174 MAmE STATE COLLEGE 



THE POTATO ROT. 



Phytophthora Infestans, DeBary. 



{Peronospora infestans, Mont.) 



Tl'e Potato Rot, Blight or Rust, as it is variously called in 

 Maine, was very bad in this State the past season. Many letters 

 asking information regarding the natui-e of this disease and its 

 remedies, were received at the Station. To meet the case a short 

 exigency bulletin was hastily prepared. Below we give for per- 

 manent record a fuller and better considered account of the 

 disease and its treatment. 



Origin and History. 

 This disease has been known in America over fifty years. It 

 has spread to all the potato growing countries of the world, caus- 

 ing more damage to the Irish potato than all other diseases com- 

 bined. It is common on the wild potato from which our cultivated 

 potato was derived. The wild potatoes are supposed to have been 

 the original source of the disease. The disease also affects 

 the tomato. For an excellent account of the history of Potato 

 Rot, the reader is referred to "Diseases of Field and Garden 

 Crops," by W. G. Smith, MacMillan & Co., London, 1884. 



Primary Causes. 



The primary cause of the Potato Rot, Blight or Rust, is a fun 

 gus parasite. It is as definite a plant as the potato, though much 

 more simple in its structure and lower in the scale of vegetable 

 life. It finds in the potato plant the conditions favorable for itJi 

 growth and attacks it, producing the disease. It reproduces it» 

 kind, especially in the summer, by organisms called spores, which 

 are as necessary for its continuance and extention as the seed ol 

 higher plants. The disease cannot spread except these spores are 

 present any more than the potato can multiply without tubers. 



(The disease can be produced in healthy plants by infecting 

 them with the spores of this fungus. Plants protected from infec- 

 tion by the spores are exempt from the diaease. This parasite is 



