Chapter 1O. 



A DISEASE OF LEAVES, SHOOTS, AND TUBERS. 



The Late-Blight disease of potatoes. Symptoms and means of 

 spreading. Diseased tubers and the wintering of the fungus. 

 Treatment of the disease, spraying and the use of resistant 

 varieties. 



The Late-Blight of potatoes caused by Phytophthora 

 infest ans is so common and wide-spread that it is generally 

 spoken of as the Potato Disease. Historically, it is cer- 

 tainly the oldest of the potato diseases, and it is probably 

 responsible for more loss to potato growers than all the 

 other diseases of the potato put together. The malady 

 first made its appearance in Europe about 1840, and the 

 Irish Potato Famine of 1845 was the result of a very severe 

 attack of Phytophthora. Whilst its ravages are seldom 

 so severe nowadays as they were in that year, the disease 

 is never altogether absent. In most seasons it makes a 

 first appearance about the middle of July, and from that 

 date to the end of the potato season it is often difficult 

 to find a field of potatoes wholly free from attack. 

 Farmers and growers generally, however, do not seem to 

 be seriously concerned so long as the tubers are not badly 

 diseased. It is an important fact, however, that wherever 



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