Planting Date and Seed Treatment Effects on Soybean in the Northeast USA.

Soybean {Glycine max (L.) Merr.} production is limited in the Northeast USA so research on optimum planting date is scarce. Soybean production is expected to increase in the heavily-trafficked region so we initiated a 2-yr study in New York that compared soybean planted in mid-May, late May, and mid-June with and without seed-applied fungicide/insecticide treatments. Soybean planted in mid vs. late May had a longer emergence time (15 vs. 6 d) and lower plant densities (35.6 vs. 39.5 plants/m²), but produced more pods/side branch (7.4 vs. 5.5), which contributed to more pods/plant (30.9 vs. 25.7) and pods/m² (1079 vs. 958, respectively). The late vs. mid-May planting date, however, had more seeds/pod (2.28 vs. 2.19), which contributed to similar seeds/m² (2180 vs. 2357) and seed yield (3.8 vs. 3.9 Mg ha^-1, respectively). Soybean planted in mid-June vs. mid-May had more plants/m² (38.0) but fewer pods/side branch (3.4), pods/plant (22.5), pods/m² (879), seeds/m² (1910), and lower seed yield (3.5 Mg ha^-1). Seed treatments did not affect plant density, pod density, and seed yield, but had inconsistent effects on seeds/pod, seeds/m², and seed mass. The results of this study indicate that there is a fairly broad optimum planting date range and that insecticide/fungicide treatment is not required for soybean production in the Northeast USA, but more research under more diverse growing conditions is necessary to corroborate these findings.