Effect of Reforestation Methods on Pine Weevil (Hylobius abietis) Damage and Seedling Survival
Abstract:Damage to Norway spruce (Picea abies (L.) Karst.) seedlings by the large pine weevil, Hylobius abietis (L.) (Coleoptera: Curculionidae), was monitored in relation to clear-cutting age and silvicultural treatments in southern Sweden. New clear-cuttings were established on four sites during five consecutive years, and seedlings were planted on them from 1989 through 1993. In total, 31 774 seedlings were planted on 20 clear-cuttings. The measures evaluated were seedling insecticide treatment, application of herbicide to ground vegetation, scarification (mound) and planting late in the season. In addition, the effects of slash removal and seedling type were studied.
The pine weevil was, by far, the dominant damaging agent. Planting without insecticide or soil treatment on fresh, one- or two-year-old clear-cuttings resulted in a mean level of weevil-caused mortality exceeding 60%. The results indicate that the risk of serious damage by pine weevils remains high until the clear-cuttings reach four or five years of age. Killing the vegetation with herbicide had no effect on pine weevil damage. Slash removal decreased damage on older clear-cuttings, but the effect was small. Scarification (mounding) strongly reduced damage. On fresh clear-cuttings the mean mortality caused by pine weevils in mounded plots was 13%, whereas it was 77% in the controls. The mounding effect varied between sites and clear-cuttings of different ages. Late planting (10 June instead of 1 May) reduced damage on two- and three-year-old clear-cuttings. Three-year-old, bare-rooted seedlings were not damaged as seriously as two-year-old, containerized ones, but the effect was probably due to the larger size of the bare-rooted seedlings. Non-lethal injury resulted in reduced seedling growth. Damage by pine weevils varied between years and within growing seasons. However, on fresh, one- and two-year-old clear-cuttings, damage was severe enough to cause high mortality during all studied years.