METCALF: WHITE PINE BLISTER RUST 329 



The disease was first positively reported in America in 1906, on 

 Ribes. No notice appears to have been taken of this warning. In 

 1909 enormous quantities of diseased pine nursery stock were im- 

 ported. Probably 95 percent of all diseased seedlings imported into 

 America came from a single nursery, that of J. Hein's Sohne at Halsten- 

 bek, Germany. This nursery, on account of its use of Ribes hedges, 

 was curiously well adapted to distribute the disease. In June, 1909, a 

 meeting was held in New York City of pathologists and foresters of 

 New England and the Middle Atlantic States, at which a further 

 alarm was definitely sounded. With one exception, all states repre- 

 sented discouraged importation of white pine from that time, but 

 commercial nurseries continued to import extensively until such 

 importation was made illegal in 1912. Unfortunately, no studies of 

 the white pine blister rust have been made in Europe by any American 

 investigator, but if European accounts of the behavior of the disease 

 can be trusted, the disease has apparently spread more rapidly and 

 with greater virulence in New England than it did in Europe. Prob- 

 ably the new climatic and host relations are more favorable to the 

 disease. In any case the problem of invasion presented by this 

 disease makes an interesting study. The black currants, especially 

 the cultivated varieties, are particularly subject to the disease and in 

 areas of scattering infection are reliable indicators of its presence. 

 It was hoped by many that the disease might prove to be only one of 

 nursery stock and reproduction, but at several points in New England, 

 New York and Minnesota, it is attacking large trees. On Ribes the 

 disease was in 1916 generally prevalent throughout New England, 

 which means that the actual infection of pine is much more general 

 than is obvious at present. Inspection of nursery stock for blister 

 rust is largely futile since the rust often incubates in pine tissue for 

 many years before becoming apparent by distorting growth or fruiting. 

 According to Ravn this incubation period may be as long as twenty 

 years. 



The control of the disease in America presents three separate 

 problems: 



First. West of the Mississippi River. In this territory the disease 

 is not known to occur, but undoubtedly has been shipped in on nursery 

 stock of either pine or Ribes. If it has not been carried into this 

 territory on nursery stock already, there is little possibility of its ever 

 getting in by natural means. During the coming season an extensive 

 survey will be made of these states to determine whether the disease 

 is or is not present. If the disease should once become established 

 under western forest conditions, its control would be hopeless. All 

 5-needle pines of this area, including the very valuable sugar pine and 



