nan Rizzardi

Conyza bonariensis biotypes resistant to the glyphosate in southern Brazil

ABSTRACT - Glyphosate is a non-selective herbicide used for over 20 years to control weeds inRio Grande do Sul. Horseweed ( Conyza bonariensis ) is a common weed in Rio Grande do Sulandtraditionallysensitive toglyphosate.However,during the lastyears,some horseweed plantshavenotshownsignificantinjurysymptomsaftertreatmentwithglyphosate,suggestingthattheyareresistanttothisherbicide.Aimingtoevaluatetheresponseof apopulationof horseweedplantsto glyphosate, one field and twogreenhouse experiments were carried out. The field experimenttreatmenthadincreasingratesofglyphosate(0,360,720,1,440,2,880and5,760 g ha -1 ),andalsotheherbicidesparaquatand2,4-Dasstandards.Thegreenhouseexperimentshadincreasingratesofglyphosate (0, 360, 720, 1,440, 2,880 and 5,760 g ha -1 ) plus the above listed check herbicidessprayed on biotypes considered resistantand on plants of one susceptible biotype. Inthe secondgreenhouse experiment, the treatments were increasing rates of glyphosate (720, 1,440 and 1 Recebido para publicacao em 9.1.2007 e na forma revisada em 31.8.2007.

Resistance of italian ryegrass (Lolium multiflorum) to glyphosate

2 , VARGAS, L. 3 , RIZZARDI, M.A. 4 e MATTEI , R.W. 5 RESUMO - O azevem e uma graminea de ciclo anual, constituindo-se com frequencia em planta infestante em lavouras de trigo do Rio Grande do Sul. Em experimentos realizados em casa de vegetacao e no campo, foi avaliada a suscetibilidade de dois biotipos de azevem ao herbicida glyphosate, bem como a eficiencia de herbicidas de acao total na dessecacao de Lolium multiflorum para a semeadura direta de trigo. O delineamento experimental foi completamente casualizado em casa de vegetacao e de blocos ao acaso em campo, com tres e quatro repeticoes, respectivamente. Foram avaliados herbicidas com mecanismos de acao distintos em diferentes doses: glyphosate, glufosinate, clethodim, haloxyfop-r e diclofop, paraquat e paraquat + diuron. Os resultados, em casa de vegetacao, evidenciam que o biotipo sensivel e totalmente controlado com glyphosate na dose de 360 g e.a. ha -1 e que doses de ate 1.440 g e.a. ha -1 nao afetam significativamente o acumulo de materia seca do biotipo resistente e produzem toxicidade inferior a 15% sobre este. Ja as doses entre 1.440 e 5.760 g e.a. ha -1 de glyphosate reduzem significativamente a producao de materia seca e resultam em toxicidade inferior a 45%. Em campo, os melhores controles de azevem foram propiciados pelos tratamentos clethodim (79,2 g ha -1 ) e diuron + paraquat (300 + 600 g ha -1 ), que nao diferiram entre si. Assim, evidencia-se que a populacao de Lolium multiflorum avaliada neste trabalho e constituida predominantemente de um biotipo resistente aos herbicidas inibidores da enzima EPSPs. Palavras-chave: herbicida, resistencia, dessecacao, EPSPs. ABSTRACT - Italian ryegrass (Lolium multiflorum) is cultivated as forage and/or cover crop in no-till system. However, it is also a serious weed in wheat and other winter cereals in Southern Brazil. Experiments were conducted at greenhouse and field conditions to evaluate the susceptibility of two ryegrass biotype to glyphosate as well as the efficacy of other herbicides on the post- emergence control of the species for sowing wheat under no-till system. The experimental design was a completely randomized design for the greenhouse experiment and a completely randomized block design for the field experiment. Herbicides with different mechanisms of action were evaluated on the weed control: glyphosate, glufosinate, clethodim, haloxyfop-r and diclofop, paraquat and paraquat+diuron. The results obtained under greenhouse conditions indicated the glyphosate susceptible biotype was controlled by the rate of 360 g e.a. ha -1 . The resistant ryegrass biotype had no reduction in dry matter production and less than 15 % phytotoxicity caused by glyphosate up to 1,440 g e.a. ha -1 . However, glyphosate rates between 1440 and 5,760 g e.a. ha -1 , respectively. The results obtained in these studies indicated that the population was composed predominantly by a biotype resistant to EPSPs inhibitor herbicides.

Interferência de populações de Euphorbia heterophylla e Ipomoea ramosissima isoladas ou em misturas sobre a cultura de soja

Euphorbia heterophylla (wild poinsettia), and, more recently, Ipomoea ramosissima (morningglory) are among the main weeds infesting soybean crop in southern Brazil. This work aimed to evaluate the effects of wild poinsettia and morningglory as single or mixed populations in coexistence with soybean. Two experimentswere conducted to compare associations of wild poinsettia or moningglory with soybean, using five ratios of wild poinsettia plants and soybean or morningglory (0:8, 2:6, 4:4, 6:2 and 8:0). In a third experiment, four soybean plants per pot were kept constant and five ratios of of wild poinsettia and moningglory plants were used (0:8, 2:6, 4:4, 6:2 and 8:0), established in two weed emergence periods related to the soybean. The results indicated that a higher reduction in soybean biomass was caused by morningglory than by wild poinsettia, when these species were established before the crop. In mixed communities, morningglory is more competitive than wild poinsettia.

Identificação de biótipos de azevém (Lolium multiflorum) resistentes ao herbicida glyphosate em pomares de maçã

Glyphosate is a wide spectrum herbicide used for over 15 years in apple orchards in Vacaria-RS for weed control in rows of trees. Usually, 3 to 4 applications per year are made at a rate of 720 to 1080 g a.e. glyphosate ha-1 (2 to 3 L ha-1 of commercial product). Ryegrass (Lolium multiflorum) is a common weed in orchards and traditionally sensitive to glyphosate. However, in the last years, some ryegrass plants have not been found to show significant toxicity symptoms after treatment with glyphosate, suggesting that they acquired resistance to this product. To evaluate the response of a ryegrass plant population to glyphosate, one field and two greenhouse experiments were carried out. The field experiment treatments had increasing rates of glyphosate (0; 360; 720; 1,440; 2,880; 5,760 and 11,520 g a.e. ha-1), in addition to the herbicides paraquat, glufosinate-ammonium, haloxyfop and diclofop-methyl as standards, sprayed at two different vegetative growth stages of ryegrass. The greenhouse experiments had increasing rates of glyphosate (0; 360; 720; 1,440; 2,880 and 5,760 g a.e. ha-1) plus the above listed check herbicides sprayed on biotypes considered resistant and on plants of one susceptible biotype. In the second greenhouse experiment, glyphosate rates (720; 1,440; 2,880; 720 + 720 and 720 + 1,440 g a.e. ha-1) were sprayed in single and sequential applications, in addition to the herbicides paraquat, glufosinate-ammonium, haloxyfop, clethodim, sethoxydim, diclofop-methyl, fenoxaprop, fluazifop, paraquat + diuron, atrazine + simazine, trifluralin, and metolachlor. Toxicicity to the herbicides was assessed at 15, 30 and 45 DAT (days after treatment). Overall, the field and greenhouse experiment results showed that the susceptible biotype is easily controlled by glyphosate and by the other postemergence herbicides tested, independent of the vegetative growth stage. In addition, the results showed that the resistant biotype, similarly to the susceptible biotype, is highly sensitive to herbicides with mode of action differing from that of glyphosate. However, the resistant biotype presents low response to glyphosate, even if used in high rates, showing that some biotypes acquired resistance to this product.

Interferência de Raphanus sativus sobre cultivares de soja durante a fase vegetativa de desenvolvimento da cultura

The characterization of soybean competitive ability, as a function of cultivar differential response, may provide valuable information for genetic crop improvement as well as weed management. Various crop characteristics may be associated with competitivity; however, in soybean, only a few studies have been carried out to identify them. A field experiment was conducted in Cruz Alta-RS during 2000/2001 to evaluate variability in soybean cultivars for competitivity against concurrent plants and to identify those holding superior competitive ability. Two competition conditions were tested (absence and presence of forage radish during the period of soybean vegetative development), combined with 11 soybean cultivars. The presence of forage radish during the first 60 days of crop development reduced soybean plant height, leaf area, shoot dry weight, and branch emission and growth. Soybean cultivars reacted differently to forage radish interference, suggesting the existence of genetic variability for competitivity, which allows for selection of soybean genotypes holding superior competitive ability. On the other hand, a greater growth suppression of forage radish plants was verified when associated with soybean cultivars CD 201 and Fepagro RS 10.

Controle de plantas daninhas em milho em função de épocas de aplicação de nitrogênio

The objective of this study was to evaluate the influence of nitrogen application time on weed interference in maize and to determine nitrogen application effect on weed control. The trial was conducted in completely randomized blocks and split-plot design, with four replications. The treatments consisted of five systems of nitrogen application on maize: 0-0-0, 150-0-0, 75-75-0, 0-150-0 and 0-75-75, corresponding, respectively, to the applied amounts of nitrogen before sowing with four and eight leaves, and six times of weed control (maize with 2, 3, 4, 5, 6 and 7 leaves) plus two controls with and without the presence of weeds. The chemical control of weeds was performed after emergence by associating the herbicides nicosulfuron and atrazine. The weed control in V2 was not efficient due to re-infestation. Anticipated applications of nitrogen increased weed density. The greatest nitrogen levels in the index-leaf occurred when nitrogen was applied in V4 and V8, regardless of weed control time. The highest grain yield and number by corn ear were obtained after weed control was performed at the phenological stage V, regardless of nitrogen application time.

Potencial alelopático de extratos aquosos de genótipos de canola sobre Bidens pilosa

The objective of this experiment was to evaluate the effect of aqueous extract of plants of canola genotypes on the germination and radicle length of hairy beggartick (Bidens pilosa). The treatments consisted of genotypes of canola Hyola 420, Hyola 401, Hyola 43, Hyola 60, Hyola 61, Y 3000, H 1432, Dln 03-02, Dln 03-04, Sdh 03-01, Sdh 03-07, sw-2797, and Sw-Eclipse. The concentrations of aqueous extract of 100, 75, 50, 25 and 0xa0% were tested. A completely randomized experimental design was used in a factorial 12xa0xxa04 (genotypes and extract concentrations) with four replications. The experiment was carried out in plastic boxes containing ot the bottom blotter paper moistened with the aqueous extract, where the hairy beggartick achenes were seeded. Seven days later, the number of germinated achenes was evaluated and the length of radicles measured. The results showed that the canola extracts negatively influenced achene germination and radicle length. The effects increased with increased extract concentrations. At low concentration, some genotype extracts presented a stimulating effect. The results showed that the variability among canola genotypes was only evident at low extract concentrations.

Influência das coberturas vegetais antecessoras de aveia-preta e nabo forrageiro na época de controle de plantas daninhas em milho

The objective of this work was to assess the effect of rape and black oats as cover crops on chemical weed control timing in corn under no-till. The experiment was arranged in a complete block design, with the treatments in subplots and four replications. The main treatment plots were cover crops and the subplots the chemical weed control timings, according to corn growth stages (1, 2, 3, 4, 5 and 6 leaves). Two control plots, one with and the other without total weed control were added to the experiment. Weed chemical control was performed in postemergence with the association of the herbicides nicosulfuron + atrazine (Sanson 0.8 L ha-1 + Primoleo 0.3 L ha-1). When chemical control was applied, the cover crop black oat showed to be more efficient on corn grain yield. Rape was found to require more criterion as to the correct timing for weed control, while black oat allowed more flexibility. The best time for herbicide application ranged from the corn growth stages of two to three leaves.

Densidade e características morfológicas de plantas de picão-preto na previsão de perdas de rendimento de grãos de soja por interferência

The adoption of integrated weed management systems depends on the ability to foresee the impact of weeds on crop grain yield potential. The objective of this research was to compare different explicative variables to use in adjusting the rectangular hyperbolic model, in order to identify which one would provide best prediction of beggarticks (Bidens pilosa and Bidens subalternans, occurring in mixed infestations) interference on soybean crop. Experiments were carried out in two environments, located at Passo Fundo and Eldorado do Sul, RS, Brazil. Various beggartick densities and three soybean seeding times (3, 7, and 11 days after cover crops desiccation) were used. Evaluations carried out were beggartick densities 20 and 30 days after soybean emergence (DAE) and at crop harvesting time, and weed plant morphological characteristics, such as leaf density, leaf area, and soil leaf coverage, all performed 20 DAE. It was detected that the explicative variable beggartick plant density provided satisfactory adjustments of the equation model; nevertheless, it does not integrate the effects of environments nor of crop seeding time, differently of what happened with the morphological characteristics. Among them, leaf density and leaf area showed greater potential for use as explicative variables in predicting soybean grain yield losses due to beggartick interference.

Anatomia foliar de Lolium multiflorum sensível e resistente ao glyphosate

This work aimed to contribute to the anatomical knowledge of the species Lolium multiflorum and to observe possible changes that may elucidate the mechanism that confers its resistance to the herbicide glyphosate. Thus, an experiment was conducted using four biotypes of this species with distinct sensitivities to the herbicide glyphosate: one susceptible (B1S) and three resistant biotypes (B2R, B3R and B4R). Analyses were conducted on the transverse and longitudinal sections of the vegetative organs of the plants at the tillering stage. Anatomically, ryegrass is characterized as having a large number of stomata and buliform cells as well as homogeneous mesophylls constituted only of palisade cells compactly distributed. Comparatively, no evident morphological differences occur that can be used to distinguish sensitive from resistant biotypes; however, the resistant biotypes, especially B3R B4R, presented higher stomatal density, compared to the others. Still, the resistant biotypes had a higher amount of intercellular spaces in the mesophyll and vascular bundles with a smaller amount of phloem compared to the xylem, which, because of their functions in the plants, may contribute to the lower sensitivity to the herbicide.