Effects of fertilization on resin canal defences and incidence of Pissodes strobi attack in interior spruce

The effects of six fertilization treatments on tree height and incidence of attack by the white pine weevil, Pissodes strobi (Peck), on interior spruce (a hybrid, Picea glauca (Moench) Voss × Picea engelmannii Parry ex Engelm.) were explored in a field study. In a corresponding laboratory study, changes in constitutive and traumatic resin canal defences in response to fertilization were measured. Incidence of weevil attack increased with fertilization intensity. This trend was explained by increased resources available for weevil feeding (adults and larvae) as a result of increased leader size and bark thickness, as well as by an observed weakening in the treeʹs constitutive resin canal defences. The ability of interior spruce to produce a traumatic resin response was not influenced by fertilization. Although incidence of weevil attack was greatest in trees from the most intense fertilization treatments, height losses due to weevil attack were not as great as height gains due to fertilization treatment. Therefore, we concluded that fertilization is a feasible option for increasing productivity of interior spruce plantations, particularly if other weevil control alternatives are implemented.