I 
Mycologisches Centralblatt, Bd. IV, Heft 2. 
Ausgegeben am 19. März 1914. 
A leaf disease of Walnuts. 
By 
FREDERICK A. WOLF, 
Alabama Polytechnic Institute, Auburn (Ala). 
(With 1 Photogr. and 6 Textfigures.) 
The production of Persian or English Walnuts in Alabama is 
in no wise to be regarded as an important industry. The reason for this 
is not to be sought in the liability of the trees to disease, for, when grown 
under favorable conditions, they are subject to comparatively few insect 
pests and fungoid maladies. The most serious walnut trouble, perhaps, 
which affects this industry in the United States, occurs in California, to 
which state the commercial production of the crop is largely confined. It 
is known as the walnut blight or bacteriosis of walnuts 1 ). Fortunately, 
so far as has been observed, this disease does not occur in Alabama. 
There has been under observation, however, at Auburn, Ala., during the 
past two years a heretofore unknown leaf disease of English walnuts. 
This disease manifests itself by the presence of numerous, irregular, 
circular to angular, dry spots, varying in size from minute specks to large, 
brown areas, 5 mm in diameter. These spots are, for the most part, 
brown in color and with a grayish center, marking the initial point of 
infection. Some may be uniformly brown on both leaf-surfaces and others 
may be quite grayish, due to the elevation of the cuticle and the consequent 
entrance of air. Frequently tissues adjacent to those invaded by the 
fungus are chlorotic. 
A single leaf may have 500—1000 or more centers of infection 
remaining quite distinct or in other cases coalescing so as to involve the 
leaf margins or tips or even the entire leaf, causing them to become dry 
and brown (s. Photogr.). During the summer of 1912, this disease was so 
severe, in a small grove in which the trouble has been studied, that the 
trees were completely defoliated twice prior to the time when the leaves 
should normally have fallen 
The organism which causes this disease is one of the imperfect fungi 
belonging to the genus Cylindrosporium. The acervuli or fruit bodies 
of this form are borne on the lower surface of the leaves. They are 
very minute and inconspicuous, measuring only 75 — 100 microns in dia¬ 
meter. They are initially subepidermal, but break through the cuticle at 
< 1) Smith, R. E., Smith, C. 0. and Ramsey. H. J., Walnut culture in Cali¬ 
fornia. Walnut blight [in pars] (Cal. Agr. Exp. Stat. Bui. 231, 320—371, figs. 78 
to 90, 1912). 
Mycologisches Centralblatt, Bd. IV. 5 
