SWEET POTATOES— SWEET POTATO DISEASES 



1953 



which is usually about May 15 or May 

 20. Toward the last the hotbed should be 

 ventilated very freely in order to harden 

 off the plants. 



"The ridges for planting sweet potatoes 

 should be three to five feet apart and the 

 plants about 14 inches apart in the row. 

 Cultivate sufficiently to keep the surface 

 soil loose and free from weeds, and the 

 vines will soon cover the ground, after 

 which no cultivation will be necessary. 

 In the warmer parts of the country the 

 seed is not bedded, but is cut in small 

 pieces and planted in the ridges instead 

 of plants. After the plants come up and 

 begin to make vines freely, pieces of the 

 vines are removed and used as cuttings 

 for planting additional areas, the cuttings 

 taking root and growing the same as 

 plants grown from seed. In this manner 

 three and four plantings are made, the 

 last being as late as the middle of .Tuly. 

 If a rainy spell be selected for making 

 and planting the cuttings, very few will 

 fail to grow, and an excellent crop may 

 be produced. 



"To the north sweet potatoes are dug 

 as soon as the vines are nipped by frost. 

 In the South the potatoes are allowed to 

 remain in the ground until a convenient 

 time for handling them, and in Florida 

 or Texas they are frequently left until re- 

 quired for use. Sweet potatoes should be 

 dug on a bright, drying day when the soil 

 is not too wet. On a small scale they may 

 be dug with a spading fork, and great 

 care should be taken that the roots do not 

 become bruised or injured in the process 

 of handling. It is desirable that the roots 

 should lie exposed for two or three hours 

 to dry thoroughly, after which they may 

 be placed in a warm, well-ventilated room 

 to cure for several days. The proper tem- 

 perature for curing sweet potatoes is from 

 80° to 90° F. and 45° or 55° F. after- 

 wards." 



Granville Lowtiieb 



SWEET POTATO DISEASES 



Bin or Soft Rot 



Rhizopus nigricans Ehr. 

 Is encountered by sweet potato grow- 

 ers. The fungus producing it may be 

 present in the plant bed and apparent as 



3 — 40 



dark spots or rotted tips on the plants at 

 setting. All such plants ought to be dis- 

 carded if avoidance of disease is sought. 

 Avoid bruising potatoes, and store in 

 dry place with good ventilation, at tem- 

 perature of about 60 degrees. The tem- 

 perature in potato houses or banks should 

 not go below 50 degrees F. at any time. 



Black Rot 



Sphaeronema fimbriatum (Ell. & Hals.) 

 Sacc. 

 The black rot of the sweet potato is one 

 of the most destructive diseases of this 

 host, and It is known to occur from New 

 Jersey southward practically throughout 

 the Atlantic coast region. The distribu- 

 tion of the fungus, however, is not com- 

 pletely known. The disease may appear 

 in the seed bed, resulting from the use 

 of infected seed roots. The disease upon 

 the seedlings is known as black shank, 

 due to the black spots or discolorations 

 on the roots and young stems. The com- 

 mercial root may be infested either as a 

 result of f)lanting diseased slips, or the 

 infection may be due to the presence of 

 the fungus in the soil. Upon the full- 

 grown root the disease appears in the 

 form of dark patches or decayed spots, 

 which, upon careful examination, and 

 especially upon removal of the skin, will 

 appear green. These spots vary in size 

 from minute flecks to extensive areas in- 

 volving practically the whole root. When 

 the roots are diseased there is no appear- 

 ance of the vegetative parts which sug- 

 gests the presence of the parasite. 



Control 



Seed roots for planting purposes should 

 be carefully selected and no slips should 

 be taken from plants in the seed beds 

 showing disease. Rotation of crops in 

 necessary to rid fields of this fungus. 

 Apparently no experiments of interest 

 have been made to determine the possibil- 

 ity of preventing the spread of the fungus 

 in stored roots. Nevertheless, any con- 

 dition favoring the accumulation of 

 moisture would be favorable to the or- 

 ganism. 



Duggar. Fungous Diseases of I'lants. 



