THE POTATO QUARANTINE. 3 
late-blight, is worst in moist, not too hot, weather, when it may 
spread with incredible rapidity, ruining the most vigorous field in 
three or four days. The same fungus spreads to the tubers, pro- 
ducing a typical dry rot in dry storage, which may become a wet 
rot in damp soil through, bacterial action. The cause of this disease 
is the late-blight fungus (PTiytophthora infestans), and its original 
habitat is believed to be South America. It gained headway soon 
'after its introduction, and in 1845 nearly destroyed the potato crop 
of Europe, especially in Ireland, and did much injury in America. 
It has been present every year since to a greater or less extent, and 
s serious outbreaks have recurred periodically when weather conditions 
■ favored its development. In North America it is most serious in the 
northeastern part of the United States and the adjacent provinces of 
Canada. Thorough spraying with Bordeaux mixture will control it, 
i but the losses are nevertheless still large. There is no hope of the 
[ extermination of this disease. Potato growers will always have it 
. to reckon with. 1 
BLACK-LEG. 
A disease marked by the blackening and shriveling or softening of 
the base of the stalk, a typical curling and yellowing of the foliage, 
: and in late cases by an infection and partial decay of the tuber has 
been introduced from Europe comparatively recently, probably 
having come first to Canada and thence to Maine, It is a bacterial 
trouble, 3 transmitted in the seed potatoes. Two points are of 
special interest: (1) The widespread distribution it has secured 
within a few years, because seed potatoes are shipped from the 
district which was the original center of infection to nearly every 
State in the Union; (2) black-leg takes on a more virulent form 
under southern conditions and may destroy 10 to 75 per cent of a 
crop in Virginia when the seed farm in the North had much less of it. 
Rigid methods of seed selection and seed treatment will control 
the disease, and these must be insisted upon. 3 
SILVER SCURF. 
An example of the rapid spread of an imported fungus is afforded 
by the silver scurf (Spondylodadium atrovirens). This is a superficial 
parasite of the potato tuber, beginning as a brown mold on the 
surface. Later the infected areas take on a glistening silvery gray 
color, and finally the tubers shrivel more or less, due to loss of 
1 A complete description of the late-blight has been given by Jones, Giddings, and Lutman, in " Investiga- 
tions of the potato fungus Phytophthora infestans," U. S. Department of Agriculture, Bureau of Plant 
Industry, Bulletin 245, 1912. Obtainable from the Superintendent of Documents, Government Printing 
Office, for 30 cents. 
2 Bacillus phytophthorus Appel and related forms. 
3 The reader desiring more information on black-leg is advised to procure Bulletin 174 of the Maine 
Agricultural Experiment Station, Orono, Me. 
