1. Companion planting with nonhosts may offer a non-insecticidal means of controlling pests, although the results of studies can be variable and species-dependent. 2. The effect of companion planting on two pests of Brassica crops, Plutella xylostella (L.) and Brevicoryne brassicae (L.), was examined using Brussels sprout as the host plant and imitation cereal plants made from green plastic as the nonhost. For P. xylostella, the effect of nonhost density was also investigated. 3. Oviposition (P. xylostella) and abundance (B. brassicae) were lower on Brussels sprout plants presented on a background of high-density imitation cereal plants (reductions of 59% and 85%, respectively). 4. The results are discussed in the context of host location by pest insects and the selection of nonhost companion plants for pest management. 5. It is concluded that nonhost plants interfere with pest host selection through disruption to visual host location processes.