4 BULLETIN 81, U. S. DEPARTMENT OF AGRICULTURE. 



moisture. Silver scurf has been known in Europe for many years, 

 but it was not noticed in America, except in one instance (by Dr. 

 Clinton in Connecticut in 1907), until 1912, when it appeared on 

 potatoes from nearly every State from Maine to Florida and westward 

 to Wisconsin. It is now thoroughly established here and, though a 

 minor trouble, adds another to the agencies which disfigure potatoes. 

 There is evidence to justify the fear that silver scurf may become 

 more injurious in the United States than it has been in Europe. 1 



Other potato parasites have come from the far West or from the 

 South. The migration of the Colorado potato beetle from the Rocky 

 Mountain region is well known. Two diseases, the southern bacterial 

 brown-rot and the Fusarium wilt, appear to be of southern, possibly 

 tropical, origin, though this is not fully established. 



THE WART DISEASE. 



Potato wart, black scab, or canker is a disease which transforms 

 the tubers into irregular, warty excrescences, at first greenish or 

 white, then black and decaying. It is a fungous disease (Synclii- 

 triura endolioticum) of comparatively recent discovery, first described 

 from Hungary in 1896 and found in England about 1902 and in 

 Westphalia in Germany in 1908. It has spread considerably during 

 the past decade until it seems firmly established in England and 

 Scotland, has gamed a foothold on the coast of Ireland, and has 

 crossed the Atlantic to Newfoundland, where Dr. H. T. Giissow, 

 Dominion botanist, discovered it in 1909. Fortunately, it has not 

 yet been found on potatoes grown in the United States. 



Most authorities consider it one of the very serious diseases of the 

 potato, as it converts the tuber into an ugly, irregular, and utterly 

 worthless article, and when established in the soil will attack the 

 succeeding crops and prevent the growing of potatoes hi such in- 

 fected soil for many years. 



The countries where the wart occurs have for the most part taken 

 vigorous measures to suppress it, and other nations have endeavored 

 to prevent its introduction. It was primarily on account of this 

 trouble that the Secretary of Agriculture issued Quarantine Order 

 No. 3, September 20, 1912, prohibiting the entry of potatoes into the 

 United States from Newfoundland, the islands of St. Pierre and 

 Miquelon, the United Kingdom (including England, Scotland, Wales, 

 and Ireland), Germany, and Austria-Hungary, although powdery 

 scab was also taken into consideration at that time. 2 



' For further details, see the paper in Circular 127, Bureau of Plant Industry, U. S. Department of 

 Agriculture, by I. E. Melhos, entitled "Silver scurf, a disease of the potato." Obtainable from the Super- 

 intendent of Documents, Government Printing Office, for 5 cents. 



'' for I . i formation on the wart disease, see Farmers' Bulletin 489. 



