CONTROL OF GABDEK DISEASES AND INSECTS, 



65 



They have a rather wide range, but, as a general rule, are not de- 

 structive except locally. They may be controlled by spraying with 

 lead arsenate when they first appear. 



CUTWORMS. 



Since sweet potato is cultivated in seed beds, cutworms do con- 

 siderable injury. Remedies are considered on pages 14 to 10. 



BLACK-ROT. 



Black-rot may occur on any of tlie underground parts of the sweet- 

 potato plant. On the tuber it is characterized by the dark to nearly 

 black, somewhat sunken, more or less circular spots on the surface. 

 Although the spots are small in the early stages, undei- favorable 

 conditions they enlarge, involving nearly the whole tuber. 



-The golden tortoise beetle {CoptocycJa bicolor) : 

 fork ; d, pupa. All enlarged. 



Beetle ; b, larva ; c, teci- 



The surface of the diseased spots has a somewliat metallic luster, and 

 the tissue just beneath is greenish. In storage the disease spreads 

 from one potato to another. 



On the stem the infection begins as a small black spot, which en- 

 larges gradually until the whole of the stem is rotted off. Sometimes 

 the infected areas extend from the potato to the surface of the soil. 

 Figure 4, page 7, shows the characteristic symptoms of this disease 

 on a young slip. Black-rot occurs in the hotbed and in the field. It 

 may come from the use of infected soil or from the use of infected 

 potatoes for seed. In the latter case the fungus grows from the potato 

 to the slips and is carried on the slips to the field. Diseased slips 

 generally die in a few weeks in the field. 



Control.— The home gardener, in buying sweet-potato plants, 

 should make sure that they are sound and healthy. Those who grow 



