Natural weed seed predators reduce crop yield loss due to weeds by 20% in cereal fields

Abstract While many herbicide active substances have been banned and weed infestation is a major threat to crop productivity, it is still unknown to what extent natural weed control provided by seed predators can help farmers manage weed communities. We aim to quantify the contribution of seed predators to crop productivity through weed control and to evaluate whether the magnitude of their influence depends on farming systems such as conservation agriculture. We set up 112 seed predator-exclusion cages in 28 cereal fields in France (14 pairs of conservation and conventional agriculture fields), surveyed weed emergence and biomass, measured crop yield and sampled the main seed predators: carabid beetles and rodents. We found that seed predators’ activity reduces the yield loss due to weeds by 20%. By extrapolation, it represents an economic gain of 285€/ha. However, the yield loss remains at 60% below the maximum crop yield potential reached in the absence of weeds. Moreover, conservation agriculture enhances weed control, but 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 weed control practices or to substantially redesign cropping systems to enhance the beneficial effects of biodiversity on crop productivity. Significance statement Although weed biomass is the main driver of decreasing the crop productivity worldwide and the use of herbicides is massively disparaged, we have not yet quantified the role played by on-farm biodiversity to control weeds. Using an experimental design set up in 28 commercial cereal fields in France, we showed that weed seed predators reduce crop yield loss due to weeds by 20%. By extrapolation, it represents an economic gain of 285€/ha. However, in the absence of any other weed control practices, the yield loss remains at 60% below the maximum crop yield potential reached in the absence of weeds. This study demonstrates the quantitative importance of considering seed predators to design pesticide-free systems.