172 Diseases of Truck Crops 



tain a thriving green appearance. In clipping the 

 tip end of such a root, the bundles appear brown in 

 color, and usually the disease may be traced'through 

 the entire length of the root. Sometimes only a few- 

 bundles in the root are affected, while in others 

 each shows the brown ring near the cambium. It 

 is better that the affected sprouts should die 

 early, for if they grow and produce roots of the 

 No. 2 type, they carry the disease to the seed bed. 

 This is more of a field than a storage trouble. In 

 large and badly infected roots in storage, the 

 fungus may produce a punky, dry rot which has 

 a peculiar cinnamon odor and a deep chocolate 

 color which may make the roots light and shriveled 

 (see fig. 2"j a-e). 



A diseased hill one year will mean several diseased 

 hills the following year. In plowing up the land for 

 sweet potatoes the original hill is broken, and the 

 stem wilt fungus is carried some distance in both 

 directions by the plow and the harrow. The culti- 

 vator, too, may, during the season, help to carry the 

 disease and induce new infections by injuring the 

 sprouts. Dead sprouts and dead hills, if left over 

 in the field, furnish material on which the fungus will 

 fruit abundantly. 



The two organisms greatly resemble each other in 

 spore form (fig. 7 c-d). Yellows is prevalent in New 

 Jersey, Maryland, Virginia, Illinois, Iowa, Alabama, 

 Arkansas, Missouri, North Carolina, Ohio, Georgia, 

 Texas, Oklahoma, and Mississippi. A conservative 

 estimate of the losses from yellows would be at least 



