Weeds? – Sown Wildflower Strips and Crop-Accompanying Flora Promote Beneficials in Cabbage Production

FiBL field trials demonstrate that sown wildflowers together with the spontaneous arable weed flora in cabbage fields can promote predatory beneficial insects and pollinators. This makes it possible to enhance the ecological value of production areas.

In organic agriculture, where chemically-synthesised pesticides are not used, beneficial insects are of key importance: these beneficials consume or parasitise pest insects and pollinate plants. To promote beneficial insects in cabbage production, the Research Institute of Organic Agriculture (FiBL) developed a special flower mixture. The aim is mainly  to promote parasitoid wasps, natural enemies of pest Lepidoptera that frequently occur in cabbage production.

Seed mixture assures eligibility for direct payments

The seed mixture containing cornflower, common vetch, buckwheat and field poppy to attract beneficials in cabbage crops has been approved as an ecological focus area (Biodiversitätsförderfläche, BFF) since 2015 and is thus eligible for direct payments under the Swiss Ordinance on Direct Payments in Agriculture. The approval of the seed mixture as a BFF measure was based on several laboratory and field trials in which the suitability of various plant species as food sources for parasitoid wasps had been tested.

In two field trials conducted on the Swiss Plateau in 2016 and 2018, FiBL tested whether the seed mixture “Nützlinge Kohlanbau” (beneficials for cabbage production) together with the spontaneously occurring arable weed flora in cabbage fields can also promote predatory insects (ground beetles, rove beetles and spiders) and pollinators (hoverflies and bees).

More predatory beneficials, more pollinators

In 2016, assessments using pitfall traps in the centre of eight cabbage fields and the associated wildflower strips sown on the margins showed that increased species richness of the arable weed flora promoted ground beetles, spiders and bees.  In addition, the number of individuals and species of hoverflies increased with higher density of spontaneous arable weed flora. In 2018, direct comparison between sown wildflower strips and the margins of six cabbage fields showed that the sown wildflower strips hosted a significantly higher bee abundance and diversity of bee species. In both 2016 and 2018, more than 90 species were recorded exclusively in the sown wildflower strips, about twice as many as in the cabbage fields. In addition, many species were more abundant (more individuals) in the sown wildflower strips than in the cabbage fields. In total, 41 endangered species were found in the sown wildflower strips and the cabbage plots, and 17 wild bee species were recorded that are of significance for the national “species and habitats” environmental objectives for the farming sector (Umweltziele Landwirtschaft, UZL).

Higher acceptance among practitioners

Some farmers fear that weeds will spread from sown wildflower strips into production areas. However, there is the added value of increased natural pest control and pollination. An increase in the ecological focus area payment for sown wildflower strips and the willingness of consumers to pay more for organic products may promote the establishment of sown wildflower strips on commercial farms. The cabbage produced as part of this study, and with the support of direct payments for ecological focus areas, has been sold as organic sauerkraut since 2018, with specific additional information on the packaging to raise consumers awareness of biodiversity directly in the supermarket.