Soil features affecting damage to conifer seedlings by the pine weevil Hylobius abietis

The influence of different soil features associated with type and soil cultivation on damage to Norway spruce seedlings caused by the pine weevil Hylobius abietis (L.) (Coleoptera, Curculionidae) was studied in a field experiment in southern Sweden. The amount of damage was lowest on pure mineral soil and highest on undisturbed humus. Cultivation of humus reduced damage, but had no significant effect on accumulated seedling mortality after 3 years compared with undisturbed humus. Seedlings planted in a humus/mineral soil mixture had higher mortality than seedlings in pure mineral soil, but lower than those in cultivated or undisturbed humus. Placing pieces of humus on top of the mineral soil increased seedling mortality, whereas similarly placed stones had no such effect. Differences in debarked area between soil treatments were only detected in the first season. In conclusion, the practical application of this work is that site preparation should provide planting positions with as much mineral soil as possible and the amount of organic matter on the soil surface should be minimized.