Levantamento fitossociológico de plantas daninhas na cultura do girassol

Abstract

RESUMO -O levantamento fitossociológico da comunidade de plantas daninhas na cultura do girassol foi realizado em duas épocas distintas: no desenvolvimento inicial da cultura (entre 20 e 40 dias após a semeadura) e na pré-colheita do girassol. As espécies de plantas daninhas foram identificadas e quantificadas pelo método do quadrado inventário (1,0 x 1,0 m), com amostragem de 12 m 2 por área. Os levantamentos foram realizados em 54 propriedades de seis municípios da região do cerrado e em 38 propriedades de oito municípios da região dos pampas, que são as duas principais regiões produtoras brasileiras. , para o Rio Grande do Sul. O índice de similaridade dentro das regiões foi de 0,91 para os levantamentos do cerrado e de 0,79 para os do Rio Grande do Sul. Entretanto, entre as regiões, os índices ficaram abaixo de 0,5, mostrando similaridade mediana entre a flora daninha do cerrado e a do Rio Grande do Sul, na cultura do girassol, nas duas épocas estudadas.Palavras-chave: competição, fitossociologia, Helianthus annuus, infestação.ABSTRACT -A phytosociological survey of the weed communities present in sunflower crop was carried out during two distinct crop stages: early development and pre-harvest. Weed species were identified and quantified according to the inventory square method (1.0 x 1.0 m), using 12 m 2 of sampling per area surveyed. At each stage, the survey was carried out on 54 farms of six counties of the "cerrado" (savanna region, Central Brazil) and 38 farms of eight counties of the "Pampas" (region in the State of Rio Grande do Sul, the Southernmost state in Brazil), which are the two main Brazilian sunflower production regions. Frequency, relative frequency, density, relative density, abundance, relative abundance, relative importance index, and similarity index were computed. A total of 60 weed species were identified, 17 of which were present in both regions. Asteraceae and Poaceae were the two main families among the 16 found. The main species present in the "cerrado" were Euphorbia heterophylla, Chamaesyce hirta, Ageratum conyzoides, Commelina benghalensis, Zea mays and Bidens sp. The most abundant species present in the State of Rio Grande do Sul were Bidens sp., Raphanus raphanistrum, Lolium multiflorum, Gnaphalium spicatum, Sonchus oleraceus, Euphorbia heterophylla, Sida rhombifolia, Digitaria sp. and Ipomea sp. Weed density was higher at pre-harvest than at the early stage of the crop, in both

Interferência de plantas daninhas na cultura do sorgo sacarino

“…Periods of interference can be determined considering the phenological stage of the crop or time periods after sowing and/or emergence. To better characterize the CPWC, it is interesting to assess the behavior of the weed community throughout the crop cycle, so that it is possible to understand the existing interactions and which species are being selected by the management system and practices in the area (Adegas et al, 2010).…”

Phytosociology of weed community in two vegetable growing systems

“…stood out in this survey, as shown in Table 4. Adegas et al (2010) stressed the importance of knowing the weed species throughout the crop cycle to enable decision making regarding the best method of control (Table 4).…”

Weed Phytosociological and Floristic Survey in Agricultural Areas of Southwestern Goiás Region

“…From the quantification of weeds by species and determination of dry biomass, one proceeded to the descriptive analysis, calculating the absolute and relative values of density (D and RDe), frequency (F, RF), dominance (ADo and RDo), and importance value index (IVI), following the same methods used by Adegas et al (2010) and Corrêia et al (2011), according to the formulas proposed by Mueller-Dombois and Ellenberg (1974), represented in the expressions below: D = total number of individuals of the species/total area (m 2 ) sampled; RDe = species density/density of all species x 100; F = number of frames where the species was found/total number of frames of the sampling; RF = species frequency/frequency of all species x 100; ADo = accumulated dry biomass of the species/total of dry biomass of the sample; RDo = dominance of the species/ dominance of all species x 100; and IVI = RF + RDe + RDo.…”

“…Families Asteraceae, Poaceae and Euphorbiaceae were the ones that contributed the largest number of species in sunflower crops in Brazilian municipalities Chapadão do Céu, Jataí and Montividiu, in Goiás (Brighenti et al, 2003, Adegas et al, 2010. These families were also representative in the soybeans rotated with maize and rice in Brazilian state Roraima (Cruz et al, 2009).…”

“…The other families (13 of the total) contributed with a single species. In sunflower cultivation in Goiás, Adegas et al (2010) have recorded 41 species distributed in 13 botanical families. Of this total, 24 species were equal to the ones in the present study.…”