Geographic distribution of ryegrass resistent to the cleothodim ... 365 GEOGRAPHIC DISTRIBUTION OF RYEGRASS RESISTENT TO THE CLETHODIM HERBICIDE IN RIO GRANDE DO SUL1 Distribuição Geográfica de Azevém Resistente ao Herbicida Clethodim no Rio Grande do Sul VARGAS, L.2, SCHNEIDER, T.3, AGOSTINETTO, D.3, and BIANCHI, M.A.4 ABSTRACT - Ryegrass is a weed of annual cycle that is present in winter crops, in orchards and vineyards of the South region of Brazil. The species is normally controlled by the glyphosate herbicide, but the continuous use of this product caused the selection of resistant biotypes. The use of ACCase inhibitor herbicides is the main alternative for the control of this species, but it has not been satisfactory in some places, thus causing suspicion of resistance to this action mechanism. Thus, the objective of this paper was to evaluate the occurrence and geographic distribution of ryegrass biotypes that are resistant to the clethodim herbicide in the state of Rio Grande do Sul. For that, seeds of ryegrass plants that survived the application of clethodim were collected in crops from the north region of RS, summing up to a total of 152 samples from 72 cities. The biotypes were submitted to the application of 120 g i.a. ha-1 (maximum registered dose) and 60 g i.a. ha-1 de clethodim (half the maximum registered dose). According to the results, among the samples of ryegrass seeds collected, there were no biotypes resistant to the clethodim herbicide when the maximum registered dose was applied and in the stage of three to four leaves. However, there were biotypes with lower susceptibility that survived half the maximum registered dose. Keywords: Lolium multiflorum, resistance, chemical control, acetyl coenzyme A carboxylase. RESUMO - O azevém é uma planta daninha de ciclo anual presente em lavouras de inverno, em pomares e vinhedos da região Sul do Brasil. A espécie normalmente é controlada pelo herbicida glyphosate, porém o uso continuado desse produto selecionou biótipos resistentes. O uso de herbicidas inibidores da ACCase é a principal alternativa para o controle dessa espécie, o qual não tem sido satisfatório em alguns locais, provocando a suspeita da ocorrência de resistência a esse mecanismo de ação. Assim, o objetivo deste trabalho foi avaliar a ocorrência e distribuição geográfica de biótipos de azevém resistente ao herbicida clethodim no Estado do Rio Grande do Sul. Para isso, sementes de plantas de azevém que sobreviveram a aplicações de clethodim foram coletadas em lavouras da região norte do RS, totalizando 152 amostras de 72 municípios. Os biótipos foram submetidos à aplicação de 120 g i.a. ha-1 (dose máxima de registro) e 60 g i.a. ha-1 de clethodim (metade da máxima dose de registro). De acordo com os resultados, entre a amostras de sementes de azevém coletadas não foram encontrados biótipos resistentes ao herbicida clethodim quando aplicada a máxima dose de registro e no estádio de três a quatro folhas. No entanto, observaram-se biótipos com menor suscetibilidade, que sobreviveram à metade da máxima dose de registro. Palavras-chave: Lolium multiflorum, resistência, controle químico, acetyl coenzima A carboxilase. INTRODUCTION intensive use of glyphosate for this end is due to its high efficiency in different vegetative In tillage system or in orchards, ryegrass stages of the species, combined with its low control is usually done by applying non- cost when compared to the other herbicides selective herbicides, mostly glyphosate. The (Christoffoleti & Lópes-Ovejero, 2003). The 1 Recebido para publicação em 7.9.2015 e aprovado em 13.11.2015. 2 Embrapa Trigo, Passo Fundo-RS, Brazil, <[email protected]>; 3 Universidade Federal de Pelotas, Pelotas- RS, Brazil, 4 CCGL-Tec/Universidade de Cruz Alta, Cruz Alta-RS, Brazil. Planta Daninha, Viçosa-MG, v. 34, n. 2, p. 365-373, 2016 366 VARGAS, L. et al. intensive use of an herbicide imposes high on the severity of the problem, making it selection pressure on the population of plants, possible to determine the resistance handling resulting in the selection of resistant biotypes and making the process of selection of resistant pre-existent in the population (Powles & Yu, biotypes slower, helping in the reactive 2010). decision making process in the control of these populations (Owen et al., 2014). In Resistance is defined as the inherent addition, mapping the resistance enables the and inheritable capability of a biotype, establishment of the resistance costs, the within a certain population, of surviving and definition of public policies and the directed reproducing after exposure to the registered technical assistance. dose of the herbicide for the control of the species, according to the application criteria In Brazil, there is no information gathering (Grazziero et al., 2009). The resistance of weeds on the area infested with ACCase inhibitor to herbicides is an evolution process, and the herbicide-resistant ryegrass. Gathering dynamics and the impact depend on several information of ryegrass populations that are factors. The factors that are able to determine resistant to ACCase inhibitor herbicides is a how the resistance is boosted are the genetic tool that will enable the identification of the diversity of the population, the existence of places where this resistance occurs and the genes resistant to a specific herbicide and determination of specific handling strategies operational factors (Powles & Yu, 2010). for each region, according to its characteristics. With this information, the decision making As an alternative for the control of process and the adoption of prevention and ryegrass populations that are resistant to resistance control strategies become possible, glyphosate, especially in pre-sowing of maize recovering the viability of cultivation in and wheat, the herbicides used are the ones these areas. The objective of this paper was to that inhibit the ACCase enzyme. The ACCase evaluate the geographic distribution of ryegrass inhibitor herbicides are applied in the weed biotypes that are resistant to clethodim in the postemergence period; they control species of state of Rio Grande do Sul. poaceae and are selective for magnoliopsida crops (Vidal & Merotto Jr., 2001). The repeated MATERIAL AND METHODS use of ACCase inhibitor herbicides resulted in the selection of biotypes resistant to this To perform this paper, we collected seeds action mechanism in Brazil. The bioecological of ryegrass plants that survived the application characteristics of the ryegrass, such as of ACCase inhibitor herbicides in crops of the genetic variability, allogamy and elevated north region of Rio Grande do Sul. The seeds production of seeds, associated to inappropriate that composed the samples came from a plant, handling strategies, make the selection of and all the collection points were identified resistant biotypes predictable and worrisome with geodetic coordinates, through the use of (Christoffoleti & López-Ovejero, 2003). the Global Positioning System (GPS). Facing a scenario of elevated resistance The harvest of seeds happened between of weeds to herbicides, it is crucial to have the months of September and November 2013, measures that recommend the handling of in properties located in the following cities: the resistance, and it is important to monitor Água Santa (3), Alto Alegre (2), Augusto crops for the identification of the resistance Pestana (2), Barra Funda (2), Barracão (4), Boa focus and the elimination of suspected plants Vista do Cadeado, Boa Vista do Incra (3), Bom (Lazaroto et al., 2008). After resistance is Progresso, Campo Novo, Capão Bonito do Sul, identified in the field, the adoption of practices Carazinho (3), Caseiros (2), Ciríaco (2), such as crop rotation, mixture of herbicides, Colorado, Condor, Coqueiros do Sul (5), Coronel localized applications and association of control Bicaco, Coxilha (2), Crissiumal (4), Cruz Alta methods reduces the impact of the problem (3), David Canabarro (2), Ernestina, Erval Seco (Hugh, 2006). (3), Espumoso (2), Frederico Westphalen, Knowing the resistant species and the Gentil, Horizontina (2), Humaitá (2), Ibiaçá (2), extension of the infested area provides insight Ibiraiaras (2), Independência (2), Joia (3), Planta Daninha, Viçosa-MG, v. 34, n. 2, p. 365-373, 2016 Geographic distribution of ryegrass resistent to the cleothodim ... 367 Julio de Castilhos (3), Lagoa Vermelha (3), maximum registered dose and the maximum Machadinho (4), Mato Castelhano, registered dose, respectively, for the control of Maximiliano de Almeida, Muitos Capões (2), ryegrass in pre-sowing of maize and wheat Nova Candelária, Novo Barreiro, Paim Filho (AGROFIT, 2015). A control treatment without (2), Palmeira das Missões (2), Panambi (4), herbicide application was also added. The Passo Fundo, Pejuçara (3), Saldanha Marinho experimental units were composed of plastic (2), Salto do Jacuí, Sananduva (3), Santa Rosa, vases with volumetric capacity of 500 mL, Santa Bárbara do Sul (3), Santa Cecília do Sul, containing commercial substrate, being Santo Augusto, Santo Cristo (2), São João da composed of five plants per vase. Urtiga, São José do Inhacorá, São José do Ouro When the plants reached a vegetative state (2), São Miguel das Missões, Seberi (2), of three to four leaves, the herbicide was Selbach, Tapejara (2), Tapera, Taquaruçu do applied, using the backpack sprayer, pressured Sul (2), Tenente Portela (2), Tio Hugo (2), Três at CO , calibrated to provide application de Maio (4), Três Passos (2), Tucunduva (3), 2 volume of 120 L ha-1 of herbicide spray, Tupanciretã (2), Tuparendi, Vacaria (2), Victor equipped with spray nozzles in the form of a Graeff, Vila Lângaro (4) and Vista Alegre fan 110.015. The Lanzar® adjuvant was also (Figure 1), summing up 152 samples of seeds used in the spray in the dose of 0,5% v/v. harvested in 74 cities. The variable evaluated was visual control After the harvest, the seeds were cleaned, at 28 days after the application of treatments identified and stored until when they would be (DAT), and the biotypes were identified, used in experiments.