Efficacy of glyphosate, glufosinate, and imazethapyr on selected weed species

Experiments were conducted to determine the efficacy, absorption, and translocation of glyphosate, glufosinate, and imazethapyr with selected weed species. In the greenhouse glyphosate, glufosinate, and imazethapyr were applied at 0.25, 0.5, and 1 times their label rates of 1,121, 410, and 70 g ha⁻⁻¹, respectively, on 10- to 15-cm black nightshade, common waterhemp, eastern black nightshade, field bindweed, giant ragweed, ivyleaf morningglory, prairie cupgrass, velvetleaf, and yellow nutsedge. Glyphosate applied at the 1-time rate caused injury greater than or similar to injury from the 1-time rate of glufosinate or imazethapyr on black nightshade, common waterhemp, eastern black nightshade, field bindweed, giant ragweed, prairie cupgrass, and velvetleaf. The 1-time rate of glufosinate injured ivyleaf morningglory and yellow nutsedge more than did the 1-time rate of glyphosate or imazethapyr. Under field conditions glyphosate caused the greatest injury to common waterhemp, prairie cupgrass, and velvetleaf across plant growth stages. Giant ragweed and ivyleaf morningglory injury was more dependent on growth stage, with the 15- and 30-cm growth stages more susceptible to glyphosate than to glufosinate or imazethapyr. Differential response of these weed species may be caused by differences in herbicide translocation. Glyphosate was translocated more in both giant ragweed and ivyleaf morningglory, and these species were injured more by glyphosate than by glufosinate or imazethapyr at the larger growth stages.Nomenclature: Glufosinate; glyphosate; imazethapyr; black nightshade, Solanum nigrum L. SOLNI; common waterhemp, Amaranthus rudis Sauer AMATA; eastern black nightshade, Solanum ptycanthum Dun. SOLPT; field bindweed, Convolvulus arvensis L. CONAR; giant ragweed, Ambrosia trifida L. AMBTR; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE; prairie cupgrass, Eriochloa contracta Hitchc. ERICO; velvetleaf, Abutilon theophrasti Medicus ABUTH; yellow nutsedge, Cyperus esculentus L. CYPES.