Interference of Palmer amaranth in corn

Abstract

Palmer amaranth (Amaranthus palmeri) is a major weed in corn (Zea mays) fields in the southern Great Plains of the United States. Field studies were conducted in 1996, 1997, and 1998 near Garden City, KS, to evaluate the effects of Palmer amaranth density and time of emergence on grain yield of irrigated corn and on seed production of Palmer amaranth. Palmer amaranth was established at densities of 0.5, 1, 2, 4, and 8 plants m−1 of corn row both concurrently at corn planting and when corn was at the three- to six-leaf stage. The control plots were weed free. The Palmer amaranth planted with corn emerged with corn, whereas that planted later emerged at the four-, six-, and seven-leaf stages of corn. The Palmer amaranth emerging with corn reduced yield from 11 to 91% as density increased from 0.5 to 8 plants m−1 of row. In contrast, yield loss from Palmer amaranth emerging later than corn was observed only when the emergence occurred at the four- and six-leaf stages. The corn leaf area index (LAI) decreased as Palmer amaranth density increased. Reduction in corn LAI from Palmer amaranth interference was smaller for the second emergence date than for the first emergence date. Seed production per Palmer amaranth plant decreased with greater density, but seed per unit area increased from 140,000 to 514,000 seeds m−2 at densities of 0.5 and 8 plants m−1 of row, respectively, when Palmer amaranth emerged with corn and from 1,800 to 91,000 seeds m−2 at the same densities for later emergence dates. Although Palmer amaranth is highly competitive in corn, this study shows that yield loss is affected more by time of emergence than by density.

Nonhybrid Progeny from Crosses of Dioecious Amaranths: Implications for Gene-Flow Research

“…Weed seed yields were between 1,800 and 91,000 seeds m À2 for the same densities when Palmer amaranth emerged when corn was at the four to seven leaf stage (Massinga et al 2001). When growing with peanut (Arachis hypogaea L.), there was a hyperbolic relationship between Palmer amaranth seed production per area and Palmer amaranth plant density; maximum seed production of 124,000 seed m À2 (1.2 billion seed ha…”

“…In Kansas, Palmer amaranth that emerged with the crop reduced corn yields 11 to 91% at densities of 0.5 to 8 plants m À1 (rows spaced 76 cm apart) (Massinga et al 2001). When Palmer amaranth emergence occurred at the four-to sevenleaf stage of corn, Palmer amaranth interference resulted in corn yield reductions of 7 to 35% at 0.5 to 8 plants m À1 (Massinga et al 2001).…”

Mechanism of extreme genetic recombination in weedy Amaranthus hybrids

“…increased from 140,000 to 514,000 as weed density increased from 0.5 to 8 plants m À1 of row, for weeds that emerged with corn (Zea mays L.) in Kansas (Massinga et al 2001). Weed seed yields were between 1,800 and 91,000 seeds m À2 for the same densities when Palmer amaranth emerged when corn was at the four to seven leaf stage (Massinga et al 2001).…”

Ajuste de modelo para quantificar o efeito de plantas daninhas e época de semeadura no rendimento de soja

“…Quando o modelo de Cousens (1985) é baseado exclusivamente na densidade de plantas daninhas, é comum superestimar esse parâmetro, inclusive ocorrendo valores superiores a 100% (Jasieniuck et al, 1999;Massinga et al, 2001). De forma similar ao verificado com os demais parâmetros do modelo, o parâmetro c não diferiu entre ambientes.…”

“…Nas equações de perdas de rendimento, X é a densidade de plantas daninhas; T é a época de semeadura. Uma análise conjunta dos resultados de validação (Tabela 2) revela que, de maneira geral, os modelos testados apresentaram capacidade previsiva satisfatória, diferentemente do que foi salientado por Webster et al (2000) e Massinga et al (2001). No entanto, é importante esclarecer que, mesmo se utilizando rendimentos de grãos de soja livre de plantas daninhas de experimentos vizinhos conduzidos na área experimental, para se calcular as perdas utilizadas na validação, o efeito das plantas daninhas foi mensurado em parcelas testemunhas contíguas aos experimentos; portanto, no mesmo ano de realização dos experimentos que propiciaram o ajuste do modelo.…”