A Bacterial Disease of Alfalfa i 5 
late stages of the blight, x 2. Field specimen, natural inoculation. 
Fig. 4, Alfalfa stem, inoculated with a 48 hour agar culture of Ps. 
medicaginis by means of needle pricks, x 2; 15 days after inoculation. 
Fig. 5, Alfalfa leaf showing diseased, yellow areas, apparently of 
water pore or stomatal infection, x 2. Field specimen, natural inocula¬ 
tion. 
SUMMARY. 
The disease has been known in Colorado since 190 4 , where, in some 
localities, it has caused the loss of practically eighty per cent of the first 
cutting. 
Within the state, it is known to occur in Eagle, Garfield, Mesa, 
Delta and Otero counties. 
The blight makes its first appearance from the first to the fifteenth 
of May, depending somewhat upon the locality. 
The stems appear watery, semi-transparent in the early stages, and 
have a yellowish, olive-green color which soon changes to amber, due to 
the appearance and subsequent drying of a thick, clear exudate. This 
dried excretion gives the stems a shiny, varnished appearance, and a 
slightly rough feel to the touch. These stems blacken in six to eight 
weeks, become very brittle and are easily broken, which fact makes it 
almost impossible to handle the crop without an immense amount of 
shattering. 
The disease seems to run its course with the first cutting, and is 
not seen again until the next year. 
The cause of the blight is a germ, Pseudomonas medicaginis, n. sp., 
which, presumably, lives in the soil and enters the plants with soil through 
stems which are cracked and split by late freezing. 
No varieties of alfalfa entirely resistant have been obtained up to 
the present time. 
As a means of control, we recommend that the frosted alfalfa be 
clipped, with the mower set low, as soon as it is reasonably certain that 
the danger from late frosts is past. This will rid the plants of the dis¬ 
eased portions, and afford an opportunity for the early growth of a new 
cutting. If this is done in time, the regular number of cuttings should be 
secured with little or no loss in tonnage. 
