WORK ON THE WHITE PINE BLISTER RUST 

 IN MINNESOTA, 1916. 



F. L. WASHBURN. 



(From S[)ecial Report and Circular 41.) 



Dear Sir : As you are aware the State of Minnesota is unexpect- 

 edly threatened by a plant disease, which is a menace, not only to the 

 white pine timber now standing, but also to the cause of reforestation, 

 upon wliich we place so much dependence for our future welfare, as 

 well as to all live leaf pines used for ornamental purposes in various 

 parts of the state, particularly upon the estates in the neighborhood of 

 our towns and cities. Another aspect in which we must view this 

 unexpected infestation is that concerned with the nurserv business and 

 allied interests, since should this disease become widespread, a quaran- 

 tine might ])e im]iosed upon all exports of certain shrubs and trees. 



The disease referred to is known as the \\'hite Pine Blister Rust 

 (Croiiartiitin ribicoia Fischer or Pcridcniiium strobi Klcb.l This is a 

 fungus parasite with two separate and distinct hosts, the white pine 

 primarily and other five-leaf pines, liml)er pine (P. flcxUis) , stone pine 

 (P. ccmbraj. both found in varying abundance in Minnesota nurseries, 

 and used thruout the state as ornamentals, as well as about seven other 

 varieties occurring in various parts of America. The other host upon 

 which it is found during the summer months is the genus Ribcs. con- 

 taining as now constituted, both currants and gooseberries, wild and 

 cultivated. Details of this relationshi]^ in the life history of the fungus 

 are given below. The disease is of European origin, and was imported 

 into this country on pine seedlings as early as 1*^)00 or earlier. In 1^09 

 large numbers of these were brought to America. ( U. S. Dept. of Agr. 

 Farmers' Bulletin 742, Spalding. ) The original home of this rust is 

 said to be Eastern Asia or Serbia, spreading thence to England and 

 northern and central Europe. The principal infestations in this coun- 

 try evidently came from Germany. 



The foreign seedlings referred to above were widely distributed be- 

 fore it was known that they were diseased : Xew York, Pennsvlvania, 

 Connecticut, Xew Hampshire, A^ermont, Massachtisetts, as well as Ohio 

 and Indiana received trees of this sort and in these states the rust 



EXPLANATION OF PLATE I. 

 A. Diseased white pine with blisters broken open, spreading the disease to any currants or 



gooseberries in the vicinity. 

 R. Early summer stage on lower surface of currant leaves, repeating on currant leaves or 



gooseberry leaves during the rest of the season, and a new crop of sjiores appearing 



every two weeks. 



C. Early summer stage much magnified. 



D. Late summer and fall stage on lower surface of a currant spreading the disease back to 



neighboring pines. Courtesy of Bureau of Plant Industry, V . S. Dep. of Agriculture. 



