8 BULLETIN 81, U. S. DEPARTMENT OF AGRICULTURE. 



OCCURRENCE IN THE UNITED STATES. 



During the past two years the pathologists of the Department of 

 Agriculture have visited every important jDotato section to look for 

 powdery scab and other diseases. Potatoes in the large markets have 

 been examined, the Plant-Disease Survey collaborators in the several 

 States have been asked to be on the watch for powdery scab, and 

 the State of Maine has been given special attention by both the 

 department and the State experiment station. 



Outside of the State of Maine no definite cases have been traced to 

 farms, but some evidence of powdery-scab infection was found by 

 Dr. Morse, of the Maine experiment station, in two sendings of pota- 

 toes from western Nebraska and Massachusetts. 



Considerable powdery scab has been found in Maine very recently. 

 This infection is most abundant on the northern border of Aroostook 

 County, but scattered cases occur elsewhere, many of which have 

 been traced directly to seed potatoes brought over from the infected 

 districts of Canada. Thus far only a very small percentage of Maine 

 farms has been found infected. 



The State authorities have taken prompt and vigorous action to 

 survey the State in order to locate all infections. An inspection 

 service has been organized, which will issue certificates of freedom 

 from powdery scab, and no potatoes known to be diseased will be 

 allowed to leave the State. Seed stock will be examined with special 

 care. 



It is believed that these measures will provide an adequate safe- 

 guard against the future spread of powdery scab to other States. 

 The State of Maine expects to quarantine all infected fields and will 

 endeavor to stamp out the disease. 



A more thorough survey of other States is now under way. The 

 evidence is veiy strong that at the present time powdery scab is not 

 "widely distributed in the United States." 



LIKELIHOOD OF SPREAD. 



That the disease has not already gained a greater foothold in spite 

 of numerous importations is perhaps the strongest argument advanced 

 by the opponents of a quarantine. This is probably a matter of 

 good fortune rather than proof of noncommunicability. The con- 

 trary evidence includes its apparent general occurrence in certain 

 foreign districts, the fact reported by Dr. Melhus that in Canada 

 those sections which use European varieties and which often import 

 seed are more infected than those using seed from American sources, 

 and the experimental evidence secured by Dr. Morse in Maine and 

 by Irish workers that the disease is readily communicable by planting 

 infected seed potatoes. 



