Palmer amaranth is native to the United States, but was discovered in 2015 in Brazil. Palmer amaranth populations in Brazil were very difficult to control using glyphosate, which resulted in many changes to standard weed management practices. A genotyping assay was used to confirm that the population detected in Mato Grosso State, Brazil, was correctly identified as Palmer amaranth and that it was not tall waterhemp. Greenhouse dose–response curves and shikimate accumulation assays showed that the Brazilian population was highly resistant to glyphosate, with an LD50 value (3,982 g glyphosate ha−1) more than twice the typical use rates and very little shikimate accumulation at 1 mM glyphosate concentrations in a leaf-disk assay. The Brazilian population was also resistant to sulfonylurea and imidazolinone acetolactate synthase (ALS) inhibitor herbicides. The resistance mechanisms in the Brazilian population were identified as increasedEPSPSgene copy number for glyphosate resistance (between 50- and 179-fold relativeEPSPSgene copy number increase) and two different alleles for target-site mutations in theALSgene (W574L and S653N). These results confirm the introduction of Palmer amaranth to Brazil using a genetic marker for species identification, as well as resistance to glyphosate and ALS inhibitors.

Conyza species are important weeds in global agriculture, especially due to their capacity to evolve resistance to multiple herbicide mechanisms of action.We aimed to evaluate the frequency and distribution of resistance to glyphosate and chlorimuron-ethyl in Conyza spp. populations from Brazil. Seed samples were collected from grain production areas across nine Brazilian states over five consecutive years ( 2014to 2018). Prior to resistance monitoring trials, dose-response assays were conducted to determine a single dose of glyphosate or chlorimuron-ethyl to discriminate resistant and susceptible populations. Resistance monitoring based on plant responses to the application of discriminatory doses of glyphosate (960 g ha -1 ) or chlorimuron-ethyl (20 g ha -1 ). Populations were classified as resistant, moderately resistant, or susceptible to either herbicide. While glyphosate resistance was highly frequent (71.2%) in all the five years, chlorimuron-ethyl resistant populations occurred at 39.8% of the total. The frequency of multiple resistance to both herbicides (35.3%) was proportional to the occurrence of chlorimuron-ethyl resistance (39.6%). Resistance to glyphosate and to chlorimuron-ethyl were found across all states evaluated.

Resumo -A solução mais comum para as falhas no controle de plantas daninhas no sistema de produção é a inclusão de herbicidas alternativos, aplicados de forma isolada ou misturados em tanque. Este trabalho foi desenvolvido com o objetivo de avaliar a eficácia e a interação de misturas de metsulfuron-methyl e glyphosate para controle de plantas daninhas. Para tanto, foram desenvolvidos dois experimentos independentes, avaliando-se diferentes bioindicadores, uma monocotiledônea (capim-amargoso -Digitaria insularis) e uma dicotiledônea (corda-de-viola -Ipomoea triloba). Os tratamentos constaram de esquema fatorial 5x5, correspondendo o primeiro fator às cinco doses do herbicida glyphosate (0, 180, 360, 540 e 720 g e.a. ha -1 ) e o segundo fator às cinco doses do herbicida metsulfuron-methyl (0; 1,2; 2,4; 3,6 e 4,8 g i.a. ha -1 ). Em ambos os experimentos se adotou delineamento experimental de blocos ao acaso, com seis repetições. A aplicação da mistura de glyphosate e metsulfuron-methyl sobre o capim-amargoso foi considerada aditiva em todas as doses utilizadas; já sobre a corda-de-viola, a adição de metsulfuron-methyl à calda de glyphosate eleva o controle absoluto da mistura, porém com magnitude aquém da esperada, o que denota caráter antagônico.Abstract -The most common solution for problems on weed control in agricultural system of production is the inclusion of alternative herbicides, applied isolated or in tank mixtures. Thus, this work was carried out with the objective of evaluating the efficacy and interaction of metsulfuron-methyl and glyphosate tank mixtures for weed control. For that, two independent trials were performed, evaluating different bioindicators, being one monocotyledonous (sourgrass -Digitaria insularis) and one dicotyledonous (morning glory -Ipomoea triloba). Treatments were consequence of a factorial combination 5x5, corresponding the first factor to five rates of glyphosate (0, 180, 360, 540 and 720 g a.e. ha -1 ) and the second factor to five rates of metsulfuron-methyl (0; 1.2; 2.4; 3.6 and 4.8 g a.i. ha -1 ). In both experiments, randomized blocks were adopted as experimental design, with six replicates. Andrade et al. Rev. Bras. Herb., v.14, n.4, e610, out./dez.2018 2/9

Background: Amaranthus hybridus, a common agricultural weed in Brazil, has been associated with complications in the management of major crops. Recently, A. hybridus biotypes with suspected resistance to the herbicide glyphosate have been observed in the state of Paraná. Objective: To characterize glyphosate-resistant Amaranthus hybridus biotypes. Methods: Three independent experiments were conducted to evaluate four biotypes of A. hybridus. Twelve doses of glyphosate were applied, including 64D, 32D, 16D, 8D, 4D, 2D, D, 1/2D, 1/4D, 1/8D, 1/16D, and a control with no herbicide. The dose D of glyphosate applied was 1080 g ha -1 ae. Four replicates for each treatment and a randomized block design were used. At 28 (DAA), the control (%) and residual dry mass of each plot were analyzed. Results: The biotypes with suspected resistance (R1, R2, and R3) had a GR 50 in the range of 3019.13 to 3316.45 g ha -1 ae and LD 50 in the range of 4081.52 to 4310.29 g ha -1 ae whereas the susceptible biotype had a GR 50 of 227.63 g ha -1 ae and LD 50 of 196.59 g ha -1 ae. Conclusions: Biotypes R1, R2, and R3 are resistant to the herbicide glyphosate.

The coffee plant is sensitive to weed competition, which negatively affects its growth and development. Thus, the proper and safe use of herbicides is extremely important for weed management to allow the crop to develop its maximum productive potential. The objective of this study was to evaluate the control efficacy of different herbicides under pre-emergence conditions and assess their selectivity for coffee crops. Two experiments were carried out in the field, in randomized block designs, with four replicates and eight treatments, totaling 32 experimental plots. The treatments were: unweeded control; weeded control; sulfentrazone + diuron 1.4 L ha -1 ; sulfentrazone + diuron 1.7 L ha -1 ; sulfentrazone + diuron 2.0 L ha -1 ; sulfentrazone + diuron with indaziflam 1.4 + 0.15 L ha -1 ; respectively, indaziflam 0.15 L ha -1 ; and oxyfluorfen + chlorimuron 3.0 L ha -1 + 0.08 kg ha -1 , respectively. The treatments were applied prior to the emergence of weeds in a directed spray between the crop rows. Evaluations of weed control in the area, phytotoxicity to the crop, branch length, and internode distance of coffee were conducted at 30, 60, 90, and 120 days after treatment application (DAA). In general, all treatments guaranteed greater than 80% efficacy up to 60 DAA. After this, some treatments suffered reductions in efficacy, and did not guarantee satisfactory control up to 120 DAA. For Digitaria nuda, the most effective treatments were those that contained indaziflam alone or in combination with sulfentrazone + diuron, and oxyfluorfen + chlorimuron for 60 DAA. In both experiments and the two species analyzed, the indaziflam treatments guaranteed efficacy percentages above 80%, even at 120 DAA. All treatments were equally selective for the coffee plants under the conditions evaluated.

Este trabalho foi desenvolvido com o objetivo de avaliar a seletividade do tembotrione à cultura do milho safrinha, quando aplicado em diferentes estádios fenológicos. O experimento foi desenvolvido em campo, em área do IFSULDEMINAS, Campus Machado, entre março e setembro de 2015. O híbrido de milho RB9006 (Riber®) foi semeado mecanicamente com densidade populacional de 80.000 plantas ha-1, à profundidade de 0,05 m, no sistema de plantio direto. Adotou-se delineamento experimental de blocos ao acaso, com cinco tratamentos e cinco repetições. As parcelas constaram de seis linhas da cultura do milho, com cinco metros de comprimento. Respeitando-se os estádios fenológicos, o herbicida tembotrione foi aplicado em dose de 100,8 g ha-1, com óleo vegetal a 0,5% v/v. As aplicações foram realizadas sobre milho em V2, V4, V7 e V10, além de testemunha sem aplicação. Todas as parcelas foram plenamente capinadas durante todo o experimento. A produtividade média da área foi de 7.010 kg ha-1, plenamente satisfatória para a condição de milho safrinha. Não foram identificadas injúrias visuais nas plantas de milho, em quaisquer dos estádios fenológicos. Não houve significância dos diferentes tratamentos para quaisquer das variáveis analisadas (grãos por fileira, fileiras por espiga, diâmetro de sabugo, massa de 1.000 grãos e produtividade). Deste modo, conclui-se que o tembotrione foi plenamente seletivo ao milho safrinha na dose recomendada pelo fabricante.

Geographical distribution and resistance level to chlorimuron of Amaranthus spp. populations in the main soybeans producing regions of Brazil. Adv Weed Sci. 2022;40(Spec2):e020220063.

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