Experiments were conducted in 2008 and 2009 in Fayetteville, AR, to determine the influence of late-season herbicide applications on control, seed reduction, seed viability, and seedling fitness of two glyphosate-resistant (GR) Palmer amaranth biotypes, one from Mississippi County (MC) and the other from Lincoln County (LC) in Arkansas. Glyphosate (870 g ae ha−1), glufosinate (820 g ai ha−1), 2,4-D amine (1,060 g ae ha−1), dicamba (280 g ae ha−1), and pyrithiobac (70 g ai ha−1) were each applied at the first visible sign of inflorescence of GR Palmer amaranth plants. Glufosinate, 2,4-D, and dicamba provided 52 to 74% control of MC GR Palmer amaranth plants 28 d after treatment (DAT). The LC biotype was larger (94 cm tall) than the MC biotype was (64 cm tall) at application and was more difficult to control. Although control of GR Palmer amaranth was inadequate, late-season applications of glufosinate, 2,4-D, and dicamba reduced seed production of the LC biotype by 75 to 87% and production of the MC biotype by 94 to 95% compared with nontreated plants. Irrespective of biotypes, glufosinate, 2,4-D, and glyphosate reduced 100-seed weight by 22% compared with the nontreated control, and viability of seeds produced by treated plants was only 45 to 61% compared with 97% seed viability in nontreated plants. Glyphosate, glufosinate, 2,4-D, or dicamba reduced cumulative seedling emergence by an average of 84% compared with the nontreated check. Seedling biomass was four times greater for the LC than for the MC biotype, suggesting greater vigor and fitness for the LC progeny. This research demonstrates that a single, late-season (early inflorescence stage) application of glufosinate, 2,4-D, or dicamba could potentially reduce seedbank replenishment of GR Palmer amaranth. Additionally, reduction in seed weight, viability, and seedling recruitment would impair the success of GR Palmer amaranth progeny in the following season.
Nomenclature: 2,4-D amine; dicamba; glufosinate; glyphosate; pyrithiobac; Palmer amaranth, Amaranthus palmeri S. Wats.
Se realizaron experimentos en 2008 y 2009 en Fayetteville, AR, para determinar la influencia de aplicaciones de herbicidas tarde en la temporada de producción sobre el control, la reducción en la producción de semilla, la viabilidad de la semilla y el desempeño de las plántulas de dos biotipos de Amaranthus palmeri resistentes a glyphosate (GR), uno del condado de Mississippi (MC) y el otro del condado Lincoln (LC) en Arkansas. Glyphosate (870 g ae ha−1), glufosinate (820 g ai ha−1), 2,4-D amine (1,060 g ae ha−1), dicamba (280 g ae ha−1) y pyrithiobac (70 g ai ha−1), fueron aplicados al primer signo visible de las inflorescencias de las plantas de A. palmeri GR. Glufosinate, 2,4-D y dicamba brindaron un control de 52 a 74% de las plantas MC de A. palmeri GR 28 días después del tratamiento (DAT). El biotipo LC fue más grande (94 cm de altura) que el biotipo MC (64 cm de altura) al momento de la aplicación y fue más difícil de controlar. Aunque el control de A. palmeri GR fue inadecuado, las aplicaciones tardías en la temporada con glufosinate, 2,4-D y dicamba redujeron la producción de semillas del biotipo LC de 75 a 87% y 94 a 95% del biotipo MC en comparación con las plantas no-tratadas. Independientemente del biotipo, glufosinate, 2,4-D y glyphosate redujeron el peso 100-semillas en 22% comparados con el testigo no-tratado, y la viabilidad de las semillas producidas por las plantas tratadas fue solamente 45 al 61% comparadas con 97% de viabilidad de las plantas no-tratadas. Glyphosate, glufosinate, 2,4-D o dicamba
