Cdnadidn Forcslrij Jouiridl, March, lUl 



1023 





The Nurseries and the White Pine Menace \ 



Concluding the Article on White Pine Blister Disease appearing in (he 

 Februarij Issue. — Bij II. T. (}ussow, Dominion Botanist. 



Until quite recently it was held 

 that the stage of the rust on the cur- 

 rant, did not winter over on the cur- 

 rant, but must start anew every yeaar 

 from some nearby infected pine. So 

 it was thought unnecessary to re- 

 strict the nursery trade in cultivated 

 bushes, since they would be shipped 

 either before or after they had been 

 infected. And it was said that, 

 though badly infected in one year, 

 the same currants planted elsewhere 

 showed no infection in the succeed- 

 ing year. 



This point is still open to cjuestion. 

 But it is noteworthy that the United 

 States, at any rate, mean to take no 

 risks, as is shewn by an amendment 

 to the Notice of Quarantine No. 7, 

 dealing with the White Pine Blister 

 Rust. The original quarantine deals 

 with the prohibition of importation 

 of all five-leaved pines, and is dated 

 21st May, 1913. The amendment 

 (No. 1) is dated 29th February, 1916, 

 and reads "... it is necessary, 

 in order to prevent the further intro- 

 duction into the United States of 

 the white pine blister rust, to forbid 

 the importation into the United 

 States from the Dominion of Canada 

 and Newfoundland of . . . all spe- 

 cies and varieties of the general Ribes 

 and Grossularia known to be carriers 

 of this dangerous disease." 



To come back to this question of 

 overwintering. If one notes, on the 

 one hand, the ever-recurrent infec- 

 tions, year after year, within the 

 danger area, and often with no pine 

 anywhere near, and, on the other 

 hand, confronts the apparent intro- 

 duction of the disease into regions, 

 where pine rust was unknown and 

 currant rust absent, — certainly these 

 factors do not by any means support 

 the general belief in the non-ability 

 of the currant rust to overwinter. 



- Up to 1916 there was no currant 

 rust at the Experimental Farm in 

 Ottawa; close search had been made, 

 but did not reveal any signs. But 

 towards August of last year some 

 fifty black currant bushes were found 

 to iDe infected — seme young ones in 

 nursery rows, and some half dozen 

 old ones close by. On enquiry, it was 

 learned that there had been planted 

 in spring a small number of a certain 

 variety purchased from near Hamil- 

 ton, a district in w^hich the rust was 

 known to exist, although no data 

 are at present available as to whether 

 the nursery, when these particular 

 shrubs came, was infected by it. 



Another question of importance 

 yet to settle is whether the spores 

 of currant rust may be carried on 

 fruit and containers from infected 

 areas, and thus be conveyed to areas 

 formerly uninfected. 



N^ursery Quarantine 



If overwintering is definitely 

 proven, and if the disease is likely 

 to be conveyed by means of spores, 

 then the problem would appear cap- 

 able of solution by a quarantine on 

 nurseries within infected areas, both 

 against shrubs and against packages 

 of fruit. This is, however, economi- 

 cally impracticable. The alterna- 

 tive — and, mark, the only alterna- 

 tive under these circumstances — is 

 the complete and systematic destruc- 

 tion of all white and other five-leaved 

 pines at present growing in that par- 

 ticular danger area. Once these have 

 gone, re-infection of currants will not 

 occur, for physical conditions promise 

 to eventually wipe out currant rust, 

 that may result from wintering over; 

 since the virulence of the fungus is 

 greatly increased by a continuance 

 of its fife cycle on the pine. Observa- 

 tions made this season by my assist- 



