Effect of flight activity of stem weevils (Ceutorhynchus napi, C. pallidactylus) and application time on insecticide efficacy and yield of winter oilseed rape

During 2010-2012, we monitored flight activity of male and female stem weevils (Ceutorhynchus napi, C. pallidactylus) using yellow water traps, the effectiveness of various application dates for the insecticide thiacloprid (72 g active ingredient/ha), and the influence on yield. The first occurrence of beetles in traps was recorded after soil temperature at 5 cm reached 8°C in all experimental years. In all years, males of C. pallidactylus dominated in the traps and the times of beetles' first occurrence. The most effective applications of thiacloprid at the stated rate were 14 days (2010), 6 days (2011), and 1 day (2012) after peak flight. Females with eggs appeared in bowls in 2010 and 2012 at first flight, while in 2011 no females were recorded. After the most effective applications, yields increased significantly in 2010 (+5% vs. the control) and in 2011 (+4%), and insignificantly in 2012 (+2%).