156 The Sweet Potato 



STEM-EOT (wilt, bxue-stem) (Plate V) 



Stem-rot, caused by the fungi Fusarium hatatatis and 

 F. hyperoxysporum, varies somewhat in appearance with 

 different varieties. The first indication of the disease 

 in the field is the dull color of the leaves affected. They 

 finally become yellowed between the veins and some- 

 what distorted, these symptoms being followed by wilt- 

 ing. On pinching open the stem of a diseased plant, 

 it will be found to be blackened inside. This discolora- 

 tion sometimes extends several feet from the hill. 

 Later the surface of the stem roughens and ruptures 

 and becomes blackened and rotted. The organism that 

 causes stem-rot may also attack the roots, forming a 

 blackened ring about % inch beneath the surface. If 

 such potatoes are used for seed, diseased sprouts are 

 likely to be developed therefrom. 



In the seed-bed, the symptoms of the disease are 

 similar to those in the field. Diseased draws can be 

 detected by the faint discoloration of the foliage and 

 the purplish tint in the tender white stem. 



Stem-rot is know to be prevalent in 'New Jersey, 

 Delaware, Maryland, Virginia, Illinois, Iowa, Kansas, 

 Alabama, and Arkansas, and to be present in Missouri, 

 N^orth Carolina, Ohio, Georgia, Texas, Oklahoma, and 

 Mississippi. It is probable that the disease occurs in 

 other states also. In some sections the disease is at 

 present relatively unimportant, owing to the fact that 

 varieties have been grown which are somewhat resis- 

 tant to it or that the sweet potato industry is compar- 

 atively new and the disease has not yet become serious. 



It is not definitely known how long the stem-rot 

 fungus will live in the soil in the absence of sweet 



