Kochia, common lambsquarters, and wild buckwheat are major problem weeds in glyphosate-resistant corn production in the northern Great Plains of the United States. Field research was conducted in 2011 and 2012 near Huntley, MT to investigate effective PRE herbicides applied alone or in premixes with or without tank-mixed pendimethalin for extended in-season residual control of the selected broadleaf weeds in glyphosate-resistant corn. Control of kochia, common lambsquarters, and wild buckwheat with recently registered herbicide premixes, including saflufenacil dimethenamid-P and S-metolachlor mesotrione, was as high as 95 and 90% at 21 and 63 d after treatment (DAT), and mostly similar to the standard atrazine treatment. Residual control of common lambsquarters and wild buckwheat from pyroxasulfone was higher at 298 compared with 149 g ai ha⁻¹ rate. Pyroxasulfone and other chloroacetamide herbicides (acetochlor or dimethenamid-P) applied alone failed to provide greater than 79, 70, and 54% residual control at 21, 35, and 63 DAT, respectively, of the weed species investigated. Residual weed control throughout the growing season was significantly improved with the addition of pendimethalin to pyroxasulfone (149 g ha⁻¹), acetochlor, or dimethenamid-P when compared with any of the three herbicides applied alone. Kochia control by pyroxasulfone, acetochlor, or dimethenamid-P tank mixed with pendimethalin was as high as 94, 92, and 81% at 21, 35, and 63 DAT, respectively. Control of common lambsquarters with the addition of pendimethalin to pyroxasulfone or acetochlor was improved to 94, 89, and 81% at 21, 35, and 63 DAT, respectively. Similarly, wild buckwheat control with acetochlor plus pendimethalin was improved to 87, 85, and 82% at 21, 35, and 63 DAT, respectively. Consistent with the extended in-season (up to 9 wk) residual weed control, pyroxasulfone, acetochlor, or dimethenamid-P treatments when tank mixed with pendimethalin had higher corn yields compared with the herbicides applied alone. The investigation on residual herbicides that provide extended in-season weed control should be continued as an important aspect of glyphosate stewardship and to mitigate the occurrence of glyphosate-resistant weed populations in grower fields.

Nomenclature: Acetochlor; dimethenamid-P; pyroxasulfone; saflufenacil dimethenamid-P; S-metolachlor mesotrione; atrazine; pendimethalin; kochia, Kochia scoparia (L.) Schard.; common lambsquarters, Chenopodium album L.; wild buckwheat, Polygonum convolvulus L.; corn, Zea mays L.

Kochia scoparia , Chenopodium album, y Polygonum convolvulus son malezas problemáticas en la producción de maíz resistente a glyphosate en las Grandes Planicies del Norte de Estados Unidos. En 2011 y 2012, se realizó una investigación de campo en Huntley, Montana, para investigar herbicidas efectivos PRE aplicados solos o en premezclas con o sin pendimethalin mezclada en tanque para el control residual de malezas de hoja ancha extendido durante la temporada de crecimiento en maíz resistente a glyphosate. El control de K. scoparia, C. album, y P. convolvulus con premezclas de herbicidas recientemente registradas, incluyendo saflufenacil dimethenamid-P y S-metolachlor mesotrione, alcanzó 95 y 90% a 21 y 63 d después del tratamiento, y fue similar al tratamiento estándar con atrazine. El control residual de C. album y de P. convolvulus con pyroxasulfone fue mayor con la dosis de 278 que con la de 149 g ai ha⁻¹. Pyroxasulfone y