61 THE DEPARTMENT OF AGRICULTURE. 



While the disease cannot exist without the primary cause the " germ " there are 

 certain other factors which influence the severity of the disease. Hence : 



(1.) Do not use alkaline fertilizer e.g., wood-ashes, lime, marl, etc. with, or 

 just before, the potato-crop. 



(2.) Do not plant the seed in contact with manure. 



(3.) Avoid heavy, wet, undrained soil. 



POWDERY SCAB (Spongospora subterranea) . 



This is also a tuber-disease only (Fig. 65). It is found in many parts of the 

 Coast and Island sections, but absent from the Interior. It resembles common scab, 

 but the spots are more even in shape, smaller, retain their individual outlines even 

 when very numerous and close together, are covered when young with the smooth 

 skin, and when mature are hollow and filled with brownish or greenish powder, 

 whence the name. The spots have also a tendency to be arranged in belts around 

 the tuber. This is a somewhat more serious disease than common scab, as when 

 severe it may go deeper into the substance of the potato and is more liable to cause 

 "wilting" in storage. All cases seen in this Province, however, belong to the 

 milder, superficial type. 



Fig. 65. Powdery scab (after Gussow). Fig. 66. Potato-canker (after Gussow). 



Control. Use sound seed, disinfect it, and avoid favouring causes as given 

 above for common scab. Where it has gained a footing, rotation and the disinfec- 

 tion of bins, cellars, and implements are necessary. Manure from" stock which have 

 been fed with uncooked infected potatoes should not be used for the potato-crop. 



SILVER SCURF (Spondylocladium atrovirens). 



This is due to a fungus which lives in the skin of the tuber. The attacked 

 skin becomes more or less silvery and glistening, usually in spots, which, however, 

 may run together until a large area of the potato is affected. The substance of the 

 tuber is not affected, and the chief injury appears to be in increased wilting in 

 storage. 



Hand-selected seed free from the disease, disinfection to kill any loose spores, 

 and rotation are the only measures known against it. 



POTATO WART OR CANKER (Clirysoplilyctis endiMotica) (Fig. 66). 



This disease is not present in this Province or in any other Province of the 

 Dominion at the present time. However, on account of its very serious nature, 

 it is of vital importance that potato-growers become thoroughly familiar with the 

 symptoms of this disease. 



Potato-wart has been gradually spreading in Northern Europe for many years. 

 It was discovered in the United States in 1918 in the State of Pennsylvania. Much 

 attention was at once given to a publicity and educational campaign, with the result 

 that the disease has been prevented from spreading. 



As the name indicates, the disease is characterized by warty outgrowths on the 

 underground portions of the plant. Tubers showing the early stages of the disease 

 have some of the eyes slightly protruding and composed of simple or compound 



