430 The Profitable Culture of Vegetables. 



been attacked, and the disease is now classed as a notifiable one, under 

 the Destructive Insects and Pests Act. It first appears near the "eyes" 

 of the tuber, causing the young sprouts to assume a brownish colour, and 

 then wrinkles or warts appear. These warts gradually increase in size and 

 grow together, forming a brown spongy mass which almost envelopes the 

 tuber and finally becomes black. The progress of the disease is well shown 

 in the illustration below. 



Potatoes infected with Black Scab or Wart Disease, 



in different stages of development. (Reduced.) 



Infected seed is most frequently the means of introducing this disease 

 into clean ground, and when it gets a footing the infection gradually 

 spreads, either through the agency of diseased haulms and tubers or by 

 infected soil being carried about on boots and tools, until all the ground is 



Potato Root infected with Black Scab or Wart Disease. (Reduced.) 



infected. The disease will survive in the ground for about six years after 

 the last crop of diseased potatoes has been taken. 



Treatment : This is entirely preventive ; nothing short of destroying 

 the tubers can kill the disease when established in the tissues. Diseased 

 tubers should be boiled or burned, and all haulm burned immediately the 



