View or print this publication - Northern Research Station - USDA ...

Table 1.--Average weevil attack on the top and bottom 25% of families at three test sites. Families were ranked by average
heights at various ages and at 15-yr dbh (diameter at breast height).
Test age
Quesnel test Red Rock test Aleza Lake test
Top Bot. Diff. Top Bot. Diff. Top Bot. Diff.
Initial ht. 6.6 10.7 4.1 31.0 42.9 11.9 56.6 68.3 11.7
3-year ht. 7.1 11.9 4.8 30.6 44.4 13.8 55.9 69.4 13.5
6-year ht. 6.6 12.1 5.5 28.8 45.1 16.3 53.6 71.3 17.7
10-year ht. 5.9 11.9 6.0 26.4 45.0 18.6 52.7 70.8 18.1
15-year ht. 5.2 13.3 8.1 23.8 49.0 25.2 50.6 73.3 22.7
DBH 6.3 11.7 5.4 28.3 44.1 15.8 55.6 70.1 14.5
Moderate to heavy weevil infestation occurred on two of these plantations (Little Benson Lake - 17%, Clearwater -
33%). As was the case with the earlier studies, the weevils again favored certain families and avoided others. Some individuals
were attacked up to five times over the years, while more than 1,700 of the 2,700 intensively studied trees at
Clearwater have never been attacked. There was high correlation between mean family attacks at the two sites (Fig. 5, r
=0.66).
A
70 A
60 A
50 AA _AA •
-_ O • AAI•
AA • •
23o _ • I i. ••_
_ 20 _, A• • • •
r = 0.66
10 • AA
0 10 20 30 40 50 60
Mean family attack at Little Benson(%)
Figure 5.--Comparison of attack percentages at Little Benson and Clearwater.
Once again the more vigorous, faster growing families were less susceptible to weevil attacks. Based on the overall
ranking at all sites, the top 25% of families suffered substantially less damage than the bottom 25% (Table 2).
Additional data collected on the Clearwater site in cooperation with Dr. Ren6 Alfaro relate to number of attacks per
tree, recovery of attacked trees, and quality traits following recovery. These data are presently being evaluated and the
results will be published elsewhere.
A
153