Biological characteristics and herbicide susceptibility of five weed species of the Amaranthus genus.

Author(s)

Saul Jorge Pinto de Carvalho

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2007-01-26

Examining board members

Pedro Jacob Christoffoleti; Ramiro Fernando Lopez Ovejero; Ricardo Victoria Filho

• Advisor: Pedro Jacob Christoffoleti

Abstract

Plant species classified in the Aramanthus genus are frequently found infesting brazilian agricultural areas, although there are few researches that evaluated the biological characteristics and the control of these species. Therefore, this work was conducted with the objective of analyzing the germination, the growth and the development, estimating the leaf area, the competitiveness and the susceptibility to herbicides of five weed species of the Aramanthus genus. The species of Aramanthus studied were: A. deflexus, A. hybridus, A. retroflexus, A. spinosus and A viridis. The experiment that evaluated the germination was conducted in the Laboratory of Seed Analyses and the others in the greenhouse of the Crop Science Department of ESALQ/USP, Piracicaba - SP, in the period comprehended between March to December 2005. About the germination, it was established that variation in the availability of light and temperature interferes in all the species of Aramanthus and the highest levels of germination were obtained in condition of photoperiod with alternating temperature (8h-light-30°C / 16h-dark-20°C). In less favorable conditions, A. viridis and A. hybridus obtained higher germination levels than all the other species. In general, A. deflexus and A. spinosus were the weed species that presented the lowest rates of germination speed. About the growth and development, it was observed that A. deflexus was the species with shortest vegetative cycle, the lowest dry mass and leaf area accumulation; however, A. retroflexus and A. hybridus were the species which reached the highest values for these variables. The leaf area estimation showed that the linear equation crossing the origin (Ar=a.(C.L)) was adequate to adjust the correlation between the linear blade dimensions and the real leaf area for all the species. About competition, it was concluded that the crop of common bean is more competitive than all the weed species of the Aramanthus genus that were studied in this work, when grown in equivalent proportion; A. deflexus and A. viridis were the species which phenology was less affected by the competition with common bean; the intraspecific competition was the most damaging to the crop of common bean, what suggests that the damages caused by the weeds are more connected with its high density of infestation than the intrinsic competitive ability of the species. The control obtained for the Aramanthus species evaluated in this research presented differences of susceptibility to post-emergence applied herbicides, mainly to trifloxysulfuron-sodium and chlorimuron-ethyl, which A. deflexus was the least susceptible species, followed by A. spinosus, A. viridis, A. hybridus and A. retroflexus. (AU)