Diversifying Cornfields by Interseeding Cover Crops: Practical Implications and the Response of Invertebrate Communities

The lack of suitable habitat conditions for beneficial organisms in simplified agroecosystems leads to unstable invertebrate communities and overreliance on chemical control of herbivores. It is possible to manage pest populations without agrichemicals by manipulating farmland so that herbivores are impaired by plant-driven bottom-up and enemy-driven top-down antagonisms. Interseeding cover crops between established crop rows is a method used by farmers to improve habitat suitability for natural enemies and hinder host-finding, feeding and movement by herbivores. Here I address three important research gaps related to interseeding cover crops. A calcium carbonate seed coating, used to improve seed-broadcasting efficiency, was tested to determine if arthropod granivores are deterred from consuming cover crop seeds. Invertebrate communities were compared between monoculture cornfields and cornfields possessing a mixture of cover crop species. Finally, neonicotinoid seed treatment, thiamethoxam, and metabolite, clothianidin, were quantified within vegetative tissue of cover crops growing between seed-treated corn to examine a potential route of exposure by non-target organisms. The addition of a calcium carbonate seed coating reduced seed granivory by invertebrates. Hairy vetch (Vicia villosa) and sorghum × sudan (Sorghum × drummondii) were especially protected. Gryllidae, Carabidae and Staphylinidae were the most abundantly collected granivores. Corn interseeded with cover crops possessed a larger abundance of surface-dwelling predators, herbivores, numerous individual taxa and total invertebrates than monocultures. Greater epigeic species richness was also recorded in cover-cropped fields. With the exception of four individual taxa, subterranean invertebrate abundances were unchanged between interseeded and monoculture corn, however, cover crops did increase species diversity below the soil surface. Interseeding did not affect species richness, diversity or arthropod abundance on corn foliage. Thiamethoxam and toxic metabolite, clothianidin, were detected in interseeded hairy vetch and cereal rye (Secale cereale) on all but one sampling dates during the corn growing season with highest concentrations in earlier samplings. On each collection date clothianidin was found at a higher level than thiamethoxam for both species. As management techniques improve interseeding cover crops has potential to become an increasingly important tool for restoring agroecosystem functions if the incompatibility of added plant diversity and existing pesticide strategies is addressed