THE POTATO QUARANTINE. 8 



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 (Phytophthora 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 

 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, 

 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, 2 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 



SELVES SCUEF. 



An example of the rapid spread of an imported fungus is afforded 

 by the silver scurf (Spondylocladium atrovvrens) . 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, Gidd ings, and Lutman, in " Investiga- 

 tions of the potato fungus Phytophthora infestans," TJ. S. Department of Agriculture, Bureau of Plant 

 Industry, Bulletin 245, IG12. Obtainable from the Superintendent of Documents, Government Printing 

 Office, for 30 cents. 



2 Bacillus -phytopliiliorUG Appcl and related forms. 



s The reader desiring more information on black-leg is advised to procure Bulletin 174 of the Maine 

 Agricultural Experiment Station, Orono, Me. 



