Cabbage – Faba bean strip cropping: biological pest control, crop compatibility and yield

Summary

Strip cropping has the potential to augment ecosystem services that reduce pest pressure and increase crop yield. The objective of this study was to assess how strip cropping white cabbage (Brassica oleracea) and faba bean (Vicia faba) affects the incidence of pests, mainly diamondback moths (Plutella xylostella) and flea beetles (Phyllotreta spp.), the abundance of natural enemies including spiders (Araneae) and parasitic wasps, and ultimately crop yields. The experimental setup consisted of three 270m2 24 plots representing 25 monocrops of faba bean and cabbage, and a plot of alternating strips of the two. The setup was established in 2018 and 2019 on an experimental field. Incidence of P. xylostella was determined through trapping of adults on yellow sticky traps; Phyllotreta spp. and Araneae abundance were determined by pitfall trapping; and parasitism rate of P. xylostella was determined through a larval exposure experiment. Crop yields were determined at harvest, and foliar damage to cabbage leaves was also assessed. The results showed that strip cropping reduced the incidence of P. xylostella in 2018 when their overall abundance was moderate, but not in 2019 when their abundance was high. Strip cropping did not affect the incidence of Phyllotreta spp. or natural enemies. Foliar damage to cabbage was significantly higher in the strip crop plot, but in 2018 the yield was also significantly higher. Faba bean yield was lower in the strip crop plot in both years. Our results indicate potential for cabbage faba bean strip cropping to reduce incidence of P. xylostella and increase cabbage yield when overall pest pressure is moderate.