972 



Canadian Forestry Journal, February, 1917 



in a small grove ol pines. Notwith- 

 standing careful search by expert 

 plant pathologists, it was found im- 

 possible to cut out all infections, and 

 new ones were found regularly after 

 each successive visit. In this case 

 the best proceeding would have been 

 the destruction of all the pines, whe- 

 ther affected or not, in this small 

 wood, when this centre of infection 

 would have been wiped out forever. 

 We have learned that the spores 

 from the pine infect wild and cul- 

 tivated currants and gooseberries. 

 These spores are mainly windborne, 

 and speculation is rife as to how far 

 these spores can be carried. This 

 is one of the most difficult problems 

 to solve, and has never been solved— 

 other than hypothetically. Insects, 

 no doubt, also play a part in the dis- 

 persal of spores. For our purposes 

 the distance spores may be carried 

 from an infected pine is of some im- 

 portance. For, without currants, or 

 similar hosts, within the radius cov- 

 ered by spore dispersal, the blister 

 rust would eventually die out with 

 the pines originally attacked, and 

 no new pine infection could occur. 



Carried Two Miles. 



Observations made in the Fonthill 

 case of Pine Rust alieady referred 

 to indicate that the matter of spore 

 dispersal, or rather the distance spores 

 may originally be carried, is of less 

 importance than the fact of the 

 spreading of the disease from currant 

 to currant throughout the summer. 

 As early as June 3rd the first infec- 

 tions on currants near, the Fonthill 

 pines were observed. On July 6th 

 the rust on the currants had been 

 spread to, approximately, two miles 

 from the original source. In this 

 connection it may be noted that each' 

 infected currant or gooseberry bush 

 serves as a source for the dispersal 

 of spores. And the most widespread 

 dispersal is. without doubt, due to 

 the currants. This spreading of the 

 disease in the stage of Currant Rust 

 takes place throughout the summer, 

 from mid-June to October: whereas, 

 from the pine, dispersal only tzakes 

 place for about eight weeks or pos- 

 sibly less, during April, May and up 

 to mid-June. 



For the practical purpose of locat- 

 ing the spread of the disease we look 

 upon the Ribes bushes as welcome 

 indicators. Thus, during the whole 

 summer, inspection of all wild and 

 cultivated Ribes may clearly indicate 

 the limitations of the present danger 

 zone. 



Pines or Currants'^ 



We notice, then, that the currants 

 are largely instrumental in the dis- 

 semination of the disease within an 

 infected locality. The Niagara Pen- 

 insula is singularly subjected to the 

 spread of this rust. On the one hand 

 there exist uncountable numbers of 

 wild Ribes, — on the other hand is the 

 importance of the district as a fruit- 

 growing centre with many hundreds 

 of large and small plantations of 

 currants, — particularly of that most 

 dangerous carrier, the black currant. 

 Hence, in this area, either the one 

 or the other host plant should be 

 exterminated. Here it would cer- 

 tainly seem that all pine trees should 

 be sacrificed. 



This sounds more serious than it 

 really is. Of course, on looking over 

 the district there may be found num- 

 erous pines, but few are of economic 

 value; even were it so, well, they are 

 worth good money now, and the 

 losses would be inconsiderable. Yet 

 there are many trees of sentimental 

 value. These latter will prove a 

 great obstacle to the control of this 

 disease. But the exemption of these 

 trees from destruction would add 

 thousands of dollars every year to 

 the cost of fighting the disease; since 

 experienced inspectors would have 

 to inspect every single remaining tree 

 most carefully, and cut out all in- 

 fected parts. And eventually the 

 inspector is sure to be blamed for the 

 destruction of the trees, if he be, as 

 most assuredly he must be, authorized 

 to cut out infections. Yet to leave 

 these trees alone, even if only soli- 

 tary or few, would, as experience has 

 shown, merely result in perpetuating 

 the disease in a region so productive 

 of secondary hosts. 



{To he concluded in March issue of the 

 Journal.) 



