Weed biodiversity and herbicide intensity as linked via a decision support system

Extensive herbicide use is one reason for the declining biodiversity of arable weeds. This study aimed to investigate (i) whether herbicide decisions recommended by a decision support system increase the weed species diversity compared to standard recommendations, and (ii) whether high weed species diversity reduces herbicide intensity, which in turn contributes to higher diversity. Data on weeds and herbicide applications in winter wheat fields in north-eastern Germany were collected in 15 field trials over 2 years. Five treatments differed in the way of decision-making for herbicide application, including two treatments according to recommendations of decision support systems.

Along the Hill's series biodiversity metrics, the untreated control had the highest species richness (13.5 m^-2) per field but showed increasingly stronger dominance structures than the treated plots (equivalent species richness: 1.7-2.0 m^-2). The treatment frequency index as a metric for herbicide intensity was significantly lowest in the decision support system with low reliability (1.07). Path models, including weed diversity and density in autumn, weed diversity in summer, and herbicide intensity as a mediating variable showed a significant decreasing effect of Shannon diversity on herbicide intensity in all treatments. Only the decision support systems reacted to low weed densities with a significant reduction of the herbicide intensity.

Higher weed species diversity contributes to lower herbicide intensity, which is ecologically and economically valuable. Decision support systems for herbicide application should have other target functions than cost reduction for contributing to biodiversity. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.