Glyphosate-resistant common waterhemp is a difficult-to-control annual broadleaf weed that has become a serious management challenge for growers in Nebraska and other states in the United States. The objectives of this study were to confirm glyphosate-resistant common waterhemp in Nebraska by quantifying level of resistance in a dose-response study, and to determine the sensitivity and efficacy of POST soybean herbicides for controlling suspected glyphosate-resistant common waterhemp biotypes. Seeds of suspected glyphosate-resistant common waterhemp biotypes were collected from seven eastern Nebraska counties. Greenhouse dose-response experiments were conducted to evaluate the response of common waterhemp biotypes to nine rates of glyphosate (0 to 16×). Common waterhemp biotypes were 3- to 39-fold resistant to glyphosate depending on the biotype being investigated and the susceptible biotype used for comparison. Results of the POST soybean herbicides efficacy experiment suggested that glyphosate-resistant biotypes, except a biotype from Pawnee County, had reduced sensitivity to acetolactate synthase (ALS)–inhibiting herbicides (chlorimuron-ethyl, imazamox, imazaquin, imazethapyr, and thifensulfuron-methyl). Glufosinate and protoporphyrinogen oxidase (PPO)–inhibiting herbicides (acifluorfen, fluthiacet-methyl, fomesafen, and lactofen) provided ≥ 80% control of glyphosate-resistant common waterhemp at 21 d after treatment (DAT). This study confirmed the first occurrence of glyphosate-resistant common waterhemp in Nebraska, and also revealed reduced sensitivity to ALS-inhibiting herbicides in most of the biotypes tested in this study.

Nomenclature: Acifluorfen; chlorimuron-ethyl; fluthiacet-methyl; fomesafen; glufosinate; glyphosate; imazamox; imazaquin; imazethapyr; lactofen; thifensulfuron-methyl; common waterhemp, Amaranthus rudis Sauer; soybean, Glycine max (L.) Merr.

Amaranthus rudis resistente a glyphosate es una maleza anual de hoja ancha difícil de controlar y que se ha convertido en un reto serio de manejo para productores en Nebraska y otros estados en los Estados Unidos. Los objetivos de este estudio fueron confirmar la resistencia a glyphosate de A. rudis en Nebraska, cuantificando el nivel de resistencia mediante estudios de respuesta a dosis, y determinar la sensibilidad y la eficacia de herbicidas POST para soja para el control de biotipos de A. rudis que se sospecha son resistentes a glyphosate. En siete condados del este de Nebraska, se colectaron semillas de biotipos de A. rudis que se sospechaba eran resistentes a glyphosate. Se realizaron experimentos de respuesta a dosis en invernadero, para evaluar la respuesta de biotipos de A. rudis a nueve dosis de glyphosate (0 a 16X). Biotipos de A. rudis fueron de 3 a 39 veces más resistentes a glyphosate, dependiendo del biotipo investigado y del biotipo susceptible usados en la comparación. Los resultados del experimento sobre la eficacia de herbicidas POST para soja sugirieron que los biotipos resistentes a glyphosate, con la excepción del biotipo proveniente del condado Pawnee, tuvieron una sensibilidad reducida a los herbicidas inhibidores de acetolactate synthase (ALS) (chlorimuron-ethyl, imazamox, imazaquin, imazethapyr, y thifensulfuron-methyl). Glufosinate y los herbicidas inhibidores de protoporphyrinogen oxidase (PPO) (acifluorfen, fluthiacet-methyl, fomesafen, y lactofen) brindaron ≥ 80% control de A. rudis resistente a glyphosate a 21 d después del tratamiento (DAT). Este estudio confirmó el primer caso de <