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AMERICAN FORESTRY 



diseased nursery stock of white pines and in no other way. 

 The parasite is a low form of plant similar to, and closely 

 related to, the wheat rust and cedar apple rust parasites. 

 The former has two phases of development; one upon 

 leaves of the barberry and the other upon the wheat 

 plant. The latter also has two phases of growth; one 

 upon the leaves of cedar and the other upon the leaves 



berries. The parasite lives in the bark of an infected 

 pine and after it once appears, produces a crop of spores 

 each spring as long as that pine lives. If there are no 

 currants or gooseberries near enough to the diseased pine 

 for the spores to be blown from the pine to the currants 

 and gooseberries the disease cannot spread any farther, 

 because the "pine" spores cannot attack pines. 



Photograph by J. Franklin Collins. 



THESE TREES ARE INFECTED 



Practically all these pines on Gerrish's Island on an arm of Portsmouth Harbor, 

 Maine, are generally infected with the pine Mister disease. 



Photograph by J. Franklin Collins. 



AN INFECTED PLOT OF PINES 



Eighty per cent of the native white pine on this random quarter-acre plot near 

 Kittery Point, Maine, were, in November, 191 6, infected by the pine blister disease. 



and fruit of the apple tree. In 

 the same way the white pine 

 blister rust has two phases 

 of growth on two distinct 

 hosts ; one phase on the young 

 bark of white pines, and the 

 other phase on leaves of 

 wild and cultivated currants 

 and gooseberries. Three dis- 

 tinct kinds of spores are pro- 

 duced in a season. 



In the spring spores are 

 formed on the diseased white 

 pine bark; they are blown 

 about by the wind and infect 

 the leaves of neighboring 

 currants or gooseberries, but 

 they cannot attack pines. 

 They are rather short lived. 



In early summer the sec- 

 ond spore form ripens on the 

 lower surface of infected 

 currant or gooseberry leaves. 

 These can attack currant or 

 gooseberry leaves but cannot 

 attack pines. The third spore 

 form ripens also on the 

 lower surface of the currant 

 and gooseberry leaves. These 

 spores are able to at tack pines 

 but not currants or goose- 



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| FEDERAL ACTION REQUIRED IN FIGHTING 

 THE PINE BLISTER DISEASE 



1. A federal quarantine prohibiting shipment of \ 



\ all five-leaved pines and all currant and goose- j 



j berry bushes beyond the western boundaries of j 



! Minnesota, Iowa, Missouri, Arkansas, and Louisi- ! 



j ana, to prevent the introduction of the pine blister I 



| disease from the eastern white-pine area into the j 



| western white-pine forests of the Rocky Mountain j 



| and Pacific Coast States. 



| 2. A federal quarantine regulation prohibiting j 



| the shipment of all five-leaved pines and all cur- j 



[ rants and gooseberry bushes from infected areas ] 

 | into regions where the disease has not yet been 



I found. This action could be taken at once and i 



j would save the public great prospective loss. At j 



[ the present time, all pine, currant and gooseberry j 



| planting stock, from nurseries or the native woods, [ 



i must be suspected of being infected. The direct j 



| loss through death of diseased pine stock, though 



I considerable, is insignificant when compared to ) 



| the cost of controlling the disease, or, if not con- = 



| trolled, the early loss of native and planted pines j 

 | which might otherwise thrive for years. 



3. Scouting should be continued on an exten- j 

 | sive scale, to determine definitely the boundaries 



I of infected areas, and to locate possible infections j 

 j in new territory. 



4. Large-scale experiments should be under- j 

 ! taken to determine the feasibility of controlling j 

 ! the pine blister disease, and the least expensive j 

 j means of accomplishing this result most ! 

 | effectively. 



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The distance that the 

 "pine" spores may be blown 

 is unknown. The greatest 

 distance definitely known is 

 about 400 feet. The spores 

 produced on currants or 

 gooseberries are known to 

 blow one-half mile or over and 

 infect other currants. How 

 much farther they may go 

 no one knows. From cur- 

 rants infection has been 

 traced to pines by McCubbin, 

 of Canada, up to an ex- 

 treme distance of 100 yards. 



This gives us an immense 

 advantage when we attempt 

 to eradicate it from a given 

 locality, the mere separation 

 of the two hosts being suffi- 

 cient to stop further spread of 

 the disease. But this in- 

 volves the sacrifice of one 

 host in any given locality. In 

 some places the removal of all 

 white pines involves less loss 

 than does the removal of 

 all currants and gooseberries; 

 while in other places the 

 reverseistrue. In either pro- 

 cedure a few hoggish people 



