Cover crop species and termination timing influence Carabidae assemblage in 3-year transition to organic

Many organic grain growers are interested in soil health, but intensive tillage is one of the most common practices used by organic growers to manage weeds and other pests. One approach to reducing tillage in organic systems is to no-till plant crops into over-wintered cover crops terminated by rolling. Careful timing of cover crop termination is critical to achieve maximum kill of the cover crop and to produce a weed-suppressive mat on the soil surface. Additionally, the cover crop mat creates habitat for arthropods, including those critical to biological control, e.g., ground and tiger beetles (Coleoptera:Carabidae). To evaluate the effects of cover crop species and timing of termination on Carabidae beetles, we conducted pitfall-trapping in an organically-managed corn (Zea mays) – soybean (Glycine max) – wheat (Triticum aestivum) rotation. Over-wintered hairy vetch/triticale (Vicia villosa/Triticosecale) occurred before corn, and cereal rye (Secale cereale) before soybean. Cover crops were terminated and corn and soybean were no-till planted into the residue mat on three dates (Early, Middle, Late). Wheat followed soybean and was established on a single date in all treatments using inversion tillage. Cover crop species influenced where the 46 species of Carabidae were captured, and determined activity-density, species richness, and community evenness. Activity-densities and species richness were greatest in the rolled hairy-vetch/triticale and both measures were generally higher in later compared to earlier termination dates for both cover crops. These results suggest that during transition to organic, cover crop termination/planting date affect conservation of the ground beetle community, with implications for biological control.