454 



SOUTHERN FIELD CROPS 



and, if necessary, to spray the vines with this or -with Paris 



green. Cutworms may be poisoned before setting the 



shps, as suggested in paragrapli 379. 



432. Fungous diseases. — Tlie enlarged root of the 



sweet-potato is suljject to various forms of decay, each 

 one due to a different germ or 

 disease-producing organism. The 

 most serious of these is the follow- 

 ing : — 



Blaclc-rot (Sphwronema fimbria- 

 turn). — The presence of this fungus 

 within the potato root causes black 

 spots on the surface (Fig. 198). 

 These spots are slightly depressed, 

 and the dark color extends deep 

 into the enlarged root, which com- 

 pletely decays in the field or during 

 storage. If diseased potatoes are 

 bedded, the slips are also diseased. 

 The remedies consist in (1) bedding 

 no tubers thus diseased; (2) de- 



FiG. 198.— Black-rot ow stroying any shps on the white 



KooT AND Sup of Sweet- r i •' i 



POTATO. stems ot which are found any dark 



spots ; and (3) rotation of crops, 



avoiding the planting of sweet-iwtatoes for two years in 



succession on the same land and avoiding any lainl where 



this disease has occurred in recent -s'cars. 



In addition to these measures, J. L. Winslow soaks the roots 

 for five minutes just before liedding, iu a weak solution of for- 

 malin, usinf>- 1 ounce of this liquid to S gallons of water. He also 

 dips the slips into a slightly stronger solution of formalin. It is 



