THE POTATO QUARANTINE. 9 



RELATIVE IMPORTANCE IN EUROPE AND THE UNITED STATES. 



Powdery scab has been in the past a minor potato disease in 

 Europe; that is to say, it has not been recognized by the public as a 

 serious trouble, nor has it engaged the time and attention of scientific 

 investigators to the extent that other potato diseases, such as leaf- 

 roll, have. Recent publications by Johnson and by Pethybridge, the 

 leading plant pathologists of Ireland, lead to the conclusion that the 

 disease is more serious there than has previously been realized, par- 

 ticularly in gardens and fields continuously cropped in potatoes, 

 where it tends to assume the cankerous stage and reduces the market 

 value of the potatoes for eating purposes. It may well be that 

 powdery scab is becoming more serious in Europe. Johnson states: 



I have no doubt myself that Spongospora scab has a good deal to do with the miser- 

 able average yield per acre of potatoes in the west of Ireland. * * * It is in some 

 districts of Ireland as injurious to potatoes as finger-and-toe is to turnips. 



DIFFERENCES IN MARKET STANDARDS. 



An important consideration in this connection is that any scab or 

 other disfigurement of the tuber reduces its market value much more 

 in the United States than in Europe. The consumer abroad does 

 not object seriously to a scabby potato. In fact, we are assured by 

 our English visitors that it is a general belief in Great Britain that 

 scab is an indication of good quality for eating purposes. In the 

 United States, however, scabby potatoes are rejected for market pur- 

 poses. In Maine they were sorted out and sold to the starch factory 

 for 50 cents per barrel as compared with $1.50 which they would 

 have brought if clean. In communities where there are no starch 

 factories the scabby potatoes are fed to stock or left lying in the 

 field. As a consequence, scab-infected fields are worthless for potato 

 growing and their market value is greatly impaired. 



SCAB DISEASES WORSE IN THE UNITED STATES THAN IN EUROPE. 



Powdery scab has not occurred in the United States to an extent 

 that permits any comparison of its virulence here with its behavior 

 in Europe. It is, however, a well-known fact that introduced 

 troubles as a class are more destructive than in the country of origin, 

 owing to differences in climate or other conditions. The several im- 

 portant potato districts of the United States — Maine, New York, the 

 trucking districts of the Atlantic seaboard, the northern Great Lake 

 district, the Red River Valley, Colorado, Idaho, Oregon, California, 

 etc.— differ exceedingly in soil and climate, and there is reason to fear 

 that powdery scab might find in one or several of these districts con- 

 ditions much more favorable than exist in Europe and that it would 

 assume a more virulent for jr.. 

 30952°— Bull. 81—14 2 



