Crop sequence and cover crop species affect Carabidae assemblages in an organically-managed cover-crop based reduced tillage cropping system

Organic grain growers mainly rely on cultural practices and biological control to regulate pests. Implementation and timing of cultural practices can affect many characteristics of the crop as a habitat for natural enemies. We evaluated the effect of cover crop termination/cash crop planting date and crop sequence on ground and tiger beetle (Coleoptera: Carabidae) activity-density and diversity in a full entry, 3-year sequence of corn (Zea mays), soybean (Glycine max), and wheat (Triticum aestivum). Hairy vetch/triticale (Vicia villosa/Triticosecale) preceded corn and cereal rye (Secale cereal) preceded soybean. Cover crops were terminated by rolling and corn and soybean were no-till planted on three dates (Early, Middle, and Late). Wheat was planted on a single date in each year into tilled soil. Carabidae beetles were sampled by pitfall trap two weeks after planting in corn and soybean, and in mid-June in wheat. Carabidae activity-density and species richness increased during the 3-year transition (p < 0.001). Corn’s location in the sequence (in year 1, 2, or 3) dictated activity-densities and species richness, as both were highest in corn (p < 0.05), but the effect of corn did not persist into the following year. The late planting date was positively associated with higher activity-densities of large beetles in corn (p < 0.05) and soybean (p < 0.05), carnivorous beetles in corn (p < 0.05) and granivorous beetles in soybean (p < 0.05). Results have strong implications for management during the transition to organic, especially in regard to the initial crop in the transition sequence.