Seedcorn maggot response to planting date, cover crops, and tillage in organic cropping systems

Seedcorn maggot, Delia platura (Meigen) (Diptera: Anthomyiidae) (SCM) is an economically important early-season pest of corn and soybean in the northern U.S. Adult SCM are attracted to decomposing plant residues for oviposition, creating potential management issues in cropping systems where growers typically use tillage to incorporate manures and create a seedbed. The use of growing degree day (GDD) models to time planting dates is an important tool for effectively managing this pest, but their use has not been examined in organic corn and soybean production. Here we report the results of two cropping systems experiments to determine the effects of cover crops, tillage, and planting date on seedcorn maggot in corn and soybean: the first during transition to organic from conventional management, and the second during the three years following organic certification in central Pennsylvania, USA. Overall, delaying planting date reduced fly emergence in corn but not soybean during the transition to organic and after certification. SCM emergence was also consistently lower in soybean than in corn. Significantly more SCM flies emerged from corn in treatments in which cover crops were managed with tillage compared to treatments in which cover crops were terminated with a roller-crimper followed by no-till planting of corn. Fly emergence was also negatively related to the proportion of legumes in the cover crop mixture preceding corn. These results can help inform decisions on cover crop mixtures, cover crop termination method, and planting date for organic growers in the Mid-Atlantic US.