Vegetable and Field Crops 



231 



Tubers from diseased vines rot rapidly and should not 

 be stored. If stored, they should be kept at as low a tempera- 

 ture as possible. It is unwise to plant potatoes in land which 

 has shown this disease upon any of its hosts, without a long 

 intervening rotation. The precautions suggested under soil 



use of clean 



seed, and special atten- 

 tion to insect control, 

 are preventive measures. 

 Black-leg ''"'•"' -^^- -^^' ^^^^ 

 (Bacillus phytophihorus 

 Appel). — • Much confu- 

 sion has arisen concerning 

 the identity of black-leg, 

 since in many instances 

 the mere occurrence of 

 a black region upon the 

 stem near the ground 

 line has led to the use of 

 the term. It is thus 

 probable that in the 

 literature of potato mal- 

 adies several distinct dis- 

 eases have been confused 

 with black-leg. 



A distinct, definite, 

 and serious disease has, however, been known in Europe 

 and England for several years under this name. Jones, 

 who studied black-leg in the field in Germany and England 

 and what appeared to be the same disease in Vermont, 

 described it essentially as follows: The earliest conspicuous 

 symptom was that the diseased plants were slightly be- 

 low normal size, of a paler or yellowish-green color, the 

 lateral branches and petioles becoming more erect and 

 the leaf blades curving upward, giving the entire plant a 

 narrowed aspect. The lower leaves, in the meantime, have 

 possibly shriveled and died. The stem was more or less 



Fig. 128. — Dry-rot caused by Fusa- 

 rium. After Coons. 



