Vegetable and Field Crops 245 



Rind-disease {Trichosphnace sacchari Mass.). — This 

 stem disease is first indicated by yellowing and drying of the 

 leaves, often followed by death of the plant. The nodes are 

 frequently discolored or black. In late stages black pycnidia 

 appear on the diseased surface. Diseased refuse should be 

 burned and cuttings should be disinfected by dipping in 

 Bordeaux mixture. 



Pineapple-disease {Thielnviopsis paradoxa v. Hohn.). — 

 This disease originates in cuttings and derives its name from 

 the odor of the affected stems. The fungus, which is a 

 wound parasite, enters through the ends of cuttings and 

 may prevent their germination, or so retard growth that 

 worthless plants develop. Dipping the cut ends in Bordeaux 

 mixture lessens infection. 



Ring-spot (Leptosphceria sacchari v. B. d. H.). — Oval, 

 gray spots, 3-5 x 5-15 mm., surrounded by narrow brown 

 rings, develop in the leaves, and bear minute, l)lack peri- 

 thecia. 



Leaf-spot {Cercospora longipes Butler). — Narrow, oval, 

 brown spots, about 2 mm. in diameter, surrounded by a 

 yellow zone, occur. 



Cacao-disease {Diplodia cacaoicola Hen.). — This is caused 

 by a fungus that also grows on cacao. It causes the canes 

 to wrinkle. 



Root-rot. This, one of the most troublesome of cane 

 diseases, is due to various fungi, one of which is a stink-horn 

 (Phallus), another Marasmius sacchari, Wak., })oth of which 

 can be recognized in late stages by the sporophores of the 

 fungi. Proper drainage and cultivation, the use of immune 

 varieties and healthy stock, the destruction of infected 

 refuse, and rotation of crops are helpful. 



SWEET CORN. See p. 283. 



SWEET POTATO -^^ ^^^ 



Soft-rot ^"^ {Fhizopus nigricans Ehr.). — The most prom- 

 inent soft-rot of the sweet potato, the only one that is com- 



