2 BULLETIN 81, TJ. S. DEPARTMENT OF AGRICULTURE. 
REVIEW OF THE POTATO-DISEASE SITUATION, 
When seeking protection from new plant diseases we must be 
guided by past experience and by our knowledge of trie general 
principles controlling the occurrence and spread of plant parasites. 
It is evident that agriculture in general bears a burden that increases 
from year to year as new diseases or insect enemies appear. In 
colonial times and up to 1840 the potato seems to have been free 
from many serious pests that have come in since. We now list 18 
or 20 diseases, not. including insects, that attack potatoes in some 11 
part of the United States. The yearly loss from them is difficult to ' 
estimate, but the injury from tuber rots and related troubles was I 
recently placed by the Department of Agriculture at over $30,000,000 
annually, and diseases which attack the crop in the field probably 
reduce the value of the harvest by another $30,000,000 per annum. I 
Not only do new parasites appear at frequent intervals, but they | 
can rarely, if ever, be exterminated. A plant disease, once estab- I 
lished here, is likely to be with us forever. Under these circumstances | 
it is to the credit of American farmers that they have, during the 
last generation, by the adoption of scientific methods of fertilization 
and culture and by spraying and seed treatment for diseases, main- -ji 
tainecl the average yield per acre of the country and in the more | 
progressive sections considerably increased it. On the other hand, I 
the average yield is still only about half what it might be, as judged I 
by European standards, and the cost of spraying, increased ferti- I 
lizers, etc.. constitutes a heavy annual tax on the grower. 
INTRODUCED PARASITES THE MORE DANGEROUS. 
Plant parasites may be divided into two classes, those endemic or 
native to the country and those introduced from other countries. 
It is a general principle, fully established by experience, that parasites 
introduced from other continents or distent parts of the same 
continent are more injurious than the native parasites of the same 
crop and more virulent and destructive in their new habitat than 
they had been at home. 
The United States has had many costly examples of this fact, 
among which may be cited the gipsy moth, the brown-tail moth, the 
codling moth, the asparagus rust, the hollyhock rust, and that recent 
immigrant from the Orient, the chestnut bark disease, which is 
threatening to destroy our chestnut forests. 
Several potato diseases are of foreign origin. The examples men- 
tioned below are of special interest. 
LATE-BUQST. 
In the period from 1830 to 1842 there was introduced into both 
Europe and America a new potato disease which causes a blighting 
of the foliage, followed by decay of the tubers. This disease, called 
