Cover crop mulch and strip-tillage influence biological control in cabbage (Brassica oleracea)

In strip-tilled fields, planting rows are tilled allowing cover crop mulch to remain between rows. Manipulating the species and height of this cover crop mulch in cabbage fields may impact abundance, predation, and parasitism of a major cabbage pest, the imported cabbageworm (Pieris rapae). We hypothesized that 1) management practices changing vertical height of mulch and 2) cover crop species with different physical structures influence predation and parasitism rates on adjacent cabbage plants. To examine these hypotheses, an experimental cabbage field was established in Michigan in fall 2011. Treatments included hairy vetch and cereal rye cover crops that were either crimped or left standing, as well as a bare soil control.  Plots were arranged in a completely randomized design with 4 replicates.  Abundance of arthropod species was recorded weekly with visual observations, yellow sticky traps, and pit-fall traps. Parasitism and predation rates were determined using sentinel prey cages and molecular gut content analysis. Our results suggest that the abundance of a major cabbage pests and biological control agents are impacted by both cover crop height and species in cabbage. Further studies are needed to determine the mechanisms responsible for arthropod responses to these management practices, including visual and chemical signaling.