BULLETIN 227. 



■ POWDERY SCAB OF POTATOES. 



W. J. Morse. 



Following the discovery of powdery scab in Maine and ad- 

 joining portions of Canada this Station has received many Let- 

 ters of inquiry as to the appearance and nature of the disease, 

 means of dissemination, methods of control, etc. Since pow- 

 dery scab is of so much importance from the standpoint of tlie 

 potato industry and since the demand for information on tlie 

 subject has been so great, it has become necessary to prepare 

 for circulation within the State a brief resume of the important 

 facts known about the disease. Naturally much O'f the material 

 here presented has been obtained from European sources, but 

 as far as possible the description of the disease and the compari- 

 sons made with potato diseases which might be mistaken for it, 

 etc., have been based upon observations made by the writer an>l 

 others in the State of Maine. 



History and Distribution oi^ the Disease. 



Some difference of opinion has existed as to how long pow- 

 dery scab has been recognized as a specific disease. This is 

 based on the question of the identity of the disease describcl 

 by Brunchorst,* in Norway in 1886 as caused by a slime-mold 

 with that described by Wallroth and others in the early forties 

 as being produced by a fungus. Pethybridge in a recent publi- 

 cation t has, in the writer's opinion, shown quite conclusively 



* Briunchorst, J. Ue'ber eine sehr verbreitete Krankhek der Kartoffel- 

 knollen. Bergens Museums Aarsberetning 1886, p. 219. 



t Pethybridge, G. H. On the Nomenclature of the Organism Causing 

 "Corky" or "Powdery-scab" in the Potato Tuber, Spongospora sub- 

 terranea (Wallr.) Johnson. Jour. Royal Hort. Soc. 38 : 524-530. 1913. 



