666 



A^IERICAN FORESTRY 



can entirely exterminate, as with the chestnut, or at least species, or the foreign species which have been introduced 



so injure as to destroy much of its commercial value, into the eastern United States, If the filamentous blister 



The virulence of such parasites cannot be foretold by the rust {Pcndcrmhim filamentosum) of the western hard 



best informed plant pathologist in the world, because the pines and the very destructive leafless mistletoe {Razoii- 

 effect of a new climate or of new hosts varies in each case, 



■Movement of P.\i«.\sites 



The problem of new parasites is by no means limited 

 to importation from over sea. Great harm can result 

 from the mo\'ement of a parasite from one part of the 

 country to another. The history of crop pests here also 

 contains valuable object lessons for the tree planter. The 

 ai)ple and pear furnish the best know examples. In the 

 early days, fire blight, scab, codlin moth, and apple mildew 

 were not present in the Northwest, The divides and 

 deserts of the Rocky Mountain region presented a bar- 

 rier which might easily have kept these diseases out of the 

 Pacific Coast region for generations. Indiscriminate and 



By courtesy of Cornell AgricuUurnl Experimettt Station. 



SCAB DISEASE OF APPLES 



This disease is prevalent throughout North America and causes an estimated 

 annual loss of S30.000.000 in this country alone, 



unregulated shipment of nursery stock from the East 

 to the West saddled the Pacific Coast with all the worst 

 pests in a short time, and many of them became even more 

 injurious in the western climate and conditions than in 

 the eastern. This took place before the present efficient 

 inspection service of California was fully developed. 



From the pathological standpoint the forests of the 

 United States may be considered as comprising three 

 reasonably distinct regions ; the East, the Rocky 

 Mountain, and the Pacific Coast, Each contains some 

 trees and parasites not present in any of the others. 

 Both of the western regions contain parasites which have 

 never had a chance to attack the eastern American tree 



Cotirtesy of Professor R. E. Smith. 



PEAR BLIGHT ON PACIFIC COAST 



What the pear blight did on the Pacific Coast, after the westerners allowed it to 

 be brought to them from the East. The orchard in which this photograph was 

 taken was completely ruined by the parasite. 



mofskya spp.) which attack the western pines ever are 

 introduced into the eastern region no one can guess how 

 much damage they may cause. Recent inoculation 

 experiments by Dr, G, G, Hedgcock have shown that one 

 of the most harmful of the leafless mistletoes of the West 

 is entirely able to attack at least four of the species of pine 

 grown in the East, In addition to these well-known para- 

 sites there are numerous less important or little known 

 western pests which, if accidentally introduced to the 

 East, might easily become verv destructive. 



On the other hand, some of the relatively isolated 

 Pacific Coast tree species, growing in a climate especially 

 favorable for fungus development, are likely to prove 

 very susceptible to the parasites of related eastern species. 

 Even such cosmopolitan species as lodgepole pine and 

 western yellow pine have already shown themselves 

 remarkably susceptible to the northeastern pitch pine blis- 

 ter rust (Cronartiuiii com ptoiiicc). Nursery stock of 

 these species, raised in a Lake .State's nurserv where 

 this rust is native, was much more seriouslv affected 

 b}" it than are any of the eastern pines, being prac- 

 tically exterminated. 



The white pine blister rust, which is very dangerously 

 near to becoming permanently established in the East, 



