BLACK SCAB OF POTATOES 



(Oedomyces leproides, Trabut.) 



This must undoubtedly be considered as the most in- 

 jurious disease that has entered this country during recent 

 times, and unfortunately promises to prove more destructive 

 to the potato crop than even the renowned ' Potato disease,' 

 caused by Phytophthora infestans. The ravages of the 

 latter are to a very marked extent dependent on weather 

 conditions, and during a fine dry summer is but little in 

 evidence. Black scab, on the other hand, when once 

 introduced into the soil, is quite independent of weather, 

 and continues its ravages from year to year. 



To add to the difficulty, no one has yet succeeded in 

 unravelling its life-history, or discovered in what way it 

 passes its time in the ground when free from a potato. It 

 is perfectly well known that when land once becomes in- 

 fested, Oedomyces retains its vitality for five years; in other 

 words, after a period of five years, potatoes planted in 

 infected land become badly diseased. It is a difficult, 

 in fact impossible matter to prevent soil infection, when 

 diseased tubers have once been planted, as in many in- 

 stances the crop of potatoes become so badly diseased that 

 many diseased tubers rot and completely decay in the soil 

 before the crop is lifted. 



Beetroot, mangolds, and some other root crops can also 

 be attacked, but cereals, peas, and beans do not suffer. 



The only effective treatment known is to apply gas-lime 



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