Effects of field vegetation control on pine weevil (<i>Hylobius abietis</i>) damage to newly planted Norway spruce seedlings

Abstract

We investigated interactions between field vegetation and seedling damage caused by a major insect pest, the pine weevil Hylobius abietis (L.), in an experiment established on a clear-cut area in southern Sweden. Scarification was performed on three occasions (May and August 1998, May 1999) and Norway spruce seedlings were planted on three occasions (August 1998, May and August 1999). To keep the mineral soil open, field vegetation and mosses were removed using herbicides. In total, seven different soil treatments including planting in untreated soil were included. Damage to seedlings by the pine weevil and vegetation around each seedling was monitored 1-2 months after each planting. Fresh scarification significantly reduced pine weevil damage and increased seedling survival. However, the open mineral soil was gradually colonised by hairy grass (Deschampsia flexuosa) and the damage-suppressing effect of scarification was reduced with time. Herbicide treatment removed field vegetation and reduced pine weevil damage significantly, especially when there was a long period between scarification and planting. We conclude that vegetation in-growth was the main factor decreasing the effect of scarification on weevil damage.