Western gall rust and insect leader damage in relation to tree size in young lodgepole pine in Alberta

In a sample of 121 young lodgepole pine (Pinuscontorta Dougl. var. latifolia Engelm.) stands in naturally regenerated cut blocks near Hinton, Alta., strong positive correlations were observed in the incidence of gall rust (Endocronartiumharknessii (J. P. Moore) Y. Hiratsuka) and leader damage from terminal weevil (Pissodesterminalis Hopp.) and from pitch twig moth (Petrova spp.) with tree size in both thinned and unthinned stands. Although tests on a selected number of the largest trees from each plot showed no significant differences in incidence of the two pest categories between thinned and unthinned stands, thinning that retains the large trees may result in an increase in relative incidence of these pests unless special effort is made to cut damaged trees and retain undamaged ones.