BULLETIN OF THE 



MPMrlTOFAfflLI 



No. 82 



Contribution from the Bureau of Plant Industry, Wm. A, Taylor, Chief, 

 April 6, 1914. 



(PROFESSIONAL PAPER.) 



POVfDERY SCAB (SPONGOSPORA SUBTERRANEA) 



OF POTATOES. 1 



By I. E. Melhus, 

 Pathologist, Cotton and Truck Disease and Sugar-Plant Investigations. 



INTRODUCTION. 



The comparatively recent discovery of Spongospora subterranea in 

 the United States makes it necessary to introduce to the potato 

 grower, importer, and pathologist a new potato disease. This disease 

 is commonly known as powdery scab, and mild attacks of it resemble 

 superficially the common Oospora scab. Its prevalence in many 

 European countries and the Dominion of Canada has prompted the 

 Secretary of Agriculture to extend, for a. time at least, the present 

 quarantine on foreign potatoes. 



Although powdery scab has probably been known to exist in 

 Europe since 1841, it was not until within the last decade that it 

 assumed an important role in pathological literature. It has been 

 most extensively studied by pathologists in the British Isles, where 

 powdery scab is said to be very common. 



In February, 1913, Spongospora was reported for the first time in 

 North America. It was collected in several provinces of Canada by 

 the Dominion Botanist, Dr. H. T. Gtissow (1913), 2 who has expressed 

 the opinion that the first introduction into Canada must have been at 

 least seven years previous. Dr. W. J. Morse (1913), of the Maine 

 Agricultural Experiment Station, and the writer (1913) obtained 

 evidence daring the summer of 1913 showing that this disease exists 

 in the United States. It seems probable that it was introduced with 

 the heavy shipments of foreign potatoes in 1911 before the quarantine 

 law against the wart disease went into effect, Sufficient evidence 

 is at hand to show that powdery scab will make inroads on the 

 potato industry unless proper precautions are taken, and it is the 



1 This paper will be of interest to plant pathologists and to potato growers in the northern and southern 

 potato-growing sections. 



2 The dates in parentheses refer to the bibliography printed at tfhe end of this bulletin. 



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