OBSTRUCTIONS TO DEVELOPMENT 121 



to the disease. Scabby seed will inoculate clean land. 

 Scabby potatoes cannot be sold. If used as fertilizer, 

 even after steaming for twenty minutes 1 or being ex- 

 posed to the weather all winter, they will inoculate the 

 land they are spread on. 



Exposing tubers to sunlight for four weeks before 

 planting reduces the percentage of scab and hastens 

 growth. 



Scab can live in the soil at least six years without a 

 known host. Beets, mangolds, turnips, and rutabagas 

 are subject to the same disease; hence in the rotation 

 these crops should be avoided, if possible. 



Varieties vary in their susceptibility to scab, 2 the 

 thicker skinned varieties being reported as most re- 

 sistant. 



It seems to be useless to treat scabby seed if they are 

 to be planted on scab-infested land. 3 



Plowing under green rye does not diminish scab, as 

 has been stated." 



Applying sulphur in the rows at the rate of 300 

 pounds per acre and more has been tried extensively, 

 but is not recommended as a practice, as it is of little 

 use on infested land. 



Diseases in Storage. WET ROT has several 

 causes. 



i. Blight or Rot (Phytophthora infestans). The 

 tissues of the tuber become soft either partially or 

 wholly, the skin shrinks, and the layer under it be- 

 comes pasty. Potatoes from light soils appear to be 



1 N. J. Report, 1899, pp. 344-345. 2 N. J. Report, 1899, p. 329; 1900, p. 417. 



3 (N. Y.) Geneva Bui. 138, p. 631. 



* (N. Y.) Geneva Bui. 138, p. 629. N. J. Report, 1900, p. 417. 



