With the shift to earlier maturing soybean cultivars, harvest interference data are needed at low weed densities that will not reduce yield, but may affect soybean quality or harvesting efficiency. Field experiments were conducted in 1995 and 1996 to determine the density of five weeds necessary to warrant desiccation treatments. There were no consistent differences in losses of harvestable soybean due to weed density. Common cocklebur increased foreign material and soybean moisture at a greater rate than did hemp sesbania, ivyleaf morningglory, or redroot pigweed, with sicklepod intermediate among these species. Soybean test weight was reduced by 17, 13, and 59 g/L for each plant/meter of row with redroot pigweed, sicklepod, and common cocklebur, respectively, whereas hemp sesbania and ivyleaf morningglory did not affect test weight. However, all species evaluated increased damaged soybean seeds by 8.2 to 11.1% for each plant/meter of row. Combine speed was not affected substantially by the weed densities evaluated.

Sicklepod (Senna obtusifolia), hemp sesbania (Sesbania exaltata), and pitted morningglory (Ipomoea lacunosa) seed production and viability in early-maturing soybean (Glycine max) were evaluated following preharvest desiccation. The herbicide combinations 1.1 kg ai/ha glyphosate plus 6.7 kg ai/ha sodium chlorate, 2.2 kg/ha glyphosate plus 3.4 kg/ha sodium chlorate, and 0.3 kg ai/ha paraquat plus 6.7 kg/ha sodium chlorate reduced sicklepod germination, emergence, and seedling growth in most cases. Oxyfluorfen at 0.3 kg ai/ha plus 3.4 or 6.7 kg/ha sodium chlorate also reduced sicklepod germination and growth. Glufosinate from 0.8 to 1.4 kg ai/ha reduced sicklepod germination but did not have a consistent effect on other seedling growth parameters. Bromoxynil at 1.1 kg ai/ha plus 3.4 kg/ha sodium chlorate reduced sicklepod germination but did not have a consistent effect on most growth parameters. A wide range of treatments reduced hemp sesbania germination, emergence, and growth to very low levels. All desiccant applications reduced pitted morningglory seed production compared to the untreated check. Glyphosate at 1.1 kg/ha plus 6.7 kg/ha sodium chlorate, 0.3 kg/ha oxyfluorfen plus 3.4 kg/ha sodium chlorate, and 0.8 or 1.1 kg/ha glufosinate reduced pitted morningglory seed production and desiccated weeds effectively. Most treatments reduced emergence in 1996, when seeds were smaller and less mature than those collected in 1995. When application volume of paraquat alone or in tank mixture decreased, germination and growth of sicklepod was reduced, indicating increased paraquat efficacy.