BACTERIAL LEAFSPOT OF DELPHINIUM 1 
By Mary K. Bryan 
Assistant Pathologist , Laboratory of Plant Pathology , Bureau of Plant Industry , 
United States Department of Agriculture 
INTRODUCTION 
The leaf spot of Delphinium (larkspur), commonly known as the “Black 
spot,” or “Black disease,” is a very destructive disease, widespread throughout 
the northern United States, more particularly in the North Atlantic States. 
Although this decorative plant has been eliminated from the gardens of some 
large estates because of its ravages, the disease has received scant attention 
from pathologists. 
The only references in pathological literature are brief notes by Dr. Erwin F. 
Smith. In “Science,” for March, 1904, 2 he gave a very brief description of the 
causal organism which he had isolated, proved pathogenic by inoculations and 
named Bacillus delphinii. Cultures were allowed to die before adequate cul¬ 
tural work was done, and although the organism was again isolated in 1907, 
pressure of other work crowded out its further study. The spots are figured by 
him in “ Bacteria in Relation to Plant Diseases,” 3 and in the same volume, page 92, 
it is stated to be one of the diseases transmitted through stomata and water- 
pores. He later 4 refers again briefly to the subject, as follows: 
“The spot disease of Delphinium (Vol. I, fig. 127) is another malady in which 
infection takes place readily through the unbroken leaf-surface and stem-surface, 
i. e., through stomata. The disease has been obtained a number of times dur¬ 
ing the last seven years by placing the bacteria in water and spraying this upon 
the plants. The leaf-serratures also blacken in this disease, and here infection 
probably occurs through the groups of water pores situated on their apex.” 
In 1920 characteristically spotted leaves were received from Woodstock, N. Y., 
from which isolations were made of a white bacterial organism. These and 
subsequent isolations from various sources have been used for the study hefre 
presented. 
HOST PLANTS 
This disease has not been reported on any plant except larkspur, being most 
destructive on th,e choice hybrid delphiniums. A few small but definite infec¬ 
tions have been produced on Aconite by rubbing the inoculum on the lower 
surface of leaves, but no natural infections have been reported on this plant. 
No infections were obtained by repeated inoculations on cultivated varieties of 
Ranunculus and Aquilegia. 
GEOGRAPHICAL DISTRIBUTION 
Specimens have been received from points in Maine, New Hampshire, Massa¬ 
chusetts, Connecticut, New York, Long Island, Pennsylvania, Illinois, and 
in one case from Portland, Oreg. One correspondent wrote in 1922, “I have just 
1 Received for publication Jan. 23, 1924. 
2 Smith, E. F. bacterial leap spot diseases. Science 19: 417. 1904. 
s Smith, E. F. bacteria in relation to plant diseases, v. 1, fig. 127. 1905. 
4 Smith, E. F. bacteria in relation to plant diseases. 2:61-62. 1911. 
Journal of Agricultural Research, 
Washington, D. C. 
( 261 ) 
Vol. XXVIII, No. 3 
Apr. 19, 1924 
Key No. G-370 
