Agronomic factors involved in low-level wild poinsettia resistance to glyphosate

Abstract

The awareness of agronomic practices that affect the resistance selection of weeds to a particular herbicide is of utmost importance in order to advocate management practices that aim to avoid or prolong the resistance. The objectives of this study were to identify and map the occurrence of the wild poinsettia's low-level resistance to glyphosate in Rio Grande do Sul State (RS), Brazil, and to define the main agronomic factors associated with the selection of these biotypes. Seed and / or soil samples in areas with suspected resistance were collected in Roundup Ready ® (RR) soybean crops in different counties in the RS region during the 2010/11 and 2011/12 seasons. A questionnaire on the operations history in the area was applied at each site in order to establish relationships between the distribution of wild poinsettia with cases of suspected resistance to glyphosate and the likely agronomic factors involved in this occurrence. The study included the response of wild poinsettia biotypes with suspected resistance to glyphosate and an analysis of the questionnaires carried out with producers. The main agronomic practices used by producers that favor the emergence of resistant biotypes were the continued cultivation of the RR ® soybean; an overdependence on the use of glyphosate; a low rate of crop rotation and efficient chemical alternatives for wild poinsettia control and management.Key words: crop rotation; 5-enolpiruvil chiquimato 3-fosfato sintase; Euphorbia heterophylla; selection pressure Fatores agronômicos envolvidos na resistência de nível baixo de leiteira a glyphosate RESUMOO conhecimento das práticas agronômicas que interferem na seleção de plantas resistentes a determinado herbicida é de extrema importância para preconizar práticas de manejo que visem evitar ou retardar a resistência. Os objetivos do trabalho foram identificar e mapear a ocorrência da resistência de nível baixo de leiteira ao glyphosate no Rio Grande do Sul (RS), e definir os pricipais fatores agronômicos associados na seleção desses biótipos. Amostras de sementes e/ou solo em áreas com a suspeita de resistência foram coletadas em lavouras de soja Roundup Ready ® em diferentes Municípios do RS nas safras 2010/11 e 2011/12. Em cada local, foi aplicado questionário sobre o histórico de manejo da área, visando estabelecer relações entre a distribuição de casos de leiteira com suspeita de resistência ao glyphosate e os prováveis fatores agronômicos envolvidos nessa característica. O estudo constou da resposta dos biótipos de leiteira com suspeita de resistência ao glyphosate e análise dos questionários realizados com os produtores. As principais práticas agronômicas utilizadas pelos produtores que favorece o surgimento de biótipos resistentes foi o cultivo continuado de soja RR ® , excessiva dependência do uso de glyphosate, baixo índice de rotação de culturas e de alternativas químicas eficientes para o controle de leiteira.

Status of weed control in imidazolinone-herbicide resistant rice in Rio Grande do Sul

“…In addition, problems with the Cyperus species were also cited several times by the farmers surveyed. This is certainly related to the recent occurrence of resistance to imidazolinone herbicides (Ulguim et al, 2017). The importance of the infestations with Cyperus species was much lower in the beginning of the Clearfield ® utilization 15 years ago, and this can be considered as one of the changes that occurred associated with the herbicide use and weed dynamics.…”

“…Nowadays, there are five weed species reported as resistant to ALS-inhibitors (Heap, 2020), which has changed the management practices compared with the first years of Clearfield ® System use. This situation is associated with monocultures and mainly with the repetitive use of herbicides with the same mode of action (Ulguim et al, 2017).…”

Resistance Mapping of the Genus Cyperus in Rio Grande do Sul and Selection Pressure Analysis

“…Questionnaire analysis allowed inferring that most of the farmers in places where seeds of plants of the genus Cyperus were collected have cultivated rice for more than six consecutive years ( Figure 2A) and that 38% of them have cultivated Clearfield ® (CL) rice in the area ( Figure 2B). This denotes the high selection pressure to ALS inhibitors in the areas, as observed in soybean crops of RS, where the majority of farmers have cultivated glyphosate-resistant soybean and used this herbicide for weed management in the area for more than seven consecutive years (Ulguim et al, 2017).…”

Weed management in Roundup Ready® corn and soybean in Southern Brazil: survey of consultants’ perception

“…The use of herbicides with different modes of action or their association was reported by 90% of soybean farmers as an important practice in the management of resistant weeds (Ulguim et al, 2017). Furthermore, in about 80% of RR soybean areas, three or more glyphosate applications per year were identified, with approximately 50% of these with the implementation of crop rotation (Vargas et al, 2013).…”