Yellow rocket, Barbarea vulgaris (R. Br.), is considered an invasive weed and occurs in temperate regions worldwide. Larvae of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), do not survive on yellow rocket despite being highly preferred over cabbage for oviposition. The possibility of reducing P. xylostella infestations in cabbage by using yellow rocket as a dead-end trap crop was tested in 2003 and 2004. Preliminary experiments in screen-houses indicated that the percentage of eggs laid on cabbage decreased as the percentage of trap crop increased. In 2003, a trap crop representing 28% of the plants in the field significantly reduced numbers of P. xylostella larvae on cabbage compared with a solid cabbage planting. Numbers of P. xylostella larvae per cabbage plant in the trap crop treatment averaged 8.2 times lower than numbers in the solid planting treatment. In 2004, a field experiment was conducted to compare four treatments (0, 5, 10, and 20% of trap crop plants) in order to identify the smallest percentage of trap crop that could provide an effective reduction of P. xylostella. To date, our research shows that yellow rocket may be a good candidate trap crop for P. xylostella.