Managing herbicide resistance doesn't pay - but acting pre-emptively does.

Abstract Globally, herbicides improve crop yields but at great environmental cost, and their overuse has caused herbicide resistance. This incurs large financial and production losses but, despite this, truly integrated weed management that might delay or prevent resistance is uncommon in intensive farming. We asked farmers to design more diversified cropping strategies aimed at controlling resistance. We estimate resulting weed densities, profits, and yields compared to prevailing practice. Where resistance is low, it is financially viable to diversify pre-emptively; however, once resistance is high, there are financial and production disincentives to adopting diverse rotations. It is therefore as important to manage resistance before it becomes widespread as it is to control it once it has evolved. The diverse rotations targeting high resistance used increased herbicide application frequency and volume, contributing to these rotations' lack of financial viability, and raising concerns about glyphosate resistance. Governments should encourage adoption of diverse rotations in areas without resistance. Where resistance is present, governments may wish to incentivise crop diversification despite the drop in wheat production, as the yield loss may eventually occur anyway under current management. Our research suggests we need long-term food security planning and more integrated policy-making across farming, environment, and health arenas.