Abstract
Redroot pigweed is one of the injurious agricultural weeds on a worldwide basis. Understanding of its interference impact in crop field will provide useful information for weed control programs. The effects of redroot pigweed on cotton at densities of 0, 0.125, 0.25, 0.5, 1, 2, 4, and 8 plants m-1 of row were evaluated in field experiments conducted in 2013 and 2014 at Institute of Cotton Research, CAAS in China. Redroot pigweed remained taller and thicker than cotton and heavily shaded cotton throughout the growing season. Both cotton height and stem diameter reduced with increasing redroot pigweed density. Moreover, the interference of redroot pigweed resulted in a delay in cotton maturity especially at the densities of 1 to 8 weed plants m-1 of row, and cotton boll weight and seed numbers per boll were reduced. The relationship between redroot pigweed density and seed cotton yield was described by the hyperbolic decay regression model, which estimated that a density of 0.20–0.33 weed plant m-1 of row would result in a 50% seed cotton yield loss from the maximum yield. Redroot pigweed seed production per plant or per square meter was indicated by logarithmic response. At a density of 1 plant m-1 of cotton row, redroot pigweed produced about 626,000 seeds m-2. Intraspecific competition resulted in density-dependent effects on weed biomass per plant, a range of 430–2,250 g dry weight by harvest. Redroot pigweed biomass ha-1 tended to increase with increasing weed density as indicated by a logarithmic response. Fiber quality was not significantly influenced by weed density when analyzed over two years; however, the fiber length uniformity and micronaire were adversely affected at density of 1 weed plant m-1 of row in 2014. The adverse impact of redroot pigweed on cotton growth and development identified in this study has indicated the need of effective redroot pigweed management.
Highlights
Redroot pigweed (Amaranthus retroflexus L.), an annual C4 weed, is listed as one of the most common dicotyledonous weeds in the world and is widely distributed in many agricultural areas [1]
Redroot pigweed at high densities resulted in strong shading of the cotton plants and prevented them from reaching their typical height; this is consistent with the competitive effect of velvetleaf (Abutilon theophrasti) on cotton observed by Cortés et al [36]
Average reductions of cotton plant height in 2013 and 2014 were approximately 13 and 2 cm, respectively, for each redroot pigweed plant m-1 of row according to regression equations, and redroot pigweed height increased about 12–18 cm for each redroot pigweed plant m-1 of row
Summary
Redroot pigweed (Amaranthus retroflexus L.), an annual C4 weed, is listed as one of the most common dicotyledonous weeds in the world and is widely distributed in many agricultural areas [1]. Considerable research has been reported on the interference and competitiveness of Amaranthus spp. species in cotton field, including tumble pigweed (A. albus), Palmer amaranth (A. palmeri), and redroot pigweed. Rushing et al [20] reported that the threshold density where initial cotton yield reductions occurred at 4–16 tumble pigweed plants 10 m-1 of row and cotton yields were reduced 8–11 kg ha-1 for each additional weed plant 10 m-1 of crop row. MacRae et al [23] found that Palmer amaranth competition could result in a significant reduction (60%) in cotton yield at an approximate density of 1.6 weed plants m-1 of row when weed plants were transplanted into 3- or 8-leaf cotton. The cotton yield loss due to redroot pigweed competition was reported to be 5–90% depending on the weed density and soil pattern [9]. Another study indicated that cotton yield and redroot pigweed density were highly correlated and the cotton yield loss ranged from 21 to 38 kg ha-1 for each redroot pigweed plant 15 m-1 of row [10]
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