Herbicide management for the control of sourgrass and mission grass and for Congo grass suppression / Manejo de herbicidas para o controle de capim-custódio, capim-amargoso e supressão de capim-ruziziensis

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Braz. J. of Develop.,Curitiba, v. 6, n. 8, p. 61857-61870. aug. 2020. ISSN 2525-8761

Herbicide management for the control of sourgrass and mission grass and for

Congo grass suppression

Manejo de herbicidas para o controle de capim-custódio, capim-amargoso e

supressão de capim-ruziziensis

DOI:10.34117/bjdv6n8-563

Recebimento dos originais: 25/07/2020 Aceitação para publicação: 25/08/2020

John Lennon Basílio da Costa

Engenheiro Agrônomo, Mestrando em produção vegetal

UniRV, Rio Verde, Goiás, Brasil, GIROAgro, coordenador técnico comercial Rua Tiradentes, quadra 31 lote 19, Santo Agostinho, Rio Verde – GO, 75904660

E-mail: fazendabasilio@icloud.com

Luiz Fernando Ribeiro Junior

Engenheiro Agrônomo, Mestrando em produção vegetal UniRV, Rio Verde, Goiás, Brasil

Pesquisador no grupo Associado de Pesquisa do Sudoeste Goiano - GAPES Av. Juscelino K Oliveira Q 55, 11 - St. Morada do Sol, Rio Verde - GO, 75909-080

E-mail: luizfribeirojr12@gmail.com

Tulio Porto Gonçalo

Engenheiro Agrônomo, Mestre em produção vegetal

UniRV, Rio Verde, Goiás, Brasil, Coordenador de pesquisa do Grupo Associado de Pesquisa do Sudoeste Goiano – GAPES

Av. Juscelino K Oliveira Q 55, 11 - St. Morada do Sol, Rio Verde - GO, 75909-080

E-mail: tulio.goncalo@gapescna.agr.br

Danillo Neiva de Andrade

Engenheiro Agrônomo, Mestre em Bioenergia e Grãos

IF Goiano, Campus Rio Verde, Rio Verde, Goiás, Brasil

E-mail: danillo.neiva@gapescna.agr.br

Aline Guimarães Cruvinel

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Braz. J. of Develop.,Curitiba, v. 6, n. 8, p. 61857-61870. aug. 2020. ISSN 2525-8761 Jhonatan Coradin

Pesquisador no grupo Associado de Pesquisa do Sudoeste Goiano- GAPES Av. Juscelino K Oliveira Q 55, 11 - St. Morada do Sol, Rio Verde - GO, 75909-080

E-mail: jhonatancoradin3@gmail.com

ABSTRACT

The objective of this work was to estimate the herbicide control action in sourgrass and mission grass, causing suppression in pre and post-emergence Congo grass. The experiment was developed at the

Centro de Inovação Tecnologia GAPES, in the municipality of Rio Verde (GO). The experimental

design was based on a randomized block with four replicates in the subdivided scheme, with nine treatments for pre-emergence, with one control with absence of application, and the others consisting in S-metolachlor (960 g ha-1), S-metolachlor (1152 g ha-1), S-metolachlor (1440 g ha-1), atrazine (400 g ha-1), atrazine (800 g ha-1), atrazine (1200 g ha-1), tembotrione (84 g ha-1), and mesotrione (120 g ha

-1_{). For post-emergence, one control with absence of application was employed, as well as mesotrione,}

tembotrione, nicosulfuron, nicosulfuron + mesotrione, nicosulfuron + tembotrione, terbuthylazine + mesotrione, mesotrione + atrazine, tembotrione + atrazine, nicosulfuron + atrazine, nicosulfuron + mesotrione + atrazine, nicosulfuron + tembotrione + atrazine and atrazine in two doses, applied in sourgrass, mission grass and Congo grass. The herbicides were applied in pre-emergence on weed sowing, while in the post-emergence period they were employed when sourgrass presented 2 to 3 tillers, mission grass presented 4 to 5 tillers and Congo grass 6 to 8 tillers. Treatments containing S-metolachlor were shown to consist the best control for mission grass and sourgrass in pre-emergence. S-metolachlor se was efficient in the control of B. ruziziensis and was therefore not indicated in the management of the intercrop. The herbicide mesotrione (or the mesotrione + atazine mixture) presented better control for sourgrass during post-emergence. The mixtures containing Nicosulfuron presented better control for mission grass during post-emergence.

Keywords: Digitaria insularis, Pennisetum setosum, Urochloa ruziziensis, Zea mays RESUMO

O objetivo do trabalho foi estimar a ação de controle dos herbicidas em amargoso e capim-custódio, ocasionando supressão no capim-ruziziensis em pré e pós-emergência. O experimento foi desenvolvido no Centro de Inovação e Tecnologia GAPES, no município de Rio Verde (GO). O delineamento experimental utilizado foi o de blocos casualizados com quatro repetições no esquema subdividido com nove tratamentos para pré-emergente, sendo uma testemunha sem aplicação, S-metolachlor (960 g ia ha-1_{), S-metolachlor (1152 g ia ha}-1_{), S-metolachlor (1440 g ia ha}-1_{), atrazine}

(400 g ia ha-1), atrazine (800 g ia ha-1), atrazine (1200 g ia ha-1), tembotrione (84 g ia ha-1), mesotrione (120 g ia ha-1). Para pós-emergência utilizou-se uma testemunha sem aplicação, mesotrione, tembotrione, nicosulfuron, nicosulfuron + mesotrione, nicosulfuron + tembotrione, terbuthylazine + mesotrione, mesotrione + atrazine, tembotrione + atrazine, nicosulfuron + atrazine, nicosulfuron + mesotrione + atrazine, nicosulfuron + tembotrione + atrazine e atrazine em duas doses, aplicados em capim-amargoso, capim-custódio e capim-ruzizensis. Os herbicidas foram aplicados em pré-emergência logo na semeadura das plantas daninhas, em pós-pré-emergência aplicou-se quando o capim-amargoso apresentava de 2 a 3 perfilhos, o capim custódio com 4 a 5 perfilhos e o capim-ruzizensis com 6 a 8 perfilhos. Os tratamentos contendo S-metolachlor proporcionam melhor controle de capim amargoso e capim custódio em pré-emergência. O S-metolachlor se mostrou eficiente no controle de B. ruziziensis, sendo assim não indicado no manejo de consórcio. O herbicida mesotrion aapresentou (ou a mistura de mesotrione + atazina apresentou) melhor controle para o capim amargoso em

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pós-Braz. J. of Develop.,Curitiba, v. 6, n. 8, p. 61857-61870. aug. 2020. ISSN 2525-8761

emergência. As misturas contendo Nicosulfuron apresentaram melhor controle em pós-emergência para o capim custódio.

Palavras-chave: Digitaria insularis, Pennisetum setosum, Urochloa ruziziensis, Zea mays

1 INTRODUCTION

The inadequate weed control is one of the main factors related to maize yield reduction (King & Purcell, 1997). Weeds compete with maize plants for sunlight, water, nutrients and space. This competition is important, especially in the early stages of crop development, with possible losses in production, which may exceed 80%, or even, in extreme cases, render the harvest unviable. Together with losses in production, the set of actions that weeds exert on the culture are named as interference, and can also be expressed by allelopathy and by hosts of pests and diseases (Vargas & Roman, 2000). Another aggravating factor is the appearance of biotypes of weeds resistant to herbicides, such as sourgrass (Digitaria insularis). Such specie presents a known resistance to the herbicides that inhibit the EPSPs (glyphosate) in Brazil (Heap, 2018). Weed resistance is today one of the main problems to be faced by different segments of the agricultural sector. Until the 1990s, the probability of selection of populations resistant to EPSP inhibitors was considered low (Heap, 2018).

The different forms of management can be used separately or in combination of two or more active formulations, aiming at effectiveness, economy and practicality (Deuber, 1997). Defining strategies and determining the best control methods are important where resistance is present (Merotto Júnior et al., 1998).

Since 1996, when the first biotype resistant to EPSPs inhibitors has been detected, 8 species have been registered in Brazil (Heap, 2018). The use of herbicides in the management, that allows residual effect in the soil, and even in pre-emergence, can be an alternative to reduce weed infestations and allows the immediate planting of the crop, causing a reduction in weed control costs (Carvalho et al., 2000).

One of the major advantages of residual herbicides is the reduction of new weed infestations, allowing an emergence of the crop in the absence of other competing species (Adegas et al., 2010). Studies have shown that in the case of sourgrass, a specie resistant to glyphosate, herbicides that inhibit ACCase are good control alternatives (Gemelli et al., 2012). On the other hand, results presented by Adegas et al. (2010) have shown differences between herbicides belonging to the chemical groups of aryloxyphenoxypropionates and cyclohexanediones, popularly known as FOPs and Dims.

In the intercropping systems between crops and fodder plants, the species are subject to competition with each other, in addition to the competition naturally exerted by weeds, which makes

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it essential to correctly plan herbicide management in the intercropping area to control weeds and partially suppress the forage (Macedo, 2009).

Tropical forage, such as Congo grass (Urochloa ruziziensis - Brachiaria ruziziensis), have been intercropped with off-season maize, presenting promising results for soil cover and animal feed (Ceccon et al., 2008). However, in order to avoid production losses in maize, it is necessary to adequately manage Congo grass, which includes adjusting the sowing density (Bernardes, 2003) and performing the correct suppression of the forage with the application of herbicides (Jakelaitis et al., 2005; Freitas et al., 2008). According to Rodrigues & Almeida (2005), the chemical management of weeds in off-season maize crop is basically performed by the application of atrazine, which controls weed dicotyledons, especially soybean seedlings, that appears due to the planting of maize after the soybean harvest.

Currently, the necessary of using graminicide herbicides, which have action on monocotyledonous species, especially in post-emergence, has grown. Although nicosulfuron is the most widely used herbicide, other formulations have recently been registered and can be used in such situations, such as mesotrione and tembotrione (Brasil, 2010).

Aiming at the best use of the maize and tropical forage intercropping, it is important to adopt herbicide management strategies to suppress the forage without causing irreversible damage and avoid that competition between maize and forage in order to prevent a reduction of productivity in the main crop.

This work aimed to evaluate the use of pre- and post-emergent herbicides in the control of sourgrass and mission grass, and the selectivity of herbicides to Congo grass intercropped with maize.

2 MATERIAL AND METHODS

The experiments were performed at the Centro de Inovação Tecnológico – CIT, from the Grupo

Associado de Pesquisa do Sudoeste Goiano – GAPES, located in Rio Verde – GO, at the geographical

coordinates 17°52’08,25’’S e 50°55’37,57’’O, during October 2017 to March 2018.

Soil of the experimental area is classified as Dystrophic Red Latosol, whose chemical and granulometric characteristics are: 15 mg dm-3 P,15 mg dm-3 S, 19 mg dm-3 K,1.5 cmolc dm-3 Ca, 0.5

cmolcdm-3 Mg, 0.1 cmolcdm-3 Al, 7.5 cmolcdm-3 H + Al, 35 g dm-3 O.M., 2.3 cmolc dm-3 SB, 5.5 cmolc

dm-3_{CEC, 9.8% V, 48% m, 49% Sand, 8% Silt, 43%, Clay. The precipitation data and the temperature}

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Figure 1. Precipitation (mm), maximum and minimum temperature (o_{C) during the experiment conduction period. Rio}

Verde (GO), 2018

The experimental design was based on a randomized block with four replications in the subdivided scheme with nine treatments for pre-emergence: S-metolachlor (960 g ha-1), S-metolachlor (1152 g ha-1), S-metolachlor (1440 g ha-1), atrazine (400 g ha-1), atrazine (800 g ha-1), atrazine (1200 g ha-1_{), tembotrione (84 g ha}-1_{), mesotrione (120 g ha}-1_{) with one control sample with absence of}

herbicides applied to sourgrass, mission grass and Congo grass.

Fourteen treatments have been used for post-emergence: mesotrione (120 g ha-1_{), tembotrione}

(84 g ha-1_{), nicosulfuron (30 g ha}-1_{), nicosulfuron + mesotrione (15 + 96 g ha}-1_{), nicosulfuron +}

tembotrione (15 + 84 g ha-1), terbuthylazine + mesotrione (330 + 70 g ha-1), mesotrione + atrazine (120 + 1200 g ha-1), tembotrione + atrazine (84 + 1200 g ha-1), nicosulfuron + atrazine (30 + 1200 g ha-1), nicosulfuron + mesotrione + atrazine (15 + 96 + 1200 g ha-1), nicosulfuron + tembotrione + atrazine (15+ 84 + 1200 g ha-1), atrazine (400 g ha-1), atrazine (1200 g ha-1) with one control sample with absence of herbicides applied to sourgrass, mission grass and Congo grass.

The planting of the grasses was manually performed on December 27, 2017 and February 2, 2018, in which the sourgrass seeds were previously left in a refrigeration at 20ºC to obtain higher germination rates, following the methodology proposed by Mondo et al. (2010), where better germination was obtained at lower temperatures, while the mission grass and Congo grass were sown directly without any previous preparation. The herbicides were manually applied in soil grooves during pre-emergence after sowing (02/02/2018). In the case of post-emergence period, the herbicides were applied when the sourgrass presented 2 to 3 tillers, the mission grass 4 to 5 tillers and the Congo grass with 6 to 8 tillers (02/02/2018), which were planted in December 2018.

The experimental plots contained 8 rows spaced by a distance of 0,5 m and displaying 5,0 m in length, three rows of sourgrass, three rows of Congo grass and two rows of mission grass, where

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different herbicides were applied, individually or in combination with other herbicides, to the planting lines.

The herbicide applications were performed by employing a CO2 pressurizing costal sprayer,

equipped with a 3 m bar, containing six spray tips of the type TT 110.02 (0,5 m between tips), with an output volume of syrup equivalent to 150 L ha-1.The environmental conditions at the moment of the applications were monitored to ensure that they would be performed in favorable conditions of temperature and wind speed, avoiding environmental interferences in the herbicide application and treatments.

The percentage of weed control was evaluated at 7, 14, 21, 28 and 35 days after application (DAA). The criterion used was based on visual inspection of emergency of the plants during the pre-emergence period, where the control (with absence of herbicide application) represented 100% emergency.

For the post-emergence test, 0% means absence of symptoms and 100% denotes for necrosis of all tissues of the aerial part, and, in the case of grasses, this scale only classified the symptoms of the leaf area at that moment, since it was not possible to predict regrowth later (SBCPD, 1995). In this sense, as an example, a 50% scale obtained for the weed control means that half of the leaf area (including stem) showed symptoms of tissue necrosis, and not that half of the plants in the plot had perished.

Initially, the assumptions considered to evaluate the experimental data were tested. To verify the homogeneity of the variances and the normality of the residues, the Barttlett and Shapiro Wilk tests were applied, respectively, using the statistical program Assistat (version 7.7 pt). In order to possess the assumptions at 0.05 significance, the deposition data has been transformed by √ (X + 0.5). After the data transformation, they were submitted to the analysis of variance and in the cases of significance, submitted to the Scott-Knott group test at 5% probability using the SISVAR program (FERREIRA, 2011).

3 RESULTS AND DISCUSSION

The results of the emergence evaluation for sourgrass and mission grass are presented in the Table 1, in which the germination means are shown, followed by their significant differences at 7 and 14 DAA. For sourgrass, treatments with application of herbicides have not presented significant differences between them, since all treatments displayed weed control in relation to the samples with absence of herbicide application. In the case of mission grass, all treatments presented better results than the control without application of herbicide at all tested doses, with emphasis on S-metolachlor,

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that was shown to be effective in pre-emergence weed control, regardless of the doses and of the treatment with the lower dose of atrazine, differing from the other treatments and from the control without herbicide application.

Table 1. Mean percentage of emergence of sourgrass and mission grass evaluated at 7, 14, 21, 28 and 35 days after application of pre-emergence herbicide treatments at the Centro de Inovação e Tecnologia – GAPES, 2018

Treatments (g ha-1₎ 7 DAA 14 DAA 21 DAA 28 DAA 35 DAA

SG MG SG MG SG MG SG MG SG MG 1. Control - 100 b 100 c 100 b 100 c 100 c 100 c 100 d 100 d 100 d 100 e 2. S-metolachlor 960 0 a 0 a 0 a 0 a 1 a 2 a 4 b 3 a 7 b 4 a 3. S-metolachlor 1152 0 a 0 a 0 a 0 a 0 a 0 a 1 a 3 a 7 b 5 a 4. S-metolachlor 1440 0 a 0 a 0 a 0 a 0 a 0 a 1 a 3 a 4 a 6 a 5. Atrazine 400 0 a 2 a 0 a 3 a 17 b 24 b 9 c 34 c 13 c 35 d 6. Atrazine 800 0 a 4 b 1 a 5 b 17 b 26 b 11 c 24 c 15 c 13 b 7. Atrazine 1200 0 a 4 b 0 a 6 b 14 b 21 b 9 c 13 b 18 c 25 c 8. Tembotrione 84 0 a 8 b 1 a 9 b 16 b 39 b 5 b 30 c 9 b 39 d 9. Mesotrione 120 0 a 10 b 1 a 11 b 17 b 29 b 4 b 31,25 c 9 b 36 d C.V. (%) 7.25 29.85 17.77 31.05 22.12 20.37 20.30 19.12 8.79 8.37 Means followed by the same letter in the columns do not differ by Scott-Knott test at 5% probability. DAA: days after application; SG: sourgrass; MG: mission grass

At 21 days, it was observed that the treatments containing S-metolachlor were statistically more efficient for pre-emergence control of the two investigated weeds, regardless of the dose, and all treatments were also shown to be effective compared to the control sample (in the absence of herbicide application).

At 28 days after application, for sourgrass and mission grass, S-metolachlor still remained in prominence by presenting better results, however, the doses of 1152 and 1440 g ha-1 displayed superior results if compared with the other treatments, even though their lower dose (400 g ha-1) also differed from the others for sourgrass. After 35 days, the best treatments were those containing S-metolachlor; however, the highest dose (1440 g ha-1) was shown to be the most efficient for sourgrass control. For mission grass, S-metolachlor displayed the best results, regardless of the employed dose. It was observed that even the treatments containing atrazine, tembotrione and mesotrione presented superior activity against the weed if compared with the control sample (in the absence of herbicide application) until 35 days after the application of the herbicides.

The herbicide S-metolachlor presented efficient weed control activity up to 35 DAA, indicating that this herbicide can be used in a management that allows the emergence of the later crop and decrease the possible effects of losses, regardless of the dose used for both sourgrass and mission grass, corroborating the report of Melo et al., (2017), in which the results obtained with pre-emergence alternative herbicides showed that atrazine (2500 g ha-1), isoxaflutole (60 g ha-1), S-metolachlor (1440

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g ha-1), clomazone (1000 g ha-1), diuron (2000 g ha-1) and flumioxazin (50 g ha-1) were efficient for the control of D. insularis up to 80 DAA.

Table 2, that displays results for the Congo grass, indicates that the treatments with the highest efficiency were those containing S-metolachlor, regardless of the dose. For the other treatments containing atrazine, tembotrione and mesotrione, it was observed better results in relation to the control sample (with absence of herbicide application), however, a suppression has also been observed, with atrazine causing a retardation in the germination at 7 and 14 DAA, with high selectivity to the crop of Congo grass and equal germination with 21 DAA on the control sample (with absence of herbicide application).

Table 2. Mean percentage of Congo grass germination evaluated at 7, 14, 21, 28 and 35 days after application of pre-emergence herbicide treatments at the Centro de Inovação e Tecnologia – GAPES, 2018.

Treatments (g ha-1₎ % germination

7 DAA 14 DAA 21 DAA 28 DAA 35 DAA 1. Control - 100 c 100 c 100 d 100 d 100 e 2. S-metolachlor 960 2 a 4 a 11 b 17 b 25 c 3. S-metolachlor 1152 2 a 4 a 6 a 7 a 13 b 4. S-metolachlor 1440 2 a 4 a 4 a 6 a 7 a 5. Atrazine 400 81 b 83 b 87 d 94 d 96 e 6. Atrazine 800 79 b 81 b 89 d 85 d 99 e 7. Atrazine 1200 79 b 81 b 81 c 88 d 96 e 8. Tembotrione 84 69 b 71 b 71 c 64 c 72 d 9. Mesotrione 120 74 b 76 b 84 c 90 d 95 e C.V. (%) 8.58 7.16 6.96 11.01 3.30

Means followed by the same letter in the columns do not differ by Scott-Knott test at 5% probability. DAA: days after application.

Table 3 shows the results of herbicides applied in post-emergence of sourgrass and mission grass. For the first weed, the best results were achieved with the commercially available mixture [atrazine + mesotrione] and mesotrione + atrazine. These treatments were composed by the mesotrione herbicides, which belong to the chemical group of triketones, whose mechanism of action is based on the inhibition of the enzyme 4-hydroxyphenyl-pyruvate dioxygenase, known as HPPD (Senseman, 2007).

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Table 3. Mean percentage of control of sourgrass and mission grass evaluated at 7, 14 and 21 DAA of post-emergence herbicides at the Centro de Inovação e Tecnologia – GAPES, 2018

Treatments (g ha-1₎ 7 DAA 14 DAA 21 DAA

SG MG SG MG SG MG 1. Control - 0 c 0 c 0 c 0 c 0 d 0 d 2. Mesotrione 120 18 b 10 b 28 b 14 b 18 b 5 c 3. Tembotrione 84 21 b 11 b 24 b 11 b 10 c 9 c 4. Nicosulfuron 30 18 b 28 a 43 b 40 a 34 b 90 a 5. Nicosulfuron + mesotrione 15 + 96 18 b 26 a 30 b 35 a 10 c 93 a 6. Nicosulfuron + tembotrione 15+ 84 11 b 24 a 30 b 36 a 23 b 84 a 7. Mesotrione + atrazine 330 + 70 51 a 11 b 73 a 11 b 64 a 6 c 8. Mesotrione + atrazine 120 + 1200 55 a 18 b 88 a 24 a 79 a 16 b 9. Tembotrione + atrazine 84 + 1200 30 b 16 b 36 b 18 b 30 b 11 b 10. Nicosulfuron + atrazine 30 + 1200 24 b 24 a 50 b 48 a 65 a 94 a 11. Nicosulfuron + mesotrione + atrazine 15 + 96 + 1200 31 b 30 a 49 b 39 a 40 b 83 a 12. Nicosulfuron + tembotrione + atrazine 15 + 84 + 1200 21 b 29 a 39 b 41 a 21 b 93 a 13. Atrazine 400 1 c 1 c 0 c 0 c 0 d 0 d 14. Atrazine 1200 1 c 2 c 0 c 0 c 0 d 0 d C.V. (%) 31.11 21.24 28.35 19.24 24.58 7.94 Means followed by the same letter in the columns do not differ by Scott-Knott test at 5% probability. DAA: days after application; SG: sourgrass; MG: mission grass.

The use of pre-emergence herbicides, coupled with post-emergence glyphosate application, results in higher productivity and small amounts of sourgrass weeds when compared to application performed exclusively during the post-emergence period (Ben et al., 2012; Toledo et al., 2015).

These treatments were followed, in weed control effectiveness, by the mixture of nicosulfuron + atrazine, presenting the best mean values up to 21 DAA, the time interval in which the maize crop is grown enough to shade the planting line and that no more competition between the weeds and the main crop is observed. It was observed that only the applications composed by atrazine, solely, were not statistically different from the control sample (with absence of herbicide application).

Regarding the other treatments based on only one herbicide, and not a mixture of different formulations, mesotrione and nicosulfuron were shown to be more effective in controlling sourgrass than tembotrione at 21 DAA at the doses used in this experiment, and the addition of atrazine improves the percentage of control for all treatments, indicating that the simultaneous application of these herbicides in the maize crop can be an alternative aiming at the better control of weeds.

Mixtures containing herbicides that inhibit photosystem II (atrazine) and the synthesis of carotenoid pigments, such as mesotrione, may have synergistic effects on weed control (Woodyard et al., 2009). This can be explained by the fact that photosystem II inhibitor herbicides act as false electron acceptors in the photochemical phase of photosynthesis, leading to the disruption of acyclic photophosphorylation.

One of the consequences of the action of these herbicides is the formation of reactive species of oxygen, capable of destroying the integrity of membranes, which leads to necrosis and death of

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leaves and other tissues. Inhibitors of carotenoid synthesis, in turn, can block the activity of enzymes such as phytoene desaturase (PDS) and ρ-hydroxy phenyl pyruvate dehydrogenase (HPPD), which are involved in routes of synthesis of pigments, such as lutein and zeaxanthin, that act dissipating energy and preventing the oxidation of chlorophyll a and b (Oliveira Junior, 2011; Matte et al., 2018).

The triple mixture of nicosulfuron + atrazine + mesotrione, rendered lower weed control of the sourgrass at 21 DAA, this probably is due to the fact that the action of the ALS inhibitors is slow, and at this moment the weed control may have been lower. However, in general, based on the data from this experiment, the addition of nicosulfuron to the mixture would not be interesting from the point of view of control and cost benefit. The addition of mesotrione to the mixture of nicosulfuron + atrazine have not altered the weed control rates, also indicating the low interest of using this mixture for the sourgrass control.

Regarding mission grass (Table 3), treatments containing only atrazine, regardless of dose, have not presented weed control when compared to the control sample (with absence of herbicide application) and all other herbicides differed significantly from the control sample or atrazine application.

At the 7, 14 and 21 days the treatments that displayed better results were those containing nicosulfuron, nicosulfuron + mesotrione, nicosulfuron + tembotrione, nicosulfuron + atrazine, nicosulfuron + mesotrione + atrazine and nicosulfuron + tembotrione + atrazine. The comparison of the above-mentioned treatments reveals that all of them contain nicosulfuron or a combination of this herbicide with other formulations, showing the efficiency of this herbicide for sourgrass control.

Regarding the tembotrione and mesotrione herbicides applied separately for the control of mission grass, both presented unsatisfactory results, thus being not recommended for the control of such weed; the addition of atrazine to the these herbicides slightly improved the weed inhibition, but still resulted in poor weed control for mission grass, thus being also not recommended for this specific target.

Table 4 shows the results of percentage of suppression or selectivity of some of the herbicides used in Congo grass. It is observed that treatments containing nicosulfuron and tembotrione do not exhibit a clear selectivity to Congo grass, differing from mesotrione and its mixtures with atrazine.

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Table 4. Mean percentage of Congo grass suppression evaluated at 7, 14 and 21 days after the application of post-emergence herbicides at the Centro de Inovação e Tecnologia – GAPES, 2018

Treatments (g ha-1₎ % Congo grass supression

7 DAA 14 DAA 21 DAA

1. Control - 0 c 0 e 0 e 2. Mesotrione 120 16 b 16 d 7 d 3. Tembotrione 84 39 a 46 a 25 c 4. Nicosulfuron 30 26 b 36 b 56 a 5. Nicosulfuron + mesotrione 15 + 96 24 b 30 c 31 b 6. Nicosulfuron + tembotrione 15+ 84 27 b 37 b 51 a 7. Mesotrione + atrazine 330 + 70 21 b 21 d 10 d 8. Mesotrione + atrazine 120 + 1200 25 b 30 c 20 c 9. Tembotrione + atrazine 84 + 1200 41 a 47 a 31 b 10. Nicosulfuron + atrazine 30 + 1200 24 b 34 b 61 a 11. Nicosulfuron + mesotrione + atrazine 15 + 96 + 1200 22 b 30 c 35 b 12. Nicosulfuron + tembotrione + atrazine 15 + 84 + 1200 40 a 49 a 50 a

13. Atrazine 400 1 c 0 e 0 e

14. Atrazine 1200 2 c 0 e 0 e

C.V. % 15.65 14.28 15.62

Means followed by the same letter in the columns do not differ by Scott-Knott test at 5% probability. DAA: days after application.

Tembotrione exerts influence in the short-term suppression of Congo grass, showing increased control up to 14 DAA. After that period, at 21 days, the greatest suppression of growth is observed for treatments containing nicosulfuron. Martins et al. (2007) evaluated the selectivity of Congo grass to herbicides applied in the post-emergence period when the plants presented three to four fully expanded leaves and obtained 58.8% of nicosulfuron intoxication at a dose of 50 g ha -1, presenting statistical differences if compared with the other treatments.

The nicosulfuron + atrazine herbicide association presented apo or control in the evaluation performed at 7 DAA, but, as other evaluations were performed, the increase in the weed control at 21 DAA was observed. Similar results were observed by Adegas et al. (2011) in which application of a mixture of nicosulfuron + atrazine (20 + 800 g ha -1_{) caused low initial intoxication in cockspur grass}

plants; it was shown that nicosulfuron inhibits growth in a few hours; however, the lesion symptoms in the plants appeared after two weeks of application (Trezzi & Vidal, 2001), corroborating the current results.

Tembotrione presented greater selectivity in relation to its association with atrazine. Hence, this herbicide can be used aiming at the inhibition of the crop of Congo grass, avoiding the competition when intercropped with maize, however the obtained results are strictly dependent of the herbicide dose and weed stage.

It is worth mentioning that the plant stages used in the application of herbicides in the current work are a preponderant factor for the obtained results and that they may not be reproduced if these stages are not similar to this study.

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The association between pre- and post-emergence herbicides culminates in an enhanced control of the weeds if compared with the application during the isolated periods, either in pre- or post-emergence.

4 CONCLUSIONS

Treatments containing S-metolachlor were shown to present the best results against sour grass and mission grass, during pre-emergence, and may be an excellent option for maize cultivation. Even at low doses for pre-emergence, the herbicide presented a high inhibition activity for Congo grass, thus not being recommended for the maize and Congo grass intercropped systems, or even for the isolated Congo grass.

The use of atrazine during pre-emergence was shown to present a great potential for both Congo grass and its intercrop with maize, displaying selectivity and control for both sourgrass and mission grass, regardless of the dose used in the experiments.

The formulations containing the herbicides mesotrione and mesotrione + atrazine presented better control results for post-emergence sourgrass and satisfactory pre-emergence control when applied separately. The mixtures containing Nicosulfuron presented better post-emergence control for the mission grass.

Tembotrione favors the suppression of Congo grass in post-emergence period.

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