32 BULLETIN 64, U. S. DEPAKTMENT OF AGRICULTURE. 
which is further improved by plowing under alfalfa just before plant- 
ing potatoes, and by the practice of extremely deep cultivation with 
special implements. 
Scab of the tubers has not been uncommon, and in some seasons 
there has been a late summer occurrence of early blight, but the most 
important disease has been perhaps the Fusarium wilt {Fusarium 
oxysporum) . This fungus was widely prevalent throughout the dis- 
trict, and its effect on the crop could be observed with especial clear- 
ness in fields where potatoes had been grown for two or three con- 
secutive years. Stem-end browning is common in Greeley potatoes, 
but the loss from Fusarium dry-rot has not been large. Crop rota- 
tion kept the loss from wilt down to a point where the disease caused 
little concern, though it is possible that a longer rotation would have 
been better. 
These details concerning the prevalence in Colorado of Rhizoc- 
tonia and Fusarium have been given at this point because they were 
at first charged with the losses due to leaf-roll. 
During the season of 1911 there was an outbreak of a potato 
disease which practically destroyed the crop in northern Colorado 
and western Nebraska. The shipments from the Greeley district 
fell from an expected 7,000 to 200 cars. The average yield of the 
3,190 acres in the Mitchell (Nebr.) district was only 14 bushels per 
acre that year, as compared with 103 in 1909, 39 in 1910, and 102 in 
1912. The cause of this extraordinary falling off in yield was the 
leaf-roll disease, though it was at first locally thought to be Fusa- 
rium and Rhizoctonia combined with the effect of the very dry and 
unfavorable weather of spring and early summer. It was predicted 
that with normal weather conditions and some improvements in 
cultural practices the disease would not be likely to recur (Corbett, 
1912). In 1912, however, very favorable conditions for growing 
crops prevailed. There was an abundance of moisture in the soil in 
the spring and favorable temperatures throughout the season. 
Nevertheless, the disease again prevailed, nearly as severely as before. 
The shipments from Greeley were about 700 cars, with half the 
normal acreage. The Scottsbluff section came through with better 
results; for, although the leaf -roll appeared in June and threatened 
a repetition of the 1911 experience, there was a revival of the crop, 
after some midsummer rains, and a fair yield. 
It now seems indisputable that the Colorado and Nebraska disease 
is the same type of leaf -roll observed in the Maine and New York seed- 
lings and that this is the trouble called "Blattrollkrankheit" by the 
Germans. There have been variations in the symptoms observed, 
but it appears that this is also the case in different parts of Germany 
or between different varieties there. The American trouble exhibits 
the rolling, the yellow color, and all the important characters de- 
