Seedcorn maggot in conventional and conservation tillage soybeans and damage effects on soybean growth and yield

Part I. Absolute population estimates, based on emergence trapping, were made for the seedcorn maggot, Hylemya platura (Meigen) (Diptera: Anthomyiidae), during germination in 4 typical Iowa soybean tillage systems (fall moldboard plow, fall chisel plow, till-plant, and no-tillage). The emergence trapping method gave acceptable levels of precision for an intensive sampling program. Although significant differences in emergence were found between tillage systems, numbers of seedcorn maggots present were not a serious problem in any system. Emergence was greatest in the fall chisel-plow system, followed by the till-plant system. Emergence in the no-till and fall moldboard-plow systems was similar. Comparisons of emergence between within-row and between-row areas in these systems suggested that germinating soybeans were not attractive for oviposition under field conditions. Surface corn residue and soil moisture were not significant factors influencing oviposition and development;Part II. Interactive damage effects of stand loss and plumule abscission from seedcorn maggot on soybean (var. Amsoy 71) growth and yield were investigated using actual- and simulated-damage methods. Stand reduction affected seed yield more than did the presence of surviving seedlings without plumules. Over all years, seed yields were greatest at 29.7 plants per 1-m row. At all plant stands, the seedlings without plumules were shorter and produced less leaf area, fewer flowers, and fewer pods than did normal plants. This retarded growth reduced leaf area index, flowers per unit area, and pods per unit area. The decrease in pods per unit area was accompanied by an increase in beans per pod. When some of the surviving seedlings lacked plumules, seed yields were reduced at poor plant stands in some years. Plant-growth characteristics were very similar for actual and simulated damage. Seed-yield comparisons between actual and simulated damage suggested that seedcorn maggot injury to cotyledons had a small, negative effect on seed yield