204 



HOWARD B. KRIEBEL 



Figure 3. An old stand of Virtus strobus on a recreation area 

 in Adams County, Wisconsin (photo courtesy of the Wisconsin 

 State Department of Agriculture) . 



The principal destructive agent of P. strobus, other than blister 

 rust, is the white pine weevil, Pissodes strobi (Peck). This insect kills 

 the terminal shoot and deforms most trees in the Northeast (Fig. 4) . It 

 also does much damage in the Lake States and Canada but is not a serious 

 pext in the southern Appalachians (Kulman and Harmann, 1965) and the 

 Midwest. Extensive planting of white pine in some areas where there is 

 presently no problem could conceivably cause an increase in the weevil 

 population and could result in widespread damage. The serious economic 

 loss in northeastern white pine stands resulting from weevil attack has 

 stimulated efforts to select and breed for resistance to weevil injury. 

 Early results indicate that weevil-resistant white pines may be developed 

 either through selection in P. strobus (Stroh and Gerhold, 1965) or by 

 interspecific hybridization (Wright and Gabriel, 1959; Heimburger, 1963). 



Chiorotic dwarf is a disease common in young plantations throughout 



the midwestern and eastern United States. The cause is now known to 



be air pollution; the response is apparently genetically controlled 

 (Dochinger and Seliskar, 1970) . 



In pure stands, eastern white pine nearly always differentiates into 

 a wide range of crown and diameter classes due to inherent variation in 

 vigor (Deen, 1933). Because the species has a tendency to retain the 

 lower branches after they die, pruning is necessary to obtain knot-free 

 lumber (Fig. 1). Apical dominance is pronounced and unweeviled trees 



