Efficacy of imazapic/imazapyr and other herbicides in mixtures for the control of Digitaria insularis prior to soybean sowing Efectividad de imazapic/imazapyr y otros herbicidas en mezclas para el control de Digitaria insularis en pre-siembra de soya Alfredo Junior Paiola Albrecht1, Leandro Paiola Albrecht1, André Felipe Moreira Silva²*, Romulo Augusto Ramos³, Everson Pedro Zeny³, Juliano Bortoluzzi Lorenzetti4, Maikon Tiago Yamada Danilussi4, and Arthur Arrobas Martins Barroso4 ABSTRACT RESUMEN Herbicide mixtures, use of multiple sites of action, and other Las mezclas entre herbicidas, el uso de múltiples sitios de acción weed management practices are necessary to avoid cases of y otras prácticas de manejo de malezas son necesarias para biotype resistance. The aim of this study was to evaluate the evitar otros casos de resistencia de biotipos. El objetivo de este efficiency of imazapic/imazapyr and other herbicides in mix- estudio fue evaluar la eficiencia de imazapic/imazapyr y otros tures to control Digitaria insularis at burndown before soybean herbicidas en mezclas para controlar Digitaria insularis en la sowing. This field research was conducted in Umuarama, State desecación antes de la siembra de soya. Esta investigación de of Parana (PR), Brazil, in the 2018/19 soybean season. The ex- campo se realizó en Umuarama, Estado de Paraná (PR), Brasil, periment was conducted in a randomized block experimental en la cosecha de soya de 2018/19. El experimento se realizó en design with four replicates and 11 treatments composed of the un diseño experimental de bloques al azar, con cuatro repe- application of glyphosate, clethodim, haloxyfop, imazapic/ ticiones y 11 tratamientos, compuestos por la aplicación de imazapyr, glufosinate, 2,4-dichlorophenoxyacetic acid (2,4-D), glifosato, cletodim, haloxifop, imazapic/imazapir, glufosinato, dicamba, triclopyr, and saflufenacil, in mixtures. Weed control ácido 2,4-diclorofenoxiacético (2,4-D), dicamba, triclopir y was evaluated as well as soybean injury and yield. An analysis saflufenacil, en mezclas. Se evaluó el control de malezas, así of variance and F-test were performed, and the treatment como el daño y el rendimiento de la soya. Se realizaron un means were compared by the Scott-Knott test. All treatments análisis de varianza y test F, y se compararon las medias de los showed great control over the weed and low crop injury rate tratamientos con el test de Scott-Knott. Todos los tratamientos while maintaining soybean yield. The application of imazapic/ mostraron un gran control sobre la maleza y una baja tasa de imazapyr in mixtures with other herbicides was effective in daño a los cultivos mientras se mantenía el rendimiento de la controlling glyphosate-resistant D. insularis in burndown soya. La aplicación de imazapic/imazapir en mezclas con otros before soybean sowing and with sequential application of herbicidas fue eficaz en el control de D. insularis resistente al haloxyfop + glyphosate at V3 stage of soybean. This chemical glifosato, en desecación antes de la siembra de soya y con apli- management was also selective for soybean. cación secuencial de haloxifop + glifosato en la etapa V3 de la soya. Este manejo químico también fue selectivo para la soya. Key words: Glycine max, acetolactate synthase (ALS) inhibitors, Palabras clave: Glycine max, inhibidores de acetolactato sintasa weed, crop injury, chemical weed control. (ALS), hierba, daño al cultivo, control químico de malezas. Introduction compete against cultivated crops (Moreira and Bragança, 2011; Lorenzi, 2014). There are four known D. insularis The weed Digitaria insularis, known as sourgrass, is na- herbicide-resistant biotypes, all found in South America, tive to tropical and subtropical areas of America. It can be from which three are glyphosate-resistant and one is re- found in pasture lands, coffee plantations, orchards, crop sistant to haloxyfop and fenoxaprop. Weed resistance is a fields, roadsides, and in abandoned fields. It is referred to as problem across the globe, and Brazil is ranked fifth with rhizomatous and produces seeds throughout the summer, 50 registered resistance cases to EPSPs, ALS, ACCase, PSII, growing in clumps. These traits allow them to aggressively PSI, PPO, and auxins (Heap, 2020). Received for publication: 21 October, 2019. Accepted for publication: 9 November, 2020. Doi: 10.15446/agron.colomb.v38n3.83046 1 Universidade Federal do Paraná, Palotina, Parana (Brazil). ² Crop Science Pesquisa e Consultoria Agronômica, Parana (Brazil). ³ Basf S.A., Santo Antônio de Posse, São Paulo (Brazil). 4 Universidade Federal do Paraná, Curitiba, Parana (Brazil). * Corresponding author: [email protected] Agronomía Colombiana 38(3), 350-356, 2020 In addition to resistance cases, as a perennial grass D. growth of susceptible plants. Chlorosis happens to sensi- insularis is hard to control, especially during flowering tive plants followed by death in 7 to 14 d after treatment development (Zobiole et al., 2016; Canedo et al., 2019). A (Oliveira Júnior, 2011; Shaner and O’Connor, 2017). study by Gazziero et al. (2019) shows that a cohabitation of six D. insularis plants m-2 among soybean crops reduces its These herbicides are applied at pre- and post-emergence, yield by 40%. Thus, appropriate managing practices includ- controlling a range of monocotyledons and dicotyledons ing different control methods are shown to be important in cereal and soybean crops and nonagricultural areas to have an efficient outcome. (Oliveira Júnior, 2011; Rodrigues and Almeida, 2018). Pi- asecki and Rizzardi (2016) report that imazapic/imazapyr The association of different herbicides, rotation of sites (premix formulation) is efficient for controlling volunteer of actions, preventive methods, among other practices corn at soybean pre-emergence. Likewise, studies by Melo are essential to manage and prevent new weed biotypes et al. (2017) show the efficiency of imazapic/imazapyr on resistant to herbicides (Green, 2018; Heap and Duke, 2018; the control of D. insularis. Neve et al., 2018; Frisvold et al., 2020). However, in the lit- erature, there are reports of the antagonist effect of 2,4-D It is believed that the imazapic/imazapyr is effective in on the action of ACCase inhibitor graminicides, due to the controlling D. insularis when applied at pre-sowing burn- translocation reduction and increase in the metabolism of down. Thus, this study aimed to evaluate the efficiency herbicides from the ariloxifenoxipropionics group (Trezzi of imazapic/imazapyr (premix formulation) and other et al., 2007). Thus, there is a need for studies on the differ- herbicides in mixtures to control D. insularis at burndown ent mechanisms of control of D. insularis. before soybean sowing. Pre-emergent herbicides used before sowing are empha- Materials and methods sized as an important tool to weed management, especially in crop fields (Byker et al., 2013; Belfry et al., 2015). In this Conditions and experimental design sense, ALS inhibitors are highlighted for weed control as This field research was conducted in Umuarama, State of pre-emergence herbicides used in soybean fields (Braz et al., Parana (PR), Brazil (23°50’25.23” S, 53°13’45.70” W) during 2017; Underwood et al., 2017). Imidazolinone herbicides are the 2018/19 crop season. The soil was classified as sandy part of the group of the acetolactate synthase (ALS) (also (11% clay, 6.5% silt, and 82.5% sand) with the following called acetohydroxyacid synthase [AHAS]) inhibiting her- chemical properties on the 0-20 cm layer: pH (CaCl2) of 4.4, -3 bicides which hamper the synthesis of the branched-chain 1.33% organic matter, and 5.78 cmolc dm cation exchange amino acids valine, leucine, and isoleucine. After their capacity. Under the Köppen classification, the climate is absorption, the herbicides are translocated to meristems classified as Cfa, and Figure 1 shows the weather conditions and apexes that are actively growing areas, inhibiting the during the time of the research. 2018/19 season, Umuarama, PR August 08, 2018 to February 06, 2019 150 40 35 125 30 100 25 75 20 ainfall (mm) 15 R 50 st temperature (°C) application sowing seuential application 10 25 5 Minimum and maximum 0 0 t t t t t t t d d d d d d d d d d d d s s s s s s s r r r r r r n n n n n n 1 1 1 1 1 1 1 3 3 3 3 3 3 2 2 2 2 2 2 t v t c n g p b v t c n g p c v c n g p c o e a e e c o e a e o e a e O J F O N S J D Au O N S D Au J N S D Au Decendial Rainfall inimum temperature aximum temperature FIGURE 1. Representation of rainfall and minimum and maximum temperature for the study site. 2018/19 season, Umuarama, PR, Brazil. Albrecht, Albrecht, Silva, Ramos, Zeny, Lorenzetti, Danilussi, and Barroso: Efficacy of imazapic/imazapyr and other herbicides in mixtures for the control 351 of Digitaria insularis prior to soybean sowing The trial site was infested by D. insularis, identified as at 7, 14, 21, 28, and 35 d after sowing (DAS). Percentage indicative of glyphosate resistance. Before application, the grades from 0% (absence of symptoms) to 100% (death of plants were at the flowering stage with 3.5 clumps m-2. The the plant) were given, based on the apparent symptoms area was previously cultivated with maize. A no-till sowing related to the plant growth stage (Velini et al., 1995). system was used for soybean, using 0.45 cm row spacing. The cultivar used was Monsoy® 6410 IPRO (Monsanto Co. By the time of harvest, at the R8 stage (full maturation) of do Brasil, São Paulo, SP, Brazil). The experiment was con- soybean plants (Fehr et al., 1971), the yield was calculated ducted in a randomized block experimental design, with using only the plot’s two central lines of 4 m long each.