The Influence of Synthetic Insecticides on the Dynamics of Cabbage Stem Weevil (Ceutorhynchus pallidactylus Marsh.) and Cabbage Pod Weevil (Ceutorhynchus obstrictus Marsh.) in Winter Oilseed Rape

摘要

Oilseed rape is affected by a complex of different crucifer pests. Cruciferous stem weevils (Ceuthorhynchus spp.) are relatively new oilseed rape (Brassica napus L.) pests in Latvia. Although currently brassica pest control is performed according to the appearance of first specimens of Ceutorhynchus or other brassica pests, for a large number of insecticide treatments a positive biological efficiency is observed (however, within a large range – 8–98%). The current application of brassica pest control may be described as preventive, which is not permitted in the integrated pest management system. The present research estimates biological efficiency and application time of synthetic pyrethroid (PIR) and combined pyrethroid+neonicotonoid (PIR+NNI) to control winter oilseed rape pest species, as well as stimulates discussion about their use. Evaluation of the monitoring data of Ceutorhynchus spp. showed that C. typhae and C. sulcicollis emerge first, but damaging species C. pallidactylus – a week later. Consequently it is not only necessary to monitor the weevils but also to identify their species in order to decide on the control measures. The combined PIR+NNI insecticide proved to have the highest biological efficiency for cabbage stem weevil control. Both classes of synthetic insecticides revealed a considerable biological efficiency for weevil control. The research suggests that effectiveness of insecticide is affected by many factors: plant development stage during the spray, agroclimatic conditions, spray quality, field location and size, distribution of pests, and crop rotation.