The Colorado Potato Industry. 17 
no better on newly broken sod than on old sand. Heavy manuring 
of the land did not help the matter. The vines were struck with 
a rust or blight. This fungus made the leaves thick and stiff, 
and undoubtedly destroyed the sap and prevented the leaves from 
carrying on their function.” 
This is a good superficial description of the effects of this 
fungus as it looks in the field. From its past history ll is evi¬ 
dent that meteorological conditions have a strong influence on the 
behavior of this fungus. Probably there has been no year since 
the growing of potatoes began in this State that the disease has 
not been present, but much of the time, at least in the more fa¬ 
vored locations, its attacks have been so light that it did not at¬ 
tract the attention of the growers. A high temperature, exces¬ 
sive moisture, alkali and a compact soil are all conditions that 
probably favor the development of the fungus. It has been gen¬ 
erally supposed that this disease is introduced into the fields with 
the seed potatoes as nearly all seed tubers have more or less of 
the fungus on their surfaces in the form of scab or the black dirt¬ 
like patches of the sclerotia stage of the disease. Experiments 
with treating the seed with formalin and corrosive sublimate show, 
however, that the disease occurs just the same whether the seed 
is infected with the disease or clean. This fungus is not confined 
to the potato plant alone. In fact it is not known just how many 
plants act as a host for it. Peas, beans, beets, alfalfa and many 
weeds are known to be subject to its attacks. The curious fact 
remains that though the fungus works on alfalfa, potatoes fol¬ 
lowing alfalfa are not generally as badly diseased and produce 
a larger crop than when they succeed themselves. 
General Appearance and Eeeects oe the Fungous on 
Potatoes. To the ordinary observer, this disease does not be¬ 
come noticeable till the middle or latter part of the growing sea¬ 
son. If the plants be examined carefully at any time from the 
first sprouting of the seed till the harvest, some of them will be 
found affected with the fungous. Plate II of Bulletin No. 92 of 
this Station shows the appearance of the disease in the first 
stages. Not infrequently if missing hills are examined at the 
time the plants are breaking through the ground the sprouts will 
be found to have started, but the stems have been girdled with a 
brown or black canker that stops growth. But if the injury is 
not serious enough to kill the plant at this stage, it will have a 
sickly yellow appearance and die soon after getting through the 
ground. From the time the plants first come up, all through the 
season, here and there through the field, will be found what the 
growers call “blighted plants.” The leaves are thickened, and 
with the White Pearl especially, the leaves draw up close to the 
