Palmer amaranth is a difficult-to-control broadleaf weed that infests corn and soybean fields in south-central and southwestern Nebraska and several other states in the United States. The objectives of this research were to confirm triazine and 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicide-resistant Palmer amaranth in Nebraska and to determine sensitivity and efficacy of POST-applied corn herbicides for control of resistant and susceptible Palmer amaranth biotypes. Seeds from a putative HPPD-resistant Palmer amaranth biotype from Fillmore County, NE were collected from a seed corn production field in fall 2010. The response of Palmer amaranth biotypes to 12 rates (0 to 12×) of mesotrione, tembotrione, topramezone, and atrazine was evaluated in a dose–response bioassay in a greenhouse. On the basis of the values at the 90% effective dose (ED90) level, the analysis showed a 4- to 23-fold resistance depending upon the type of HPPD-inhibiting herbicide being investigated and susceptible biotype used for comparison. This biotype also had a 9- to 14-fold level of resistance to atrazine applied POST. Results of a POST-applied herbicide efficacy study suggested a synergistic interaction between atrazine and HPPD-inhibiting herbicides that resulted in > 90% control of all Palmer amaranth biotypes. The resistant biotype had a reduced sensitivity to acetolactate synthase inhibiting herbicides (halosulfuron and primisulfuron), a photosystem-II inhibitor (bromoxynil), and a protoporphyrinogen oxidase inhibitor (fluthiacet-methyl). Palmer amaranth biotypes were effectively controlled (≥ 90%) with glyphosate, glufosinate, and dicamba, whereas 2,4-D ester provided 81 to 83% control of the resistant biotype and > 90% control of both susceptible biotypes.
Nomenclature: 2,4-D; atrazine; bromoxynil; dicamba, fluthiacet-methyl; glufosinate; glyphosate; halosulfuron-methyl; lactofen; mesotrione; primisulfuron-methyl; pyrasulfotole; tembotrione; thiencarbazone-methyl; topramezone; Palmer amaranth, Amaranthus palmeri S. Wats; corn, Zea mays L; soybean, Glycine max (L.) Merr.
Amaranthus palmeri es una maleza de hoja ancha difícil de controlar que infesta campos de maíz y soya en el centro y oeste del sur de Nebraska y en varios otros estados en los Estados Unidos. Los objetivos de esta investigación fueron confirmar la existencia de A. palmeri resistente a triazine y herbicidas inhibidores de 4-hydroxyphenylpyruvate dioxygenase (HPPD) en Nebraska y determinar la sensibilidad y la eficacia de herbicidas para maíz aplicados POST para el control de biotipos de A. palmeri susceptibles y resistentes. Semillas de A. palmeri con resistencia putativa a HPPD provenientes del condado Fillmore, NE fueron colectadas de un campo de producción de maíz en el otoño de 2010. La respuesta de los biotipos de A. palmeri a 12 dosis (0 a 12×) de mesotrione, tembotrione, topramezone, y atrazine fue evaluada en un bioensayo de respuesta a dosis en un invernadero. Con base en los valores del nivel de dosis efectiva de 90%, los análisis mostraron una resistencia de 4 a 23 veces mayor dependiendo del tipo de herbicida inhibidor de HPPD investigado y del biotipo susceptible usado como comparación. Este biotipo también tuvo un nivel de resistencia a atrazine POST de 9 a 14 veces mayor. Los resultados del estudio de eficacia de herbicidas aplicados POST sugirieron una interacción sinérgica entre atrazine y herbicidas inhibidores de HPPD que resultó en >90% de control de todos los biotipos de A. palmeri
