White pine weevil (Pissodes strobi (Peck)) damage was surveyed at three interior spruce (Picea glauca x engelmannii) fertilization research installations to document the effects of different fertilizer regimes and frequencies on weevil attack incidence. Weevil attack rates increased with fertilization intensity at a site with well-established and evenly distributed weevil populations. From 24% (unfertilized) to 54% (repeatedly fertilized) of trees were attacked at least once over the 6-year study period. The longer, thicker leaders of fertilized trees likely increased the resources available for weevil feeding and oviposition. A dilution of the leader's resin canal defence system may have also contributed to higher levels of weevil attack in repeatedly fertilized trees. However, despite the more frequent weevil damage to fertilized trees, the height losses caused by weevil attack were less than the height gains due to fertilization. The other two sites had smaller, or less evenly distributed, weevil populations, reflected in much lower weevil attack rates and fertilizer-stimulated attack impacts. Results indicate that the beneficial effects of fertilization on the growth of young interior spruce plantations likely outweigh the negative effects associated with increased incidence and severity of leader damage from the white pine weevil.
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Updated April 18, 2007