112 THE POTATO 



America. The leaves become brown on the margin 

 and die. It is caused by drought, and is more prevalent 

 on light soils. Irrigation and seledlion of vigorous 

 varieties, more care in cultivation, and fertilizing are 

 suggested. At Wisconsin Experiment Station,' Green 

 Mountain, Rural New Yorker No. 2, Everett's Heavy 

 Weight, and Colossal proved most resistant in 1896. 



Sun Scald.'^ — Its eflFedl is similar to that of tip burn. 

 It is more prevalent in the Southeastern United States, 

 and is often noticed when long-continued damp weather 

 is followed by several hot, bright days. 



2. Weeds. — These injure the plant by using water 

 and other plant-food, crowding the plant, preventing 

 the free circulation of air, and in these ways reducing 

 the vitality and rendering the potato more subjedt to 

 disease. 



3. Diseases Due to Parasitic Fungi and Bacte- 

 ria. — Eate Blight or Rot ^ {Phytophthora mfestans). 

 — There is reason to believe that this disease has existed 

 for ages in the western parts of South America, and 

 was disseminated over Europe a long time before 

 its presence was recognized. It seriously injured the 

 crops of potatoes in the United States and Canada 

 in 1843, and reappeared the following year. In July, 

 1845, it was first dete(5led in Europe, in Belgium, and 

 within two months thereafter it was recorded in Eng- 

 land, Ireland, Scotland, France, Germany, Denmark, 

 and Russia. Since that time it has never been entirely 



• Wis. Report, 1896, p. 240. " U. S. D. A. Farmers' Bui. 91, p. to. 



' (N. Y.) Cornell Bui. 113, pp. 297-302. Vt. Bui. 49, pp. 90, 91; Bui 72, p. 

 13. U. S. D. A. Farmers' Bui. 91, p. S. 



