Terbuthylazine, atrazine, and atrazine + mesotrione for weed control in second-crop maize in Brazil1

INTRODUCTION

To minimize the problems caused by tolerant or resistant weeds, integrated weed management is essential, which includes rotating crops herbicide action mechanisms.(12) For maize cultivation, terbuthylazine or atrazine application stands out as an alternative or complementary to glyphosate applications. These herbicides are triazines with the mecha-nism of action of photosystem II (PSII) inhibitors, effective in controlling weeds in maize crops in pre-emergence or initial post-emergence.(36)

As options with a broader spectrum of action in post-emergence of maize, carotenoid biosynthesis inhibitors such as mesotrione combined with PSII inhibitors can be highlighted.(78) The pre-formulated atrazine + mesotrione mixture has shown promise,(9) demonstrating synergistic effects in a number of situations.(1011)

Terbuthylazine has proved to be more effective than atrazine, in mixtures with glyphosate, in controlling Digitaria spp.(12) and other grasses,(6) or equivalent to atrazine in controlling broadleaf weeds and Benghal dayflower (Commelina benghalensis),(6) in post-emergence application in maize. The literature remains scarce internis of comparing terbuthylazine and atrazine, especially under growing conditions in Brazil, since terbuthylazine was registered in the country in 2020.

Triazines have low to moderate soil sorption coefficients, moderate water solubility, and low volatility, making them vulnerable to leaching. This can lead to decreased weed control effectiveness and contaminated groundwater.(13) Due to this and other aspects, some herbicides in this group are no longer authorized in some countries; for example, atrazine is not authorized in the European Union, while terbuthylazine is permitted.(14)

It is important to investigate and assess the efficacy of terbuthylazine in weed control in Brazil, especially because of a possible atrazine ban in the country. Thus, the aim of the present study was to assess the efficacy of terbuthylazine, atrazine, and atrazine + mesotrione, alone or in mixtures with glyphosate, in weed control for post-emergence application in maize.

MATERIALS AND METHODS

Site description

The experiment was conducted in the western region of Parana state (PR), Brazil, in second-crop maize following soybean cultivation between the months of February and July. For the 2020-2021 erop season, the experiment was conducted in two areas in Maripa (area 1: 24°24'31.8"S 53°51'40"W; area 2: 24°24'30"S 53°51'44"W), and for the 2021-2022 erop season, in three areas in Maripa (area 1: 24°25'17.0"S 53°51'57.9"W; area 2: 24°24'33.2"S 53°51'42.7"W) and Francisco Alves (area 3: 24°03'58.2"S 53°48'36.7"W). The region's climate is classified as Cfa, according to Köppen's classification, and the meteorologi-cal conditions for the period are shown in Figure 1.

The soil of the experimental sites is classified as very clayey for Maripa and sandy for Francisco Alves. No-till planting was performed in the booth erop seasons, planting maize hybrid P3858 PWU in the Maripa areas in both seasons and Feroz VTP3 in Francisco Alves, all of which are tolerant to glyphosate and glufosinate.

For the 2020-2021 erop season, area 1 was infested with C. benghalensis and grasses {Digitaria spp., Urochloa spp. e Sorghum spp.), area 2 with C. benghalensis, Brazil pusley (Richardia brasiliensis), greater beggarticks {Bidens subalternans), sourgrass {Digitaria insularis) and Sorghum spp. For both areas, there was low infestation at the time of application, new emergency flows were observed from the application to the control evaluation

For the 2021-2022 erop season, the three areas were infested with C. benghalensis (>20 plants m2) and volun-teer soybean (up to 5 plants m2) in the control (without application) at 35 days after application (DAA). The weeds were already present at the time of application, for C. benghalensis increases in infestation were observed due to new emergence flows.

Experimental design

The experiments were arranged in a completely ran-domized block design with four replications, and the experimental units consisted of 6 x 4 m plots with rows 0.45 m apart. The use of fertilization practices, erop installation and phytosanitary management were carried out in accordance with Embrapa(15) (2015) recommendations.

For the 2020-2021 season, five treatments were used, consisting of the application of terbuthylazine (Sonda(r)), atrazine (Primóleo(r)), atrazine + mesotrione (Calaris(r)). For the 2021-2022 season, six treatments were used, consisting of terbuthylazine, atrazine, atrazine + mesotrione, and glyphosate (Xeque Mate(r)) (Table 1). Applications occurred in post-emergence of maize (V4-V5) using a C02 pressurized backpack sprayer equipped with six AIXR 110.015 nozzles (Teejet(r)), at a pressure of 2 kgf cm2 and a speed of 3.6 km h1, providing an application volume of 150 L ha1.

Assessments, data collection, and statistical analysis

Weed control was assessed at 35 days after application (DAA), and maize plant damage symptoms at 7, 14, 21, 28, and 35 DAA. For all these assessments, scores were assigned using visual analyses for each experimental unit (0 for no damage, up to 100% for plant death), considering significantly visible symptoms on the plants according to their development.(16) For yield, ears were collected from the 4 central rows along 4 meters of each plot. The grains produced in each plot were weighed, and the moisture content corrected to 13%. Based on these data, yield was calculated in kg ha1. For the 2021-2022 erop season, yield was assessed only in area 1.

The data obtained were submitted to analysis of vari-ance (ANOVA) using the F-test (p < 0.05), and treatment means were compared using Tukey's test (p < 0.05). The analyses were carried out using Sisvar 5.6 software.07'

RESULTS

2020-21 erop season

The efficacy of treatments for controlling C. benghal-ensis was low in area 1, with a maximum of 18.8%, which may be due to higher initial infestation and the seed bank. In area 2, control reached up to 89.3% with the application of atrazine + mesotrione, not differing from terbuthylazine (1,200 g ai ha1) with 85.8%, both superior to atrazine, at 70.5% efficacy (Table 2).

The herbicide treatments were equally effective in controlling sourgrass (Digitaria insularis), with scores ranging from 76.3 to 92% in area 2. In the overall control of grasses, atrazine was less effective in area 1 with 70%, while other herbicide treatments showed similar efficacy ranging from 82 to 90.8%. Equivalent herbicide treatments were observed in controlling broadleaf weeds, with efficacy ranging from 73.8 to 86.3% for Brazilpusley (Richardia brasiliensis) and from 92.5 to 96% for greater beggarticks (Biclens subalternans) (Table 2).

The efficacy of weed control treatments affected maize yield, with lower yields observed for treatments with less effective control. For the control without application, yield was 1,640 kg ha1 (area 1) and 2,723 kg ha1 (area 2), the treatments with herbicide applications provided yield of up to 4,336 kg ha"1 (area 1) and 3,663 kg ha1 (area 2) (Figure 2). Weed interference with yield was confirmed by the absence of damage symptoms on maize plants due to herbicide application.

2021-2022 erop season

In area 1, herbicide treatments did not differ, with control scores ranging from 82.5 to 90.3% for C. benghalensis. In area 2, the highest control was 55%, achieved with atrazine + mesotrione + glyphosate, similar to terbuthylazine (1,200 g ai ha1) + glyphosate, with 50%. In area 3, the most effective treatments were terbuthylazine + glyphosate at doses of 1,200 and 1,000 g ai ha1, achieving control rates of 85 and 91.3%, respectively. Terbuthylazine (1,200 g ai ha1) + glyphosate was the only treatment consistently effective in controlling C. benghalensis in the three areas (Table 3).

For controlling volunteer soybeans and B. subalternans, herbicide treatments showed similar efficacy in all areas, ranging from 72 to 99%. In area 2, terbuthylazine + gly-phosate at doses of 1,200 and 1,000 g ai ha1 demonstrated effective control of grasses, achieving rates of up to 87.5%, superior to atrazine + mesotrione + glyphosate (70%) and showing no significant difference from other herbicide treatments (Table 3).

Similar to the previous growing season, no visual damage symptoms were observed in maize plants due to herbicide application. There were no yield differences in area 1, even when compared to the untreated control (2.484 kg ha1), with average yield for treatments 2.653 kg ha1 (Figure 3).

DISCUSSION

The results of this study demonstrate that terbuthylazine or atrazine + mesotrione, mainly in combination with glyphosate, are effective in controlling C. benghalensis in nearly all areas. When atrazine was not combined with mesotrione, it tended to be less effective, which was a note-worthy finding. This differs from the findings of Bottcher et al.(6) (2022) who found no differences between atrazine or terbuthylazine in controlling this weed.

Commelina benghalensis is an important weed in affect-ing maize yield,(1820)and an essential aspect of management systems. The complexity of C. benghalensis canbe attribut-ed to its high reproductive flexibility, found in various re-gions worldwide as an exotic species, producing both aerial and underground seeds in addition to reproducing asexually from stem fragments. Furthermore, its recognized glyphosate tolerance hinders chemical control in post-emergence maize.(21) Commelina benghalensis is a monocotyledon weed but not grass, and is thus not susceptible to grass her-bicides, nor are all broadleaf herbicides effective against it.

The use of triazines, beyond the relevance for the control of C. benghalensis, is also crucial for controlling volunteer soybeans in maize.(22,23) In Brazil, it is common to plant maize as a second erop after soybean in the spring-sum-mer, as in the present study. Other studies underscore the potential of volunteer soybeans to reduce maize yield.(2425) Overall, in the present study, terbuthylazine, atrazine, or atrazine + mesotrione were equally effective in controlling volunteer soybeans.

For the control of broadleaf weeds and volunteer soybeans, there was some equivalence among herbicide treatments. The efficacy of terbuthylazine or atrazine is supported by other studies in pre-emergence control of broadleaf weeds in maize, mainly in mixtures with other herbicides.(2629)

Other studies also highlight the efficacy of atrazine + mesotrione in controlling different weed species,(9,30) including the effectiveness of the formulated premix,(67) with noticeable synergism. Mesotrione is an important post-emergent herbicide for weed control in maize.(8,31"33) Adding mesotrione is important because it tends to enhance the efficacy of the mixture with atrazine, given that in this study and others, atrazine was less effective against grasses than terbuthylazine/612'

The results of this study indicate the use of terbuthyla-zine for weed control in maize. The efficacy of terbuth-ylazine was equivalent to that of atrazine in controlling broadleaf weeds and tends to be better in controlling grasses (Digitaria insularis, Sorghum spp., and others) or C. benghalensis, characterizing terbuthylazine as an alternative solution in weed management in second erop maize in Brazil.

No damage symptoms were observed in maize, and when differences in yield were observed, they were due to differences in treatment efficacy in weed control. In the 2020-2021 erop season, yield in the untreated control was 62.2% (area 1) or 25.7% (area 2) lower compared to the treatment with higher yield. Despite competition with weeds, in the 2021-2022 erop season the untreated control did not show a reduction in yield. This may be related to the low yield observed in the experiment average.

The maize yield in competition with C. benghalensis and other weeds was also reduced in a study by Bottcher et al(6) (2022), with an average decrease of 36% when chemical control was not performed. Grasses, also found in the present study, can also interfere with agronomic performance in maize, with reductions of approximately 40%inyield.(34)

Another noteworthy point in this study is the post-emer-gence application of glyphosate in maize. The mixture of glyphosate with atrazine is well-established in weed management in this crop.(35"36) Triazines display little or no action in post-emergence weed control, with a greater effect in pre-emergence or early post-emergence. In this respect, post-emergence control canbe complemented with glyphosate, for example.

In this study, glyphosate was not used in the 2020-2021 erop season due to low weed infestation at the time of application, indicating the possibility of not using this herbicide in post-emergence maize in these situations. Even under conditions of higher infestations in post-emergence, effective control without glyphosate is possible, using mesotrione(8) or even glufosinate,(37) making it relevant to investigate the efficacy of mesotrione and glufosinate in mixtures with terbuthylazine. It is important to note that glyphosate is an important herbicide for weed control in soybeans and maize, but there are several cases of resistance to this herbicide for many weeds. As such, characterizing management without the use of glyphosate is essential in weed control and preventing resistant biotype selection, in the context of integrated weed management.

CONCLUSION

Terbuthylazine or atrazine + mesotrione, either alone or in combination with glyphosate, was effective in post-emergence weed control in maize, with a broad spectrum of action. Applying atrazine, alone or in combination with glyphosate, was effective in controlling broadleaf weeds.

ACKNOWLEDGEMENTS, FINANCIAL SUPPORT AND FULL DISCLOSURE

The authors would like to thank the Universidade Estadual de Maringa (UEM), Universidade Federal do Parana (UFPR), Supra Pesquisa team at UFPR, Crop Pesquisa, and Iharabras S.A. Indüstrias Quimicas (Ihara).

This study was carried out with the support of the Coor-denagao de Aperfeigoamento de Pessoal de Nivel Superior - Brazil (CAPES) - Financial Code 001.

There is no conflict of interest in conducting and pub-lishing the work.

AUTHOR CONTRIBUTIONS

Conceptualization: Leandro Paiola Albrecht ; Alfredo Junior Paiola Albrecht (c); Aderlan Ademir Bottcher (c); Matheus Greguer de Carvalho (c); Rafael Tanaka Torigoe (c).

Data curation: Leandro Paiola Albrecht (c); Alfredo Junior Paiola Albrecht ; Aderlan Ademir Bottcher (c); Matheus Greguer de Carvalho ; Maikon Tiago Yamada Danilussi ; André Felipe Moreira Silva

Formal analysis: André Felipe Moreira Silva (c).

Investigation: Leandro Paiola Albrecht (c); Alfredo Junior Paiola Albrecht ; Aderlan Ademir Bottcher (c); Matheus Greguer de Carvalho ; Maikon Tiago Yamada Danilussi ; Willian Felipe Larini

Methodology: Leandro Paiola Albrecht (c); Aderlan Ademir Bottcher (c); Maikon Tiago Yamada Danilussi (c); André Felipe Moreira Silva ; Willian Felipe Larini (c).

Project administration: Leandro Paiola Albrecht (c); Alfredo Junior Paiola Albrecht (c); Aderlan Ademir Bottcher (c); Rafael Tanaka Torigoe (c).

Software: Aderlan Ademir Bottcher ; Matheus Greguer de Carvalho (c); André Felipe Moreira Silva (c).

Resources: Leandro Paiola Albrecht (c); Alfredo Junior Paiola Albrecht ; Rafael Tanaka Torigoe (c).

Supervision: Leandro Paiola Albrecht (c); Alfredo Junior Paiola Albrecht (c).

Validation: Leandro Paiola Albrecht ; Alfredo Junior Paiola Albrecht (c).

Visualization: Leandro Paiola Albrecht ; Alfredo Junior Paiola Albrecht (c); André Felipe Moreira Silva(c); Rafael Tanaka Torigoe (c).

Writing - original draft: Leandro Paiola Albrecht (c); Alfredo Junior Paiola Albrecht ; Aderlan Ademir Bottcher (c); André Felipe Moreira Silva (c).

Writing - review & editing: Matheus Greguer de Carvalho (c); Maikon Tiago Yamada Danilussi (c); Willian

Felipe Larini ; Rafael Tanaka Torigoe

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