74 
Colorado Experiment Station 
potatoes ill a hill are worthless. The disease does not affect the 
plant above the ground. 
The fungus causing potato wart lives from year to year in the 
soil or on diseased tubers. Crop rotation and the use of resistant 
varieties offer the best methods of control after the disease has be- 
come established. 
Early Blight (Alternaria solani) (77), (70)— Early blight is a 
leaf spot disease that is often very prevalent in Colorado. Eoundish 
brown spots marked with concentric rings are produced on affected 
leaves. The disease seldom causes great loss, but in severe cases some 
injury is produced. The disease is more severe in moist localities. 
Early blight may be controlled by spraying with Bordeaux mixture 
(5-5-50). Spraying should begin early before the blight becomes 
serious. 
Tip-Burn (Hopper-Bum) (70) — This disease which is character- 
ized by a browning and burning of the tip and margins of the leaves 
is common in Colorado. For many years it Avas thought to be a phys- 
iological disease caused by unfaAmrable moisture relations. Recent 
work, however, indicates that an insect, the potato leaf hopper, is 
largely responsible for the trouble. Probably both factors are 
involved. 
Spraying to control the leaf 'hopper should i*educe the amount of 
the disease. 
Potato scab. (After Stakman and Tolaas.") 
