8 BULLETIN 81, TT. 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 potato 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 very 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. 
