midsummer, as the 

 dead leaves show more plainly. Early the next spring after 

 the new leaves appear, all leafless twigs and branches should be 

 removed. If these measures are not taken, large trees may 

 often be killed after a few years. Care should be exercised to 

 prune the twigs at least six inches below the cankered area, 

 since the mycelium which spreads in the sapwood must all be 

 removed (see under symptoms). 



Reference 



Ingram, Delia E. A twig blight of Quereus prinus and related species. 

 Jour. Agr. Res. 1 : 339-346, pi. 38, figs. 1-7. 1914. 



Stkumella Canker 



Caused by Strumella coryneoidea Sace. and Winter 



This canker of oak has been found to be common and de- 

 structive in Pennsylvania. Although not definitely reported 

 elsewhere, the fungus is known to occur in Missouri, Massa- 

 chusetts and New York. Its range may thus be supposed to 

 include northeastern United States. In Pennsylvania the 

 canker is found on white, scarlet, red, yellow and chestnut oak. 

 It also occiu-s destructively on the American chestnut. The 

 most damage is reported on red and yellow oak. 



Symptoms. 



Two types of cankers with intermediate gradations are de- 

 scribed. The most conspicuous form is found on red and 

 yellow oak and resembles the European apple-tree canker, 

 caused by Nectria galligena. The development of the cankers 

 of this type is slow. They are elliptical in outline and consist 

 of a depressed decayed center surrounded by concentric folds 



