Dec. 17, 1917 
Bacterial-Blight of Barley 
641 
adjacent six-row varieties, having evidently spread from the Chevalier 
plot. The following season this same plot of soil was replanted with 
clean barley, and none of the disease reappeared. Our conclusion is, 
therefore, that probably under Wisconsin conditions the disease usually 
comes from organisms overwintering with the seed rather than in the 
soil, although the organism is capable of living over the winter in the 
dry, blighted straw. 
It is doubtless carried with the seed to new localities, and not only 
its overwintering but its long-range dissemination is thus accounted for. 
For local dissemination in the field water is apparently the chief agent, 
although thrips and aphids may possibly play a considerable part. As 
already shown, surface application of the organism by spray or otherwise 
without wounding suffices for infection. The abundant bacterial 
exudate from blighting tissues is readily distributed by beating rain or 
trickling dew and may doubtless be carried farther, though in lesser 
amounts, by visiting insects. The prompt hardening of this exudate 
into resinous masses preserves the vitality of the organism for a long 
time without hindering this mode of water dissemination, since the dry 
exudate again quickly softens and diffuses upon the application of water. 
(PI. 48, A.) 
CONTROL MEASURES 
It is not practicable to exercise any control measures aiming to check 
the spread of the disease after it appears in the barley field. On the 
other hand, the conclusion of the writers that its overwintering and 
long-range dissemination occur chiefly, if not wholly, with the seed 
encourages the hope that practical control measures may be developed. 
Ordinarily it may suffice to avoid the use of seed from badly infected 
fields or localities when these conditions are known. In case of doubt 
it seems probable that seed disinfection may greatly reduce the danger 
of introducing the disease, if not eliminate it altogether. The writers 
have not as yet had opportunity for a convincing trial of this matter. 
An experiment bearing upon it was, however, made in March, 1916, as 
follows: Barley grain harvested from an infected field in 1914 had mean¬ 
while lain dry in the laboratory. Isolations from the glumes then (1916) 
showed the organism still alive. After soaking this grain for two hours 
in formaldehyde solution (1 part of Merck's 40 per cent formalin in 
320 parts of water) attempts to isolate the organism from the material 
failed. These results should not, however, be given too great weight, 
since negative results had also been obtained with some samples of 
untreated seed suspected of harboring the organism. Owing to the 
high degree of sensitiveness of the organism to mercuric chlorid, it is 
probable that this will be even more reliable for use as a seed disin¬ 
fectant. The hot-water method may also prove useful, especially if 
later studies show that the organisms penetrate the kernel. 
23718°—17-2 
