ABSTRACT Second-generation glyphosate-tolerant maize (Roundup Ready 2, RR2) is characterised by the expression of the cp4epsps gene. Despite some studies suggesting possible undesirable effects from the application of glyphosate in RR2 maize, other reports have demonstrated glyphosate selectivity for RR2 plants, with minor damage symptoms, if any, and with no negative effects on the chlorophyll indices. The aim of this study was to evaluate the effect of different types of glyphosate management, formulations and rates of application on chlorophyll indices and the agronomic performance of an RR2 maize genotype expressing the cp4epsps gene. Five experiments were conducted in a full factorial design (2 x 5 x 5) to evaluate two types of management, two formulations and five rates of glyphosate. Damage symptoms, chlorophyll indices and variables related to agronomic performance (plant height, stem diameter, yield and 100-grain weight) were evaluated. Similar crop responses were found for each of the glyphosate formulations (potassium salt and isopropylamine salt) and types of management (single application and sequential application) under test, indicating that the use of glyphosate-based commercial products affords flexibility in terms of formulation and frequency of application. Glyphosate formulated as potassium salt or isopropylamine salt and applied to RR2 maize either in a single application (full rate) or in two sequential applications (each at half rate) has a similar effect and may therefore be used without distinction. However, it is important to consider the rate of application since high rates of glyphosate (especially greater than 1,440 g ae ha-1) may affect the development and production of RR2 maize.

RESUMO A competição de plantas daninhas é um desafio para os produtores de arroz em monocultivo no contexto de espécies resistentes a herbicidas e plantas daninhas difíceis de manejar usando o controle químico. Diversificar a rotação de culturas por meio de sistemas integrados de produção agropecuária (SIPA) pode ser uma alternativa para enfrentar esse desafio. Como o banco de sementes de plantas daninhas reflete práticas de manejo, este estudo teve como objetivo avaliar o impacto de um arrozal tradicional e quatro SIPA em terras baixas sobre o banco de sementes de plantas daninhas, em um experimento de longa duração localizado em Cristal, RS, Brasil. Os tratamentos consistiram em cinco sistemas de cultivo: T1 - monocultivo de arroz; T2 - integração arroz-pecuária; T3 - integração soja-arroz-pecuária; T4 - integração soja-milho-arroz-pecuária; e T5 - integração arroz-pecuária, em pastagens cultivadas e campo nativo. O banco de sementes foi avaliado no quarto ano experimental, outubro de 2016, em três profundidades do solo (0-5; 5-10 e 10-20 cm). No médio prazo, a diversificação do arrozal por meio de SIPA não afetou o tamanho do banco de sementes. No entanto, em T1 as sementes estavam distribuídas ao longo do perfil do solo, em contraste com os demais sistemas de cultivo, onde as sementes de plantas daninhas se acumularam na profundidade de 0-5 cm. Arranjos de SIPA que compreendem a integração de culturas de verão e pastagens hibernais diminuem a proporção de plantas daninhas ciperáceas na camada superficial do banco de sementes do solo. A diminuição do banco de sementes de arroz daninho é mais pronunciada nos arranjos de SIPA em terras baixas que integram diferentes culturas de verão em rotação com pastagens hibernais.

ABSTRACT Weed competition is a challenge to rice monocropping growers in the context of herbicide resistant weeds and difficult weeds to manage using chemical control. Diversifying crop rotations through integrated crop-livestock systems (ICLS) can be an alternative to face this challenge. As weed seedbank reflects management practices, this study aimed to assess the impact of a traditional paddy field and four lowland ICLS on the weed seedbank, in a long-term ICLS experiment located in Cristal, RS, Brazil. Treatments consisted of five cropping systems: T1 - rice monocropping; T2 - rice-beef cattle integration; T3 - soybean-rice-beef cattle integration; T4 - Sudan grass-soybean-maize-rice-beef cattle integration; and T5 - rice-beef cattle integration in cultivated and natural grassland. The seedbank was assessed in the fourth experimental year, Oct-2016, at three soil depths (0-5; 5-10 and 10-20 cm). In a mid-term temporal scale, the diversification of paddy field through ICLS did not affect weed seedbank size. However, seeds in T1 were equally distributed along the soil profile, in contrast to the other cropping systems, where weed seeds accumulated in the 0-5 cm depth. Lowland ICLS designs that comprises the integration of summer crops with grazing winter cover crops decrease the proportion of Cyperaceae weed species in the topsoil seedbank. The depletion of weedy rice seedbank is more pronounced in lowland ICLS designs that integrates different summer crop in rotation with grazing cover crops.

RESUMEN El pasto amargo (Digitaria insularis) es una de las principales malezas en el cultivo de soya. Para controlar su crecimiento, se requiere un aumento de las tasas de herbicida para simplificar su manejo al ser una planta con alta capacidad vegetativa y producción de semillas. Esto implica seleccionar los biotipos de Digitaria insularis resistentes a herbicidas Sin embargo, aún existe cierta información contrastante que considera el antagonismo de los herbicidas auxínicos sintéticos en las mezclas con inhibidores de ACCase y glifosato, para el control de malezas resistentes o tolerantes a los herbicidas. El estudio tuvo como objetivo evaluar el control de D. insularis con mezclas de herbicidas aplicados en la pre-emergencia y pos-emergencia del cultivo de soya y se verificó el posible antagonismo entre los herbicidas inhibidores de ACCase con auxinas sintéticas y otros latifolicidas. El experimento se realizó en Palotina, Paraná, (Brasil) y Corpus Christi, Canindeyú (Paraguay). Los tratamientos consistieron en mezclas de glifosato, inhibidores de ACCase (cletodim, haloxifop) y latifolicidas (2,4-D, triclopir, dicamba, carfentrazona, saflufenacil, clorimurón). Se utilizó un diseño de bloques al azar. El control de arvenses fue satisfactorio sólo en Palotina después de la aplicación secuencial en pos-emergencia. Allí se observó un control efectivo de D. insularis en la pre-emergencia, para algunas mezclas que presentaron glifosato+ACCase+carfentrazona, saflufenacil o clorimurón. Se observó antagonismo para todas las auxinas sintéticas en ambas ubicaciones. En Corpus Christi las mezclas de herbicidas no fueron efectivas, incluso con la aplicación de glifosato+cletodim en la pos-emergencia de soya. Aunque se obtuvo un control ineficaz para tratamientos compuestos con auxinas sintéticas, la aplicación en post-emergencia de soya aumentó el nivel de control, con resultados finales satisfactorios para todos los tratamientos.

ABSTRACT Sourgrass (Digitaria insularis) is one of the main weeds in the soybean crop. In order to control its growth, an increase of herbicide rates is required to simplify its management as it a plant with high vegetative capacity and seed production. It implies to select the herbicide-resistent Digitaria insularis biotypes. Nevertheless, some information is still contrasting the antagonist of synthetic auxinic herbicides, associated with glyphosate and ACCase inhibitors mixtures, for the control of weeds resistant or tolerant to herbicides. This study aimed to evaluate the D. insularis control, with a mixture of herbicides applied in soybean pre-emergence, with sequential application in soybean post-emergence, and to check possible antagonism between ACCase inhibitors herbicides with synthetic auxins and other latifolicides. The experiment was conducted in Palotina, Paraná (Brazil) and Corpus Christi, Canindeyú, (Paraguay.) The treatments consisted of associations of glyphosate, ACCase inhibitors (clethodim, haloxyfop), and latifolicides (2,4-D, triclopyr, dicamba, carfentrazone, saflufenacil, chlorimuron). A randomized block design was used. Only in Palotina, the weed control was satisfactory after sequential application in post-emergence. An antagonism for all synthetic auxins was observed with glyphosate+clethodim or haloxyfop mixtures, in both locations. As a result, in Palotina an efficacious control of perennial D. insularis was found in pre-emergence burndown for some mixtures such as glyphosate+ACCase inhibitor added to carfentrazone, saflufenacil, or chlorimuron. Antagonism was observed for all synthetic auxins, in both locations. In Corpus Christi, the herbicide associations were not effective, even with the post-emergence application in soybean of glyphosate+clethodim. With ineffective control for treatments composed with synthetic auxins, the post-emergence application in soybean increased the weed control with satisfactory final controls for all treatments.

RESUMEN Juntas, Conyza bonariensis, C. canadensis y C. sumatrensis presentan 105 casos reportados de biotipos resistentes a herbicidas tales como glifosato, paraquat y los inhibidores de la acetolactato sintasa (ALS). Se cree que la aplicación de herbicidas pre-emergentes en mezclas con desecantes es efectiva para controlar Conyza spp. en el manejo pre-siembra de la soya. El objetivo de este estudio fue evaluar la eficacia de sulfentrazona/ diuron, imazetapir/flumioxazin y diclosulam, en mezcla con diquat, paraquat o glufosinato, en el control de Conyza spp. Se realizaron dos experimentos de campo en diseño de bloques al azar con cuatro repeticiones. Los tratamientos consistieron en la aplicación de herbicidas pre-emergentes en mezclas con desecantes, además del tratamiento control (sin aplicación), para un total de 10 tratamientos. El control de Conyza spp. se evaluó a los 7, 14, 21, 28 y 35 d después de la aplicación del herbicida, y se evaluaron los síntomas de daño en las plantas de soya a los 14, 21, 28 y 35 d después de la aplicación del herbicida. Los herbicidas sulfentrazona/diuron, imazetapir/flumioxazin y diclosulam en mezclas con diquat, paraquat o glufosinato, fueron efectivos para controlar Conyza spp. en la pre-siembra de la soya, destacando buenas opciones para la rotación de herbicidas antes y después de la emergencia. Las mezclas con diclosulam mostraron un mayor potencial de daño a las plantas de soya que sulfentrazona/diuron y imazetapir/flumioxazin.

ABSTRACT Together, Conyza bonariensis, C. canadensis and C. sumatrensis show 105 reported cases of biotypes resistant to herbicides like glyphosate, paraquat, and acetolactate synthase (ALS) inhibitors . The application of pre-emergent herbicides combined with burndown herbicides is believed to be effective in controlling Conyza spp. during soybean pre-sowing management. The objective of this study was to evaluate the efficacy of sulfen-trazone/diuron, imazethapyr/flumioxazin, and diclosulam in mixtures with diquat, paraquat, or glufosinate on the control of Conyza spp. Two field experiments were conducted in a randomized block design with four replicates. Treatments consisted of the application of pre-emergent plus burndown herbicides, besides the weedy control treatment (without application), for a total of 10 treatments. The control of Conyza spp. was evaluated at 7, 14, 21, 28, and 35 d after herbicide application, and symptoms of injury in soybean plants were evaluated at 14, 21, 28, and 35 d after herbicide application. The herbicides sulfentrazone/diuron, imazethapyr/flumioxazin, and diclosulam in combination with burndown herbicides diquat, paraquat, or glufosinate were effective in controlling Conyza spp. in the pre-sowing management of soybean, highlighting good options for pre- and post-emergent herbicide rotations. Mixtures with diclosulam showed a higher potential for injury to soybean plants than sulfentrazone/diuron and imazethapyr/flumioxazin.

RESUMEN Las mezclas entre herbicidas, el uso de múltiples sitios de acción y otras prácticas de manejo de malezas son necesarias para evitar otros casos de resistencia de biotipos. El objetivo de este estudio fue evaluar la eficiencia de imazapic/imazapyr y otros herbicidas en mezclas para controlar Digitaria insularis en la desecación antes de la siembra de soya. Esta investigación de campo se realizó en Umuarama, Estado de Paraná (PR), Brasil, en la cosecha de soya de 2018/19. El experimento se realizó en un diseño experimental de bloques al azar, con cuatro repeticiones y 11 tratamientos, compuestos por la aplicación de glifosato, cletodim, haloxifop, imazapic/imazapir, glufosinato, ácido 2,4-diclorofenoxiacético (2,4-D), dicamba, triclopir y saflufenacil, en mezclas. Se evaluó el control de malezas, así como el daño y el rendimiento de la soya. Se realizaron un análisis de varianza y test F, y se compararon las medias de los tratamientos con el test de Scott-Knott. Todos los tratamientos mostraron un gran control sobre la maleza y una baja tasa de daño a los cultivos mientras se mantenía el rendimiento de la soya. La aplicación de imazapic/imazapir en mezclas con otros herbicidas fue eficaz en el control de D. insularis resistente al glifosato, en desecación antes de la siembra de soya y con aplicación secuencial de haloxifop + glifosato en la etapa V3 de la soya. Este manejo químico también fue selectivo para la soya.

ABSTRACT Herbicide mixtures, use of multiple sites of action, and other weed management practices are necessary to avoid cases of biotype resistance. The aim of this study was to evaluate the efficiency of imazapic/imazapyr and other herbicides in mixtures to control Digitaria insularis at burndown before soybean sowing. This field research was conducted in Umuarama, State of Parana (PR), Brazil, in the 2018/19 soybean season. The experiment was conducted in a randomized block experimental design with four replicates and 11 treatments composed of the application of glyphosate, clethodim, haloxyfop, imazapic/ imazapyr, glufosinate, 2,4-dichlorophenoxyacetic acid (2,4-D), dicamba, triclopyr, and saflufenacil, in mixtures. Weed control was evaluated as well as soybean injury and yield. An analysis of variance and F-test were performed, and the treatment means were compared by the Scott-Knott test. All treatments showed great control over the weed and low crop injury rate while maintaining soybean yield. The application of imazapic/ imazapyr in mixtures with other herbicides was effective in controlling glyphosate-resistant D. insularis in burndown before soybean sowing and with sequential application of haloxyfop + glyphosate at V3 stage of soybean. This chemical management was also selective for soybean.

RESUMO A rotação de culturas é essencial no manejo de espécies de plantas daninhas resistentes a herbicidas. Objetivou-se avaliar o efeito de sistemas consorciados de milho com braquiária ou crotalária nos parâmetros qualitativos e quantitativos do banco de sementes de plantas daninhas, ao longo da sucessão de milheto, milho e feijão. Além disso, o efeito desses sistemas de rotação de cultura na seleção de espécies específicas de plantas daninhas do banco de sementes também foi avaliado. O delineamento experimental foi em blocos casualizados, com quatro repetições. Os tratamentos foram representados por três sistemas de cultivo em sucessão: milheto, milho solteiro, feijoeiro; milheto, milho consorciado com braquiária, feijoeiro; milheto, milho consorciado com crotalária, feijoeiro. Foram calculados os seguintes índices fitossociológicos: densidade, frequência e importância relativa, diversidade e equitabilidade. As produtividades de grãos de milho e de feijão também foram quantificadas. Foram identificadas 23 espécies de plantas daninhas, divididas em 12 famílias, com destaque para Poaceae, sendo as mais importantes Alternanthera tenella, Commelina benghalensis, Eleusine indica e Phyllantus tenellus. O sistema de cultivo com milho solteiro apresentou menor densidade e diversidade de plantas daninhas, com elevada importância para E. indica. Os sistemas de consórcio na safra anterior, como garantia de maior diversidade de plantas daninhas, podem ser utilizados como ferramentas alternativas, diferentes dos herbicidas, para controlar plantas daninhas e melhorar a produtividade do feijoeiro. Em relação ao controle de plantas daninhas no feijoeiro, Crotalaria spectabilis apresentou melhores resultados no sistema consorciado de milho anterior do que Urochloa ruziziensis.

ABSTRACT Crop rotation is critical in the management of herbicide-resistant weed species. This study aimed to evaluate the effect of intercropping systems of maize with brachiaria or crotalaria on qualitative and quantitative parameters of the weed seedbank, along the succession of pearl millet, maize and common bean. Moreover, the effect of these crop rotation systems on the selection of specific weed species of the seedbank was also evaluated. The experimental design was randomized blocks, with four replications. The treatments were represented by three cropping systems in succession: pearl millet, single maize, common bean; pearl millet, maize intercropped with brachiaria, common bean; pearl millet, maize intercropped with crotalaria, common bean. The following phytosociological indexes were calculated: density, frequency and relative importance, diversity and equitability. The grain yield of maize and common bean were also quantified. Twenty-three weed species were identified, divided into 12 families, highlighting the Poaceae one, with the most important being Alternanthera tenella, Commelina benghalensis, Eleusine indica and Phyllanthus tenellus. The cropping system with single maize presented a lower density and diversity of weeds, but with a high selection of E. indica. The intercropping systems in the previous crop, as a guarantee of a higher weed diversity, could be use as alternative tools, different from the herbicides, to control weeds and improve the common bean yield. Regarding the weed control in the common bean, Crotalaria spectabilis presented better results in the previous maize-intercropping system than Urochloa ruziziensis.

Estudos foram conduzidos na Estação Experimental de Citricultura de Bebedouro, SP para avaliar a resposta de biótipos de buva resistentes aos herbicidas glyphosate, bromacil + diuron, diuron e paraquat isolados e em mistura, e o efeito de uma aplicação seqüencial com glyphosate. O delineamento foi o de blocos casualizados com quatro repetições e sete tratamentos.. Os herbicidas foram aplicados com pulverizador costal, à pressão constante (mantido por CO2 comprimido), munido com barra com três bicos do tipo TT110015 com um consumo de calda equivalente a 150 L ha-1. O controle foi avaliado visualmente, através de escala percentual de notas. Para o controle geral das plantas daninhas os melhores resultados foram obtidos com diuron isolado e com glyphosate em mistura com bromacil + diuron, enquanto para o controle da buva não houve diferença entre os tratamentos. Depois da aplicação seqüencial, o melhor tratamento para o controle de buva foi com diuron e bromacil+diuron.

Studies were conducted at Estação Experimental de Citricultura de Bebedouro, SP to evaluate the response of glyphosate-resistant horseweed and hairy fleabane biotypes to herbicides glyphosate, bromacil + diuron, diuron e paraquat isolated and in mixture and effect of a sequential application of glyphosate. The experimental design was of complete randomized blocks with four replication and seven treatments. The herbicides were applied with costal sprayer, constant pressure with three nozzles TT110015, the equivalent spray volume was 150 L ha-1. The control was visually evaluated, trough percentile note scale. The best results were obtained to general control of weed with diuron isolated and glyphosate in mixture with bromacil + diuron while to glyphosate-resistant horseweed and hairy fleabane there was no difference between the treatments. After sequential application to Conyza sp control, the best treatment was obtained associated with diuron and bromacil+diuron.

O Brasil é o maior produtor mundial de feijão, mas a interferência das plantas daninhas pode causar reduções de produtividade entre 15% e 80%, devido a fatores como cultivar de feijoeiro e espécies de plantas daninhas presentes na área. Objetivou-se com este trabalho avaliar os efeitos de seis espécies de plantas daninhas sobre o crescimento e a produtividade de duas cultivares de feijoeiro, em duas safras. Observou-se que as plantas eudicotiledôneas causam maior interferência na cultura, principalmente Amaranthus viridis e Raphanus raphanistrum. Todas causam perdas na produção do feijoeiro, exceto Eleusine indica, a menos competitiva. A cultivar ´Rubi´ é mais produtiva e mais competitiva que a ´Carioca´, e a maior produtividade é atingida na safra da seca. A escolha da cultivar e da data correta para a semeadura podem ser estratégias de manejo no controle de invasoras.

Brazil is the world's largest producer of bean, but weed interference can cause yield losses between 15 to 80% due several factors such as bean cultivar and weed species in the area. The objective of this study was to evaluate the effects of six weed species on growth and productivity of two bean cultivars, in two sowing seasons. It was observed that the dicot plants cause more interference in the crop, especially Amaranthus viridis and Raphanus raphanistrum. All cause losses in bean yield except Eleusine indica that was less competitive. The ´Rubi´ bean cultivar is more productive and competitive than ´Carioca´, and the higher production is achieved during the drought sowing season. The choice of cultivar and correct season for sowing may be management strategy as in weeds control.