I 



WHITE-PINE BLISTER RUST. 83 



In 1909 it was learned that great quantities of infected young white 

 pines had been imported from Europe in 1907, 1908, and 1909. 

 (Fig. 1.) With conditions as they appeared to be, it was beHeved 

 that eradication might be possible, and this was attempted. The 

 disease was held in check in such shipments of diseased trees as 

 could be located. But many could not be located. Moreover, for 

 years before, as was subsequently learned, nurserymen and private 

 individuals had imported from Europe many infected white pines. 

 These we had no means of knowing about until too bte, since the 

 importers and planters did not inform us concerning them, even after 

 the publication of warnings against the disease. Such diseased im- 

 portations have been the center s from which most of our large out- 

 breaks have started. So far as we can learn no Federal agency has 

 imported white pines upon which this disease has been found. 



More complete knowledge of the life history of the fungus has shown 

 that it is impossible to eradicate it where both Ribes and white pines 

 are native and abundant, after the seciospores are once set free in 

 quantity. If both pines and Ribes be removed from a given area 

 the disease may be eradicated in that area but it will have escaped 

 beyond that area by means of the aciospores. This happened in 

 Minnesota and Wisconsin, where all the white pines and Ribes were 

 removed from large infected areas. 



The removal of pines has been accomplished in a few cases. Entire 

 plantings of imported pine stock were destroyed soon after they were 

 found to be diseased, and in these cases Ribes were also removed or 

 were absent from the area treated. The forestry officials of the State 

 of New York took the lead in this work, destroying 1,200,000 imported 

 trees in their nurseries in 1910 and 1911. A number of plantations 

 were also destroyed in New York, New Jersey, and Vermont (131, 139). 

 As early as 1912, the total destruction of diseased lots of imported 

 white pines (133) was urged rather than weeding out only those 

 which were visibly diseased. Public opinion would not permit this 

 to be done in the wholesale manner that was necessary for efficiency. 

 Yet this was the one efficient manner of handling such imported trees 

 (136) before generally infected areas had developed. 



SEPARATION OF THE TWO HOSTS. 



The fact that each form of spore will infect but one of the hosts, at 

 once indicates that a separation of these hosts will prevent the further 

 progress of the parasite within the control area. If the pines only 

 are removed, the disease will bo likely to die out on the Ribes, since 

 it apparently ovei'Nvdnters on them only infrequently; if the Ribes 

 are removed, the disease is isolated on that particular lot of pines, 

 where it overwinters (if the diseased trees are not also found and 

 removed) and produces new crops of reciospores each spring. The 



