The effect of tillage regime, row spacing, and seeding rate on feeding damage by flea beetles, Phyllotreta spp. (Coleoptera: Chrysomelidae), in canola in central Alberta, Canada

Abstract

Feeding damage by the flea beetles, Phyllotreta cruciferae (Goeze) and Phyllotreta striolata (Fabricius) (Coleoptera: Chrysomelidae), was assessed on Polish ( Brassica rapa L.) and Argentine ( Brassica napus L.) canola grown under conventional and zero tillage regimes, with three different row spacings (10, 20, and 30 cm) and three seeding rates (5.0, 7.5, and 10.0 kg ha -1 or 120, 180, and 240 plants m -2). The studies were conducted during three field seasons (1994, 1995, and 1996) at Vegreville in central Alberta, Canada. Flea beetle damage was determined when plants were in the seedling stage by estimating the percentages of cotyledon and true leaf area eaten by the insects. Plants of B. rapa were consistently damaged to a greater degree than were plants of B. napus. In all three years of study, significantly greater damage was caused to plants of both species of canola grown in a conventional tillage regime compared with a zero tillage regime. Treatment effects of row spacing and seeding rate on flea beetle damage were more variable. In 1994 and 1996, statistically significant reductions in plant damage occurred with an increase in seeding rate and row spacing for both species of canola; however, these differences were not significant for either canola species in 1995. Results of our study suggest that seed treatment with the insecticide lindane, used routinely in central Alberta to reduce herbivory by flea beetles, is probably not necessary in this region when canola is grown under a zero-till regimen. Regardless of tillage regime, our regression analyses determined that flea beetle damage can be reduced by increasing seeding rates and row spacings from those currently recommended for canola production, a practice that is also compatible with reducing crop damage from other important canola pests.