28 
Colorado Experiment Station 
POTATO DISEASES 
Late Blight .—This disease, so destructive in the East, does 
not occur in Colorado. The climatic conditions of the State do 
not favor the development of the disease, as it requires a humid 
atmosphere with high temperature. The reported occurrence of 
late blight in Colorado has in every case turned out to be the 
fusarium disease. It is indeed fortunate for the State that the 
late blight does not find a congenial home here, as the fighting 
of this disease entails considerable expense. 
Early Blight .—It occurs in the State, especially in the warm, 
heavily irrigated valleys of the Western Slope. Some seasons 
when rainfall is above the normal and Avhen the temperature is 
relatively high, it causes considerable damage to the grower. It 
occurs during the month of July, and is easily distinguished bv 
dark brown patches or rings on the foliage. In extreme cases, the 
whole foliage becomes aflfected, and the leaves drop off, and often 
kill the plant. In milder cases, it reduces the yield and the po¬ 
tatoes produced are small and worthless. 
v8praying with Bordeaux mixture is eflfective, but it should be 
done before the disease has made any headway. If the weather 
conditions are such as to encourage the development of the disease, 
the grower should spray before the disease makes its appearance. 
Its rapid spread over the field and the rapid progress of the dis¬ 
ease makes the application of the Bordeaux of little efifect if the 
disease has gained a firm foothold. During the last five years, 
in only one season has this disease done any damage. 
Fusarium .—This disease is present in every potato growing 
district of the State, and is the most destructive disease with which 
the grower has to deal. It remains in the soil for a number of 
years, and there is probably not a potato field in the State where 
the disease cannot be found. It is favored in its development by 
hight temperature, moisture, and poor soil drainage. In heavy 
soils, the disease appears to be particularly bad. It may be intro¬ 
duced into the soil either by previous crops, or, we believe, by the 
seed. The fact that the disease remains in the soil for a number 
of years makes the subject of crop rotation important to the 
grower, and is one of the main reasons why we advocate the 
growing of potatoes only one year on the same piece of land with¬ 
out the intervention of other crops. 
The presence of the disease in seed potatoes can easily be 
ascertained by the cutting off of a thin slice of the potato at the 
stem end. A dark circular discoloration just inside of the skin 
