The Potato Industry oe Colorado. 39 
When the plant stem was split lengthwise, it was found that the 
sap wood or vascular tissue of the plant was discolored from the 
base of the stem to some distance above the ground line. The plant 
was often blackened from the vascular tissue out and in some cases 
it was rotted off at the base. Investigation was made of this dis¬ 
ease and it was found that it was caused by a fungus known as 
Fusarinm. In the cross section of the potato stem showing the 
vascular structure of the stem, the hyphae of this fungus are shown 
growing across the cell spaces. Apparently this fungus acts on the 
circulation of the plant, much as roots of cottonwood, willow or 
alfalfa do in a tile drain.f 
fit is probable, also that the fungus does other damage to the plant 
as well as stopping the circulation. A careful examination of fields in 
all parts of the State show that this disease is almost always present, 
more or less. If growers will go through fields in August they will occa¬ 
sionally find plants that appear to be maturing early. They are turning 
yellow and showing signs of dying. If these stems are pulled up and split, 
you will nearly always find the yellow discolored area running up the 
stem just outside the pith tissue. This disease is most noticeable when 
the plants are young, and in fields where potatoes follow potatoes. In 
fact it is quite probable that the difference between yields where pota¬ 
toes follow potatoes, and alfalfa ground in the Greeley district is largely 
due to the ravages of this fungus. No remedy is known for this disease. 
Two preventative measures may be adopted: First, that of rotating the 
crops so that potatoes will not follow potatoes; and the second, cleaning 
the seed by exposing to the light and air, so that the spores of this fungus 
will be largely killed, and the tubers made resistant. The planting of a 
whole seed is always desirable where this disease is liable to occur. The 
development of the disease is favored by wet soils and high temperatures. 
Where soils are porous and not too wet, little trouble has been ex¬ 
perienced from this disease. 
