FARMERS BULLETIN 856. 



plants for larger fields should procure Farmers' Bulletin 714, which 

 gives directions for growing healthy plants in seed beds. 



STEM-ROT. 



"When sweet-potato plants are affected with stem-rot, the leaves 

 turn a dull yellow and become somewhat puckered, then wilt and die, 

 beginning at the tip of the vine. The inner wood of the vine is 

 blackened. 



Rotate crops; secure healthy plants. 



Fig. 77. — The smaller sweet-potato sawfly {Schizoccriis ehenus) : a, h, Larva ; 



segments of larva showing spines ; e, eggs deposited under leaf ; ^ , male sawfly ; $ , an- 

 tenna of female sawfly. AU much enlarged ; c, d, greatly enlarged. 



Foot-rot causes small black or brown spots on the stem near the j 

 soil, which enlarge until the plant is girdled and the vine wilts ' 

 and dies. . 



Control. — The disease is carried from the hotbed by young plants. .; 

 The remedy, therefore, is to set out only plants that are healthy. . 



STORAGE ROT. 



Decay of sweet potatoes in storage may be traced to one of the 

 foregoing diseases or to soft-rot. This is due to wounds or bruises or 



