A survey of 174 fields was conducted to investigate performance of herbicides applied after winter wheat harvest on weeds across western and southern Nebraska during August and September 1998. Glyphosate plus 2,4-D plus atrazine was applied on 32%, glyphosate plus 2,4-D or dicamba on 24%, paraquat plus atrazine on 23%, glyphosate on 8%, ICIA0224 plus 2,4-D or atrazine on 10%, and atrazine plus 2,4-D on 3% of the fields. These treatments controlled 85 to 100% of the weeds except atrazine plus 2,4-D, which controlled 30%. The frequency of occurrence of the most prevalent summer annual grasses was as follows: green foxtail, 65%; barnyardgrass, 46%; stinkgrass, 41%; witchgrass, 39%; and longspine sandbur, 36%. The most common broadleaf weeds and their frequency were redroot pigweed, 32%; tumble pigweed, 30%; tall waterhemp, 28%; and kochia, 25%. Virginia groundcherry, 22%; common milkweed, 11%; yellow woodsorrel, 9%; and field bindweed, 6% were the most common perennial weeds. The five most difficult weeds to control were yellow nutsedge, spotted spurge, Virginia groundcherry, common milkweed, and toothed spurge, with control ratings of 0, 3, 17, 26, and 33%, respectively. These weeds were not controlled with glyphosate or mixtures containing glyphosate. Only 35% of the fields were treated before summer annual grasses had headed. Late applications required higher herbicides rates for effective control.
Nomenclature: Atrazine; 2,4-D; dicamba; glyphosate; ICIA0224 (glyphosate trimethylsulfonium salt); paraquat; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; common milkweed, Asclepias syriaca L. # ASCYS; field bindweed, Convolvulus arvensis L. # CONAR; green foxtail, Setaria viridis (L.) Beauv. # SETVI; kochia, Kochia scoparia (L.) Schrad # KCHSC; longspine sandbur, Cenchrus longispinus (Hack.) Fern. # CCHPA; redroot pigweed, Amaranthus retroflexus L. # AMARE; spotted spurge, Euphorbia maculata L. # EPHMA; stinkgrass, Eragrostis cilianensis (All.) E. Mosher # ERACN; tall waterhemp, Amaranthus tuberculatus (Moq.) J. D. Sauer # AMATA; toothed spurge, Euphorbia dentata Michx. # EPHDE; tumble pigweed, Amaranthus albus L. # AMAAL; Virginia groundcherry, Physalis virginiana Mill. # PHYLC; witchgrass, Panicum capillare L. # PANCA; yellow nutsedge, Cyperus esculentus L. # CYPES; yellow woodsorrel, Oxalis stricta L. # OXAST; winter wheat, Triticum aestivum L.
Additional index words: AMAAL, AMARE, atrazine, conservation tillage, CYPES, 2,4-D, dicamba, ECHCG, ecofallow, ecofarming, ERACN, glyphosate, KCHSC, KSHSC, no-till, OXAST, PANCA, paraquat, SETVI, weed management.
