Aspectos técnicos sobre resistência de plantas daninhas a herbicidas

O objetivo deste trabalho é discutir alguns aspectos relacionadosà resistência de plantas daninhas a herbicidas, bem como expor as principais práticas para prevenção e controle dessas plantas

Herbicidas no controle de Chloris distichophylla (Falso-capim-de-rhodes)

The weed Chloris distichophylla (Lag) has been selected in areas of orchards and RR soybean in the Rio Grande do Sul- RS (Brazil), resulting of its possible tolerance to the herbicide glyphosate. This selection occurs due to intense use of this herbicide in the last years resulting in a disturb caused by the high pressure selection imposed by the herbicide occurs, resulting in selection of tolerant plants. The objective of this study was to evaluate the effectiveness of herbicides pertaining the different mechanisms of action in the control of the Chloris distichophylla and the possible tolerance of this species in three growth stages to the glyphosate herbicide. Three experiments were carried out in the College of Agronomy of the UFRGS in Porto Alegre – RS (Brazil) through the experimental design completely randomized with four replications. C. distichophylla in early growth stages was not tolerant to glyphosate. Moreover, the atrazine, glufosinate, glyphosate and paraquat herbicides showed high control when the weed had four leafs, whereas the fluazifop, imazapyr and mesotrione herbicides had showed satisfactory control.O falso-capim-de-rhodes (Chloris distichophylla) tem sido selecionado em áreas de fruticultura e soja transgênica no Rio Grande do Sul, em função de sua possível tolerância ao herbicida glyphosate. Esta seleção ocorre devido à utilização intensa deste herbicida nestes sistemas de cultivo, o que acarreta em elevada pressão de seleção do herbicida sobre as plantas tolerantes. O objetivo deste trabalho foi avaliar a eficácia de herbicidas pertencentes a diferentes mecanismos de ação no controle do falso-capim-de-rhodes e a possível tolerância desta espécie em três estádios de desenvolvimento ao herbicida glyphosate. Foram realizados três experimentos em casa de vegetação na Faculdade de Agronomia da UFRGS, em Porto Alegre – RS, utilizando-se o delineamento experimental inteiramente casualizado e quatro repetições por tratamento. Pode-se verificar que, nos estádios de 4, 8 e 15 folhas, o falso-capim-de-rhodes não foi tolerante ao glyphosate. Ainda, no estádio de 4 folhas, os herbicidas atrazine, glufosinate, glyphosate e paraquat apresentam controle eficaz e os herbicidas fluazifop, imazapyr e mesotrione apresentaram apenas controle satisfatório

Controle de papuã (Urochloa plantaginea) e produtividade de milho em solo argiloso através de formulação e doses de atrazina com liberação controlada

A utilização de herbicidas com formulações com liberação controlada poderá se constituir em uma ferramenta importante para reduzir problemas de lixiviação e garantir a eficácia desses produtos. O objetivo do presente trabalho foi comparar a eficiência de controle de Urochloa plantaginea (UROPL) e o rendimento de grãos de milho entre uma formulação de atrazina comercial (WG) e uma formulação de liberação controlada (xerogel). O delineamento utilizado foi o de blocos ao acaso, em parcelas subdivididas, com quatro repetições, em um esquema (2x7)+1. Nas parcelas principais, foram locadas as formulações de atrazina (WG e xerogel) e, nas subparcelas, as concentrações dos herbicidas (0, 2400, 3200, 3600, 4200, 5400 e 8000g de atrazina ha-1). Foram determinados os níveis de controle e densidade de plantas de UROPL e o rendimento de grãos da cultura do milho. A elevação das doses de atrazina resultou em aumento dos níveis de controle de UROPL. Em avaliações realizadas aos 28 e 35 dias após a aplicação, a atrazina xerogel demonstrou eficiência agronômica superior à formulação WG. Não ocorreram diferenças de rendimento de grãos de milho em parcelas tratadas com diferentes formulações e níveis de atrazina

Competitive ability of bean cultivars with Urochloa plantaginea

The objective of this work was to evaluate the competitive ability of carioca bean cultivars BRS FC104, BRS FC402, IAC Imperador, IAC Milênio, IPR Tangará, and SCS Riqueza in the presence of Alexandergrass (Urochloa plantaginea) in different proportions of plants in association. The experiments were carried out in a greenhouse in a completely randomized design with four replications. The treatments were arranged according to the proportions of beans and Alexandergrass plants: 100:0, 75:25, 50:50, 25:75, and 0:100 or 40:00, 30:10, 20:20, 10:30, and 0:40 plants per pot. The competitiveness of the species was analyzed using diagrams applied to replacement experiments and also through relative competitiveness indices. At 30 days after crop emergence, leaf area (LA), height (HP), diameter (DP), and shoot dry mass (SM) of the plant shoots were measured, as well as variables related to the physiology of the species. There was competition among carioca bean cultivars in the presence of Alexandergrass regardless of the proportion of plants, causing decreases in DP, LA and SM. Basically, there is competition for the same environmental resources between beans and Alexandergrass. Highlights: There is competition between bean and Alexandergrass, for the same environmental resources; There is varietal difference - IAC Imperador and SCS 205 Riqueza are the most competitive ones; The escape to competition is the best approach to guarantee yield in Alexandergrass-infested fields.The objective of this work was to evaluate the competitive ability of carioca bean cultivars BRS FC104, BRS FC402, IAC Imperador, IAC Milênio, IPR Tangará, and SCS Riqueza in the presence of Alexandergrass (Urochloa plantaginea) in different proportions of plants in association. The experiments were carried out in a greenhouse in a completely randomized design with four replications. The treatments were arranged according to the proportions of beans and Alexandergrass plants: 100:0, 75:25, 50:50, 25:75, and 0:100 or 40:00, 30:10, 20:20, 10:30, and 0:40 plants per pot. The competitiveness of the species was analyzed using diagrams applied to replacement experiments and also through relative competitiveness indices. At 30 days after crop emergence, leaf area (LA), height (HP), diameter (DP), and shoot dry mass (SM) of the plant shoots were measured, as well as variables related to the physiology of the species. There was competition among carioca bean cultivars in the presence of Alexandergrass regardless of the proportion of plants, causing decreases in DP, LA and SM. Basically, there is competition for the same environmental resources between beans and Alexandergrass. Highlights: There is competition between bean and Alexandergrass, for the same environmental resources; There is varietal difference - IAC Imperador and SCS 205 Riqueza are the most competitive ones; The escape to competition is the best approach to guarantee yield in Alexandergrass-infested fields