Results and Conclusions 



1 , Prevalence cf Root Diseases 



In the examination of beetle-attacked trees, only visible root infection 

 diagnosed as the work of Armillaria mellea was recorded because of inability 

 to determine other causes of infection when the work was begun. Because the 

 results of line-tree examinations had shown Armillaria mellea to be the main 

 cause of infection, the absence of data on other causes of root infection in 

 the beetle-attacked trees should not gravely impair the value of the data. 

 Data given in table 3 on incidence of infection by Armillaria mellea in trees 

 attacked by the mountain pine beetle show that of the trees examined in four 



Pable 3, — Incidence and degree of infection by Armillaria mellea 



in the roots of beetle-attacked western white pine trees. 



Year of 





Trees 



Unin- 



: Infected trees 

 : circumference 



, grouped by fraction of 

 of root collar killed 





beetle 

 attack 



: Drainage 



exam- 

 ined 



fected 

 trees 



: Under 



1/4 __ 



1/4 



2/4 



3/4 



4/4 



Total 







Number 



Percent 



•Percent Percent 



Percent 



Percent Percent 



Percent 



1938 



.Deception 



23 



61 



: 17 



9 







4 



9 



100 





Kelley 



11 



36 



: 37 



9 











18 



100 





Both 



drainages 



34 



53 



23 



9 







3 



12 



100 



1937 



Deception 



42 : 



31 



31 



7 



10 



7 



14 



100 





Kelley k 

 Yellow Dog 



16 : 







19 



31 



6 



31 



13 • 



100 





Both : 

 drainages 



58 



22 



27 



14 



9 



14 



14 



100 



Both : 

 years : 



All : 

 drainages : 



92 : 



34 



26 



12 



5 



10 



13 



100 



drainages, 47 percent of the trees attacked by beetles in 1938 were infected as 

 compared with 78 percent of the trees attacked in 1937. These figures cannot, 

 however, be unqualifiedly compared with the incidence figures for the trees 

 examined on arbitrarily located lines, because not all trees were in the same 

 drainages and because many of them had been dead for a year. Averaging all 

 drainages and both years, the incidence of infection for beetle-attacked trees 

 was approximately 7 percent greater than for the line trees. But for the 

 trees attacked by the beetle in 1938, which are roughly comparable with the 



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