Residual Herbicides used in Combination with Glyphosate and Glufosinate in Corn (Zea mays)1

Weed management strategies are needed to control weeds in corn that emerge after postemergence (POST) application of glyphosate or glufosinate. Field trials were conducted from 1996 to 1999 to determine if residual herbicides could be used with glyphosate or glufosinate to provide season-long weed control in glyphosate-resistant or glufosinate-resistant corn. Preemergence (PRE) applications of several residual herbicides followed by POST applications of glyphosate or glufosinate were compared with POST tank mixtures of glyphosate or glufosinate with residual herbicides. All residual herbicides used in combination with glyphosate, when compared with glyphosate alone, increased control of redroot pigweed and common lambsquarters by an average of 20% and resulted in a 4 to 19% increase in control of giant foxtail. Each residual herbicide tank mixture with glufosinate, when compared with glufosinate alone, increased control of common ragweed and giant foxtail. In most instances, weed control was similar for total POST and for PRE followed by POST systems. Velvetleaf control was reduced by 12% when glyphosate was tank mixed with a half rate of atrazine compared with a full rate of atrazine. Common lambsquarters control was reduced by 13% when glyphosate was tank mixed with a half vs. a full rate of acetochlor. Glufosinate tank mixed with half rates of acetochlor atrazine, flumetsulam, or pendimethalin reduced control of velvetleaf compared with the full rate of these products. Corn yields were not affected by residual herbicide application timings or rates of residual herbicides.Nomenclature: Acetochlor; atrazine; flumetsulam; glufosinate; glyphosate; pendimethalin; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; giant foxtail, Setaria faberi L. # SETFA; redroot pigweed, Amaranthus retroflexus L. # AMARE; velvetleaf, Abutilon theophrasti Medik. # ABUTH; corn, Zea mays L. ‘DK 493GR’, ‘DK 493RR’.Additional index words: Glufosinate-resistant corn, glyphosate-resistant corn, herbicide-tolerant crops, metolachlor, soil-applied herbicides.Abbreviations: POST, postemergence; PRE, preemergence.