SOME DISEASES OF THE POTATO. 



145 



adapt itself to other root crops ; hence such should not be sown on in- 

 Cereals, Peas, and Beans may be sown with safety. 



fected ground. 



Bacterial Disease (Bacillus solanacearum, Smith). 



This disease, which has proved very destructive to Potatos in the 

 United States, has occurred once or twice in this country. The leaves 

 wilt and die, the stem changes colour and shows black streaks. When 

 a diseased tuber is cut across, a dark ring, more or less intense, depending 

 on the progress of the disease, is present some little distance from the 

 outside. 



The most certain means of checking the spread of this pest is to be 

 assured that the sets are free ftom disease. This can only be ascertained 



Fig. 29.— Black Scab or Warty Disease of Potatos. {Gardeners' Chronicle.) 



by cutting, as externally the Potato may appear perfectly sound, whereas 

 the suggestion of a brown ring inside points to disease. 



Potato Scab (Sorosporium scabies, Fisch.). 



This disease, characterised by the presence of scurvy or scab-like 

 patches on the skin of the Potato, is very prevalent during certain seasons, 

 and although the edible property of the tuber is not injured, the market 

 value is much depreciated. A second form of scab, superficially resem- 

 bling the one described above, caused by an organism called Oospora 

 scabies, Thax., also occurs. 



The disease is prevented in both cases by steeping seed Potatos for 

 two hours in half a pint of formalin mixed with 15 gallons of water. 



L 



