14 The Colorado Experiment Station 
prevention and treatment. 
Where the areas under cultivation reach such tremendous pro¬ 
portions as the alfalfa fields on the mountain ranches, all schemes 
for soil sterilization are obviously impracticable at the outset. The 
same may be said of the use of germicides to be applied to the plants 
either in the form of sprays or otherwise, for even though some 
such means should be discovered by which the infection could be 
prevented, the cost would undoubtedly make it prohibitive. Ob¬ 
viously, then, as stated before, the only practical way of combating 
and controlling the blight is by the introduction of resistant varie¬ 
ties. What is being done in this direction has been mentioned 
before. 
Our field observations during the past year seem to indicate 
that immunity to the disease is closely related to resistance to late 
spring freezing. On the one hand, those plants which were severely 
injured by the late spring frost were, without exception, the first 
to show the disease and were the worst infected later in the season; 
on the other hand, those varieties which grew from hardy stock and 
which suffered only slightly from the frost, were more nearly free 
from the blight. This coming year we shall endeavor to determine 
whether the relation between disease resistance and frost resistance 
is a constant one, and if it proves to be such, then we shall attempt 
to stamp out the trouble by securing frost resistant varieties. 
In the meantime, we recommend, as a means of control, that 
the frosted alfalfa be clipped as soon as one is reasonably certain 
that there is no more danger from frost. By this means, the frost 
split stems, in which the disease appears to originate, will be gotten 
rid of, thus affording an opportunity for the early growth of a new 
cutting. Prof. P. Iv. Blinn, who has charge of the Experiment 
Station work at Rocky Ford, informs the writer that this practice 
of early clipping to remove the frost bitten shoots, which retard 
growth, is rapidly growing in favor among the farmers in his 
locality. 
acknowledgment. 
The writer wishes to thank Prof. B. O. Longyear and Miss 
M. A. Palmer for the preparation of the colored plate. 
EXPLANATION OF PLATE. 
Fig. 1, Alfalfa stem, inoculated by smearing the freshly scraped 
stem with a 48 hour culture of Ps. medicaginis, x 2; 4 0 days after in¬ 
oculation. 
Fig. 2, Diseased alfalfa stem showing the yellowish, olive green 
color, characteristic in the early stages, x 2. Field specimen, natural 
inoculation. 
Fig. 3, Diseased alfalfa stem showing the blackened condition in the 
