White pine weevil management

Fertilization and weevil attack

In British Columbia, forest fertilization is widely viewed by forest planners as a potentially viable strategy for sustaining the flow of harvested wood from interior forests. Preliminary research indicates that interior spruce plantations are potentially responsive to nutrient additions, however; large-scale fertilizer operations tend to cause increased incidence of white pine weevil (Pissodes strobi) damage.

Fast growing spruce, such as those produced by fertilization, are more susceptible to weevil attack than unfertilized spruce

Collaborative research, between the Canadian Forest Service and the BC Ministry of Forests, indicated that fast growing spruce, such as those produced by fertilization, are more susceptible to weevil attack than unfertilized spruce. In the interior, the use of fertilizers can cause weevil attack rates to increase up to 30% depending on fertilization intensity.

However, while incidence of weevil attack was greatest in trees from the most intense fertilization treatments, we found that on average height growth gains due to fertilizer treatments surpassed height losses due to weevil attack. Thus, the beneficial effects of fertilization on the height growth of young interior spruce plantations outweigh the negative effects associated with increased incidence of leader damage from the white pine weevil. To date however, weevil induced losses due to decreased lumber quality have not been quantified therefore losses due to weevil may be underestimated.

Weevil attack rates in trees from intense fertilization regimes were higher than attack rates in unfertilized trees.
Figure 1. Weevil attack rates in trees from intense fertilization regimes were higher than attack rates in unfertilized trees.

Long description

The trend towards increased weevil attack with increasing fertilization intensity is likely due to a number of fertilizer-induced changes in the host tree that influence aspects of the weevil’s biology. To date we have conducted studies that indicate that fertilization influences:

  1. Leader dimensions: Not only are weevils attracted to trees with long thick leaders, but enhanced leader length, diameter and bark thickness due to fertilization also increase the resources available for feeding and oviposition and positively affect the reproductive capacity of the weevil.
     
  2. Host defenses: Resistance to weevil attack has been correlated with bark resin canal density in both interior and Sitka spruce. Fertilization causes a weakening of the tree’s defenses by reducing the number of resin canals on a per area basis, present in the bark.
     
  3. Bark nutrient content: Fertilization causes an increase in nitrogen, potassium and phosphorus concentrations in the bark of interior spruce leaders. The increased nutrient availability may increase weevil fecundity and offspring survival rates, which may help to explain our observations of higher weevil attack rates in the more intense fertilization treatments.

When combined with genetically improved stock and the development of weevil resistant genotypes and improved pest management strategies, intensive fertilization may offer great potential for improving the productivity of second-growth spruce plantations in the interior of British Columbia.

Therefore we conclude that fertilization is a viable option for increasing productivity in interior spruce, particularly if other weevil control alternatives are implemented.

Additional references

vanAkker, L., R.I. Alfaro and R. Brockley. 2004. Effects of fertilization on resin canal defenses and incidence of Pissodes strobi attack in interior spruce. Can. J. For. Res. 34(4): 855-862

BC Forest Practices Code. 1996. Terminal Weevils Guidebook. Government of British Columbia.

Contacts

Dr. René I. Alfaro
Canadian Forest Service
Pacific Forestry Centre
506 West Burnside Rd.
Victoria, B.C. V8Z 1M5
(250) 363-0660
email: rene.alfaro@canada.ca

Robert Brockley
British Columbia Ministry of Forests
Kalamalka Research Station
3401 Reservoir Road
Vernon, B.C. V1B 2C7
(250) 260-4768
email: Rob.Brockley@gems7.gov.bc.ca

Acknowledgements

Research funding was provided by the Province of BC through the Forestry Innovation Investment Research Program.

Fertilization and weevil attack

Project status

  • On-going

Team members