Interactions between reduced rate of imazethapyr and multiple weed species–soyabean interference in a semi‐arid environment

Abstract

Yousefi AR, Gonzalez‐Andujar JL, Alizadeh H, Baghestani MA, Rahimian H & Karimmojeni H (2012). Interactions between reduced rate of imazethapyr and multiple weed species–soyabean interference in a semi‐arid environment. Weed Research.52, 242–251. Summary Field experiments were conducted to evaluate Xanthium strumarium and Amaranthus retroflexus competitive ability with soyabean under unsprayed and sprayed (half the recommended rate of imazethapyr) conditions. Weed density combinations of 0, 4, 8 or 12 plants m−1 of row for A. retroflexus and 0, 2, 4 or 8 plants m−1 of row for X. strumarium were established alone, and in all possible combinations. When X. strumarium and A. retroflexus were grown at the same density, X. strumarium contributed 60–69% of the total weed biomass depending on weed density. The half rate of imazethapyr reduced the biomass of both weed species by 90% as compared with untreated plots. Untreated A. retroflexus and X. strumarium reduced soyabean yields to 1911 kg and 1656 kg ha−1, respectively, while with the reduced rate of herbicide, the yield only decreased to 3612 kg and 3453 kg ha−1 respectively. The total weed density required to cause a 5% soyabean yield loss was 0.16 and 0.32 plants m−1 of row with no‐herbicide treatment, while with the half rate of imazethapyr, it increased up to 2.78 and 4.32 plants m−1 in 2007 and 2008 respectively. Owing to the higher competitive ability of X. strumarium, it should be given a greater priority for control than A. retroflexus in soyabean grown in a semi‐arid environment. The half rate of herbicide significantly decreased the competitive ability of X. strumarium and A. retroflexus indicating that, in soyabean, application of this rate might be more cost‐effective and more environment‐friendly than the recommended ones.

Maize and Weed Growth under Multispecies Competition

“…If the interaction becomes irrelevant ( = 0), as assumed by Kim et al (2006) and Yousefi et al (2012), TCL of the mixture density could be expressed by the equivalent density of the most competitive species. [3] as described by Yousefi et al (2012). [3] as described by Yousefi et al (2012).…”

“…procedure (equation) can be used to relate the biomass or seed of species j to the density of either species (Yousefi et al, 2012). procedure (equation) can be used to relate the biomass or seed of species j to the density of either species (Yousefi et al, 2012).…”

“…The total competitive load (TCL) is the sum of density equivalents of both species. If the interaction becomes irrelevant ( = 0), as assumed by Kim et al (2006) and Yousefi et al (2012), TCL of the mixture density could be expressed by the equivalent density of the most competitive species. Total competitive load was calculated as described by Fu and Ashley The relationship between multispecies weed densities and biomass or seed production by given weed species was analyzed using Eq.…”

“…Total competitive load was calculated as described by Fu and Ashley The relationship between multispecies weed densities and biomass or seed production by given weed species was analyzed using Eq. [3] as described by Yousefi et al (2012).…”

Intercropping of fenugreek as living mulch at different densities for weed suppression in coriander

“…This yield reduction is very likely caused by the competition for light, water and nutrients between the living mulch and main crop (Thorsted et al, 2006). Plant density has been shown to be a main factor which changes the outcome of competition in plant community (Yousefi et al, 2012). In some cases, increased plant density leads to quicker canopy closure, increased crop interference and greater weed suppression, resulting in increased yields (Kolb et al, 2012;Jamshidi et al, 2013).…”