Weed control provided by seed predators saves 20 % crop yield in cereal fields

Although many herbicide active substances have been banned, and while weed infestation is a major threat to crop productivity, the extent to which natural weed control provided by seed predators can help farmers manage weed communities remains unknown. The contribution of seed predators to crop productivity through weed control was quantified, and it was assessed whether farming systems such as conservation agriculture played a role in bolstering their impact. A total of 112 seed predator-exclusion cages were set up in 28 cereal fields in France (14 pairs of plots, in which one plot was managed under conservation agriculture and the other under conventional agriculture). Weed emergence and biomass were surveyed, crop yield was measured, and the main seed predators—carabid beetles and rodents—were sampled. A 20 % reduction in yield loss due to weeds was found to be caused by seed predator activity, which was extrapolated to an economic gain of 285 €/ha. However, a whole 60 % of the maximum crop yield potential reached in the absence of weeds remains lost. Moreover, while conservation agriculture enhances weed control, this does not translate into increased crop yield. This study demonstrates the tangible importance of considering seed predators for weed control but highlights the need to combine this approach with other weed control practices or to substantially redesign cropping systems to enhance the beneficial effects of biodiversity on crop productivity. • Seed predators reduced weed-induced crop yield losses by 20 %, corresponding to an economic gain of €285 ha⁻¹ yr⁻¹ . • This study provides the first quantification of the impact of seed predators on crop yield through weed biomass reduction. • Conservation agriculture enhanced weed control via increased seed predator biomass but did not significantly improve yield. • Effective weed management requires combining natural control with complementary agronomic practices to achieve sustainable productivity.