32 BULLETIN 64, U. S. DEPARTMENT OF AGEICULTUEB. 



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 bhght, 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 

 Httle concern, though it is possible that a longer rotation would have 

 been better. 



These details concernmg 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-roU. 



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-roU 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 growuig 

 crops prevailed. There was an abundance of moistiu-e 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-roU 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 m 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- 



