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. O uso intensivo do herbicida glifosato selecionou populações de Conyza spp. resistentes a este herbicida, desta forma, existe a necessidade da indicação de herbicidas alternativos bem como o estádio de desenvolvimento adequado para o controle dessas populações. Objetivou-se identificar alternativas para o controle de buva resistente ao glifosato, aplicadas em diferentes estaturas da planta daninha. Para isso, foram conduzidos experimentos a campo, nos anos agrícolas 2016/17 e 2017/18. Os tratamentos avaliados foram: glifosato (540 g e.a. ha-1), glifosato (1080 g e.a. ha-1), glifosato (2160 g e.a. ha-1), glifosato (3240 g e.a. ha-1), glifosato + 2,4-D (1080 + 1005 g e.a. ha-1), glifosato + saflufenacil (1080 + 49 g e.a./i.a. ha-1), paraquate (400 g i.a. ha-1), diquate (400 g i.a. ha-1), Glufosinato de amônio (600 g i.a. ha-1) e testemunha sem aplicação, aplicados nas plantas com no máximo 5 cm; plantas entre 6 e 15 cm; e plantas entre 16 e 25 cm. Os resultados evidenciaram que nenhuma dose do glifosato controlou as plantas daninhas, e com exceção do 2,4-D que necessita de complemento com aplicação sequencial de outro herbicida de contato, todas as alternativas apresentaram-se viáveis para o controle de plantas de Conyza spp. com no máximo 5 cm de estatura.