404 Diseases of Economic Plants 



lower sides of the leaf spots arc small, concentrically ar- 

 ranged, black acervuli. 



The disease has been troublesome on black-walnut in 

 Delaware, Iowa, Maryland, and West Virginia. 



Blight ■^-^' '^-^ (Pseudomonas juglandis Pierce). — This 

 blight known in 1901 only on the Pacific coast is now recorded 

 in California, Oregon, Texas, Louisiana, Maryland, Delaware, 

 Pennsylvania, and New York on English-walnut. 



Black cankered spots upon the young nuts, which fall pre- 

 maturely, or similar spots upon the young, green shoots are 

 characteristic. Chief damage is to the nuts, l)ut in seasons 



Fig. 215. — Bacterial blight of walnuts. After R. E. Smith. 



favorable to blight much of the terminal growth is killed and 

 the succeeding crop is thereby reduced. 



Spraying is of questionable value. Care should be taken 

 to select resistant trees for propagation. 



Melaxuma ^-'^ (Dothiorella gregaria Sacc). — In this dis- 

 ease, reported from California, black sunken cankers develop 

 on the trunk and larger limbs, and the leaves on the smaller 

 limbs suddenly wilt. The first indication of disease is often a 

 black area like a blotch of tar on the gray ])ark. Excision and 

 disinfection should l)e practiced. 



Other walnut troubles are : Die-back, often due to lack of or 



