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1 March 2016 Tall Waterhemp ( Amaranthus tuberculatus) and Palmer amaranth ( Amaranthus palmeri) Seed Production and Retention at Soybean Maturity
Lauren M. Schwartz, Jason K. Norsworthy, Bryan G. Young, Kevin W. Bradley, Greg R. Kruger, Vince M. Davis, Larry E. Steckel, Michael J. Walsh
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Abstract

Two of the most problematic Amaranthus species in soybean production today are tall waterhemp and Palmer amaranth. This study determined the percentage of tall waterhemp and Palmer amaranth seed that was retained by the weed at soybean maturity to assess the likelihood of using at-harvest weed seed control tactics for soil seedbank management. Palmer amaranth plants were collected from fields in Arkansas, Tennessee, Illinois, Missouri, and Nebraska, and tall waterhemp plants were collected from fields in Nebraska, Missouri, Wisconsin, and Illinois. Collected plants were assessed for at-harvest weed seed retention in 2013 and 2014. Within 1 wk of soybean maturity, Amaranthus plants were harvested and the loose soil and debris beneath the plants were swept into a pan with a hand broom to collect any shattered seed. Percent seed retention ranged from 95 to 100% for all states both years, regardless of species. There was a strong correlation between weed biomass (g) and total seed production (no. plant−1) in that the larger the plant, the more seeds it produced. However, there was no correlation between percent seed retention and weed biomass, which indicates that regardless of plant size and likely time of emergence, seed retention is high at the time of crop maturity. Overall, this study demonstrated that there is great opportunity for Palmer amaranth and tall waterhemp seed capture or destruction at soybean harvest. It is likely that nearly all of the seeds produced for both Amaranthus species passes through the combine during harvest to be returned to the soil seedbank. Thus, there is continued need for research focused on developing and testing harvest weed seed control tactics that aim at reducing the soil seedbank and lowering risks for evolution of herbicide resistance.

Nomenclature: Palmer amaranth, Amaranthus palmeri S. Wats.; tall waterhemp, Amaranthus tuberculatus (Moq.) Sauer; soybean, Glycine max (L.) Merr.

Dos de las especies de Amaranthus más problemáticas en la producción de soja, hoy en día, son Amaranthus tuberculatus y Amaranthus palmeri. Este estudio determinó el porcentaje de semilla de A. tuberculatus y A. palmeri que fue retenido por la maleza al momento de la madurez de la soja, para evaluar la probabilidad de usar tácticas para el control de semilla de malezas durante la cosecha para el manejo del banco de semillas. Plantas de A. palmeri fueron colectadas en campos en Arkansas, Tennessee, Illinois, Missouri, y Nebraska, y plantas de A. tuberculatus fueron colectadas en campos en Nebraska, Missouri, Wisconsin, e Illinois. Las plantas colectadas fueron evaluadas por su retención de semilla al momento de la cosecha en 2013 y 2014. A la semana de la madurez de la soja, las plantas de Amaranthus fueron cosechadas y el suelo suelto y los residuos vegetales debajo de las plantas fueron removidos con una escoba de mano y fueron depositados en un contenedor para colectar semilla que hubiera caído al suelo antes de la cosecha. El porcentaje de retención de semilla varió de 95 a 100% en todos los estados y en ambos años, sin importar la especie. Hubo una correlación alta entre la biomasa de la maleza (g) y el total de semilla producida (no. planta−1), así entre más grande la planta, más semilla produjo. Sin embargo, no hubo una correlación entre el porcentaje de retención de semilla y la biomasa de la maleza, lo que indica que sin importar el tamaño de la planta y el momento de emergencia, la retención de la semilla es alta al momento de la madurez del cultivo. En general, este estudio demostró que existe una gran oportuni

Lauren M. Schwartz, Jason K. Norsworthy, Bryan G. Young, Kevin W. Bradley, Greg R. Kruger, Vince M. Davis, Larry E. Steckel, and Michael J. Walsh "Tall Waterhemp ( Amaranthus tuberculatus) and Palmer amaranth ( Amaranthus palmeri) Seed Production and Retention at Soybean Maturity," Weed Technology 30(1), 284-290, (1 March 2016). https://doi.org/10.1614/WT-D-15-00130.1
Received: 18 August 2015; Accepted: 1 September 2015; Published: 1 March 2016
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