Healthy soils, rising pests? Stopping plowing improves soil quality but increases wireworm infestation: evidence from a long-term field study

Conventional tillage (i.e. plowing) is often associated with soil degradation and a loss of biodiversity. In response, reduced tillage has increasingly been promoted as a sustainable alternative for its positive impacts on soil structure, water dynamics, and biodiversity. However, reduced tillage not only favors beneficial soil-dwelling organisms, but also pests. In this field study, we examined the effects of five years of reduced tillage on the physical properties of the soil and the dynamics of Agriotes wireworm populations (Elateridae), which are increasingly widespread pests. Our results show that tillage reduction led to stable edaphic conditions and a redistribution of organic matter, creating a favorable environment for wireworms. While our results demonstrate the beneficial effects of reduced tillage on aggregate stability, they also indicate a concomitant increase in soil bulk density, suggesting a reduction in water-holding capacity. Monitoring of wireworm populations revealed their aggregated distribution and their increase in abundance in infested areas year on year. Monitoring soil moisture revealed that tillage reduction improved water dynamics, enhancing infiltration and reducing evaporation. This could potentially favor the development of wireworms. Surprisingly, wireworm size distribution showed a higher proportion of young instars in plowed plots, evidencing that, firstly, the lack of soil cover does not prevent oviposition and that injury caused by plowing targets more the last instars rather than young larvae. While reduced tillage improves key soil health indicators, our findings suggest a potential trade-off in terms of increased pest pressure. Our study highlights the importance of adopting a holistic approach when designing sustainable cropping systems, as well as considering the services and dis-services they provide.