CONTROL OF THE BLACK-ROT AND STEM-ROT OF THE SWEET 



POTATO. 1 



By L. I.. Harter, Pathologist, Cotton and Truck Disease and Sugar-Plant 



Investigations. 



INTRODUCTION. 



This article outlines some of the precautions necessary to reduce 

 the widespread loss of the sweet-potato crop by the black-rot 2 and 

 stem-rot 3 organisms. Several papers on sweet-potato diseases are in 

 press or in preparation, but as they will not appear before the coming 

 planting season the following brief suggestions are published for the 

 information of the growers interested. It should be stated at the 

 outset that the following recommendations are merely tentative and 

 may require modification when experiments that are now under way 

 are completed. They include, however, what is believed at the pres- 

 ent time to be the most effective means of control. 



While there are a number of diseases of sweet potatoes, the most 

 important are stem-rot, or yellow rot, and black-rot, or black shank. 

 Both of these diseases affect the stem and roots of the plants. 



Stem -rot is characterized by a blackening of the fibrovascular 

 bundles of the plant, which can be readily recognized by pinching 

 open the epidermis. The organism enters the potato at the stem end 

 and is visible there by the blackened ring just beneath the epidermis. 



Black-rot affects the plant from a little above the soil line down 

 into the ground, causing a black, rotted appearance of the affected 

 part of the stem. On the potato it appears as a black circular spot, 

 which greatly enlarges in storage. These two diseases, then, find 

 most congenial surroundings in the roots, or, in other words, in the 

 "seed." 



Experiments and observations have shown that both the field and 

 hot bed are very common sources of infection. To control these dis- 

 eases three, things are therefore imperative: (1) Clean seed, (2) the 

 hotbed and surroundings must be free of the organisms, and (3) the 

 plants must be set on soil where these parasites are not present. If it 

 is possible to meet these requirements the crop should be free from 

 disease. 



i Issued Feb. 22. 1913. 



2 Sphoeronema flmbriatum (Ell. and Hals.) Sacc. 



8 Fusarium batatatis Wollenw. Mss. 



[Cir. 114 1 



