Systemic insecticide and gibberellin reduced cone damage and increased flowering in a spruce seed orchard

Insects feeding in conifer cones are difficult to control with nonsystemic insecticides. Newly developed systemic insecticides that can be injected into tree trunks may be a possible way of reducing both insect damage and negative side-effects to the surrounding environment, compared with conventional spraying. Several insecticides that could be injected into tree stems were tested on Picea abies (L.) Karst. In one experiment, insecticides (bifenthrin, deltamethrin, abamectin, and imidacloprid) were injected during flowering; in a second experiment two of these insecticides (abamectin and imidacloprid) were injected 1 yr before the expected flowering. In the second experiment insecticide treatment was also combined with treatments with the flower stimulating hormone, gibberellin (GA(4/7)). The only insecticide that reduced damage was abamectin, both after injection during flowering and after injection 1 yr before the expected flowering. Injections with GA(4/7) increased flowering and were as efficient as the conventional application method of drilling but abamectin was not effective in combination with the drilling method. There was no negative effect of the insecticide injections on seed quality. The injections were ineffective against the seed chalcid Megastigmus strobilobius (Ratzeburg), which was found to have an unexpected, negative effect on seed quality. Our results suggest that it may be possible to reduce damage from certain insect species, and to increase flowering by injecting abamectin and GA(4/7) in the year before a cone crop.