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ABSTRACT: Herbicide promotes physiological and biochemical changes even in tolerant species. The objective of this study was to evaluate the interference of the herbicides clodinafop-propargyl and 2,4-D in the antioxidant system of wheat, and iodosulfuron-methyl in wheat and ryegrass. Two studies, divided into three experiments, were conducted in an entirely randomized design in a greenhouse and phytotron. The first study tested herbicides iodosulfuron-methyl, clodinafop-propargyl, 2,4-D, and a control without application in wheat. The second, divided into two experiments with wheat and ryegrass, tested iodosulfuron-methyl doses (0, 1.75, 3.5, and 7.0 g a.i. ha-1). The variables analyzed were the concentrations of chlorophylls a, b, carotenoids, hydrogen peroxide (H2O2), lipid peroxidation (TBARS), electrolyte leakage, and antioxidant system activity. The herbicide treatments iodosulfuron-methyl, clodinafop-propargyl, and 2,4-D decreased the concentrations of chlorophylls and carotenoids in wheat plants. The herbicides promoted oxidative stress with increased H2O2 and TBARS concentrations. Increasing the dose of iodosulfuron-methyl provided a reduction in the activity of the enzymatic antioxidant system in wheat and ryegrass.

Resistance to acetolactate synthase (ALS) inhibitors have increased recently in South Brazil where the major weeds of flooded rice (barnyardgrass and weedy rice) have evolved resistance to imazapyr+imazapic. The aim of this research was to evaluate a growth medium for tissue regeneration of tillers in barnyardgrass, as well as an agar-based bioassays test (also from tillers) to detect susceptible and resistant biotypes of weedy rice and barnyardgrass to imazapyr+imazapic in vitro. Greenhouse experiments were conducted to detect ALS-resistant (R) and susceptible (S) weedy rice and barnyardgrass biotypes, and bioassays were carried out to evaluate an adequate growth medium for barnyardgrass tiller regeneration and determine the concentration of herbicide to distinguish R and S plants. The culture medium that provided a suitable barnyardgrass growth was MS 50% with the addition of benzylamino-purine. The tissue regeneration in vitro with the growth medium containing imazapyr+imazapic allowed to discriminate between R and S barnyardgrass and weedy rice plants. The concentration required for satisfactory control of susceptible barnyardgrass and weedy rice explants grown in vitro was 0.9 μM and 1.3 μM of imazapyr+imazapic herbicide, respectively. The bioassay in vitro using tiller regeneration provides an opportunity to predict effectively imazapyr+imazapic resistance in barnyardgrass and weedy rice.

ABSTRACT: Weedy rice (Oryza sativa L.) is the most problematic weed in rice fields due to the few control management alternatives to control it, because of the genetic similarity with the crop. Different cropping systems (regarding soil preparation before sowing) have been used as options to control the persistence and emergence of the weed seedbank. Therefore, the objective of this study was to evaluate the longevity and vertical distribution of weedy rice seeds in the soil seedbank after 22 years of different rice cropping systems. Data was analyzed as a two-way factorial, with cropping systems carried out for 22 years [no-tillage (NT), conventional tillage (CT), wet direct-seeded (WDS)] as one factor and sampling depth (0-2, 2-5, 5-10 and 10-20 cm) as the other factor. The number of whole and deteriorated seeds per m-2 were assessed, as well as the viability (%). No effect between the systems were detected up to 5 cm, however at 5-10 cm CT and WDS showed higher amount of seeds, and WDS at 10-20 cm. As the sampling depth increased, NT showed fewer amount of seeds, while less reduction of the soil seedbank was observed in WDS. CT and WDS spread viable seeds in the soil profile from 0 to 20 cm depth. After 22 years there are viable weedy rice seeds up to 10 cm of depth in the three cropping systems and there is no difference among them up to 5 cm of depth, demonstrating the serious problem of the seedbank for this species.

Conyza spp. é uma espécie de difícil controle, principalmente quando se encontram com maior estatura e em estádios mais avançados de desenvolvimento. O estudo objetivou avaliar a eficiência de controle de 2,4-D colina e da mistura formulada de 2,4-D colina e glifosato em Conyza spp. com diferentes estaturas e estádios de desenvolvimento. Os fatores avaliados foram três estaturas de Conyza spp. (1-2; 10-12 e 25-30 cm); dois herbicidas [2,4-D colina (EC) e 2,4-D colina + glifosato (ED)]; e doses destes herbicidas correspondentes a 0x, 1/2x, 1x, 2x e 4x a dose recomendada. O herbicida ED proporcionou melhor controle comparativamente ao EC em todas as doses e estaturas avaliadas. O controle de Conyza spp. deve ser realizado em estágios iniciais de desenvolvimento, pois ambos os herbicidas nas doses iguais ou superiores as doses de registro são eficazes para o controle, o que não ocorre em estatura maiores que 10 cm ou estágio de 19 folhas.

The study of herbicide dynamics in the soil and their interaction with the components of the environment makes it possible to ensure the selectivity of crops and the agronomical efficiency. The aim of this research was to evaluate the influence of soil physicochemical properties on the emergence and growth of soybean, with pre-emergence application of various saflufenacil rates. An experiment was carried out in a greenhouse with a completely randomized design, testing different soil types containing “Erechim”, “Santa Maria” and “Eldorado do Sul”, at different saflufenacil rates: 0, 12.5, 25, 50, 100, 200, 400 g a.i. · ha–1. The application was performed 1 day after soybean sowing, and analyzed variables were: the phytotoxicity emergence of seedlings, dry mass and height of the soybean. The saflufenacil effective dose of 50% response in soybean (ED50) and the characteristics of the soils showed that the soil contained clay and sand which were the components most related to the saflufenacil availability to the plants. A lower ED50 by phytotoxicity to the soybean was found in soil with lower and greater content of clay and sand, respectively. The physicochemical properties of soil influenced the saflufenacil activity, having greater potential of injury to soybean in the soil from Eldorado do Sul, due to its clay and sand content.

The drought stress tolerance may differ among species and cultivars. The drought effect on plants depends on the impact on the plant’s physiological, biochemical and molecular processes, as well as on its ability to adapt under these conditions. This study aimed to evaluate the physiological and biochemical responses, and determine the expression of the genes OsAPX2, OsHSP24.15, OsHSP71.10and OsHSP85.88 under drought conditions in rice, weedy rice and barnyardgrass. A greenhouse experiment was performed in a complete randomized design, with four replications and two factors: water conditions (well-watered and water deficit) and plant species [rice (Oryza sativa cv. Puitá), weedy rice (Oryza spp.) and barnyardgrass (Echinochloa spp.)]. Under drought conditions, the rice and weedy rice plants showed more cellular damage than the barnyardgrass, and the three species showed a reduced photosynthetic rate. C3 plants (rice and weedy rice) increased the damage to lipids and proteins at 5 days of drought. However, for C4 plants (barnyardgrass), the drought conditions did not affect the biochemical parameters. The expression of the OsHSP85.88 gene increased in the three plants exposed to water deficit.

The shifting of rice planting date to early spring improved weed control, which is important to achieve high yield. However, early planting date exposes rice seedlings to cold stress, slowing crop establishment and affecting herbicide selectivity. The objective of this study was determine the effects of cold stress and bispyribac-sodium application on rice seedlings’ gene expression and physiological patterns. The experiment was performed in greenhouse in a factorial arrangement, and treatments included: factor A – two planting dates: late September and early November; factor B consisted in bispyribac-sodium application at rate of 50 g ai ha−1 and untreated check. Bispiribac-sodium caused greatest injury to rice seedlings at the early planting date. Lipid peroxidation and total phenol accumulation was stimulated by low temperature but, was not affected by bispyribac-sodium application. Gene expression of OsSOD, OsCAT, OsAPX, OsDREB1A, OsCDPK13, OsCYP72A2, OsGSTL2 and OsGSTU10 were responsive to low temperature and presented upregulation when exposed to the herbicide, providing evidence of an interaction between temperature and herbicide applications. Cold stress likely affects herbicide metabolism and effect rice seedling e oxidation mechanism response to herbicide.

A utilização indiscriminada de herbicidas na cultura do arroz tem provocado uma pressão de seleção de biótipos de arroz-vermelho resistentes aos herbicidas imidazolinonas. Diante disso, métodos alternativos de controle de plantas daninhas tornam-se uma alternativa para esta situação, tal como a busca de novos ingredientes ativos em compostos aleloquímicos de plantas. O trabalho foi realizado com objetivo de avaliar o potencial alelopático de diferentes concentrações do extrato aquoso de folhas de cultivares de arroz irrigado na germinação e no vigor de sementes de arroz-vermelho. O delineamento experimental adotado foi inteiramente casualizado, com quatro repetições, em esquema fatorial 4 x 5, onde: fator A - Extrato de folhas frescas das cultivares de arroz (BRS Querência, Irga 424, Roxinho e Cica 07) e fator B - Concentrações do extrato (0, 25, 50, 75 e 100%). Os extratos foram obtidos de folhas das plantas das cultivares em estádio reprodutivo R3 (saída da panícula). Estas foram trituradas em água destilada e posteriormente diluídas nas concentrações. Avaliaram-se a germinação, primeira contagem da germinação, índice de velocidade de germinação, comprimento da parte aérea e de raiz e massa seca da parte aérea e de raiz. De maneira geral, o efeito alelopático é maior nas cultivares desenvolvidas mais recentemente, sendo o extrato da cultivar IRGA 424, na concentração de 25%, o mais nocivo para o desempenho fisiológico de sementes de arroz-vermelho.

Ryegrass management has been difficult by the occurrence of resistant biotypes to several herbicides with different action mechanisms. Since herbicides mixes and rotations are an important alternative for resistant weed management, the objective of this work was to evaluate the interaction of the dose of the herbicides glufosinate and atrazine on ryegrass control and its seeds’ quality exposed to their association. For this study, three experiments were carried out using factorial design in field, laboratory, and greenhouse conditions. Two factors (A and B) were evaluated in each experiment, where factor A and B represented the doses of glufosinate and atrazine, respectively. Ryegrass control was evaluated in field experiment, while germination percentage and Emergence Speed Index (ESI), were obtained in laboratory and greenhouse analyses, respectively. The data were submitted to variance analysis (P≤0.05) and the significant results were analyzed through response surface graphs. For ryegrass control data, the effect of the interaction was analyzed by the Colby method; glufosinate provides efficient ryegrass control, but its association with atrazine reduces the efficiency, being characterized as an antagonism between molecules. Glufosinate herbicide application, independent of atrazine presence, reduced the ryegrass seeds quality at the post-flowering stage.

Na cultura do trigo a dessecação em pré-colheita com herbicidas pode influenciar a produtividade e a qualidade fisiológica das sementes. O trabalho teve por objetivo quantificar a produtividade, a qualidade fisiológica e o resíduo em sementes de trigo. O delineamento experimental adotado foi em blocos ao acaso, com quatro repetições, sendo que os tratamentos contaram de cultivares de trigo (BRS 177 e BRS Umbu); dessecação com herbicidas (2,4-D; paraquate; glifosato; glufosinato de amônio; metsulfuron metílico; e, testemunha); e, épocas de maturação (antes e após a maturação fisiológica). As variáveis analisadas foram o peso de mil sementes; peso hectolitro; número de antécios por espiga; produtividade; qualidade fisiológica das sementes, através dos testes de vigor e germinação; e, resíduos nas sementes, após a aplicação dos herbicidas em pré-colheita. A dessecação em pré-colheita com herbicida realizada em estádio posterior a maturidade fisiológica, em geral, não altera a qualidade fisiológica e a produtividade de trigo das cultivares BRS 177 e BRS Umbu. A aplicação de metsulfuron metílico e paraquate não apresentam efeitos residuais nos grãos independente da época de aplicação, enquanto a aplicação de glufosinato de amônio, glifosato e 2,4-D, quando aplicados anterior à maturidade fisiológica, geram níveis de resíduo nos grãos de trigo.

The differential growth and yield response of plant species to rising carbon dioxide concentrations and climatic change may alter species diversity within biomes. The Pampa Biome in South America is an important grassland biome of agronomic and environmental importance. Acanthostyles buniifolius (Chirca) is one of the most important weeds in natural pasture areas widely distributed in southern South America and can adversely affect livestock production. The current study was designed to identify possible responses of Chirca to CO2 concentration ([CO2]) and drought that would indicate higher adaptation and potential proliferation within the Pampa Biome. Chirca plants were cultivated at two CO2 concentrations (400 (a[CO2]) and 700 (e[CO2]) µmol mol−1) and two water conditions (under water restriction—15% of the pot capacity; and plants without water restriction—pot capacity). Besides growth parameters, we also determined water potential (ѱw), relative water contents (RWC), proline, glycine betaine, total soluble sugars, hydrogen peroxide, lipid peroxidation, superoxide dismutase (SOD), ascorbate peroxidase (APX) activity, chlorophyll A and B, carotenoids and root dry mass (RDM). Plants exposed to e[CO2] are more efficient in water use and have a greater increase in root dry mass, enabling greater adaptation to climate-induced droughts. Among the biochemical changes observed in the plants under drought stress, the accumulation of proline, glycine betaine, and total soluble sugars were the most evident mechanisms allowing plants to tolerate drought stress by osmotic adjustment.

Abstract Background: Enlist E3™ soybean is tolerant to 2,4-D, glyphosate and ammonium-glufosinate and were developed for effective management of herbicide resistant weeds such as glyphosate Herbicides, even being selective, can cause damage to crop metabolism, affect growth and development and interfere with seed physiological quality. Objective: The aim of this research was to evaluate the physiological quality of Enlist E3™ soybean seeds submitted to herbicide application. Methods: The field trial was carried out in a randomized block design with four replications. The treatments tested were 2,4-D choline + glyphosate, 2,4-D choline, glyphosate + 2,4-D amine and ammonium-glufosinate; and control without application, sprayed at V6 soybean growth stage. After harvest, the seeds were submitted to first germination count, accelerated aging, germination speed index, shoot and root length, shoot and root dry mass and electrical conductivity tests. Results: The management of Enlist E3 soybeans with Enlist herbicides (2,4-D choline + glyphosate and 2,4-D choline) as well as glyphosate + 2,4-D amine and glufosinate did not negatively impact soybean parameters such as: vigor, germination count, accelerated aging, germination speed, aerial part and primary root length, aerial part and root dry mass and electrical conductivity. Conclusions: Those herbicides can be recommended to be used on post emergence (V6) of Enlist E3 soybean.

Abstract Background: The resistance of weeds to herbicides is a problem that has been increasingly studied because of its great importance in agriculture and rapid growth of this phenomenon worldwide. The quick detection of resistant plants is extremely important for resistance management. Weed resistance to herbicides can be detected through field, greenhouse and laboratory tests. A fast way of detecting resistance is using tissue culture method, where is possible to use resistant plant clones and obtain results faster than whole-plant method in greenhouse. Objective: The aims of the research were to detect the resistance of blackjack to herbicides inhibitors of the acetolactate synthase (ALS), addition in vitro cultivation; determine the herbicide concentration of imazethapyr to 95% control of the susceptible plant population; evaluate explants growth; and, determine the herbicide concentration added to the culture medium where is possible to distinguish a resistant from a susceptible plant. Methods: Experiments were carried out in greenhouse and tissue culture laboratory. Screening was performed to select resistant and susceptible biotypes, tests for specie establishment and dose response curves in vitro were made. Results: The herbicide concentration added to the culture medium that provided 95% susceptible biotype control and efficiently differentiated susceptible biotype from resistant one was 0.6μM of imazethapyr. Conclusions: This method helps recommendations of weed management and provides a quick decision to alternative control of this specie, thus avoiding major damage to the crops.

Abstract Background: Competition with weeds and the lack of selective herbicides registered for birdsfoot trefoil crops affect their development and limit their productivity. Objective: This study aimed to evaluate selectivity of post-emergent herbicides for weed control in birdsfoot trefoil crops. Methods: Experiments were carried out in a greenhouse and on a field, in both vegetative and reproductive development stages of birdsfoot trefoil crops. Treatments were composed of post-emergent herbicides recommended for soybean, corn and garlic cultivation. Phytotoxicity (PHYTO), plant height (HEI), shoot dry matter (SDM) and root dry matter (RDM) were evaluated. Data were submitted to the analysis of variance and when means were significant, they were compared by the Duncan’s Test (p≤0.05). In order to determine post-emergent herbicides which were selective to the crop, those that provided PHYTO below or equal to 15% were recommended, since they did not significantly interfere with morphological variables HEI, SDM and RDM, by comparison with the control. Results: Unlike results found in the vegetative stage, birdsfoot trefoil plants were more tolerant to phytotoxic effects of herbicides imazethapyr, chlorimuron-ethyl, cloransulam-methyl and fomesafen in the reproductive stage. The variables were negatively affected by the herbicides bentazon, glyphosate and carfentrazone-ethyl, with PHYTO higher than 40% at 20 days after treatment in the vegetative stage. Conclusions: Herbicides imazethapyr, chlorimuron-ethyl and flumetsulam, when applied as post-emergent ones, regardless of the development stage of the species, are selective to birdsfoot trefoil crops, without affecting crop development, whereas herbicides cloransulam-methyl and fomesafen are not selective to them.

Abstract Background: Plants synthesize compounds of specialized metabolism to defend themselves against biotic and abiotic stresses. These compounds could be used as models for pesticide development. Among the species that have not yet been studied for the potential to produce active compounds is the kidney leaf mud plantain (Heteranthera reniformis). Objective: The goal was to evaluate the effect of hexanic, ethyl acetate and methanolic extracts of H. reniformis leaves on cress (Lepidium sativum) seed germination to determine which one have the highest biological activity; and to evaluate different concentrations of extract with the highest biological activity on lettuce (Lactuca sativa), barnyard grass (Echinochloasp.) and giant arrowhead (Sagittaria montevidensis) germination. Methods: The seeds were placed on petri dishes containing two sheets of germitest paper, and after the application of the extract, they were sealed and placed in growth chambers with controlled temperature and photoperiod. The variables analyzed were 1st and 2nd germination count, germination speed index and length of the aerial part and roots. Results: The ethyl acetate extract provided greater phytotoxicity on cress than the other extracts. In general, the highest concentration of ethyl acetate extract was the most efficient in reducing variables for all species. Conclusions: The ethyl acetate extract of H. reniformis presents inhibitory activity on the seeds of cress, lettuce, giant arrowhead and barnyard grass, but this activity was dependent on the concentration of the extract and the species studied. H. reniformis synthesizes compounds with phytotoxic activity and purification of extracts is required to isolate, identify and characterize the action mechanism of the compounds with herbicide activity, so that in the future these can be used as models for the development of herbicides.

Levels of weed infestation can be inferred from climate information since every species requires specific conditions for its germination process. This study aimed to evaluate weed species and their emergence flow in hilly areas, when subjected to different environmental conditions of temperature and luminosity. Two experiments were carried out in a completely randomized design with four replications. In the first experiment, treatments used plastic films (no film; film just on top; partially closed film; and fully closed film), whereas the second experiment used black polyethylene covers (0; 35; 50; and 80%). Weed emergence in the area was monitored daily, until the establishment of the emergence flow. Soil temperature, solar radiation interception and soil moisture were also monitored. For the analysis of species subjected to every type and level of covers, phytosociological parameters and the emergence speed index were calculated. Data were submitted to analysis of covariance and, when they were significant, the Tukey test (p ≤ 0.05) was applied. A hierarchical cluster analysis was performed to relate factors and experimental levels to distribution intervals of climate covariates. Increase of 8.5°C in soil temperature favors the emergence of crabgrass, while reducing the emergence of alexander grass, morning glory, beggartick and sida. The main species that adapted to decrease in temperature and solar radiation are sida, alexander grass and crab grass. Besides, decrease in radiation increases the number of magnoliopsida species and enables all species to establish faster.

(1) Background: Eragrostis plana Ness is a invasive C4 perennial grass in South America and very adaptable to environmental stresses. Our hypothesis is that there is a transgenerational cross-talk between environmental stresses and weed response to herbicides. This study’s objectives were to: (1) evaluate if E. plana primed by drought stress (DRY), a sub-lethal dose of quizalofop-p-ethyl (QPE), or a combination of both drought and herbicide stresses (DRY × QPE), produce a progeny with decreased sensitivity to quizalofop and (2) investigate the potential mechanisms involved in this adaptation; (2) Methods: A population of E. plana was isolatedly submitted to treatments for drought, quizalofop or drought plus quizalofop for two generations. The progenies were analyzed for sensitivity to the herbicide quizalofop and performed biochemical, chromatographic and molecular analyses.; (3) Results: In the G2 generation, the quizalofop-treated CHK population had reduced stomatal conductance and increased hydrogen peroxide and lipid peroxidation. On the other hand, there was no change in stomatal conductance, hydrogen peroxide level, and lipid peroxidation in the quizalofop-treated DRY population. In addition, this population had increased antioxidant enzyme activity and upregulated CYP72A31 and CYP81A12 expression, which was accompanied by reduced quizalofop-p-ethyl concentrations; (4) Conclusions: E. plana demonstrated a capacity for transgenerational adaptation to abiotic stresses, with the population exposed to drought stress (DRY) becoming less sensitive to quizalofop-p-ethyl treatment.

Abstract: The objective of this work was to compare wild poinsettia (Euphorbia heterophylla) biotypes as to their morphological characteristics, as well as to determine their genetic similarity in the state of Rio Grande do Sul, Brazil, and to confront the light compensation point of susceptible biotypes and of biotypes with low-resistance level to glyphosate. Besides the morphology analysis, the study included the genetic characterization, by AFLP, of susceptible (GR50= 58.65 g ha-1 a.e.) biotypes and of biotypes with low resistance (GR50= 310.36 g ha-1 a.e.) to glyphosate. The competitive ability of the biotypes was inferred according to their light compensation point. The observed morphological characteristics do not allow to differentiate biotypes as to their geographical location, or their resistance level to glyphosate. The genetic analysis identified low genetic diversity among the 15 tested biotypes, with a large amount of subgroups. The biotypes with low resistance formed an isolated group. The susceptible biotypes showed the lowest values of light compensation point and, possibly, they have a greater competitive ability under low-luminosity conditions. The evaluated characteristics do not enable to differentiate genotypes with different levels of glyphosate resistance.

The Wild Poinsettia (Euphorbia heterophylla L.) has elevated potential to reduce the soybean yield and is a difficult to control plant due to herbicide resistance. The objectives of this study were to determine the changes in the photosynthetic physiological parameters, secondary metabolite levels, cellular damage, and antioxidant system activity in soybean plants and Wild Poinsettia biotypes with a low level of resistance or susceptibility to glyphosate in competition with soybeans. Two replacement series experiments were conducted in a greenhouse under competition between soybeans and the low-level resistant biotype (experiment I) or susceptible biotype (experiment II). The treatments consisted of different proportions of soybean plants and Wild Poinsettia [100:0 (pure stand of soybean), 50:50, and 0:100 (pure stand of Wild Poinsettia)] and different evaluation periods (the 2013/14 and 2014/15 growing seasons). The following parameters were analyzed: the chlorophyll, carotenoid (CRT), total phenol, hydrogen peroxide (H2O2), and lipid peroxidation levels and the catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD) enzyme activity. Generally, competition between the soybeans and the Wild Poinsettia biotypes did not alter the photosynthetic parameters or the photosynthetic pigment levels of the crop. For the weed biotypes, competition with the soybeans negatively affected photosynthesis. Greater losses of chlorophylls and CRTs were observed for the susceptible biotype when in competition with soybeans, whereas the opposite trend was observed for the biotype with a low level of resistance. No cellular damage or alterations in antioxidant system enzyme activity was observed, which indicated a lack of oxidative stress.

The goosegrass ( Eleusine indica (L.) Gaertn) is an annual plant that has a low - level resistance to glyphosate (LLRG), resulting in control failure in genetically modified soybean crops for resistance to this herbicide. Alleles related to resistance may cause changes in the plant biotype, such as inferior competitive ability. Thus, the objective of this work was to evaluated the competitive ability of soybean crops and susceptible and resistant (LLRG) goosegrass biotypes. Replacement series experiments were conducted with soybean crops and goosegrass biotypes. The ratios of soybean to susceptible or resistant (LLRG) goosegrass plants were 100:0, 75:25, 50:50, 25:75 and 0:100, with a total population of 481 plants m - 2 . The leaf area, plant height and shoot dry weight were evaluated at 40 days after emergence of the soybean crops and weeds. The soybean crop had superior competitive ability to the susceptible and resistant (LLRG) goosegrass biotypes. The soybean crop showed similar competitive ability in both competitions, either with the susceptible or resistant (LLRG) goosegrass biotypes. The intraspecific competition was more harmful to the soybean crop, while the interspecific competition caused greater damage to the goosegrass biotypes competing with the soybean crop

In the State of Rio Grande do Sul (RS), Southern Brazil, glyphosate has not been capable of controlling wild poinsettia (Euphorbia heterophylla L.) in soybean fields, thus, suggesting resistance to this herbicide. Therefore, this study aimed at evaluating sensitivity of wild poinsettia biotypes to glyphosate, identifying the occurrence of resistance of wild poinsettia to the herbicide in RS state and determining the resistance factor of wild poinsettia biotypes under suspicion, besides assessing other herbicides as alternative controls. Two greenhouse experiments, which lasted two years, were conducted by a completely randomized design with four replications. Six biotypes (Factor A) and eight doses of glyphosate (Factor B) were used for getting the dose-response curve. Regarding the alternative control, post-emergence herbicides for soybean and corn crops were tested. Control and dry mass of the shoot were analyzed as variables. Resistance factors of resistant biotypes 20.2 and 21.1 were 4.83 and 5.29, respectively, by comparison with the susceptible biotype (11.4). In RS state, there has currently been high selection pressure due to the intensive use of glyphosate against wild poinsettia plants, as the result of the occurrence of biotypes 20.2 and 21.1 which have low levels of resistance to glyphosate and very little control by ALS-inhibiting herbicides. Therefore, an alternative to mitigate the problem is the use of herbicides with different mechanisms of action.

In 2002, a survey carried out in rice paddies in the Rio Grande do Sul (RS) state reported the occurrence of nine species of jointvetch (Aeschynomene). Due to their semi-aquatic habit, some species adapted to irrigated rice fields, which led to their being considered the worst broadleaf weed in RS. Although farmers have successfully implemented weed management practices, Aeschynomene plants have reportedly escaped chemical control. This study aims to identify the species of Aeschynomene that occur in rice fields in RS and to evaluate the reasons why escapes are occurring. A survey was carried out by collecting mature seeds from individual adult plants. A questionnaire on the management practices employed in each field was administered to 54 farmers and 18 extension agents, each of whom was responsible for one of the surveyed rice fields. This survey found four species of Aeschynomene are present in rice fields in RS: A. denticulata, A. indica, A. rudis, and A. sensitiva. The results suggest that the explanation for escapes may lie in the management practices adopted by farmers, which are focused on the control of weedy grasses. Escapes are also associated with problems such as the lack of irrigation uniformity and out-of-stage, late herbicide applications.

As plantas daninhas presentes no trigo competem por diversos fatores exercendo impacto negativo na produtividade da cultura. Nesse contexto, o objetivo do estudo foi analisar morfologicamente o trigo e o azevém, em resposta ao estresse causado pela competição. Conduziuse experimentos em delineamento completamente casualizado, com 4 repetições, sendo o série de substituição com população de 64 plantas por vaso. Os tratamentos constaram de proporções de plantas de trigo e azevém. As proporções testadas foram: 100/0 (estande puro de trigo), 75/25, 50/50, 25/75 e 100/0% (estande puro de azevém). A cultivar de trigo Fundacep Horizonte apresentou habilidade competitiva superior ao azevém; a competição intraespecífica foi mais prejudicial ao trigo, enquanto que, a interespecífica causou maior prejuízo para o azevém

Resumo: O objetivo deste trabalho foi identificar e comparar valores adaptativos dos biótipos de azevém (Lolium multiflorum) resistente e suscetível ao herbicida iodosulfuron e avaliar sua habilidade competitiva com o trigo (Triticum aestivum). Para avaliar o valor adaptativo, os biótipos foram semeados em vasos e coletados a cada 10 dias após a emergência, até os 80 dias. Em cada coleta, avaliaram-se estatura, área foliar e massa seca da parte aérea, e, a partir destas avaliações, foram calculadas variáveis indiretas para comparar o crescimento entre os biótipos. A habilidade competitiva foi determinada em experimento de série de substituição, tendo-se variado a proporção da cultura e do competidor. As proporções testadas foram: 100:0 (estande puro do trigo), 75:25, 50:50, 25:75 e 0:100% (estande puro do biótipo de azevém resistente ou suscetível); já as variáveis avaliadas foram área foliar e massa seca. Os resultados dos estudos comparativos de crescimento mostraram similaridade entre os biótipos de azevém resistente e suscetível ao iodosulfuron, o que não caracterizou efeito pleiotrópico decorrente da resistência. Quanto à habilidade competitiva, a competição interespecífica é prejudicial para o biótipo resistente, enquanto, para o biótipo suscetível, independe o competidor. A cultura do trigo mostra habilidade competitiva superior a dos biótipos de azevém resistente e suscetível.

Understanding the physiological defense behavior of plants subjected to herbicide application may help to identify products with higher or lower capacity to cause oxidative stress in crops. This study aimed at evaluating the effect of herbicides in the antioxidant activity of rice plants. The experimental design was completely randomized, with six replications. Treatments consisted of the herbicides bentazon (photosystem II inhibitor; 960 g ha-1), penoxsulam (acetolactate synthase inhibitor; 60 g ha-1), cyhalofop-butyl (acetyl coenzyme-A carboxylase inhibitor; 315 g ha-1) and a control. After the herbicides application, samples of rice shoots were collected at 12, 24, 48 and 96 hours after application (HAA). The components evaluated were hydrogen peroxide (H2O2), lipid peroxidation and activity of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT). Bentazon (up to 24 HAA) and penoxsulam (48 and 96 HAA) reduced the CAT activity. Moreover, these herbicides increased the levels of H2O2, lipid peroxidation and SOD activity, indicating a condition of oxidative stress in rice plants. The cyhalofop-butyl herbicide did not alter the antioxidant activity, showing that it causes less stress to the crop.

Barnyard grass (Echinochloa sp.) is one of the main rice weeds. Knowledge of its emergence can support management measures. The present study models barnyard grass emergence at different flooded rice sowing periods. Furthermore, the effectiveness of the hydrothermal time model in estimating barnyard grass emergence is analyzed. Field emergence was monitored three times a week during two sowing times (October and November) and two growing seasons (2017/18 and 2018/19), in rice sown and unsown areas. Data were converted to cumulative emergence based on total seedlings. Soil temperature and moisture data were used to determine hydrothermal time. The sowing in October led to a continuous emergence of barnyard grass, while the sowing in late November led to different emergence rates. The highest emergence rates of barnyard grass occur in the first sowing time. The hydrothermal time model is adequate to estimate barnyard grass emergence in both sowing times.

Synergic effects of glyphosate and saflufenacil have been reported to control Conyza spp. However, the mechanism of this synergic combination is unknown. The objectives of this study were to investigate the effects of the combination of glyphosate and saflufenacil on the control and resistance status of glyphosate-resistant (GR) C. bonariensis, as well as on oxidative stress and lipidic peroxidation. Glyphosate-resistant and glyphosate-sensitive (GS) biotypes were treated with different rates of saflufenacil, glyphosate, and glyphosate combined with saflufenacil. The combination of glyphosate (1480 g ae ha−1) and saflufenacil (≥15 g ha−1) presented the best control of GR plants compared with their individual effects. It also reduced the resistance factor from 19.6 to 4.6 (4.3-fold) and represents a good alternative for resistance management. The combination of glyphosate and saflufenacil resulted in higher oxidative stress and lipidic peroxidation compared with the effects of either herbicide alone. The oxidative stress and lipid peroxidation promoted by the combination of the herbicides occurred earlier after treatment and remained at higher levels over a longer period (12–192 h) compared with their individual results. The combined oxidative stress and lipid peroxidation at high levels over a long time is likely to be one reason that the combination of glyphosate and saflufenacil effectively controls GR C. bonariensis.

Italian ryegrass (Lolium multiflorum; LOLMU) is one of the most troublesome weeds in temperate regions in the world. This weed species interfere with wheat, corn, rye, and oat, causing significant crop yield losses. This species has evolved glyphosate resistance, making it difficult to control. The mechanisms of glyphosate resistance are still unknown, and an understanding thereof will favor the development of new strategies of management. The present study is the first transcriptome study in LOLMU using glyphosate-resistant and -sensitive biotypes, aiming to identify and to provide a list of the candidate target genes related to glyphosate resistance mechanism. The transcriptome was assembled de novo, producing 87,433 contigs with an N50 of 740 bp and an average length of 575 bp. There were 92 and 54 up- and down-regulated genes, respectively, in the resistant biotype, while a total of 1683 were differentially expressed in the sensitive biotype in response to glyphosate treatment. We selected 14 highly induced genes and seven with repressed expression in the resistant biotype in response to glyphosate. Of these genes, a significant proportion were related to the plasma membrane, indicating that there is a barrier making it difficult for glyphosate to enter the cell.

The successive use of Roundup Ready crops may difficult the management of volunteer plants originated from seed losses during harvest. In soybean, volunteer corn plants can exhibit higher interference and cause reduce yield depending on their density. The aim of this study was to quantify the economic threshold level (ETL) in soybean as a function of the competition of volunteer corn and to evaluate the chemical control in different phenological stages of development. The ETL and chemical control experiments were conducted in the field, under completely randomized and randomized block designs with one and three replicates, respectively. The variables analyzed were yield and ETL as functions of the competition of different volunteer corn populations (control, 1, 2, 4, 6, 8, 10, 12, 16, 20, 24 and 32 plants m-2) and the chemical control with acetyl coenzyme-A carboxylase (ACCase) inhibitor herbicides alone or mixed with glyphosate in different phenological stages of development (V2-V3, V4-V5 and V6-V8) that were evaluated at seven, 14 and 21 days after application (DAA). The results showed higher competitive potential of volunteer corn in which the presence of one plant m-2 reduces the soybean yield in 17%. The ETL ranged from 0.14 to 0.78 plants m-2 and the control of volunteer corn must be carried out in low populations. The use of ACCase inhibitors herbicides alone or mixed with glyphosate demonstrated greater than 85% control in the V2-V3 phenological stage independent of the period evaluated. The effectiveness of all herbicides decreased with application delay with a control level above 87%, in the V6-V8 phenological stage, obtained only for fluazifop and haloxyfop herbicides alone or in mixed with glyphosate at 14 and 21 days after application.

ABSTRACT: In Brazil, horseweed is one of the most important weeds because of the resistance to herbicides and high competitive for the crops. A large of losses were reported in major crops such as soybeans, wheat and corn, where the use a no-tillage system and the herbicide resistance promote better establishment. A correct understanding of the way temperature influences germination enables the prediction of the regions with the highest potential for colonization by this weed and thus facilitates its control. The objective of this study; therefore, was to discern the ways temperature affected the germination, viability and longevity of horseweed seeds. Testing was done at 10, 20 and 30°C, while evaluation occurred on days 0, 15, 30, 45 and 60. Seeds were packed in a nylon mesh bag (5x5cm), with 10g of upland soil (Yellow Red Argissolo, sandy loam texture), placed in transparent plastic boxes at 0 to 0.5cm soil depth, at the temperatures specified. Percentage of remaining seeds, first and second germination counts, abnormal seedlings, and dead, dormant, viable and non-viable seeds, were assessed. Horseweed seeds achieve secondary dormancy at 10, 20 and 30°C, while their quality and the longevity showed damage at 20 and 30°C temperatures.

ABSTRACT: The interference of glyphosate resistant hairy fleabane (Conyza bonariensis) has caused yield losses in soybean crop. Knowledge of the economic threshold is an important aspect for the economic management of resistant weeds. Because of it, the interference of the glyphosate resistant hairy fleabane density on the soybean yield loss was evaluated, as well as to estimate the economic threshold. Two experiments were conducted to verify the effect of different weed densities on the yield of two soybean cultivars (BRS Estância and BMX Turbo). Weed density ranged from 0 to 124 plants m-2. The yield of the BRS Estância decreased by 1.4% to the increase of one single plant, while for the BMX Turbo the loss was 25.9%. Soybean yield and economic threshold were lower for the BMX Turbo cultivar compared to the cultivar BRS Estância, which can be attributed to the genotype, competitive ability, weed development stage and/or environment. Increases in crop yield expectation, soybean price and herbicide efficiency reduce the economic threshold, indicating that the adoption of control measures should be taken when the weed density is low. Due to the high cost of hairy fleabane control, it is only feasible at high densities.

ABSTRACT: The objective of this study was to evaluate the relative competitive ability of soybean with different development stages of hairy fleabane. Two experiments were conducted in greenhouse, in a completely randomized design. In the experiment it was tested soybean and hairy fleabane competition at different stage of development (rosette and 15 cm height) at the proportions 100:0, 75:25, 50:50, 25:75 and 0:100, and total plant population was 315 plant m-2. The variables evaluated were plant height, leaf area, and shoot dry matter (leaves and stems). Competitive analysis was performed by diagrams and interpreting the competitiveness index. The soybean has greater competitive ability that horseweed for both development stages. The intraspecific competition is more intense for soybean when in hairy fleabane rosette stage, and the competitive relations are equivalent between soybean and hairy fleabane of 15 cm tall. The both hairy fleabane stages were injured in the soybeans competition.

Resumo:O objetivo deste trabalho foi identificar, na micobiota de Sagittaria montevidensis, espécies de fungos fitopatogênicos com potencial bioherbicida, bem como avaliar sua seletividade para a cultura do arroz irrigado. Foram avaliadas as espécies de fungos Fusarium oxysporum e F. semitectum da micobiota de S. montevidensis e seis níveis de concentração de esporos (0, 1x103, 1x104, 1x105, 1x106 e 1x107 esporos mL-1), aplicados sobre plantas de S. montevidensis em estádio de uma folha sagitada e sobre plantas de arroz no estádio de desenvolvimento R4. Avaliou-se a progênie da cultura. Os isolados de F. oxysporum e F. semitectum apresentaram maior incidência sobre as plantas de S. montevidensis; porém, não foram eficazes no controle da espécie quando aplicados no estádio de plântula com uma folha sagitada. A aplicação de F. oxysporum e F. semitectum na fase de floração das plantas de arroz irrigado causa perdas no rendimento, redução no vigor das sementes produzidas e redução no comprimento radicular e da parte área.

Dose-response experiments were carried out to evaluate the sensitivity of imidazolinone-resistant red rice to nonselective herbicides currently used in rice-soybean rotation in Rio Grande do Sul. Two red rice biotypes previously identified as resistant and susceptible to the imidazolinone herbicides were treated with imazapic plus imazapic, glyphosate and glufosinate under nine herbicide rates. A non-linear log-logistic analysis was used to estimate the herbicide rate that provided 50% red rice control and dry weight reduction (GR50). Imidazolinone-resistant red rice exhibited greater GR50 values than imidazolinone-susceptible biotype for imazapyr plus imazapic. In contrast, both imidazolinone-resistant and susceptible red rice showed similar GR50values for glyphosate and glufosinate. These results indicate that glyphosate and glufosinate effectively control imidazolinone-resistant red rice at similar herbicide rates used to control imidazolinone-susceptible; however, integrated weed management practices must be adopted in rice-soybean rotation to delay resistance evolution of red rice populations to glyphosate and glufosinate

Acetolactate synthase inhibitors are the main group of herbicides used in winter crops in Southern Brazil where their intensive use has selected for herbicide-resistant biotypes of radish. The resistance affects the efficacy of herbicides, and identifying the resistance mechanism involved is important for defining management strategies. The aim of this study was to elucidate the resistance mechanism of radish biotypes by quantifying the enzyme activity, ALS gene sequencing and evaluating the response of biotypes to iodosulfuron and imazethapyr herbicide application after treatment with a cytochrome P450 monooxygenase inhibitor. The susceptible (B1) and resistant (B4 and B13) biotypes were from wheat fields in the Northwest of Rio Grande do Sul State. The results demonstrated that the enzyme affinity for the substrate (KM) was not affected in biotypes B4 and B13 but that the Vmax of the resistant biotypes was higher than that of biotype B1. The resistant biotypes showed no differential metabolic response to iodosulfuron and imazethapyr herbicides when inhibited by malathion and piperonyl butoxide. However, gene sequencing of ALS showed a mutation at position 574, with an amino acid substitution of tryptophan for leucine (Trp-574-Leu) in resistant biotypes.

Os herbicidas utilizados no Sistema Clearfield(r) de produção de arroz irrigado caracterizam-se por serem móveis no solo. Tal mobilidade contribui para a contaminação ambiental e intensificação do residual no solo. A irrigação por inundação utilizada na lavoura arrozeira é uma das principais causas de livixiação de imidazolinonas, contudo, manejos alternativos de irrigação podem contribuir para sua diminuição. Assim, o objetivo do trabalho foi estimar, através de bioensaio, a lixiviação de imidazolinonas frente a diferentes manejos de irrigação. Para isso, foram conduzidos dois experimentos em casa de vegetação e em colunas de solo. Em ambos, foram testados três manejos de irrigação, sendo eles: contínuo, intermitente e capacidade de campo. Os herbicidas foram aplicados na superfície do solo e, após 48 horas, iniciou-se a irrigação. Aos 45 e 90 dias de irrigação, para o primeiro e segundo experimentos, respectivamente, as colunas de solo foram cortadas longitudinalmente e realizou-se bioensaio utilizando solo das diferentes profundidades. Os resultados permitem concluir que a mistura formulada imazapic + imazapyr apresenta maior lixiviação. Para os herbicidas testados isoladamente, o imazapic lixivia mais, seguido do imazethapyr e imazapyr. Os manejos de irrigação contínuo e intermitente não diferem entre si e promovem maior lixiviação dos herbicidas, quando comparado ao solo na capacidade de campo

O uso intenso de herbicidas com o mesmo mecanismo de ação na cultura do arroz (Oryza sativa L.) tem selecionado biótipos resistentes, como, por exemplo, o arroz-vermelho (planta daninha) resistente aos herbicidas imidazolinonas. Por essa razão, este trabalho foi desenvolvido com o objetivo de avaliar a resistência de arroz-vermelho ao herbicida imazapyr + imazapic, na região sul do Rio Grande do Sul, e o controle do biótipo resistente de arroz-vermelho com os herbicidas alternativos clethodim e glyphosate. Foram realizados três experimentos, em delineamento casualizado, arranjados em esquema fatorial. No primeiro experimento, o fator A testou biótipos de arroz-vermelho [ORYSA 184 (resistente) e ORYSA 188 (susceptível)], o fator B comparou herbicidas (imazapyr + imazapic, clethodim e glyphosate) e o fator C avaliou doses dos herbicidas (0; 0,5; 1; 2; 4; 8; 16 e 32 vezes a dose recomendada). No segundo, compararam-se biótipos de arroz-vermelho e doses do herbicida imazapyr + imazapic (0; 0,5; 1; 2; 4; 8; 16; 32 e 64 vezes a dose recomendada). No terceiro, testaram-se biótipos de arroz-vermelho e doses diferentes do herbicida imazapyr + imazapic para cada biótipo. O biótipo ORYSA 184 é resistente ao imazapyr + imazapic, quando aplicada a dose máxima de registro e estádio indicado. Os herbicidas clethodim e glyphosate, detentores de mecanismos de ação alternativos, controlam o biótipo resistente ORYSA 184 de arroz-vermelho.

Os herbicidas do grupo das imidazolinonas são amplamente utilizados no cultivo de arroz irrigado para o controle das principais plantas daninhas. Esses herbicidas comportam-se como ácidos ou bases fracas, dependendo do pH, podendo, dessa forma, influenciar na sua lixiviação. O objetivo deste estudo foi avaliar o efeito da elevação do pH, através da calagem, na lixiviação de imazethapyr e imazapyr em solo de cultivo de arroz irrigado. Foram coletadas amostras indeformadas de solo com pH natural próximo a 4,8 em uma lavoura de arroz irrigado sem histórico de aplicação de imidazolinonas. As colunas de solo foram coletadas utilizando-se um extrator e constituíram-se nas unidades experimentais da primeira fase do experimento. O experimento foi conduzido em casa de vegetação, arranjado em esquema fatorial, sendo o fator A constituído por solo com pH natural e solo com calagem. O fator B foi constituído pelos herbicidas imazethapyr e imazapyr (todos a 100g i.a. ha-1), aplicados sobre a superfície das colunas de solo. O fator C foi constituído das profundidades de amostragem (5 em 5cm). Os resultados mostram que a alteração do pH influencia na lixiviação dos herbicidas testados, quando aplicados em solo de cultivo de arroz irrigado. O solo calcareado apresenta maior lixiviação dos herbicidas imazapyr e imazethapyr.

A utilização do herbicida glyphosate para o controle químico das espécies de gramas-boiadeiras nas lavouras orizícolas não tem se mostrado eficiente. Nesse contexto, a investigação do controle dessas espécies com o glyphosate torna-se de fundamental importância, uma vez que não estão disponíveis no mercado herbicidas seletivos para o controle dessas em pós-emergência na cultura do arroz irrigado. Em vista do exposto, o objetivo do presente estudo foi avaliar a suscetibilidade das gramas-boiadeiras a diferentes formulações de glyphosate. Foram conduzidos dois experimentos em casa de vegetação em esquema fatorial. No primeiro experimento, o fator A constituiu-se de duas formulações de glyphosate (sal potássico e isopropilamina) e o fator B de nove doses dos herbicidas (zero; 175; 350; 700; 1400; 2800; 5600; 11200; 22400g e.a. ha-1). No segundo experimento, o fator A constituiu-se de duas espécies de gramas-boiadeiras (Leersia hexandra e Luziola peruviana), o fator B de três formulações do glyphosate (sal amônio, potássico e isopropilamina) e o fator C de nove doses dos herbicidas (zero; 87,5; 175; 350; 700; 1400; 2800; 5600; 11200g e.a. ha-1). Com base nos resultados obtidos, foi possível observar que as espécies apresentaram diferença de suscetibilidade ao herbicida glyphosate. Além disso, Leersia hexandra foi mais sensível em comparação a Luziola peruviana. As formulações de glyphosate influenciaram na suscetibilidade das espécies ao controle, sendo que, Roundup Transorb R® e Roundup Ultra® proporcionam melhor controle das espécies de gramas-boiadeiras.

Conyza bonariensis (hairy fleabane) is one of the most problematic and widespread glyphosate-resistant weeds in the world. This highly competitive weed species significantly interferes with crop growth and substantially decreases crop yield. Despite its agricultural importance, the molecular mechanisms of glyphosate resistance are still unknown. The present RNA-Seq study was performed with the goal of identifying differentially expressed candidate transcripts (genes) related to metabolism-based non-target site glyphosate resistance in C. bonariensis. The whole-transcriptome was de novo assembled from glyphosate-resistant and -sensitive biotypes of C. bonariensis from Southern Brazil. The RNA was extracted from untreated and glyphosate-treated plants at several timepoints up to 288 h after treatment in both biotypes. The transcriptome assembly produced 90,124 contigs with an average length of 777 bp and N50 of 1118 bp. In response to glyphosate treatment, differential gene expression analysis was performed on glyphosate-resistant and -sensitive biotypes. A total of 9622 genes were differentially expressed as a response to glyphosate treatment in both biotypes, 4297 (44.6%) being up- and 5325 (55.4%) down-regulated. The resistant biotype presented 1770 up- and 2333 down-regulated genes while the sensitive biotype had 2335 and 2800 up- and down-regulated genes, respectively. Among them, 974 up- and 1290 down-regulated genes were co-expressed in both biotypes. In the present work, we identified 41 new candidate target genes from five families related to herbicide transport and metabolism: 19 ABC transporters, 10 CYP450s, one glutathione S-transferase (GST), five glycosyltransferases (GT), and six genes related to antioxidant enzyme catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD). The candidate genes may participate in metabolic-based glyphosate resistance via oxidation, conjugation, transport, and degradation, plus antioxidation. One or more of these genes might ‘rescue’ resistant plants from irreversible damage after glyphosate treatment. The 41 target genes we report in the present study may inform further functional genomics studies, including gene editing approaches to elucidate glyphosate-resistance mechanisms in C. bonariensis.

O trigo (Triticum aestivum L.) é a cultura de maior importância econômica entre os cereais de inverno. Realizaram-se dois experimentos para avaliar o efeito do tratamento de sementes com fungicidas no atraso da emergência da cultura e a influência de épocas de aplicação de N sobre variáveis morfofisiológicas e componentes de produtividade da cultura do trigo. O primeiro, em casa de vegetação e delineamento experimental inteiramente casualizado, testou os tratamentos de sementes triadimenol (25,11 g i.a. ha-1), carboxina + tiram (75 g i.a. ha-1), e testemunha sem tratamento. O segundo experimento foi realizado a campo, em parcelas subdivididas, cujo fator A, arranjado na parcela, testou os diferentes tratamentos de sementes e o fator B, na subparcela, constou de épocas de aplicação de nitrogênio (N): sem aplicação, 100% na base (B), 50% B + 50% no início do afilhamento (IA), 50% B + 50% com as primeiras espiguetas visíveis (PEV); 50% IA + 50% PEV. O tratamento de sementes com triadimenol reduziu o IVE e o número de afílhos planta-1 de trigo em relação ao tratamento com carboxina + tiram, que reduziu o número de grãos espiga-1, sem influenciar a produtividade do trigo. O fracionamento da aplicação do N, sendo a segunda aplicação no estádio PEV, promoveu benefício sobre os componentes da produtividade do trigo.

O objetivo deste trabalho foi comparar a habilidade competitiva relativa de milhã com as culturas de arroz irrigado e de soja. Realizaram-se cinco experimentos, nas safras de 2009/2010 e 2010/2011, em delineamento inteiramente casualizado, com quatro repetições. Os tratamentos consistiram de proporções de plantas de milhã e arroz irrigado ou soja (100:0, 75:25, 50:50, 25:75 e 0:100%). A área foliar e a massa de matéria seca da parte aérea foram avaliadas aos 45 dias após a emergência. A competição entre milhã e arroz irrigado ou soja ocorre pelos mesmos recursos do ambiente. Plantas de milhã apresentam menor habilidade competitiva por indivíduo do que o arroz irrigado e a soja, quando ocorrem na mesma proporção de plantas. Quando as culturas do arroz irrigado ou da soja estão associadas ao milhã, a competição intraespecífica predomina, enquanto, para a planta daninha, prevalece a competição interespecífica como a mais prejudicial.

Os herbicidas usados na cultura do arroz Clearfield® podem persistir no ambiente e causar danos no arroz não tolerante, cultivado em sucessão. Esse dano pode ser de intensidade variável, dependendo, dentre outros fatores, do movimento ascendente do herbicida para região de absorção do sistema radicular das plantas. O objetivo desta pesquisa foi verificar o efeito da altura do lençol freático no movimento ascendente do herbicida composto pela mistura formulada de imazethapyr e imazapic. Para isso, foram coletados lisímetros de solo com auxílio de tubos de PVC (15x30cm). O herbicida foi aplicado na superfície inferior dos lisímetros, onde foram simulados diferentes profundidades do lençol freático (0, 5, 10, 15 e 25cm da superfície do solo). Os lisímetros permaneceram nessa condição por período de 150 dias, quando foram cortados longitudinalmente, seccionados em porções de 5cm (0-5 a 25-30cm) e realizado bioensaio com a cultivar de arroz não tolerante, IRGA 417. Com os resultados obtidos, foi possível concluir que ocorre movimento ascendente da mistura formulada dos herbicidas imazethapyr e imazapic ao longo do perfil do solo de várzea durante o período da entressafra do arroz irrigado, sendo este maior quando o lençol freático está localizado mais próximo da superfície do solo. O movimento ascendente através da diluição do herbicida na solução do solo ocorre por fluxo de massa através do arraste pela água, transportada por capilaridade para zonas mais superficiais do solo.

Objetivou-se avaliar espécies vegetais com potencial alelopático, associados às práticas de manejo e ao uso de herbicida nicosulfuron, no controle de plantas daninhas e nos componentes de produtividade da cultura do milho. O delineamento experimental utilizado foi em blocos ao acaso, com quatro repetições. O experimento foi composto por três fatores: espécies de cobertura, manejo das coberturas e aplicação ou não de herbicida nicosulfuron em pós-emergência. As variáveis avaliadas foram: número de plantas daninhas, número de fileiras de grãos, número de grãos por fileira, número de grãos por espiga e produtividade de grãos de milho. A cobertura de azevém, em geral, reduz o número de plantas daninhas emergidas e favorece o desempenho produtivo do milho. O manejo das plantas de cobertura com roçada e retirada da palha reduz a produtividade do milho. A maior produtividade do milho, foi observada com a aplicação de nicosulfuron em pós-emergência, independente da cultura de cobertura ou do manejo adotado. The objective of the study was evaluate the allelopathy of cover species, associated to management practices and use of nicosulfuron herbicide on the productive performance of corn. The experimental design consisted of complete randomized block with four replications. The treatments were: cover species, cover management and application or not of post-emergence herbicide. The variables evaluated were: number of weeds, number of rows kernels, number of kernels rows, number of kernels ear and grain yield of corn. Lolium multiflorum, reduced the number of emerged weeds and provides the best results in productive performance. The management simulated grazing, does not favor the yield of corn. The application of nicosulfuron in post-emergence, along with the allelopathic activity increases the productive performance of corn, regardless of cover crop or soil management.

O objetivo deste trabalho foi avaliar a resistência de capim pé-de-galinha (Eleusine indica) ao glifosato, em lavouras de soja transgênica; avaliar o efeito de aplicações de glifosato em diferentes estádios de desenvolvimento; identificar práticas agronômicas associadas à seleção de biótipos resistentes; e avaliar a eficiência dos herbicidas cletodim, fluazifope-P-butílico, clomazona, glufosinato de amônio e glifosato nas plantas resistentes. Plantas escapes ao tratamento com glifosato foram coletadas em 24 propriedades, no Rio Grande do Sul. As plantas foram cultivadas em casa de vegetação, tendo-se avaliado a sua resistência ao glifosato. Os acessos resistentes foram selecionados e avaliados quanto ao efeito da aplicação do glifosato em diferentes estádios de crescimento e quanto à sensibilidade aos herbicidas. Foi aplicado um questionário aos produtores para identificação das práticas agronômicas associadas às falhas no controle. O controle de E. indica pelo glifosato é mais efetivo com a aplicação em estádios iniciais de desenvolvimento. Práticas agronômicas, como uso contínuo de baixas doses do herbicida, aplicação em estádios de desenvolvimento avançados das plantas daninhas (mais de um afilho) e a ausência de rotação de culturas foram relacionadas às falhas de controle observadas. Os herbicidas cletodim, fluazifope-P-butílico e glufosinato de amônio são alternativas eficientes para o controle de E. indica.The objective of this work was to evaluate the resistance of goose grass (Eleusine indica) to glyphosate application in transgenic soybean crops; evaluate the effect of glyphosate applications in different growth stages; identify the main agronomic practices associated with the selection of resistant biotypes; and evaluate the effect of the herbicides clethodim, fluazifop-p-butyl, clomazone, glufosinate ammonium, and glyphosate on resistant plants. Plants that survived glyphosate application were collected on 24 properties in the state of Rio Grande do Sul, Brazil. Plants were grown in greenhouse and their resistance to glyphosate was evaluated. The resistant accessions were selected and evaluated as to the effect of glyphosate application on different growth stages and to their sensitivity to the herbicides. A questionnaire was given to producers in order to identify agronomic practices associated with control failures. The control of E. indica by glyphosate is more effective at initial growth stages. Agronomic practices, such as continued use of low doses of glyphosate, application on advanced weed growth stages (more than one tiller), and absence of crop rotation were related to the observed control failures. The herbicides clethodim, fluazifop-p-butyl, and glufosinate ammonium are efficient alternatives to control E. indica.

Weeds cause reduction in the rice yield. Little is known about the competitive ability of yellow nutsedge (Cyperus esculentus) with rice and the extent of the economic threshold (ET). The aim of this study was to determine the fit of the regression model to estimate hyperbolic yield losses and ET of yellow nutsedge in rice due to the cycle of cultivars (BRS Querência - Early cycle and IRGA 424 - mid cycle). For this, a field study of competition in the agricultural year 2010/11 was conducted. Yield losses and ET of yellow nutsedge in rice crop is function on the competitive ability of rice cultivar used. The use of rice cultivar with early cycle, BRS Querência, increases the ETs of weed in rice crops compared to the use of IRGA 424, mid-cycle. The hyperbola satisfactorily estimated yield losses that yellow nutsedge causes in rice crops. The explanatory variable, population of yellow nutsedge, was the best fitted to the model. Increases in yield, price paid for rice and control efficiency promoted by the herbicide and decreased cost of weed control, promote ET reduction in yellow nutsedge in rice crops, justifying the adoption of control measures of smaller populations of the weed.

The objective of the study was to evaluate the influence of cover crops extracts on growth and development of Bidens pilosa. The experimental design was completely randomized in factorial scheme 4 x 3 x 5 with four replications. The factor A was composed by cover crops (Brassica napus; Raphanus sativus; Trifolium vesiculosum; Lolium multiflorum), B was parts plants (whole plant, shoot and root system) and C extracts concentrations (0; 1, 2.5, 5 and 10% weight / volume). Variables evaluated were: speed of germination; germination percentage; length and dry matter of shoot and root. Extracts of Brassica napus followed by extracts of Trifolium vesiculosum, in general, had more allelopathic potential. The shoots of the cover crops, presented in general larger allelopathic activity. Allelopathic activity on germination and development of Bidens pilosa increases with the increment of extracts concentration, of differents plants parts. The speed germination is the best indicator of allelopathic activity of cover crops on Bidens pilosa. Objetivou-se com o trabalho avaliar a influência de extratos de culturas de cobertura de estação estival de inverno sobre o crescimento e desenvolvimento de Bidens pilosa (picão-preto). O delineamento experimental foi inteiramente casualizado, arranjado em esquema fatorial 4 x 3 x 5, com quatro repetições. O fator A foi constituído pelas culturas de cobertura (canola, nabo-forrageiro, trevovesiculoso e azevém), o B pelas partes da planta (planta inteira, parte aérea ou sistema radicular) e o C pelas concentrações dos extratos vegetais (0; 1; 2,5; 5 e 10% peso/volume). Foram avaliados o índice de velocidade de germinação, a percentagem de germinação e comprimento e massa seca da parte aérea e radicular. Os extratos de canola seguidos dos de trevo-vesiculoso, apresentaram maior potencial alelopático. A parte aérea das culturas de cobertura foi a que apresentou a maior atividade alelopática. A atividade alelopática sobre a germinação e o desenvolvimento de picão-preto aumentou com o incremento da concentração dos extratos, das partes vegetais. O índice de velocidade de germinação foi o melhor indicador de atividade alelopática de culturas de cobertura sobre o picão-preto.

Cyperus difformis L. is a weed occurrence in flooded rice, that it has been presenting control difficulty due to ALS inhibiting herbicides resistance. The objectives of this work was to determine necessary rate 50% control of the population (C50) and reduce 50% of the production the aerial dry mass (GR50) in resistant and susceptible biotypes of C. difformis and evaluate the control of these biotypes with alternative herbicides recommended for that species. For that, two experiments were performed at green house of FAEM/UFPel arranged in a completely randomized design, with four replicates. The experiment I were consisted of resistant (CYPDI 9) and susceptible of C. difformis biotype and rate of the pyrazosulfuron-ethyl herbicide, corresponding to 0, 0,5, 1, 1,5, 2, 2,5, 3, 4, 6, 8, 16, 32 and 64 times de registered rate (20g ha-1). The evaluated variables were visual control and aerial dry mass (MPAS) to the 28 days after the application of the treatments (DAT). In the experiment II the treatments were consisted of the same biotype (CYPDI 9 and CYPDI 8), nine herbicides azimsulfuron (6g ha-1); bentazon (900g ha-1); bispyribac-sodium (48g ha-1); carfentrazone-ethyl (40g ha-1); ethoxysulfuron (72g ha-1); glyphosate (900g ha-1); penoxsulam (36g ha-1); propanil (3600g ha-1) and pyrazosulfuron-ethyl (20g ha-1) and checks that didn't applied herbicide. The evaluated variables were: visual control for the herbicides to the 14, 21 and 28 DAT, foliate area and MPAS to 28 DAT. Before the results, it can be concluded that the resistance of the C. difformis biotype to pyrazosulfuron-ethyl is elevated and it makes unfeasible her control for the herbicide and the herbicides carfentrazone-ethyl, bentazon e propanil holders of alternative action mechanisms to the pyrazosulfuron-ethyl, control the resistant biotype of C. difformis.Cyperus difformis L. é planta daninha ocorrente em lavouras de arroz irrigado, que tem apresentado dificuldade de controle devido à resistência a herbicidas inibidores de ALS. O objetivo da pesquisa foi estimar a dose necessária para controlar 50% da população (C50) e reduzir 50% da produção de massa da parte aérea seca (GR50) em biótipo resistente e suscetível de C. difformis e avaliar o controle destes biótipos com herbicidas alternativos recomendados para a espécie. Para isso, foram conduzidos dois experimentos em casa de vegetação, em delineamento experimental completamente casualizado, com quatro repetições. O experimento I constou de biótipo resistente (CYPDI 9) e suscetível (CYPDI 8) de C. difformis e doses do herbicida pyrazosulfuron-ethyl, correspondendo a 0; 0,5; 1; 1,5; 2; 2,5; 3; 4; 6; 8; 16; 32 e 64 vezes a dose registrada (20 g ha-1). As variáveis avaliadas foram controle visual e massa da parte aérea seca (MPAS) aos 28 dias após a aplicação dos tratamentos (DAT). No experimento II os tratamentos constaram dos biótipos (CYPDI 9 e CYPDI 8), nove herbicidas: azimsulfuron (6g ha-1); bentazon (900g ha-1); bispyribac-sodium (48g ha-1); carfentrazone-ethyl (40g ha-1); ethoxysulfuron (72g ha-1); glyphosate (900g ha-1); penoxsulam (36g ha-1); propanil (3600g ha-1) e pyrazosulfuron-ethyl (20g ha-1) e testemunha que não recebeu herbicida. As variáveis avaliadas foram: controle visual aos 14, 21 e 28 DAT, área foliar (AF) e MPAS aos 28 DAT. A resistência do biótipo de C. difformis ao pyrazosulfuron-ethyl é elevada e inviabiliza seu controle pelo herbicida e, os herbicidas carfentrazone-ethyl, bentazon e propanil, detentores de mecanismos de ação alternativos ao pyrazosulfuron-ethyl, controlam o biótipo resistente de C. difformis.

Studied the weed control and the changes of biomass and microbial soil properties at crop cultivated both genetically modified and non altered soybeans because of glyphosate or imazethapyr herbicide applications. Soybean cultivations were tested (BRS 244RR), genetically modified and BRS 154, non modified) and herbicides (glyphosate and imazethapyr), and control treatment with weed. Variables were evaluated for phytotoxicity to the crop, control of Raphanus raphanistrum (wild radish), Digitaria sp. (crabgrass) and Brachiaria plantaginea (alexsandregrass), total organic carbon (TOC), microbial biomass carbon (MBC), basal respiration (BR) and metabolic quocient (QCO2). The herbicide glyphosate, applied as a single dose or sequentially, effectively controls the weeds wild radish, crabgrass and alexsandregrass and increases microbial activity, basal respiration and metabolic quocient. The microbial metabolism was not affected by the fact that the genotype or not genetically modified, but the use of the herbicide glyphosate.Estudou-se o controle de plantas daninhas, as variações da biomassa e do metabolismo microbiano do solo em áreas cultivadas com soja geneticamente modificada e não modificada, em função da aplicação dos herbicidas glifosato ou imazetapir. Testaram-se cultivares de soja (BRS 244RR, geneticamente modificada e BRS 154, não modificada) e herbicidas (glifosato e imazetapir), e tratamento controle com capina. Como variáveis foram avaliadas a fitotoxicidade à cultura, controle de Raphanus raphanistrum (nabo), Digitaria sp. (milhã) e Brachiaria plantaginea (papuã), teores de carbono orgânico total (COT), carbono da biomassa microbiana (CBM), respiração basal (RB) e quociente metabólico (QCO2). O herbicida glifosato, aplicado em dose única ou seqüencial, controla eficientemente as plantas daninhas nabo, milhã e papuã, e aumenta a atividade microbiana, a taxa de respiração basal e o quociente metabólico. O metabolismo microbiano do solo não foi afetado pelo genótipo, geneticamente modificado ou não, mas sim pelo uso do herbicida glifosato.

The objective this study was to monitor pesticide residues in groundwater at three different times and in seven regions producing rice in southern Brazil, in the 2007/08 season. Imazethapyr and fipronil were found in all regions studied. All groundwater samples from the Planície Costeira Interna to Lagoa dos Patos and Santa Catarina contained at least one pesticide. The lowest number of contaminated samples were detected in the Southern region. The highest frequency of contaminated samples was found after drainage of the rice fields. Only fipronil exceeded limits of potability, in 27% of samples, according European Community criteria.