Managing cabbage seedpod weevil in canola using a trap crop-A commercial field scale study in western Canada

Cabbage seedpod weevil is a relatively new pest of canola (oilseed rape) in the Prairie Ecozone of western Canada. In some years, in southern Alberta, farmers have had to resort to costly aerial insecticide applications to protect their canola crops. In this study, we evaluated perimeter trap cropping as a strategy to manage weevils in large commercial fields of canola. A total of 11 experimental fields (with perimeter trap crops) and nine conventional fields without trap crops were studied from 2000 to 2003. Field perimeters of Brassica rapa planted at the same time as the main crop of B. napus flowered ∼1 week earlier and effectively concentrated weevil populations that were sprayed with insecticide. The perimeter trap crop kept weevil populations below threshold levels in the main crops when fields were large and square (1600 m×1600 m). However, further research is required to develop management tools that augment the efficacy of trap crops in situations where fields are small or narrow (<400 m wide), especially when populations are several times the economic threshold. Pod damage was less than 12% in the main crops of experimental fields where only the trap crops were sprayed which was comparable to that of conventionally managed fields. The savings in chemical insecticides, labor and time, as well as possible integration with other IPM strategies such as biocontrol, make perimeter trap cropping an important tool for cabbage seedpod weevil management.