OBSTRUCTIONS TO DEVELOPMKNT II9 



tubers and a good rotation of crops will aid in com- 

 batting the trouble. 



Scab {Oopsora scabies Than.). — Thaxter has shown 

 that this fungus is the chief cause of scab (Fig. 38), 

 although Roze claims that the primary cause is badle- 

 rial, and that the fungus Oospora scabies and other 

 organisms follow, causing the familiar rough and 

 cankerous appearance of scab. Other causes are also 

 given.' An enormous amount of work has been ex- 

 pended on this disease, and still no absolute preventive 

 is known if the land is inoculated with the trouble. 



Treatment. — Of a large number of substances used 

 for treating the seed potatoes, soaking them in a solu- 

 tion of formalin, i pound to 30 gallons of water, for 2 

 hours is the most effedtive. Soak the potatoes before 

 cutting them, and if they are not planted at once 

 spread them thinly to dry. If left in bags they will 

 heat and the buds be ruined. After soaking two or three 

 lots of potatoes the solution should be changed, as it 

 loses its efficacy. A big cheese-vat or sheep-dipping 

 vat, in which several bags may be placed at a time, is 

 useful. A small block and tackle will enable one man 

 to lift large bags in and out of the vat, and suspend 

 them to permit of some drainage. 



The following points are of importance. 



An acid condition of the soil is injurious to the 

 growth of scab. L,ime, wood ashes, and barn manure 

 aid the growth of scab, while sulphate of ammonia, 

 muriate of potash, sulphate of potash, kainit, acid phos- 

 phate, and dissolved bone render the soil less favorable 



1 W. Va. Special Bui. 44, pp. 2S5-6. 



