258 VEGETABLE FOES AND DISEASES 



in the tubers selected for seed they should be steeped 

 in a solution of half a pint of formalin and fifteen 

 gallons of water for two hours, which, according to 

 Professor Arther, is a complete specific for American 

 Potato Scab, though this has nothing in common with 

 Potato Scab as understood in the British Islands. 

 Formalin, however, is a poison, and must only be used 

 for sets. 



AMERICAN POTATO SCAB (Oospora scabies). 



This troublesome disease has only been thoroughly 

 investigated in America. It usually attacks the tubers 

 while young, forming rough patches known as scab on 

 the skin. The fungus causes a deep black-brown dis- 

 colouration of the substratum, and frequently the 

 affected tubers produce abnormal growths or swell- 

 ings similar to super-tuber ing. When the tubers are 

 freshly dug up a delicate greyish mould is present on 

 the diseased patches, but these fine whitish threads 

 soon dry up and disappear when exposed to the 

 atmosphere. It reproduces itself by means of spores, 

 which remain in the soil for some years, and not only 

 infect Potatoes, but Beet, Carrots, Swede Turnips and 

 Cabbages. 



Prevention. Destroy all diseased tubers by burn- 

 ing, or if fed to stock boil them before use. Land 

 which has produced scabbed crops, either of Potatoes 

 or Beets, must not be planted with Potatoes in the 

 following year. Avoid the use of rank stable or farm- 



