Smeet Potato 317 



Stem-kot (Fusarium batatis or Fusarium hyperoxys- 

 porum). — Leaves of affected plants become dull in color and 

 yellow between the veins. Diseased vines wilt and the interior 

 of the stems is blackened. Control: Disease-free potatoes ob- 

 tained by selecting tubers from healthy plants in the field 

 should be used for propagation. It is also advisable to treat 

 the tubers just before planting five to ten minutes in a solu- 

 tion made by dissolving one ounce of corrosive sublimate in 

 eight gallons of water. Treated potatoes should be rinsed 

 in water then dried in the sun. Careful sanitary measures 

 in the hotbed are important. After being used once in the 

 hotbed, soil should be removed and the framework and earth 

 surrounding it drenched with a solution of formaldehyde or 

 copper sulfate. Crop rotation is important since infection may 

 take place in the field if plants are set in contaminated soil. 



Black-rot {Sphceronema flmbriatiim) . — Sunken black spots 

 somewhat circular in shape appear on the surface of affected 

 potatoes or other underground parts of the host. The lesions 

 frequently enlarge and extend up the stem to the surface of 

 the soil. The stem often rots off. Control: Selection of 

 disease-free tubers for use in propagation is essential. Crop 

 rotation and non-infected soil in the seed-bed, as recommended 

 for the control of stem-rot, is important. 



ToETOisE BEETLES (Cassida Mvittata, C. nigripes, Coptocycla 

 hioolor, C. signifera, and Chelymorpha argus). — Small convex 

 beetles of changeable color that feed on the foliage in both the 

 adult and larval stage. The larvse have the peculiar habit 

 of retaining their cast skins and excrement in a mass on a 

 fork composed of two spines which extends forward over the 

 back. Control: Spray with arsenate of lead (paste), 2 lbs. in 

 50 gals, water, taking care to hit the underside of the leaves. 



Sweet potato weevil (Oylas fornvicarius) . — A slender snout- 

 beetle, 1/4 in. long; the head is black, prothorax and legs red- 

 dish and the wing-covers bluish black. The larvse burrow 

 in all^ directions through the tubers, causing decay. The life- 

 cycle is completed in about a month, one brood following an- 

 other as long as food is available. Control: Kotate crops and 



