Protejarea fructificaţiei laricelui european (Larix decidua Mill.) împotriva insectelor conurilor şi seminţelor prin injectarea dimetoatului în tulpinile arborilor [Stem injection of dimethoate for control of European larch (Larix decidua Mill.) cone and seed insects]

The systemic insecticide dimethoate (0.20 g active ingredient and 0.30 g active ingredient per cm dbh, in 1990 and 1991 respectively) was injected into European larch trees to determine its effectiveness in controlling cone and seed insects. Percentages of cones and seeds damaged by insects and germination of seeds were assessed. The treatments were more effective against the larvae of Strobilomyia spp. and Retinia perangustana, and less effective against those of Resseliella skuhravyorum. The percentages of seeds damaged by the above mentioned pests were diminished by 47-94 %, 37-83 % and 30-39 % respectively. In addition, the treatments increased the percentage of filled seeds, and consequently the overall effectiveness was of 55.2 % in 1990, and 86.6 % in 1991. They did not reduce the percentage of germinated seeds. The best results have been obtained when the treatment was conducted earlier, that means at the beginning of R. skuhravyorum eggs hatching. Therefore, we reccomend the treatment to be done just prior to female bud flush