Weed Phytosociological Survey in Irrigated Rice

Levantamento Fitossociológico de Plantas Daninhas na Cultura do Arroz Irrigado

F.S. NUNES C.E. SCHAEDLER D.M. CHIAPINOTTO About the authors

ABSTRACT:

The phytosociological method helps evaluate the vegetation composition. The objective of this study was to identify and quantify the main weed species present in irrigated rice. The phytosociological survey was carried out in three mainly rice monoculture, Clearfield® technology using properties in Itaqui-RS, between 2013 and 2014. For each property and period, a ½ ha representative area was selected and 10 random samples were collected, using a quadrat square of 1 m2. The sample colletion was conducted in two periods of time: during the irrigated rice crop initial growth and during the cereal’s pre-harvesting phase. All collected plants were identified and counted, allowing for their frequency, relative frequency, density, relative density, abundance, relative abundance, relative importance index and similarity index to be calculated. Eleven weed species belonging to five families were identified. Poaceae and Cyperaceae occurred more frequently. During the initial growth of rice, the Poaceae family presented the largest index of relative importance, mainly to Echinochloa crus-galli, Echinochloa colona and Digitaria horizontalis. Overall, there was a reduction in plant density in the pre-harvest period. However, Echinochloa colona and Oryza sativa occurred in density levels that may interfere with the cereal yield. Aeschynomene denticulata, Cyperus iria and Oryza sativa are not controlled efficiently, indicating possible cases of herbicide resistance. Our conclusions emphasize the importance of correct weed species identification for the management of Echinochloa colona and Cyperus ferax. Integrated management practices are necessary for efficient weed control, avoiding productivity loss in the region’s flooded rice fields.

Keywords:
phytosociology; Oryza sativa; identification

RESUMO:

O método fitossociológico permite avaliar a composição da vegetação. Objetivou-se neste estudo identificar e quantificar as principais plantas daninhas ocorrentes na cultura do arroz irrigado. O levantamento fitossociológico foi realizado no município de Itaqui-RS, entre 2013 e 2014, em três propriedades, em que predomina a monocultura e tecnologia Clearfield®. Em cada propriedade foi selecionada uma área representativa de ½ ha, onde foram realizadas 10 amostragens aleatórias, utilizando quadrado inventário (1 m2). A coleta ocorreu em duas épocas: durante o crescimento inicial da cultura e na pré-colheita do cereal. Após cada coleta, as plantas foram identificadas, sendo registradas a frequência, frequência relativa, densidade, densidade relativa, abundância, abundância relativa, índice de importância relativa e índice de similaridade. No total, foram identificadas 11 espécies de plantas daninhas, pertencentes a cinco famílias. As famílias Poaceae e Cyperaceae ocorreram com maior frequência. Durante o crescimento inicial do arroz, observou-se amplo índice de importância relativa da família Poaceae, principalmente para Echinochloa crus-galli, Echinochloa colona e Digitaria horizontalis. De modo geral, houve redução na densidade de plantas no período de pré-colheita. No entanto, Echinochloa colona e Oryza sativa ocorreram em níveis de densidade que podem interferir na produtividade do cereal. Aeschynomene denticulata, Cyperus iria e Oryza sativa não são controladas de modo eficiente, indicando possíveis casos de resistência a herbicidas. Salienta-se a importância da correta identificação das espécies para o manejo de Echinochloa colona e Cyperus ferax. São necessárias práticas de manejo integrado para controle eficiente das plantas daninhas, evitando perdas de produtividade em lavouras de arroz irrigado da região.

Palavras-chave:
fitossociologia; Oryza sativa; identificação

INTRODUCTION

Irrigated rice growing is characterized by a high occurrence of a veriety of weed species (Sosbai, 2014Sociedade Sul-Brasileira de Arroz Irrigado - Sosbai. Arroz irrigado: recomendações técnicas da pesquisa para o sul do Brasil. Santa Maria: 2014. 192p. ). Weeds cause significant losses in rice crops, by competing for water before the flood period, for light, for mineral nutrients and through indirect actions (acting as parasites hosts), lowering both productivity and grain quality (Cobucci and Noldin, 2006Cobucci T., Noldin J.A. Plantas daninhas e seu manejo. In: Santos A.B., Stone L.F., Vieira N.R.A., editores. A cultura do arroz no Brasil. 2ª.ed. Santo Antônio de Goiás: Embrapa; 2006. p.633-81.). This way, they constitute the greatest biotic limiting factor to the cereal’s productive potential (Agostinetto et al., 2011Agostinetto D. et al. Resistência de Cyperus difformis L. ao herbicida pyrazosulfuron-ethyl e alternativas de controle. Semina: Ciênc Agr. 2011;32:839-48.).

Weed interference in irrigated rice growing varies according to the weed species, the infestation intensity, the cultivar and the field handling (Panozzo et al., 2009Panozzo L.E. Métodos de manejo deCyperus esculentusna lavoura de arroz irrigado. Planta Daninha. 2009;27:165-74.). This way, identifying the species in an area, as well as its relative significance (frequency, density and dominance), is the first step to the adequate weed handling. Species identification and classification then allows for an informed decision on the best way to handle the weed (Oliveira and Freitas, 2008Oliveira A.R., Freitas S.P. Levantamento fitossociológico de plantas daninhas em áreas de produção de cana-de-açúcar. Planta Daninha. 2008;26:33-46.).

Correct weed identification is crucial, as each species has a different settlement potential and interference capacity among different kinds of growing practices (Cruz et al., 2009Cruz D.L.S. Levantamento de plantas daninhas em área rotacionada com as culturas da soja, milho e arroz irrigado no cerrado de Roraima. Agroambiente On-line. 2009;3:58-63.). It should also be noted that the establishment of an infesting community in a certain area varies according to each place’s edaphoclimatic conditions and to the local cultivating practices. There may also occur differences among regions due to different crop implantation system (Adegas et al., 2010Adegas F.S. et al. Levantamento fitossociológico de plantas daninhas na cultura do girassol. Planta Daninha. 2010;28:705-16.).

Weed botanical identification and quantification may be achieved through the phytosociological method (Braun-Blanquet, 1979Braun-Blanquet V. Fitosociología, bases para el estudio de las comunidades vegetales. Madrid: H. Blume; 1979. 820p.). This method may provide specific data like frequency, density and abundance, as well as the relation between each weed species and the total weed population in a given area, representing an important inference tool about the target weed flora (Erasmo et al., 2004Erasmo E.A.L., Pinheiro L.L.A., Costa N.V. Levantamento fitossociológico das comunidades de plantas infestantes em áreas de produção de arroz irrigado cultivado sob diferentes sistemas de manejo. Planta Daninha. 2004;22:195-201.).

The phytosociological survey is of special concern, since it will allow for decisions about which actions will be carried out in handling the weed, as well as how and when each action should be performed (Oliveira e Freitas, 2008Oliveira A.R., Freitas S.P. Levantamento fitossociológico de plantas daninhas em áreas de produção de cana-de-açúcar. Planta Daninha. 2008;26:33-46.). The Rio Grande do Sul state’s Western Border is the largest irrigated rice producing region in Brazil (IRGA, 2013Instituto Rio Grandense do Arroz - IRGA. Produtividade municipal - safra 2012/ 2013. [accessed in: October 14 2016] Available at: Available at: http://www3.irga.rs.gov.br/uploads/anexos/1374499016 File: SAFRA_2012_13_RS_MUNICIPAL.pdf .
http://www3.irga.rs.gov.br/uploads/anexo...
). Nevertheless, there are no studies on the local weed population’s composition.

In this paper, we describe the phytosociological survey of weed in Rio Grande do Sul Western Border irrigated rice cultures.

MATERIAL AND METHODS

The phytosociological survey was carried out in three irrigated rice producing areas, all located in Itaqui, a city in Rio Grande do Sul Western Border, between 2013 and 2014. In this region, rice is mostly grown in soils of the classes Plinthsol, Gleysol, Chernozem and Planosol (Plintossolo, Gleissolo, Chernossolo e Planossolo, respectively, in the Brazilian Soil Classification System), making up for 76.57% of the area, occurring in a plane and lightly undulated area of restricted drainage. The most prevalent soil class is the Plinthsol Argilluvic petroplinthic euthrophic (56.78%), followed by the Gleysol Haplic Tb euthrophic typical (11,13%), the Chernozem Ebanic carbonatic vertic (7.93%) and the Planosol Haplic euthrophic arenic (0,73%) (Bohn Gass et al., 2015Bohn Gass S.L. Estruturação do banco de dados e caracterização básica do município de Itaqui, RS, Brasil, para fins de seu Zoneamento Ecológico-Econômico. In: Anais do 17º Simpósio Brasileiro de Sensoriamento Remoto - SBSR. 2015. João Pessoa: INPE; 2015. p.4073-81. ). The climate is of the Cfa (Köppen) type, subtropical humid, with hot summers and without a definite dry season (Kuinchtner et al., 2001Kuinchtner A., Buriol G.A. Clima do Estado do Rio Grande do Sul segundo a classificação climática de Köppen e Thornthwaite. Disciplin Scien. 2001;2:171-82.).

The studied estates are mainly dedicated to rice monoculture, using the Clearfield® production system with the Puitá INTA-CL cultivar (Sosbai, 2014Sociedade Sul-Brasileira de Arroz Irrigado - Sosbai. Arroz irrigado: recomendações técnicas da pesquisa para o sul do Brasil. Santa Maria: 2014. 192p. ). This technology uses imidazolinone resistant rice genotypes, aiming mainly at the handling and control of weed rice (Menezes et al., 2013Menezes V.G. et al. Associação de glyphosate e imidazolinonas no controle de arroz-vermelho em arroz Clearfield®.Ciênc Rural. 2013;43:2154-9. ). Property 1 is characterized by the growth of rice/rice and Property 2 by rice/fallow. In both cases, the Clearfield® technology has been used for the last six consecutive years, regardless the manufacturer recommendations to the contrary. In Property 3, also characterized by a rice/rice cycle, this was the first year the Clearfield® technology was used. Weed handling is achieved by the chemical method.

The phytosociological survey was conducted in two periods of time: 1) between November and December 2013, during the irrigated rice cultivation initial growth (CI) - this stage occurred up to 25 days after seeding (DAS), when the rice plants were up to the V4 stage (Counce, 2000Counce P.A. et al. A uniform, objective, and adaptative system for expressing rice development. Crop Sci. 2000;40:436-43.) to a tiller, and before the chemical handling of the weed; and 2) the second collection occurred between February and March 2014, during the cereal’s pre-harvesting period (PRÉ).

In properties 1 and 2, the weed gathering was conducted in November (CI) and February (PRÉ); in property 3 in December (CI) and March (PRÉ). The evaluation procedure used a quadrat square of 1 m2, as suggested by Braun-Blanquet (1979Braun-Blanquet V. Fitosociología, bases para el estudio de las comunidades vegetales. Madrid: H. Blume; 1979. 820p.). For each property and period, a ½ ha representative area was selected and 10 random samples were collected. After the sample gathering, the weeds found in each are were cut close to the ground, pressed between paper sheets and sent to the laboratory, where they were botanically identified into family, gender and species, by an expert and through the use of specialized literature (Lorenzi, 2014Lorenzi H. Manual de identificação e controle de plantas daninhas, plantio direto e convencional. 7ª.ed. Nova Odessa: Instituto Plantarum; 2014. 384p.).

Besides the botanical identification, the following parameters were calculated, following Mueller-Dombois e Ellemberg (1974Mueller-Dombois D., Ellemberg H.A. Aims and methods of vegetation ecology. New York: John Wiley and Sons; 1974. 574p.): frequency (F), relative frequency (Fr), density (D), relative density (Dr), abundance (A), relative abundance (Ar) and the relative importance index (Ir).

The weeds similarity index was determined between both the two different periods (CI and PRÉ) and the different properties. The index was calculated according to Sorensen (1972Sorensen T.A. Method of stablishing groups of equal amplitude in plant society based on similarity of species content. In: Odum E.P. Ecologia. 3ª.ed. México: Interamericana; 1972. p.341-405.) proposal:

A dissimilarity matrix by “1-IS” was generated from each similarity index. This way, it was possible to build a dendrogram by the unweighted pair-group method using arithmetic averages (UPGMA) (Sneath and Sokal, 1973Sneath P.H., Sokal R.R. Taxonomia numérica: os princípios e práticas de classificação numérica. São Francisco: WH Freeman; 1973. 573p.).

RESULTS AND DISCUSSION

The phytosociological survey identified eleven (11) distinct weed species from five botanical families (Table 1) infesting the irrigated rice cultures in Itaqui, Rio Grande do Sul Western Border. The Poaceae was the most representative weed family found in the phytosociological survey, with six (6) species, followed by the Cyperaceae (2), the Alimastaceae (1), the Fabaceae (1) and the Malvaceae (1). With the sole exception of the Sida rhombifolia (Malvaceae), all species found are typical of and/or adapted to humid environments (Lorenzi, 2014Lorenzi H. Manual de identificação e controle de plantas daninhas, plantio direto e convencional. 7ª.ed. Nova Odessa: Instituto Plantarum; 2014. 384p.).

Table 1
List of weed found in the irrigated rice tillages in the city of Itaqui, Rio Grande do Sul Western Border, in properties 1, 2 and 3, distributed by family and species - 2013/2014

In property 1, five weed species, grouped in four families, were identified during the initial growth (CI): Poaceae, Fabaceae, Cyperaceae and Alismataceae, with 117, 16, 10 and 2 specimens, respectively. The species with the largest relative importance index was the Echinochloa crus-galli (Table 2). In the pre-harvesting period, six weed species from three families were identified: Poaceae, Cyperaceae and Fabaceae, with 51, 6 and 5 specimens, respectively. The species with the largest relative importance index were the Oryza sativa and the Echinochloa colona (Table 3).

Table 2
First survey - Weed species found during the irrigated rice initial growth phase in properties 1, 2 and 3. Itaqui-RS, 2013
Table 3
Second survey - Weed species found during the irrigated rice pre-harvest phase in properties 1, 2 and 3. Itaqui-RS, 2014

In property 2, eight weed species, grouped in four families, were identified during CI: Poaceae, Malvaceae, Cyperaceae and Fabaceae, with 361, 41, 10 and 3 specimens, respectively. The species Digitaria horizontalis had the largest relative importance index, followed by the Echinochloa colona (Table 2). In the pre-harvesting period, six weed species from the families Poaceae and Cyperaceae were identified, with 22 and 9 specimens, respectively. The species Oryza sativa and Cyperus iria obtained the largest relative importance index (Table 3).

In property 3, four weed species, grouped in two families, were identified during CI: Poaceae and Malvaceae, with 243 and 3 specimens, respectively. The Digitaria horizontalis had the largest relative importance index, followed by the Echinochloa colona (Table 2). In the pre-harvesting period, four weed species from the families Poaceae and Malvaceae were identified, with 22 and 6 specimens, respectively. The species Digitaria horizontalis had the largest relative importance index (Table 3).

A high relative importance index was found for the Poaceae family, specially for Echinochloa crus-galli, Echinochloa colona and Digitaria horizontalis, in all three observed areas, during the rice initial growth phase. The densities of 10.7, 10.5 and 18.3 plants m-2, observed respectively in properties 1, 2 and 3, are at levels capable of interfering in the studied grain yield (Tabela 2). According to Vidal (2010Vidal R. Interação negativa entre plantas: inicialismo, alelopatia e competição. Porto Alegre: Ribas Antônio Vidal; 2010. 132p.), the critical interference prevention period for weed in irrigated rice was found to be between 10 and 40 days after the emergence. In order to avoid eventual loses, effective control measures must be taken before that period.

Altogether, the weed plants m-2 density was lower in all three studied properties during the pre-harvest period, when compared to the irrigated rice initial growth period. However, in property 1 the number of Echinochloa colona was higher during pre-harvest, and the Oryza sativa species also arose. Their density levels were 1.8 and 2.8 plants m-2, respectively. The most economically damaging weed in the majority of the regions composing the Rio Grande do Sul irrigated rice agro-industrial sector is the weedy rice (Oryza sativa) (Menezes et al., 2013Menezes V.G. et al. Associação de glyphosate e imidazolinonas no controle de arroz-vermelho em arroz Clearfield®.Ciênc Rural. 2013;43:2154-9. ).

The weedy rice emergence leads to economical, social and environmental losses (Agostinetto et al., 2005Agostinetto D. et al. Níveis de dano econômico para decisão de controle de genótipo simulador de arroz-vermelho em arroz irrigado. Rev Bras Agrocien. 2005;11:175-83. ); and since this weed presents morphophysiological similarities to the rice, it is had control effectively with herbicides (Sartori et al., 2014Sartori G.M.S. et al. Germinação de arroz irrigado e de biótipos de arroz-vermelho submetidas a diferentes temperaturas. Rev Ciênc Agron. 2014;45:319-26. ). As for the presence of Echinochloa spp, studies have shown that 20 plants m-2 can reduce rice productivity by a margin up to 80% (Vandevender et al., 1997Vandevender K.M., Costello T.A., Smith Jr. R.J. Model of rice (Oryza sativa) yield reduction as a function of weed interference. Weed Sci. 1997;45:218-24.).

The first survey was carried out before the tillage’s chemical handling; in the second survey, the reduction in the populations of certain weed species was lower than expected. According to Sosbai (2014Sociedade Sul-Brasileira de Arroz Irrigado - Sosbai. Arroz irrigado: recomendações técnicas da pesquisa para o sul do Brasil. Santa Maria: 2014. 192p. ), a minimum reduction of 90% should be expected. Nevertheless, in property 1, the Aeschynomene denticulata was reduced by 68.7% and the Cyperus iria by 40,0%, while the number of specimens in the Oryza sativa population grew 280%. The same happened in property 2, where the C. iria and the O. sativa populations were reduced by 30% and 20%, respectively (Tables 2and3).

These figures may be related to some species’ ability to produce two generations during the same crop, as in the case of the Cyperus iria (Galinato et al., 1999Galinato M.I., Moody K., Piggin C.M. Upland rice weeds of South and Southeast Asia. Makati City: IRRI; 1999. 156p.). However, the continuous use of the Clearfield® technology, in which the chemical handling employ herbicides with similar action mechanisms, may select for resistant weed populations. According to Lamego et al. (2009Lamego F.P. et al. Cross-resistance ofBidens subalternansto acetolactate synthase inhibitors in Brazil. Weed Res. 2009;49:634-41.), the reiterate use of herbicides with the same action mechanisms during a long time results in the selection of resistant specimens.

Another fact corroborating the herbicide resistant flora selection hypothesis is that in property 3, where the Clearfield® technology was introduced in that same year, the same tendency was not observed. All weeds presented a satisfactory reduction, with the sole exception of the Sida rhombifolia (Table 3). However, as this species is more commonly found in soy cultures (Fleck et al., 2004Fleck N.G. et al. Interferência de picão-preto e guanxuma com a soja: efeitos da densidade de plantas e época relativa de emergência. Ciênc Rural. 2004;34:41-8.), the correct active ingredient for its control may not have been used. So, the Clearfield® technology efficiency for weed control, when correctly used, is attested.

As for the similarity index, it allows for the evaluation of weed diversity, varying between 0 and 1. Since we used a dendrogram obtained from a dissimilarity matrix built using the grouping method (UPGMA), the lowest value indicates that all species are common in the compared areas, while the highest value indicates no common species. These informations are relevant to understand the variation of species in relation to the handling methods and practices adopted in each case (Concenço et al., 2013Concenço G. et al. Phytosociological surveys: tools for weed science. Planta Daninha. 2013;31:469-82.). So, the low and medium indexes between properties (Figure 1) show that the weed composition varied among the different studied places.

Figure 1
Dendrogram obtained from a dissimilarity matrix built using the grouping method (UPGMA), from data gathered int the phytosociological surveys conducted in properties 1, 2 and 3, during initial growth and pre-harvest phases of the irrigated rice cultures. Itaqui-RS, 2013/2014.

Examining the dendrogram between the two periods of time in the survey, property 3 obtained the highest similarity, with the same species being present during the irrigated rice initial growth and the pre-harvesting phases. In properties 1 and 2, a higher dissimilarity was observed between the species present in the two periods of time. This higher dissimilarity may indicate the incorrect handling of weed.

In property 1, the Echinochloa colona occurred only in the second evaluation. The active ingredients imazethapyr and (imazapyr + imazapic), commonly used in the Clearfield® technology for weed chemical handling, are recommended solely for the Echinochloa crus-galli control. The same reason would explain the appearance of Cyperus ferax e Leersia hexandra during property 2 second evaluation (Tables 2and3). Both cases emphasize the importance of correct weed identification, as the choice of the active ingredient depends on the species present at the target place (Erasmo et al., 2004Erasmo E.A.L., Pinheiro L.L.A., Costa N.V. Levantamento fitossociológico das comunidades de plantas infestantes em áreas de produção de arroz irrigado cultivado sob diferentes sistemas de manejo. Planta Daninha. 2004;22:195-201.).

The present phytosociological survey results indicate that the rice monoculture, even using fallow land, associated with a rice variety with low competing capability and the inadequate use of the Clearfield® technology, does not allow for an effective weed control in the Rio Grande do Sul Western Border. An effective control requires integrated handling strategies, in order to avoid significant crop losses.

The widespread use of the Puitá INTA-CL cultivar should be reconsidered, as it presents a low competitive capability against the weed species (Rubin et al., 2014Rubin R.S. et al. Habilidade competitiva relativa de arroz irrigado com arroz-vermelho suscetível ou resistente ao herbicida imazapyr + imazapic. Arq Inst Biol. 2014;81:173-9.).

So, the adoption of a culture handling is indispensable, allowing for the selection of more competitive cultivars and also for culture rotation. We also underline the importance of the herbicides active ingredients rotation in the surveyed areas, since the species Aeschynomene denticulata, Cyperus iria and Oryza sativa are not being efficiently controlled, possibly due to the selection pressure induced by the repeated and inadequate use of the Clearfield® technology herbicides.

There is a possibility that the Echinochloa colona and the Cyperus ferax are being handled incorrectly. In order to avoid herbicide resistant weed selection under the conditions found in the studied areas, the chemical handling could be carried out with glyphosate during the pre-sowing period and with clomazone or propanil after emergence, to control the Echinochloa colona. For the Cyperus ferax, bentazone or oxyfluorfen should be used (Agrofit, 2016Agrofit - Sistema de consulta a agrotóxicos registrados no Brasil. Ministério da Agricultura, Pecuária e Abastecimento. Defesa Sanitária Vegetal. [accessed in: July 12 2016] Available at: Available at: http://www.agricultura.gov.br/agrofit .
http://www.agricultura.gov.br/agrofit...
).

The phytosociological survey allows us to identify and to quantify the main weed species present in the region’s irrigated rice tillages. It is, in this way, a fundamental tool to determine the most efficient way to handle the weed.

REFERENCES

  • Adegas F.S. et al. Levantamento fitossociológico de plantas daninhas na cultura do girassol. Planta Daninha. 2010;28:705-16.
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    » http://www.agricultura.gov.br/agrofit
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  • Fleck N.G. et al. Interferência de picão-preto e guanxuma com a soja: efeitos da densidade de plantas e época relativa de emergência. Ciênc Rural. 2004;34:41-8.
  • Galinato M.I., Moody K., Piggin C.M. Upland rice weeds of South and Southeast Asia. Makati City: IRRI; 1999. 156p.
  • Instituto Rio Grandense do Arroz - IRGA. Produtividade municipal - safra 2012/ 2013. [accessed in: October 14 2016] Available at: Available at: http://www3.irga.rs.gov.br/uploads/anexos/1374499016 File: SAFRA_2012_13_RS_MUNICIPAL.pdf
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  • Lamego F.P. et al. Cross-resistance ofBidens subalternansto acetolactate synthase inhibitors in Brazil. Weed Res. 2009;49:634-41.
  • Lorenzi H. Manual de identificação e controle de plantas daninhas, plantio direto e convencional. 7ª.ed. Nova Odessa: Instituto Plantarum; 2014. 384p.
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  • Panozzo L.E. Métodos de manejo deCyperus esculentusna lavoura de arroz irrigado. Planta Daninha. 2009;27:165-74.
  • Rubin R.S. et al. Habilidade competitiva relativa de arroz irrigado com arroz-vermelho suscetível ou resistente ao herbicida imazapyr + imazapic. Arq Inst Biol. 2014;81:173-9.
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Publication Dates

  • Publication in this collection
    2018

History

  • Received
    15 Sept 2016
  • Accepted
    03 Nov 2016
Sociedade Brasileira da Ciência das Plantas Daninhas Departamento de Fitotecnia - DFT, Universidade Federal de Viçosa - UFV, 36570-000 - Viçosa-MG - Brasil, Tel./Fax::(+55 31) 3899-2611 - Viçosa - MG - Brazil
E-mail: rpdaninha@gmail.com