The interplay of intercropping, wildflower strips and weeds in conservation biological control and productivity

Diversifying agroecosystems is instrumental to reduce pesticide use in agriculture. While different diversification practices have the potential to reduce pests, their integration at the agroecosystem level and the evaluation of their multifunctional effects remain limited. Through a two-year field experiment conducted in Germany, we tested whether associating intercropping (faba bean-wheat, followed by breadseed poppy-barley) with pluriannual wildflower strips strengthens the biological regulation of aphid pests and weeds, and enhances cropping system productivity. The contribution of flowering weeds to conservation biological control was also analysed. Aphid colonization rates, but also predator colonization and predation rates, on bean and poppy were consistently lower in intercropping compared to sole cropping. Associating wildflower strips to intercropping enhanced aphid predation in bean-wheat intercropping, and further reduced aphid colonization at 10 m distance from the flower strip but not at 20 m in poppy-barley intercropping. Weed biomass was strongly reduced in intercropping compared to sole crop bean and poppy, and did not significantly affect bean and poppy yields in intercropping. The cover of one flowering weed species, Matricaria recutita, was negatively correlated to aphid colonization rate and positively correlated to predation rate in bean-wheat intercropping. In poppy-barley intercropping, M. recutita flowers were visited more often by predatory hoverflies in plots adjacent to wildflower strips. Finally, land equivalent ratio, measuring land-use efficiency, was consistently higher than 1, and the highest in bean-wheat intercropping associated to wildflower strips. The study shows that intercropping is key to control multiple pests and enhance land-use efficiency, and demonstrates that associating wildflower strips to intercropping can strengthen biological control and cropping system productivity. Flowering weeds, maintained at an acceptable level through intercropping, turn out to be relevant functional biodiversity in interacting with wildflower strips to support natural enemies for conservation biological control.

Methods
The data are retrieved from a field experiment conducted in Germany (50°47’14N, 7°16’38E; city: Hennef) in organic farming conditions during the years 2020-2022.

The experiment tested whether increasing crop diversity (sole cropping vs. intercropping) and field margin management (wildflower strip vs. crop strip) affects biological control of insect pests (aphids), weed biomass and productivity (crop yield, land-equivalent ratio). In addition in the intercropping systems, the experiment analysed the relationship between weed flowers and insects towards biological control.

Studied crops were faba bean (Vicia faba) and wheat (Triticum aestivum) in 2020-2021, and breadseed poppy (Papaver somniferum) and barley (Hordeum vulgare) in 2022.

All data were collected in quadrats (1m2 surface). One quadrat is always defined by the type of “Margin” (flower vs. control), “Cropping_system” (intercropping, sole cropping) and “Distance_(m)” (10 vs. 20, sometimes also 10_weed_free) and the experiment “Block” (1 to 4).

For more information, please refer to the Material and Methods of the published article.