Relative time of redroot pigweed (Amaranthus retroflexusL.) emergence is critical in pigweed-sorghum [Sorghum bicolor(L.) Moench] competition

Abstract

Redroot pigweed is a common weed in sorghum fields throughout the southcentral United States including Kansas. In 1994 and 1995, field studies were conducted at two sites near Manhattan, KS, to determine the influence of redroot pigweed densities and times of emergence on sorghum yield and yield components. Redroot pigweed was sown at densities of 0.5, 1, 2, 4, and 12 plants meter−1of row within a 25-cm band over the sorghum row at planting and at the three- to four-leaf stage of sorghum. A rectangular hyperbola was used to describe the relationship between crop yield loss and weed density. Because of the instability of both coefficientsI(percentage yield loss at low weed density) andA(percentage yield loss at high weed density), our results do not support the use of a model based exclusively on weed number to estimate sorghum yield loss across all locations within a region. A quadratic polynomial equation that accounts for the time of weed emergence relative to the crop growth stage is suggested as an alternative method to estimate sorghum yield loss. At the densities studied, the time of pigweed emergence relative to the sorghum leaf stage was critical for the outcome of sorghum-pigweed competition. Significant sorghum yield losses occurred only when pigweed emerged before the 5.5-leaf stage of sorghum. An examination of yield components suggested that the yield loss was a result of a reduction in number of seeds per head.

Early season height differences as robust predictors of weed growth potential in maize: new avenues for adaptive management?

“…60 cm; this relationship progressively strengthened as the maize canopy developed. Our results are also consistent with evidence from critical period studies demonstrating that later emerging weeds tend not to impact crop yield (Martin & Field, 1988; Knežević et al. , 1997).…”

Population genetic structure of the noxious weed Amaranthus retroflexus in Central Europe

“…Their vigorous aggressive growth and production of allelopathic chemicals allow them to compete strongly against other plants and significantly reduce grain yield and quality (Keeley et al, 1987;Knezevik et al, 1997;Murphy et al, 1996). Besides reduced yields, which have been observed in several crops (Gossett et al, 1992;Klingaman and Oliver, 1994;Vizantinopoulos and Katranis, 1998), compounds that may induce toxicosis and death in livestock have been documented in A. retroflexus (Kerr and Kelch, 1998).…”

Competition for canopy cover between accessions of Phalaris minor that are susceptible and resistant to ACCase inhibiting herbicides

“…The onset of competition can affect the plant growth pattern (Knezevic et al , Uscanga‐Mortera et al ). Wiederholt and Stoltenberg (1996, 1996b) observed a linear relationship in biomass accumulation and leaf area in Digitaria sanguinalis and Setaria faberi biotypes that were R or S to ACCase inhibitors.…”