Abstract: Seeds of giant foxtail (Setaria faberi, 4,000 seeds/m2) or velvetleaf (Abutilon theophrasti, 3,000 seeds/m2) were added to the seed bank to determine the effect of increases in weed density on herbicide efficacy in corn (Zea mays). A herbicide program consisting of SAN 582 applied preemergence followed by a postemergence application of dicamba plus atrazine was evaluated at four levels (0.0, 0.3, 0.7 and 1.0 times the label rates). At a site with low initial weed densities, the addition of velvetleaf or giant foxtail seed to the seed bank did not influence herbicide efficacy at the 1.0× rate at 9 wk after planting (WAP). Giant foxtail densities were greater 9 WAP in augmented areas than in the native seed bank plots at both the 0.3× and 0.7× rates, whereas with velvetleaf, higher densities in augmented plots were seen only at the 0.3× rate. In areas with high native weed densities, addition of seed of either species resulted in an increase in final weed densities at all herbicide rates.
Nomenclature: Atrazine, 6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine; dicamba, potassium salt of 3,6-dichloro-2-methoxybenzoic acid; SAN 582 (proposed name, dimethenamid), 2-chloro-N-(2,4 dimethyl-3-thienyl)-N-(2-methoxy-1-methylethyl)acetamide; giant foxtail, Setaria faberi Herm. #3 SETFA; velvetleaf, Abutilon theophrasti Medic. # ABUTH; corn, Zea mays L.
Additional index words: Weed seed bank, ABUTH, SETFA.
Abbreviations: POST, postemergence; PRE, preemergence; WAP, weeks after planting.