BULLETIN OF THE 
UOTMIIOFAlOll 
NO. 82 
Contribution from the Bureau of Plant Industry, Wm. A. Taylor, Chief 
April 6, 1914. 
(PROFESSIONAL PAPER.) 
POWDERY 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 1S41, 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. Giissow (1913), 2 who has expressed 
the opinion that the first introduction into Canada must have been at 
least seven je&rs previous. Dr. W. J. Morse (1913), of the Maine 
Agricultural Experiment Station, and the writer (1913) obtained 
evidence during 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. 
309.51°— 14 
