26 
Colorado Agricultural College 
POTATO DISEASES 
Late Blight .—This disease so destructive in the East does not 
occur in Colorado. At least it has done no damage so far as we 
know. 
Early Blight .—It occurs in the State, and, under favorable 
conditions, does considerable damage. The favorable conditions 
are, high temperature accompanied with high humidity. The disease 
generally occurs late in July and early in August, and is easily dis¬ 
tinguishable by dark brown patches and rings on the foliage. In 
extreme cases, the whole foliage of the plant becomes affected and 
may drop off and kill the plant so far as future growth is concerned. 
This greatly reduces the yield, as the potatoes do not have time to 
develop to their normal size. So far as we know, the disease is 
confined to the foliage in this State and does not seem to attack the 
tubers. 
Spraying with Bordeaux Mixture before the disease appears 
will, if thoroly done, prevent its appearance, but after the disease 
has once gotten a foothold and becomes distributed over the field, 
the application of Bordeaux will not eradicate it. Bordeaux Mix¬ 
ture is not a cure, but a preventative. Due to the fact that Early 
Blight does not occur annually, but only during favorable seasons, 
our growers, as a rule, do not spray to insure their crop against 
losses from this trouble, tho yearly application of Bordeaux to the 
potato vines would insure against its appearance and the losses 
caused by it. 
Fusarium Disease .—This disease is found in every potato 
growing section of the State and is the most destructive disease 
with which the potato grower has to deal. The disease is favored 
by high temperature, moisture and poor soil drainage. In heavy 
adobe soil, the disease appears to be particularly bad. It is in¬ 
troduced into the soil either by a previous crop, or thru diseased 
seed potatoes. The fact that the disease may remain in the soil for 
more than one year makes the subject of rotation important to the 
potato grower, and it is one of the reasons why we advocate grow¬ 
ing potatoes only one year on the same piece of land without the 
intervention of other crops. 
The most common way of dissemination of this disease is by 
the seed. The grower can easily ascertain for himself whether the 
seed potatoes are free from Fusarium or not by cutting off a thin 
slice at the stem end. (See figure 8 .) If the meat on the cut surface 
of the tuber shows a dark circle extending around it, this indicates 
the presence of the disease, and such seed should not be planted, 
as it will work its way thru the seed potato up to the stem and 
