Wheat companion plants reduced aphid and flea beetle infestations in Brassica vegetable crops in a multiple-year field study in central Germany

Alternative pest control systems such as companion plants are increasingly gaining importance owing to a reduced range of available synthetic insecticides and more rigorous regulation of their use in the EU. Therefore, we evaluated the effects of Brassica vegetables grown with wheat companion plants on relevant pests, respective natural enemies and harvest weight. Six trials were conducted in white cabbage and three in Chinese cabbage between 2017 and 2021. We identified an overall aphid-regulating effect for Brevicoryne brassicae (L.) and Myzus persicae (Sulz.) (Hemiptera: Aphididae) in white cabbage and a regulating effect on flea beetles (Phyllotreta spp.) (Coleoptera: Chrysomelidae) in both tested Brassica crops. Feeding by cabbage root fly Delia radicum L. (Diptera: Anthomyiidae) larvae on white cabbage roots was not consistently affected. Natural enemies including ladybirds (Coleoptera: Coccinellidae), hoverfly larvae (Diptera: Syrphidae), spiders (Araneida), ground beetles (Coleoptera: Carabidae), and rove beetles (Coleoptera: Staphylinidae) were assessed on crop plants or in pitfall traps. The activity density of rove beetles was increased by wheat companions in both Brassica crops, while that of ground beetles was reduced in white cabbage. The weight of harvested white cabbage was reduced by wheat companions, varying between a mean reduction of 7.67% and 40.08% in different experiments. In conclusion, wheat companion plants can be an additional tool for regulating pests in Brassica vegetables. However, competition effects on crop yield and the compatibility with other cultivation aspects, e.g. crop rotation, have to be considered.