86 MAINS AGRICULTURAL EXPERIMENT STATION. I907. 



It is not known how long the fungus will remain active in the 

 soil without the presence of a susceptible crop. Various writers 

 have reported a large amount of infection on land where no 

 root crop has been grown for from 5 to 7 years and Jones and 

 Edson* cite a case of probable slight soil infection after a lapse 

 of presumably 25 or more years. 



However, by rotation of crops, and proper attention to soil 

 management and fertilization it is possible to materially decrease 

 the. amount of scab in an infected soil. Land which has pro- 

 duced a crop of badly scabbed potatoes should at once be given 

 over to other crops as corn, grains, grasses and clovers, for as 

 long a time as possible. Wood ashes or lime should not be 

 applied and such commercial fertilizers as are used should be 

 selected, as far as possible, from the materials mentioned on page 

 84 as not tending to increase scab. "Souring" the soil by 

 green manuring or plowing under of a green crop such as clover 

 should be resorted to, especially just before a crop of potatoes 

 is again to be grown upon the soil. This has been practiced 

 successfully by Alva Agee of Ohio, using rye as the green crop.f 

 He reports growing 7 successful crops of potatoes on land 

 which in the beginning was so badly infected with scab that the 

 crop was unmarketable. Winter rye was sown in the fall and 

 turned under the first warm days in the spring when about a 

 foot high. Each year the conditions of the crop improved till 

 the third year the appearance of the tubers was excellent and on 

 the seventh year 285 bushels per acre were raised and those 

 nearly free from scab. Aside from the cover crop no fertilizer 

 was used except phosphoric acid in the form of acid phosphate. 

 This system would produce best results on a neutral or slightly 

 alkaline soil and probably would not be' entirely successful on a 

 soil which is strongly alkaline, as the decaying crop would very 

 likely not produce acid enough to leave an excess in the soil. 

 Failures in the use of rye in this manner for one season have 

 been reported,^ but it may be that the soil was too alkaline to 

 produce the required effect. 



There it not sufficient experimental evidence to say how nearly 

 an infected soil can be cleared of scab germs or how soon pota- 



* Vt. Exp. Sta. Rep. 14, p. 232, (1901), 

 t Penn Dept of Agr. Bui. 105, p. 84. (1902). 



t Mass. Exp. Sta. Rep. 8, p. 217, (1890); N. Y. (Geneva) Exp. Sta. Bui. 138, p 629, 

 (1897). 



