2 BULLETIN 64, U. S. DEPARTMENT OF AGRICULTURE. 
The more clearly this danger is made apparent to the growers and 
the more general and concerted their efforts to combat it the greater 
the likelihood that the final result will place the potato industry on a 
higher plane than it occupies to-day. The same system of seed 
selection and treatment and crop rotation that will free the potato 
fields of wilt, leaf -roll, and curly-dwarf will at the same time not only 
bring under control the blackleg and some other diseases, but will 
insure the maintenance of the strains cultivated in their most vigorous 
and productive condition and free from objectionable mixtures with 
other varieties. 
Past experience warrants these statements. The history of potato 
pathology is a story of the gradual recognition and differentiation of 
previously confused diseases and the introduction of control measures 
that brought with them more progressive cultural practices. From 
about 1845 the late-blight, PJiytophthora infestans, occupied the cen- 
ter of the stage and is still one of the most destructive diseases (Jones, 
Giddings, and Lutman, 1912). 1 It causes heavy losses in nearly all 
the potato districts of the world, especially in cool and humid seasons. 
In the United States, however, there are many sections where Phy- 
tophthora occurs somewhat rarely. An examination of a map pre- 
pared by Dr. Erwin F. Smith and published in the Annual Report of 
the Department of Agriculture for 1885 shows that the losses from 
late-blight and rot were even then recognized to be mainly in the 
northern tier of States. This has been confirmed by an annual plant- 
disease survey of the United States, which has been made during the 
past 12 years under the direction of the writer. This survey shows 
conclusively that Phytophthora as a common parasite of the potato 
is limited to the Northeastern States east of the Mississippi River, 
with only sporadic outbreaks in southeastern trucking regions, in the 
Puget Sound district, and occasionally elsewhere. This disease is 
now successfully combated by spraying with Bordeaux mixture, and 
it is to be expected soon that more disease-resistant varieties will 
introduce a new era of late-blight control. 
To the southward it has been found that early blight, Alternaria 
solani (E. and M.) J. and G., and tip-burn play a greater role than 
Phytophthora in the injury to the potato crop. Early blight is 
apparently not so common in the cooler and more uniform climate 
of northern Europe. Nor does one find there that tip-burn is as 
eommon as here, where high summer temperatures combine with 
the injuries of flea beetles and other insects to cause excessive trans- 
piration and its consequent marginal burning of the leaves. Here 
also the logical line of attack seems to be the production of varieties 
possessing heat resistance. 
* All references to literature are indicated in the text by the name of the author and the year of publi- 
cation. For full citations, see the list at the end of this bulletin. 
