Seed production from weeds that are missed by herbicide application can affect future weed populations and management decisions. It may be possible to expand the utility of computerized weed management decision aids to include an estimate of weed seed production resulting from selected treatments based on crop yield potential. Field studies were conducted in soybean near Columbia, MO, to determine whether weed control recommendations based on crop yield potential from a computerized weed management decision aid influence weed seed production in two soybean row spacings. At approximately 28 d after planting, weed densities and heights were entered into WeedSOFT® to generate a list of treatments ranked by predicted crop yields. Treatments included: (1) highest predicted crop yield in a glyphosate-resistant system, (2) highest predicted crop yield in a nonglyphosate-resistant system, (3) a 10% yield reduction, (4) a 20% yield reduction, and (5) an untreated control. These treatments were applied to soybean grown in 38- and 76-cm rows. Treatments that provided 90% or higher control of an individual species at 22 d after treatment usually produced less seed than untreated checks. Weed seed production based on early-season herbicide efficacy showed a linear relationship and was relatively predictable (r2 ≥ 0.52) for the predominant weed species. For less dominant weed species, weed seed production was not strongly correlated (r2 ≤ 0.27) to early-season herbicide efficacy but apparently influenced by control of other weed species. Narrow row spacing reduced giant foxtail biomass both years but did not reduce common ragweed and ivyleaf morningglory biomass. Narrow rows did not decrease giant foxtail, common ragweed, and ivyleaf morningglory seed production.
Nomenclature: Glyphosate; common ragweed, Ambrosia artemisiifolia (L.) #3 AMBEL; giant foxtail, Setaria faberi (L.) Herrm. # SETFA; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; soybean, Glycine max.
Additional index words: Decision support system, herbicide decision aid.
Abbreviations: AP, at planting; DAT, days after treatment; HPMY-G, highest percent maximum yield that used glyphosate-resistant soybean; HPMY-NG, highest percent maximum yield that did not use glyphosate.