Herbicide performance in the control of Conyza spp. where three plant heights

Intensive use of the herbicide glyphosate has led to herbicide resistant Conyza spp. populations. Thus, there is a need to indicate alternative herbicides and the appropriate developmental stage for controlling these populations. This study identifies alternatives for controlling glyphosate-resistant horseweed, with treatment applications at different plant heights. For this purpose, field experiments were conducted in the 2016/17 and 2017/18 crop years. The evaluated treatments were: glyphosate (540 g ae ha-1), glyphosate (1080 g ae ha-1), glyphosate (2160 g ae ha-1), glyphosate (3240 g ae ha-1), glyphosate + 2.4-D (1080 + 1005 g ae ha-1), glyphosate + saflufenacil (1080 + 49 g ae/ai ha-1), paraquat (400 g ai ha-1), diquat (400 g ai ha-1), ammonium glufosinate (600 g ai ha-1), and control (without application). These treatments were applied to plants with a maximum of 5 cm; plants between 6 and 15 cm; and plants between 16 and 25 cm. The results showed that glyphosate did not control weeds, regardless of rate. With the exception of 2,4-D, which needs complementation with sequential application of another contact herbicide, all alternatives were viable for the control of Conyza spp. plants with a maximum height of 5 cm.

Importance of sequential herbicide application in the control of Elephantopus mollis / A importância da aplicação sequencial no controle de Elephantopus mollis

Popularmente conhecida como pata de elefante ou sussuaiá, Elephantopus mollis, é uma espécie que recentemente surgiu como uma planta daninha em lavouras de cultivos de grãos. Objetivou-se com este estudo avaliar a sensibilidade diferencial de biótipos de E. mollis oriundos de áreas agrícolas e não agrícolas e determinar as melhores combinações de herbicidas aplicados em diferentes estádios de desenvolvimento para o controle desta espécie. Foram realizados três experimentos. No experimento de sensibilidade diferencial foram utilizados dez herbicidas em dois biótipos em duas fases de desenvolvimento. O experimento de dose resposta foi conduzido com oito doses de sete herbicidas. O experimento a campo foi realizado em uma área que apresenta problemas com a planta daninha para validar os resultados dos experimentos anteriores. O biótipo oriundo de área agrícola apresentou menor sensibilidade aos herbicidas quando comparado ao biótipo oriundo de área não agrícola. Os herbicidas de contato inicialmente apresentam controle superior, mas logo a planta apresenta rebrote em função de gemas presentes no colo da planta. A aplicação isolada de 2,4-D com doses entre 1005 e 1675 g e.a ha-¹ possui controle de 25%. Quando o 2,4-D é seguido da aplicação de paraquat (400 g i.a ha-¹) o controle passa a ser entre 51 e 68%. O melhor tratamento para o controle de plantas desenvolvidas é a mistura de 2,4-D + glyphosate (1340 + 1080 g e.a ha-¹) com aplicação sequencial de paraquat.(AU)

Elephantopus mollis, popularly known as elephant paw or sussuaiá, is a species that has recently emerged as a weed affecting grain crops. This study aimed to evaluate the differential sensitivity of biotypes of E. mollis obtained from agricultural and nonagricultural areas and to determine the best combinations of herbicides applied at different stages of development for controlling this species. Three experiments were conducted. In the differential sensitivity experiment, 10 herbicides were used in 2 biotypes in 2 stages of development. The dose-response experiment was conducted using 8 doses of 7 herbicides. The field experiment was conducted in an area with weed issues to validate the results of previous experiments. The biotype from the agricultural area showed lower sensitivity to herbicides than the biotype from the nonagricultural area. The contact herbicides initially presented better control; however, the weed shortly showed re-growth due to the presence of buds in the plant crown. Isolated application of 2.4-D amine at doses between 1005 and 1675 g a.e. ha-¹ demonstrated 25% control. When 2,4-D amine was followed by paraquat application (400 g a.i. ha-¹), the control observed was between 51% and 68%. The best treatment for the control of completely developed weeds is 2,4-D amine + glyphosate mixture (1340 + 1080 g a.e. ha-¹), followed by sequential paraquat application.(AU)

Crop rotation and tillage system on the Italian ryegrass seed bank after long-term field management

Italian ryegrass (Lolium multiflorum Lam.) is a troublesome weed widely found in temperate Brazilian fields with several herbicide-resistant populations. Soil seed bank is the main source of future infestations and can be strongly affected by agricultural practices, such as crop rotation and tillage system. Therefore, this study evaluated the long-term effects of different crop rotation and tillage systems on the seed bank of Italian ryegrass. Data were collected in 2012 and 2013 in a field managed since 1985 under conventional-tillage and no-tillage and subjected to three cropping systems (monoculture, total, and partial rotation) compared to the control plot. The samples were collected at three soil depths (0-5, 5-10, and 10-20 cm) using a cylindrical soil sampler, and infestations in the field were evaluated with a sample frame of 1 m². All cropping systems reduced the soil seed bank of Italian ryegrass, regardless of soil management and sampling depths comparing to the control plot. Total and partial rotation were more effective than soil tillage to reduce the seed bank. A larger number of seeds was observed on the surface layer (0-5 cm) for all cropping systems with more uniform distribution in the soil profile in conventional-tillage. Infestation of Italian ryegrass was greater for monoculture under no-tillage in both years, whereas in total and partial rotation, regardless of soil tillage, infestations remained below 40 seedlings m². Thus, strategies to reduce the soil seed bank and infestations of Italian ryegrass should focus on cropping systems with crop rotation and no-tillage.(AU)

Crop rotation and tillage system on the Italian ryegrass seed bank after long-term field management

Italian ryegrass (Lolium multiflorum Lam.) is a troublesome weed widely found in temperate Brazilian fields with several herbicide-resistant populations. Soil seed bank is the main source of future infestations and can be strongly affected by agricultural practices, such as crop rotation and tillage system. Therefore, this study evaluated the long-term effects of different crop rotation and tillage systems on the seed bank of Italian ryegrass. Data were collected in 2012 and 2013 in a field managed since 1985 under conventional-tillage and no-tillage and subjected to three cropping systems (monoculture, total, and partial rotation) compared to the control plot. The samples were collected at three soil depths (0-5, 5-10, and 10-20 cm) using a cylindrical soil sampler, and infestations in the field were evaluated with a sample frame of 1 m². All cropping systems reduced the soil seed bank of Italian ryegrass, regardless of soil management and sampling depths comparing to the control plot. Total and partial rotation were more effective than soil tillage to reduce the seed bank. A larger number of seeds was observed on the surface layer (0-5 cm) for all cropping systems with more uniform distribution in the soil profile in conventional-tillage. Infestation of Italian ryegrass was greater for monoculture under no-tillage in both years, whereas in total and partial rotation, regardless of soil tillage, infestations remained below 40 seedlings m². Thus, strategies to reduce the soil seed bank and infestations of Italian ryegrass should focus on cropping systems with crop rotation and no-tillage.

Importance of sequential herbicide application in the control of Elephantopus mollis / A importância da aplicação sequencial no controle de Elephantopus mollis

RESUMO: Popularmente conhecida como pata de elefante ou sussuaiá, Elephantopus mollis, é uma espécie que recentemente surgiu como uma planta daninha em lavouras de cultivos de grãos. Objetivou-se com este estudo avaliar a sensibilidade diferencial de biótipos de E. mollis oriundos de áreas agrícolas e não agrícolas e determinar as melhores combinações de herbicidas aplicados em diferentes estádios de desenvolvimento para o controle desta espécie. Foram realizados três experimentos. No experimento de sensibilidade diferencial foram utilizados dez herbicidas em dois biótipos em duas fases de desenvolvimento. O experimento de dose resposta foi conduzido com oito doses de sete herbicidas. O experimento a campo foi realizado em uma área que apresenta problemas com a planta daninha para validar os resultados dos experimentos anteriores. O biótipo oriundo de área agrícola apresentou menor sensibilidade aos herbicidas quando comparado ao biótipo oriundo de área não agrícola. Os herbicidas de contato inicialmente apresentam controle superior, mas logo a planta apresenta rebrote em função de gemas presentes no colo da planta. A aplicação isolada de 2,4-D com doses entre 1005 e 1675 g e.a ha-1 possui controle de 25%. Quando o 2,4-D é seguido da aplicação de paraquat (400 g i.a ha-1) o controle passa a ser entre 51 e 68%. O melhor tratamento para o controle de plantas desenvolvidas é a mistura de 2,4-D + glyphosate (1340 + 1080 g e.a ha-1) com aplicação sequencial de paraquat.

ABSTRACT: Elephantopus mollis, popularly known as elephant paw or sussuaiá, is a species that has recently emerged as a weed affecting grain crops. This study aimed to evaluate the differential sensitivity of biotypes of E. mollis obtained from agricultural and nonagricultural areas and to determine the best combinations of herbicides applied at different stages of development for controlling this species. Three experiments were conducted. In the differential sensitivity experiment, 10 herbicides were used in 2 biotypes in 2 stages of development. The dose-response experiment was conducted using 8 doses of 7 herbicides. The field experiment was conducted in an area with weed issues to validate the results of previous experiments. The biotype from the agricultural area showed lower sensitivity to herbicides than the biotype from the nonagricultural area. The contact herbicides initially presented better control; however, the weed shortly showed re-growth due to the presence of buds in the plant crown. Isolated application of 2.4-D amine at doses between 1005 and 1675 g a.e. ha−1 demonstrated 25% control. When 2,4-D amine was followed by paraquat application (400 g a.i. ha−1), the control observed was between 51% and 68%. The best treatment for the control of completely developed weeds is 2,4-D amine + glyphosate mixture (1340 + 1080 g a.e. ha−1), followed by sequential paraquat application.

Importance of sequential herbicide application in the control of Elephantopus mollis / A importância da aplicação sequencial no controle de Elephantopus mollis

Popularmente conhecida como pata de elefante ou sussuaiá, Elephantopus mollis, é uma espécie que recentemente surgiu como uma planta daninha em lavouras de cultivos de grãos. Objetivou-se com este estudo avaliar a sensibilidade diferencial de biótipos de E. mollis oriundos de áreas agrícolas e não agrícolas e determinar as melhores combinações de herbicidas aplicados em diferentes estádios de desenvolvimento para o controle desta espécie. Foram realizados três experimentos. No experimento de sensibilidade diferencial foram utilizados dez herbicidas em dois biótipos em duas fases de desenvolvimento. O experimento de dose resposta foi conduzido com oito doses de sete herbicidas. O experimento a campo foi realizado em uma área que apresenta problemas com a planta daninha para validar os resultados dos experimentos anteriores. O biótipo oriundo de área agrícola apresentou menor sensibilidade aos herbicidas quando comparado ao biótipo oriundo de área não agrícola. Os herbicidas de contato inicialmente apresentam controle superior, mas logo a planta apresenta rebrote em função de gemas presentes no colo da planta. A aplicação isolada de 2,4-D com doses entre 1005 e 1675 g e.a ha-¹ possui controle de 25%. Quando o 2,4-D é seguido da aplicação de paraquat (400 g i.a ha-¹) o controle passa a ser entre 51 e 68%. O melhor tratamento para o controle de plantas desenvolvidas é a mistura de 2,4-D + glyphosate (1340 + 1080 g e.a ha-¹) com aplicação sequencial de paraquat.

Elephantopus mollis, popularly known as elephant paw or sussuaiá, is a species that has recently emerged as a weed affecting grain crops. This study aimed to evaluate the differential sensitivity of biotypes of E. mollis obtained from agricultural and nonagricultural areas and to determine the best combinations of herbicides applied at different stages of development for controlling this species. Three experiments were conducted. In the differential sensitivity experiment, 10 herbicides were used in 2 biotypes in 2 stages of development. The dose-response experiment was conducted using 8 doses of 7 herbicides. The field experiment was conducted in an area with weed issues to validate the results of previous experiments. The biotype from the agricultural area showed lower sensitivity to herbicides than the biotype from the nonagricultural area. The contact herbicides initially presented better control; however, the weed shortly showed re-growth due to the presence of buds in the plant crown. Isolated application of 2.4-D amine at doses between 1005 and 1675 g a.e. ha-¹ demonstrated 25% control. When 2,4-D amine was followed by paraquat application (400 g a.i. ha-¹), the control observed was between 51% and 68%. The best treatment for the control of completely developed weeds is 2,4-D amine + glyphosate mixture (1340 + 1080 g a.e. ha-¹), followed by sequential paraquat application.

Proporção entre plantas de soja e plantas competidoras e as relações de interferência mútua / Proportion among soybean and competitor plants and the relations of mutual interference

O objetivo deste trabalho foi comparar as habilidades competitivas relativas de plantas de soja e de genótipos competidores por meio do arranjo em série de substituição. Foram realizados seis experimentos na UFRGS, em Porto Alegre-RS, em 2001 e 2002. Os tratamentos constituíram-se de cinco proporções de plantas de soja e do genótipo competidor: 100:0; 75:25; 50:50; 25:75 e 0:100. A soja foi representada pelos cultivares "IAS 5" e "Fepagro RS 10" e os competidores por nabo ou pelo cultivar de soja "Fundacep 33". Os tratamentos foram dispostos em delineamento experimental inteiramente casualizado, com quatro repetições. A análise da competitividade foi efetuada por meio de diagramas aplicáveis ao arranjo de substituição e interpretação de índices de competitividade. Constatou-se que a proporção entre plantas de soja e de nabo alterou a relação de competição entre essas espécies, mas que a proporção entre plantas de soja de diferentes cultivares não modificou tal relacionamento. O nabo foi mais competitivo que os genótipos de soja "IAS 5" e "Fepagro RS 10", enquanto a competitividade de "Fundacep 33" equivaleu-se à desses cultivares.

The objective of this study was to compare the competitive abilities of soybean plants with those of competitor genotypes through the design of replacement series. There were performed six experiments at UFRGS, in Porto Alegre - RS, in 2001 and 2002. The treatments tested were five proportions of plants among soybean and competitor genotypes: 100:0; 75:25; 50:50; 25:75; and 0:100. Soybean was represented by the cultivars 'IAS 5' and 'Fepagro RS 10', and the competitors by forage radish or by the soybean cultivar 'Fundacep 33'. The treatments were arranged in a completely random experimental design, with four replications. The competitivity analysis was accomplished through diagrams applicable to the substitutive design and interpretation of competitive indexes. It was proved that the proportion among soybean plants and forage radish plants changed the competition relation among these species, but that the proportion among soybean plants from different cultivars did not altered such relationship. Radish was more competitive than the soybean cultivars 'IAS 5' and 'Fepagro RS 10', whereas the competitivity of 'Fundacep 33' genotype was equivalent to these cultivars.

Perdas de rendimento de grãos de soja causadas por interferência de picão-preto e guanxuma / Soybean grain yield losses due to interference by beggatticks and arrowleaf sida

O grau de interferência mútua entre plantas daninhas e cultivadas pode ser afetado pelas espécies concorrentes e por seu nível populacional. O objetivo deste trabalho foi avaliar a possibilidade de uso do modelo da hipérbole retangular na previsäo das perdas de rendimento de gräos de soja causadas por picäo-preto (Bidens spp.) e guanxuma (Sida rhombifolia L.). Para isso, foram realizados dois experimentos em campo no Município de Eldorado do Sul-RS, nos anos de 1999/00 e 2000/01. Os tratamentos constaram de densidades de plantas de picäo-preto ou de guanxuma, as quais foram alocadas de acordo com níveis populacionais de ervas encontrados naturalmente na área experimental. Constatou-se que as perdas de rendimento causadas por incrementos nas densidades de picäo-preto e de guanxuma aumentaram de forma näo linear. O modelo da hipérbole retangular propicia melhores ajustes quando utiliza perdas do rendimento de gräos do que perdas da matéria seca da soja no florescimento ou do rendimento biológico da soja. por meio da comparaçäo dos parâmetros obtidos para o modelo testado, conclui-se que picäo-preto interfere mais negativamente na cultura do que guanxuma