BackgroundPlant diversification, especially sowing crops with the addition of companion plants has been demonstrated as a suitable practice to increase insect pest control in multiple cropping systems. Since the ban on use of neonicotinoid seed treatments in oilseed rape (OSR), the harvested area has reduced significantly in Europe, mainly because of the damage caused by cabbage stem flea beetle (Psylliodes chrysocephala). Several companion plants such as legumes and other species of Brassicaceae have been reported as potential companions for OSR but robust evaluation of their efficiency to reduce cabbage stem flea beetle damage in replicated trials is lacking.ResultsFour field trials were conducted in the UK and Germany to test the effect of different companion plants, or the addition of straw mulch, on cabbage stem flea beetle adult feeding and larval infestation in OSR. We found significant differences in the level of feeding damage between treatments in all experiments. Combinations of OSR with cereal companion plants or with straw mulch showed the strongest reduction in adult feeding damage. A protective effect of legumes was also observed in one trial. Differences in larval infestation were also observed between treatments but were not consistent and might be more related to the OSR plant biomass than to treatments.ConclusionThis study shows that companion planting can protect OSR crops from cabbage stem flea beetle adult feeding damage. We show for the first time that not only legumes, but also cereals and the application of straw mulch can have a strong protective effect on the crop. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The Colorado potato beetle (CPB) is an exceptionally challenging potato pest. Some regenerative farmers have reported that the use of transferred green manure mulch can considerably reduce CBP damage. Previous studies confirm this observation, but mainly with straw mulch, which is rarely used in Central Europe, and not embedded in the new regenerative cropping approach. For this, six trials conducted between 2014 and 2019 were evaluated, comparing CPB infestation in potatoes with and without transferred mulch as well as under a plough as a minimum till regime. In three out of six experiments, compost application was an additional factor. (I) Over all experiments, mulch significantly reduced initial infestation (−24%), egg masses (−27%) and larvae (−75%). Compost and reduced tillage added to these effects; (II) Mulch mainly resulted in delayed CPB infestation; (III) In a particularly warm season, when a second generation of CPB managed to emerge, regulatory effects of the mulch were not sufficient; (IV) Combination of transferred nutrient rich green manure mulch with reduced tillage, compost and other regenerative or agro-ecological techniques is recommended to achieve maximum regulation of CPB.