Apr. 19, 1914 
Bacterial Leaf spot of Delphinium 
269 
TECHNICAL DESCRIPTION 
Bacterium delphinii (EFS). 
A short nonsporiferous rod with rounded ends; usually single or in pairs, some¬ 
times in short chains; flagella 1 to 6 bipolar: capsules, aerobic, white, but produc¬ 
ing a blue-green fluorescence in cultures; diastasic action weak; liquefies gelatin; 
does not reduce nitrates; clears milk without coagulation; blues, then reduces 
litmus milk; produces ammonia but no hydrogen sulphid or indol; forms acid 
from dextrose, galactose, levulose, and with more difficulty from saccharose, but 
not from lactose, maltose, glycerin or mannit; does not produce gas from any of 
these carbon compounds; grows well in Uschinsky’s, Fermi’s and Cohn’s solu¬ 
tions; optimum temperature 25° C., maximum 30°, minimum 1°, or less; thermal 
death point 50°; Gram-negative; not acid-fast; stains readily with carbol fuchsin 
and gentian violet; is pathogenic to delphiniums, producing dead black spots 
on the leaves, stems and flower buds. 
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CONTROL METHODS 
It has been found impractical to do any control work in Washington. The 
delphinium plant does not reach its best development here, preferring the cooler 
northern States. The organism also is very sensitive to high temperatures. 
Moreover, isolations kept on culture media over winter have lost much of their 
virulence and by the time fresh isolations can be obtained from northern material 
the weather here has become unfavorable to both host and parasite. Control 
studies should therefore be made in a region where the disease prevails. 
A few suggestions may be made, however. It seems probable that the organism 
winters-over in the soil since it is rather resistant to cold and drying, and since 
infection generally appears first on the lower leaves, suggesting the spattering of 
infected soil by rain. On this theory all diseased material should be gathered 
and burned. Drenching the soil surrounding the plants with alkaline Bordeaux 
mixture before growth begins in the spring and later spraying both the soil and 
the lower surface of early leaves with Bordeaux mixture should prevent infection 
from this source. 
SUMMARY 
The black spot of delphinium is a bacterial disease widespread in the north¬ 
ern part of the United States and is very destructive to choice hybrid varieties. 
The bacteria gain entrance to the plant through the water pores and stomata, 
causing irregular tarry black spots on the leaves and sometimes on stems and 
flower buds. 
The causal bacterium has been isolated and successful infections obtained by 
spraying with water suspensions of young subcultures from single colonies. 
For control of the disease it is suggested that all diseased material be col¬ 
lected and burned and that the surrounding soil and early leaves be sprayed with 
Bordeaux mixture. 
Since the flagella have been demonstrated to be polar, the name of the organism 
becomes Bacterium delphinii (EFS). 
