28 
Colorado Experiment Station. 
The Evidence of a F'ungus or Infection Factor in Leae-Roll 
Disease in Colorado. 
first .—The two regions which had the disease the most severely 
are tied together by one of them securing the major portion of its 
seed from the other. < 
Second .—In the Greeley district, in 1911, the soil heat would 
lead us to expect trouble, but the weather conditions in 1912 were 
ideal. In that year the United States grew the largest crop of pota¬ 
toes that it ever grew and had the larg'est yield per acre since the 
Government has made estimates of yields. Nevertheless, the crop 
in the Greeley district was very little better than in 1911, in spite 
of new seed, and much change in crop rotation. Some active factor 
of infection must have been carried over in the soil, and must have 
been distributed universally over the district by wind, water, tools 
and potato storage. 
Third .—With decreased acreage of potatoes for 1912, 1913 and 
1914, and a season in 1015 showing a large deficiency in temper¬ 
ature (according to the September report of the Denver branch of 
the Weather Bureau) for May, June, July and August, and some 
deficiency for September, but no better a season than 1912 and with 
chansre of soil and seed as in T012. the Greelev district has a record 
crop on a small acreage. Some hidden injurious factor has been 
lessened. 
Irrigation water affords a readv means foi* the distribution of 
any microscopic life, and I am indebted to Dr. L. R. Jones, of the 
University of Wisconsin, for his opinion that Fusarmm might be 
distributed by the wind. 
In Iowa, conditions which potatoes have to meet are much the 
same as in the Greelev district. We have less soakage, but we have 
large areas requiring artificial drainage and much soil which is 
heavier than that at Greeley. We have more heat. We have no 
district that has for a long time specialized, with success, in pota¬ 
toes. No less than five districts that once grew many potatoes are 
producing less, and some none, for .shipment, and in all such districts 
poorer shape and yields have been reasons for reduction of acreage. 
We have one area of deep, sandy loam, naturally drained, that prom¬ 
ises to produce many potatoes permanently. We have another very 
large area of deep, loess soil, naturally drained, where potatoes do 
well. We have no large area on tile-drained soil where potatoes 
are a reliable crop. 
We may regard it as an axiom that where seed potatoes cannot 
be maintained for some years conditions for potato health are not the 
