Fungous Diseases of Colorado Crop Plants 39 
(3) The spores of the fungus are uninjured in passing through 
the digestive tracts of livestock, and hence reach the field in the 
manure. Do not feed uncooked scabby potatoes to livestock. 
(4) If the disease becomes prevalent in a soil, practice crop ro¬ 
tation, not returning to potatoes for 4 or 5 years. 
Fusarium Wilt or Blight. —The serious reverses that pota¬ 
to growing has undergone the last few years in Colorado have been 
ascribed to Fusarium wilt or blight. That it is the only cause of the 
epidemics is doubtful. However, it is quite certain that it is largely 
responsible. 
In regard to the symptoms of Fusarium wilt, we quote from 
Professor B. O. Longyear, of this station: 
“This trouble first manifests itself in the field by the wilting and 
yellowing of the lower leaves of plants that have reached the height of 
ten to twelve inches. In bad cases the entire foliage appears to suffer 
as though the plant were not getting sufficient moisture. Later on, the 
tips of the leaves turn brown and dry up, leading to the trouble com¬ 
monly known as ‘tip burn.’ The edges of the leaves commonly roll in¬ 
ward during the heat of the day, although they may partially revive dur¬ 
ing the night. 
“Badly affected plants will be found to have the root hairs and 
rootlets rotted away and often the larger roots appear sickly. Cross- 
sections of the main root often appear brownish in the region of the 
vascular bundles or woody part. Under the microscope thin sections of 
such roots and of the lower part of the stem will show the delicate fila¬ 
ments of the fungus which pass upward through the water-conducting 
tubes of the plant and eventually clog them to such an extent that the 
fiow of sap is greatly obstructed. This is what causes the wilting and 
eventual drying of the foliage of the plant. 
“The fungus also passes into the tuber-bearing stems under ground 
and frequently enters the stem end of the tuber for some distance. In 
bad cases the stem end of the tuber may be rotted away and the pres¬ 
ence of the fungus deeper in is indicated by the browning of the vascu¬ 
lar ring shown in a cross-section of the tuber. The fungus may also 
enter the tuber from the soil through any bruise, crack, or other break 
in the skin. Attacks of insect larvae upon the tubers are often followed 
by this disease through the wounds which the ‘worms’ produce. 
“Under conditions of plenty of moisture and high temperature, 
this disease makes it most rapid progress and may reach its culmina¬ 
tion at about the time when the tubers are ordinarily half to two-thirds 
grown. When a plant once shows the infection to any marked degree, 
all further growth ceases. The plants seem to stand still and eventu¬ 
ally wilt down entirely or else struggle along in a dwarfed and sickly 
condition for some time. 
“A common source of infection in newly planted fields is through 
the use of tubers for seed that already contain the fungus. Another 
