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Damages to seedlings by the pine weevil, Hylobius abietis (L.), are one of the major problems when regenerating conifers in Sweden. Insecticide treatment of seedlings has so far been the most common way to protect seedlings from damages. However, the use of protections based on various physical feeding barriers is increasing. This development is in part due to that all major Swedish forest companies are FSC certified and certified companies are obliged to phase out their use of insecticides. Merit Forest (imidacloprid) was up to recently the only approved insecticide that certified companies could get an exemption to use.

This report presents results from an experiment with two trials. One trial includes 12 different treatments of containerized seedlings of Norway spruce (Picea abies [L.] Karst.) and the other trial includes four treatments; three of them on bare-rooted seedlings and one on TePlus seedlings of Norway spruce. The duration of the experiment was three years. The trials were conducted at the same three locations, all in unscarified soil.

For the containerized seedlings, the insecticide Hylobi Forest applied twice on the seedling, once before planting and once the following spring in the field, had the best effect against pine weevil damages. Highest survival had all treatments with insecticides applied twice to the seedlings, the coating Conniflex, and the single application of the insecticide Forester. Seedlings coated with Borrkax and Bugstop, the shield MultiPro and a single application with Merit Forest had equally high survival. Their survivals were significantly higher than the survival of the untreated control seedlings but significantly lower than seedlings applied twice with Merit Forest.

In the trial with bare-root seedlings Merit Forest, applied twice, gave the highest survival and best effect against pine weevil damages. Also Bugstop on the TePlus seedlings were rather effective against pine weevil damages, but both Merit Forest and Bugstop treated seedlings had rather few seedlings killed by pine weevils.

This study is part of the Swedish Hylobius Research Program at the Swedish University of Agricultural Sciences, that is financed by the forestry sector through their contribution of 0,03 SEK per insecticide treated seedling.