NORTHERN 



IDAHO 



FOREST 



RESOURCES 



A N D 



I N D U S T R I E .> 



The Disease and Insect Problem 



FIRE is only the largest of the three chief factors of 

 forest destruction in northern Idaho. Two com- 

 panion scourges, disease and insects, must be 

 battled it man is to obtain the maximum of benefit from 

 the forest. 



White Pine Blister Rust 



The white pine blister rust was accidentally introduced 

 into British Columbia from EAirope in 1910. From Canada 

 it worked southward, reaching northern Idaho in 1923. 

 Since then, infection has spread throughout the western 

 white pine belt ot the State. 



The subtlest weapon of the white pine blister rust is its 

 unheralded approach. It casts no billow ot gray smoke 

 into the summer skv. It makes no open threat to lives and 

 property. The very indirectness ot its mode ot attack has 

 impeded the mobilization ot public opinion tor its control. 

 Yet this disease is so deadly, once it has taken hold, that 

 it is in some respects a greater threat to the western white 

 pine industry ot tomorrow than is fire (tig. 36). 



Blister rust is a parasitic tungus disease affecting the 

 five-needle pines, ot which western white pine is one. It 



spreads to pine from currant and gooseberry plants, enters 

 the tree through the needles, and grows in the inner bark. 

 Once in the bark, the canker spreads in two directions, 

 around the branch and toward the tree trunk. If the 

 branch lacks vigor or the point ot infection is far from the 

 bole, the branch may die before the disease reaches the 

 trunk and the spread will be halted. In very young trees 

 with short lower branches, infection soon results in death. 

 The older the tree, the farther the needles are from the 

 lower part of the trunk and the fewer there are near the 

 ground where infecting spores are most abundant; also the 

 more likely the tree is to shade out the plants from which 

 the infection comes. Consequently, the older trees are 

 less likely to be attacked; points of infection are fewer and 

 less dangerous, and the trees are better able to withstand 

 killing of branches and loss of needles. Even without 

 control work, it seems probable that some of the vounger 

 western white pine stands would reach maturitv where 

 sources ot infection are locally light, and that a considerable 

 proportion ot the stands above perhaps 60 or 80 years would 

 escape serious damage in the period before logging. 



Pathologists say of blister rust that "Without control 

 white pine cannot be perpetuated in 

 this region" '° — commercially speaking, 

 ot course. Because no extensive losses 

 have yet resulted, this appears to be a 

 strong statement. But these patholo- 

 gists have been able to forecast the 

 course ot the disease up to the present 

 time, and it therefore apjH'ars that this 

 warning is worth heeding. 



Control Efforts 



The control ot blister rust is pxissibic 

 and practicable because o\ the alternate 

 host required tor its developnient. 

 White pine blister rust is never trans- 

 mitted from pine to pine, but always 

 from pine to species ot riK's (wild cur- 

 rant and giHiscbcrrN plants) on which 



[•"iciiRE ib.^Young white pi'ie jianjj, iuih aj this, tire ihiealeiieJ with elimination/tom the iommercieU- 

 forest cletssifiealion unless ti/iite pine i/hter nut ii kept in cheek. 



•''Smwson, H. F„ »iistkr m$T coxtroi. \h 

 THF ISl *ND EMPIHE. Jour. FoTCStrV .^T; S4*-<5i 

 19.W. 



48797f.° U- -C 



37 



