D. Agostinetto

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.

Competitividade relativa entre cultivares de arroz irrigado e biótipo de arroz-vermelho

The objective of this study was to compare the relative competitive abilities between two rice cultivars and a red rice biotype. Greenhouse experiments were carried out at the Universidade Federal do Rio Grande do Sul, in the 2001/2002 growing season, in a completely randomized design, with four replications. The treatments were arranged in a replacement series assay, with five plant proportions of rice cultivars and competitor biotype being established: 100:0; 75:25; 50:50; 25:75 and 0:100, respectively. Rice was represented by the cultivars IRGA 417 and EEA 406, and the competitors by a red rice genotype as well as by EEA 406 cultivar, mimicking red rice. Competitive analysis was accomplished through diagrams usually applied to replacement series studies, plus use of relative competitive indices. The plant variables evaluated were: tillering, plant height, leaf area, and shoot dry mass. Red rice negatively modified plant tillering, plant height, leaf area, and shoot dry mass of both rice cultivars, proving superior competitive ability. The rice cultivars IRGA 417 and EEA 406 did not change their morpho-physiological plant characteristics when in association with each other, regardless of plant proportions among them, presenting equivalent competitive abilities.

Níveis de dano econômico para decisão de controle de capim-arroz (Echinochloa spp.) em arroz irrigado (Oryza sativa)

Economic weed threshold (EWT) for monitoring barnyardgrass infestation in flooded rice farms allows the adoption of crop management measurements and a rational use of herbicide. The objective of this study was to determine EWT for barnyardgrass based on a single year in function of barnyardgrass populations, rice varieties and flooding timings. Thus, two trials were carried out using a completely randomized design with no replications. The first trial treatments consisted of six rice varieties: BRS-Atalanta, IRGA 421 (very short cycle); IRGA 416, IRGA 417, Avaxi (short cycle) and BRS-Fronteira (medium cycle); as well as ten barnyardgrass populations. The second trial treatments were flooding timings: 1, 10 and 20 DAT (days after herbicide treatment) and barnyardgrass populations. The estimated EWT for barnyardgrass varied in function of the adopted management practices in the flooded rice crop. The estimated EWT for rice IRGA 416 and 417 was greater than that of the other cultivars when in barnyardgrass competition. Flooding timing delay reduced EWT for the BRS-Pelota rice variety. Increased potential yield losses, product value and herbicide efficiency as well as reduced control price reduced EWT, rendering viable the adoption of management practices at low barnyardgrass density when competing with flooded rice.

Relative Competitive Ability of Wheat (Triticum aestivum) Intercropped with Italian Ryegrass (Lolium multiflorum) or Wild Radish (Raphanus raphanistrum)

Replacement series experiments make possible the study of inter and intraspecific competition, based on the fact that the yield of the species under competition can be determined by comparing with plants in monoculture. The objective of this work was to investigate the relative competitive ability of wheat crop with the weeds Italian ryegrass or wild radish. Three experiments were conducted under greenhouse at UFPel, in 2006. The treatments were conducted in a completely randomized design, with four replications, with the treatments arranged in replacement series. The proportions of wheat plants and competitors Italian ryegrass or wild radish were: 100/0, 75/25, 50/50, 25/75 and 0/100, always with a total population of 900 plants m-2. Competitiveness statistical analysis consisted in applying diagrams to the replacement series and interpreting the competitiveness indices. The competitive relationships between wheat and ryegrass or between wheat and wild radish plants are altered by the proportion of plants that compose the association. Wheat shows superior competitive ability to ryegrass but inferior to wild radish when the species have similar proportions of plants in the associations and when these species occur in the same ecological niche.

Estimativa das perdas de produtividade de grãos em cultivares de arroz (Oryza sativa) pela interferência do capim-arroz (Echinochloa spp.)

The objectives of this research were to evaluate the level of barnyardgrass interference in flooded rice cultivars and to compare explicative variables aiming to identify the variable providing better data adjustment to a mathematical model. Thus, a field experiment was carried out during the 2005/2006 growing season, with rice cultivated under the conventional system. Treatments consisted of six rice cultivars differing in life cycle duration and ten barnyardgrass plant populations. Variables were evaluated 28 days after rice emergence. The rectangular hyperbolic model was tested to describe the relationship between rice grain yield loss and explicative variables in plants, dry weight, soil coverage and leaf area. Rice grain yield losses due to barnyardgrass interference may be satisfactorily estimated by the hyperbolic model. IRGA 421, 416, and 417 rice cultivars were the most competitive, attaining suitable data fitting to the model tested for all evaluated variables. The variable Barnyardgrass plant population presents better adjustment to the model than do shoot dry matter mass, soil cover, or leaf area.

Período crítico de competição de plantas daninhas com a cultura do trigo

Several factors limit wheat crop yield, with competition imposed by weed plants being the most outstanding. The objective of this study was to determine the critical period of weed interference in wheat crop and the effects of competition on morphological variables and yield components. This field experiment was carried out at Centro Agropecuario da Palma, Capao do Leao, RS, Brazil. Factors tested were periods of coexistence and weed plant control in FUNDACEP 52 wheat cultivar. Periods of coexistence and/or control were: 0, 7, 14, 21, 28, 35, 42 and 126 days after emergence (DAE). Results obtained for variables at the end of each control period or coexistence, and at harvesting, showed that wheat yield components were not affected by competition with weed plants and that effective control measures should be taken between 12 and 24 days after emergence.

Manejo de Conyza bonariensis resistente ao herbicida glyphosate

Horseweed (Conyza bonariensis), which belongs to the Asteraceae family, is a weed species widely spread in Brazil. Horseweed biotypes resistant to glyphosate, the main herbicide used in Roundup Ready soybean fields, were identified in the states of Rio Grande do Sul and Parana. The aim of this study was to evaluate the effect of different winter and pre-sowing management techniques on soybean plant population of C. bonariensis resistant to glyphosate. The results showed that the population of C. bonariensis is larger in areas maintained fallow than in areas planted with wheat or oats during the winter. Wheat and oats were found to exert a suppressive effect on the population of C. bonariensis, providing greater ease of control with herbicide before seeding in the culture used in succession. The control of glyphosate-resistant C. bonariensis was satisfactory when post-emergence herbicides were used in wheat crop and glyphosate and 2,4-D or glyphosate paraquat diuron in pre-planting soybeans.

Competitividade relativa de soja com arroz-vermelho

To reduce weed plant infestation, especially red-rice, areas traditionally cultivated with flooded rice in Rio Grande do Sul, Brazil, are being intercropped with soybean under a rotation system. The objective of this study was to quantify competitive abilities between soybean crop and red-rice biotype. Treatments were arranged in substitution series, with five proportions being used (0:16, 4:12, 8:8, 12:4 and 16:0) of soybean and red-rice, in a randomized complete block design, with four replications. Air dry matter and leaf area of the plants were evaluated. Competitiveness was analyzed through diagrams applied to substitution experiments and competitiveness indexes. Soybean presents higher competitive ability for environment resources than red-rice. Soybean crop production increases when close to a red-rice plant than to a soybean plant.

Interferência de capim-arroz (Echinochloa spp.) na cultura do arroz irrigado (Oryza sativa) em função da época de irrigação

The adoption of new weed management methods for flooded rice, aiming to reduce the use of herbicides requires quantitative knowledge about the weed-crop interference relations. The objectives of this research were to evaluate flooding start timing influence on the rice crop and barnyardgrass interference in the crop, as well as to compare the explicative variables plant population, dry weight, soil covering and leaf area to identify the one providing a better data adjustment to the model. Thus, a trial was carried out during the 2005/2006 growing season, arranged in a completely randomized design, with no replication. The treatments were flooding timing at: 1, 10 and 20 days after herbicide treatment (DAT), and barnyardgrass populations of 0, 6, 8, 14, 20, 28, 42, 66 and 200; 0, 4, 6, 50, 66, 88, 92 and 200; 0, 10, 12, 32, 42, 74, 166, 174 and 178 plants m-2, for flooding at 1, 10 and 20 DAT, respectively, resulting in 26 experimental units. Crop yield loss in function of the explicative variables population, canopy dry mass, leaf area and soil coverage of barnyardgrass plants were related by the rectangular hyperbole non-linear regression. The rectangular hyperbole appropriately estimates crop yield loss of flooded rice due to barnyardgrass interference. Flooding anticipation modifies the competitive ability of rice plants cv. BRS-Pelota in relation to barnyardgrass plants. The variable plant population fits better to the model, when compared to the other variables.

Habilidade competitiva relativa de milhã em convivência com arroz irrigado e soja

The objective of this work was to compare the relative competitive ability of crabgrass with flooded rice and soybean crops. Five experiments were performed in the 2009/2010 and 2010/2011 seasons, in a completely randomized design with four replicates. The treatments consisted of plant proportions of crabgrass, flooded rice or soybean (at 100:0, 75:25, 50:50, 25:75 and 0:100%). Leaf area and shoot dry weight were evaluated at 45 days after emergence. The competition between crabgrass and flooded rice or soybean occurs for the same environment resources. Crabgrass plants have a lower individual competitive ability than flooded rice and soybean, when they occur in the same proportion of plants. When flooded rice or soybean are associated with crabgrass, the intraspecific competition dominates, while for the weed the interspecific competition prevails as the most harmful.