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Does doses and time of 2,4-D application interfere in the physiology and wheat grains yield components?

ABSTRACT

The identification of the application stage and correct dose of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide is important so that wheat is not harmed. In view of this, the objective of this study was to evaluate the effect of 2,4-D doses applied at different development stages of wheat crop. The experiment was conducted in a randomized block design, arranged in a 4 × 5 factorial scheme, with four replications. In factor A, the application stages (before tillering, tillering, first node and booting) were allocated and the doses of 2,4-D (0, 349, 698, 1047 and 1396 g.ha–1) were allocated in factor B. The variables evaluated were phytotoxicity at 7, 14, 21, 28 and 35 days after application of the treatments (DAT), photosynthetic activity, CO2 internal concentration, stomatal conductance, efficient water use and carboxylation efficiency. The number of spikes·m–2, spike length and number of full and sterile grains were determined in the preharvest. Thousand grain mass, grain yield and hectoliter weight were determined after harvest. The results demonstrate that the herbicide caused phytotoxicity to wheat, being greater in increasing doses and mainly before tillering, causing grain sterility and decreased productivity. The other yield components did not present difference when increasing the dose and application in different stages as well as the physiological variables. The increase of the 2,4-D doses applied before tillering and in the booting stage caused linear decrease in wheat grain yield.

Keywords
Triticum aestivum ; phenological stages; hormonal herbicide; winter cereal

INTRODUCTION

Wheat crop demonstrates importance for use in human food, with a world growth of 1.2%, reaching 755 million tons in the 2020/2021 season (FAO, 2022FAO – Food and Agricultural Organization. FAOSTAT data base for agriculture. Available from: https://www.fao.org/statistics/en/. Acessed on: 15 Oct. 2022.
https://www.fao.org/statistics/en/...
). For the same season, the crop had an increase in the estimated area sown in Brazil, as well as in productivity and in production consequently (CONAB, 2022CONAB – Companhia Nacional de Abastecimento. Série Histórica das Safras: Trigo. Brasília: Conab, 2022. Available from: https://www.conab.gov.br/info-agro/safras/serie-historica-das-safras/itemlist/category/913-trigo. Acessed on: 15 Oct. 2022.
https://www.conab.gov.br/info-agro/safra...
).

In wheat, there are many factors that end up limiting grain productivity, such as weather changes, management and especially the competition caused by weeds, which compete for nutrients, water and light (AGOSTINETTO et al., 2008AGOSTINETTO, D.; RIGOLI, R.P.; SCHAEDLER, C.E.; TIRONI, S.P.; SANTOS, L.S. Período crítico de competição de plantas daninhas com a cultura do trigo. Planta Daninha, Viçosa, v.26, n.2, p.271-278, 2008. https://doi.org/10.1590/S0100-83582008000200003
https://doi.org/10.1590/S0100-8358200800...
; GALON et al., 2019GALON, L.; BASSO, F.J.M.; CHECHI, L.; PILLA, T.P.; SANTIN, C.O.; BAGNARA, M.A.M.; FRANCESCHETTI, M.B.; CASTOLDI, C.T.; PERIN, G.F.; FORTE, C.T. Weed interference period and economic threshold level of ryegrass in wheat. Bragantia, Campinas, v.78, n.3, p.409-422, 2019. https://doi.org/10.1590/1678-4499.20180426
https://doi.org/10.1590/1678-4499.201804...
; TAVARES et al., 2019TAVARES, L.C.; LEMES, E.S.; RUCHEL, Q.; WESTENDORFF, N.R.; AGOSTINETTO, D. Criteria for decision making and economic threshold level for wild radish in wheat crop. Planta Daninha, Viçosa, v37, e019178898, 2019. https://doi.org/10.1590/s0100-83582019370100004
https://doi.org/10.1590/s0100-8358201937...
; COLOMBO et al., 2022COLOMBO, M.; ALBRECHT, L.P.; ALBRECHT, A.J.P.; ARAÚJO, G.V. de; SILVA, A.F.M. Agronomic performance of wheat under post-emergence herbicide application. Pesquisa Agropecuária Tropical, Goiânia, v.52, e69908, 2022. https://doi.org/10.1590/1983-40632022v5269908
https://doi.org/10.1590/1983-40632022v52...
). When weeds infest wheat crop, they generate losses in grain productivity, quality of wheat grains, in addition to being hosts for insects and diseases. If not controlled, weeds can generate yield losses between 18% and 82% (GALON et al., 2015GALON, L.; CASTOLDI, C.T.; FORTE, C.T.; KUJAWISKI, R.; DAVID, F.A.; PERIN, G,F.; RADÜNZ, A.L.; AGAZZI, L.R.; ROSSETTI, J.; RADÜNZ, L.L. Efficacy and phytotoxicity of herbicides applied for the handling of weeds that infest wheat. Revista Brasileira de Herbicidas, Londrina, v.14, n.2, p.128-140, 2015. https://doi.org/10.7824/rbh.v14i2.405
https://doi.org/10.7824/rbh.v14i2.405...
), in addition to increasing production costs and reducing the producer’s profits (LAMENGO et al., 2013LAMEGO, F.P.; RUCHEL, Q.; KASPARY, T.E.; GALLON, M.; BASSO, C.J.; SANTI, A.L. Habilidade competitiva de cultivares de trigo com plantas daninhas. Planta Daninha, Viçosa, v.31, n.3, p.521-531, 2013. https://doi.org/10.1590/S0100-83582013000300004
https://doi.org/10.1590/S0100-8358201300...
; TAVARES et al., 2019TAVARES, L.C.; LEMES, E.S.; RUCHEL, Q.; WESTENDORFF, N.R.; AGOSTINETTO, D. Criteria for decision making and economic threshold level for wild radish in wheat crop. Planta Daninha, Viçosa, v37, e019178898, 2019. https://doi.org/10.1590/s0100-83582019370100004
https://doi.org/10.1590/s0100-8358201937...
; COLOMBO et al., 2022COLOMBO, M.; ALBRECHT, L.P.; ALBRECHT, A.J.P.; ARAÚJO, G.V. de; SILVA, A.F.M. Agronomic performance of wheat under post-emergence herbicide application. Pesquisa Agropecuária Tropical, Goiânia, v.52, e69908, 2022. https://doi.org/10.1590/1983-40632022v5269908
https://doi.org/10.1590/1983-40632022v52...
).

In the competition with weeds for factors such as light, the plant uses a greater amount of photoassimilates for stem elongation and less for production of dry mass and leaf area, thus compromising productivity and quality of grains (AGOSTINETTO et al., 2008AGOSTINETTO, D.; RIGOLI, R.P.; SCHAEDLER, C.E.; TIRONI, S.P.; SANTOS, L.S. Período crítico de competição de plantas daninhas com a cultura do trigo. Planta Daninha, Viçosa, v.26, n.2, p.271-278, 2008. https://doi.org/10.1590/S0100-83582008000200003
https://doi.org/10.1590/S0100-8358200800...
; LAMEGO et al., 2013LAMEGO, F.P.; RUCHEL, Q.; KASPARY, T.E.; GALLON, M.; BASSO, C.J.; SANTI, A.L. Habilidade competitiva de cultivares de trigo com plantas daninhas. Planta Daninha, Viçosa, v.31, n.3, p.521-531, 2013. https://doi.org/10.1590/S0100-83582013000300004
https://doi.org/10.1590/S0100-8358201300...
). Weeds that most frequently infest wheat crop and that have caused greater damage due to competition or because they are problematic in relation to control are ryegrass (Lolium multiflorum), turnip (Raphanus raphanistrum and Raphanus sativus) and black oat (Avena strigosa) (LAMEGO et al., 2013LAMEGO, F.P.; RUCHEL, Q.; KASPARY, T.E.; GALLON, M.; BASSO, C.J.; SANTI, A.L. Habilidade competitiva de cultivares de trigo com plantas daninhas. Planta Daninha, Viçosa, v.31, n.3, p.521-531, 2013. https://doi.org/10.1590/S0100-83582013000300004
https://doi.org/10.1590/S0100-8358201300...
). To manage these weeds, several strategies can be used, one of the most used control methods for ease, lower cost and effectiveness when compared to other methods is chemical control, with the use of herbicides (TIMOSSI; FREITAS, 2011TIMOSSI, P.C.; FREITAS, T.T. Eficácia de nicosulfuron isolado e associado com atrazine no manejo de plantas daninhas em milho. Revista Brasileira de Herbicidas, Londrina, v.10, n.3, p.210-218, 2011. https://doi.org/10.7824/rbh.v10i3.123
https://doi.org/10.7824/rbh.v10i3.123...
; COLOMBO et al., 2022COLOMBO, M.; ALBRECHT, L.P.; ALBRECHT, A.J.P.; ARAÚJO, G.V. de; SILVA, A.F.M. Agronomic performance of wheat under post-emergence herbicide application. Pesquisa Agropecuária Tropical, Goiânia, v.52, e69908, 2022. https://doi.org/10.1590/1983-40632022v5269908
https://doi.org/10.1590/1983-40632022v52...
).

One of the herbicides widely used for weed chemical control in wheat is 2,4-dichlorophenoxyacetic acid (2,4-D), which is a synthetic auxin used in two ways, as a growth regulator and as an herbicide to control dicotyledonous weeds infesting different crops (MORTENSEN et al., 2012MORTENSEN, D.A.; EGAN, J.F.; MAXWELL, B.D.; RYAN, M.R.; SMITH, R.G. Navigating a critical juncture for sustainable weed management. Bioscience, Washington, v.62, n.1, p.75-84, 2012. https://doi.org/10.1525/bio.2012.62.1.12
https://doi.org/10.1525/bio.2012.62.1.12...
; SKIBA; WOLF, 2017SKIBA, E.; WOLF, W.M. Commercial phenoxyacetic herbicides control heavy metal uptake by wheat in a divergent way than pure active substances alone. Environmental Sciences Europe, Nantes, v.29, n.1, p.1-6, 2017. https://doi.org/10.1186/s12302-017-0124-y
https://doi.org/10.1186/s12302-017-0124-...
). 2,4-D in plants generates an accumulation of abscisic acid and ethylene, which are products that induce the production of reactive oxygen species, which are responsible for increasing oxidative stress (GROSSMANN, 2010GROSSMANN, K. Auxin herbicides: current status of mechanism and mode of action. Pest Management Science, Sussex, v.66, n.2, p.113-120, 2010. https://doi.org/10.1002/ps.1860
https://doi.org/10.1002/ps.1860...
).

There are some wheat characteristics that must be considered to make correct use of the 2,4-D herbicide, such as number of tillers and phenological stages, and this product is indicated to be applied in the crop until the appearance of the first visible node (FRANCO; EVANGELISTA, 2018FRANCO, F.A.; EVANGELISTA, A. Informações técnicas para trigo e triticale – Safra 2018 / XI Reunião da Comissão Brasileira de Pesquisa de Trigo e Triticale. Cascavel: Coodetec, 2018.). Application after the first node can cause a reduction in yield components due to interference caused by the herbicide on sporogenesis (ROMAN et al., 2006ROMAN, E.S.; VARGAS, L.; RODRIGUES, O. Manejo e controle de plantas daninhas em trigo. (Embrapa Trigo. Documentos Online, 63). Passo Fundo: Embrapa Trigo, 2006. Available from: https://www.infoteca.cnptia.embrapa.br/bitstream/doc/852518/1/pdo63.pdf. Acessed on: 6 June 2020.
https://www.infoteca.cnptia.embrapa.br/b...
).

Further studies on the use of 2,4-D can significantly help producers to apply the herbicide correctly and more consciously, minimizing damage and improving the quality of grains during the harvest.

The hypothesis of this work is that application of high doses of 2,4-D at different stages of the crop causes an increase in phytotoxicity, a negative effect on physiological variables and on the components of wheat grain yield. Therefore, the objective of this work was to study the effect on the physiological and productive characteristics of wheat when applying doses of 2,4-D at different stages of crop development.

MATERIAL AND METHODS

The experiment was carried out in the field, in the experimental area of the Federal University of Fronteira Sul (UFFS), Campus Erechim, Rio Grande do Sul state, in the 2018/19 crop year, in a no-tillage system in the straw, desiccating the vegetation with the herbicide glyphosate at a dose of 1080 g a.e.·ha–1, 20 days before wheat sowing. The soil is classified as typical aluminoferric red latosoil (EMBRAPA, 2013EMBRAPA – Empresa Brasileira de Pesquisa Agropecuária. Sistema brasileiro de classificação de solos. Brasília: Embrapa Solos, 2013.). Soil fertility correction was carried out according to chemical analysis and following the fertilization recommendations for wheat (FRANCO; EVANGELISTA 2018FRANCO, F.A.; EVANGELISTA, A. Informações técnicas para trigo e triticale – Safra 2018 / XI Reunião da Comissão Brasileira de Pesquisa de Trigo e Triticale. Cascavel: Coodetec, 2018.).

The experiment was installed in a randomized block design, arranged in a 4 × 5 factorial scheme, with four replications. Factor A was composed by stages of application of 2,4-D herbicide (before tillering, at tillering, at the appearance of the first visible node and in boot stage) and factor B by doses of 2,4-D (0, 349, 698, 1047, and 1396 g·ha–1 acid equivalent).

The experimental units had an area of 13.6 m2, with 16 rows with 5 m long and spaced at 0.17 m. The wheat cultivar ‘ORS Vintecinco’ was sown with a seeder/fertilizer at an average density of 330 seeds·m–2 or a density of 3,330,000 plants·ha–1. As base fertilization, 350 kg·ha–1 of the NPK formula 05-30-15 was used. In topdressing, 75 kg·ha–1 of N in urea form was applied, in two different stages, 40% in the tillering and 60% of the dose in crop elongation.

Treatments were applied with a precision backpack sprayer, pressurized with CO2, equipped with four DG 110.02 fan spray nozzles, under constant pressure of 2.0 kgf·cm–2 and 3.6 km·h–1 displacement speed, which provided 150 L·ha–1 of herbicide spray flow. The environmental conditions at the treatments application of the treatments in the wheat crop are shown in Table 1.

Table 1
Environmental conditions at the time of treatment application on wheat. UFFS, Campus Erechim, 2018.

Phytotoxicity assessments of wheat plants were carried out at 7, 14, 21, 28 and 35 days after treatment application (DAT). Percentage scores were assigned to assess phytotoxicity, with 0% corresponding to the absence of phytotoxicity to the crop and 100% for death of wheat plants (SBCPD, 1995SBCPD – Sociedade Brasileira da Ciência das Plantas Daninhas. Procedimentos para instalação, avaliação e análise de experimentos com herbicidas. Londrina: SBCPD, 1995.). At 30 days after application of the last stage of crop development, variables related to the physiology of wheat plants were determined, such as photosynthetic activity (A: µmol·m–2·s–1), internal concentration of CO2 (Ci: µmol·mol–1), stomatal conductance (Gs: mol·m–1·s–1), efficient water use (UEA: mol CO2·mol H2O–1) and carboxylation efficiency (EC: mol CO2·m–2·s–1). The physiological variables of wheat were determined with an infrared gas analyzer, brand ADC, model LCA PRO (Analytical Development Co. Ltd, Hoddesdon, UK), in five plants per experimental unit, always using the last leaf completely expanded of the crop. Two blocks were measured a day, between 8:00 and 11:00 am, so that the environmental conditions were as homogeneous as possible during the analyses.

In preharvest of wheat, number of spikes·m–2, number of full and sterile grains and the spike length (cm) were determined at the Laboratory for Sustainable Management of Agricultural Systems at UFFS. The number of spikes·m–2 was determined by counting in the center of each experimental unit, using a square measuring 0.5 × 0.5 m. The number of full grains and sterile grains was determined by counting and, using a graduated ruler, the length of ears was measured, after randomly harvesting 10 wheat plants in each experimental unit.

Harvest was carried out manually with a useful area of 5.1 m2 and yield components were determined with the harvested grain mass. The hectoliter weight (HW) kg·hL–1 was determined using a Dalle Molle scale, model 40. The thousand grains mass (g) was determined by counting 8 repetitions of 100 grains each, subsequently extrapolating the mass to thousand grains. Grain yield was determined by extrapolating weights to kg·ha–1. The values of HW, thousand grain mass and grain yield were corrected for 13% moisture.

Data were submitted to variance analysis by F test, and being significant, to the quantitative factor (2,4-D doses), regressions were applied, and to the qualitative factor (wheat development stages), the average separation test Scott-Knott. All tests were performed at p ≤ 0.05.

RESULTS AND DISCUSSION

There was interaction between the factors tested (doses and application stages) for the variables; phytotoxicity at 7, 14, 21, 28, and 35 DAT, full grains per ear and sterile grains per ear. For grain yield, there was a difference between 2,4-D doses and application stages, but there was no interaction between the factors. There was no interaction between the factors and no significant difference between their levels for the physiological variables (photosynthetic activity, internal CO2 concentration, stomatal conductance, efficient water use, and carboxylation efficiency), spikes·m–2, spike length, TW and thousand grains mass of wheat.

The results demonstrate application of herbicide 2,4-D herbicide caused phytotoxicity of 5% to 15%, at 7 DAT, being lower for low doses and higher for high doses and applications before tillering. (Table 2). At 14 DAT, there was an increase in phytotoxicity for application before the tillering stage and a decrease for applications made later. In the evaluations in 21 and 28 DAT, decreases in phytotoxicity were observed for all stages.

Table 2
Phytotoxicity (%) at 7, 14, 21, 28, and 35 days after application of treatments (DAT) in ‘ORS Vintecinco’ wheat as a function of the application of 2,4-D herbicide doses at different stages of crop development.

It was observed that in application of 2,4-D before wheat tillering, the symptoms persisted until the end of evaluations, with 5% phytotoxicity, even for the lowest dose used, different from what happened in other stages, which no longer showed damage symptoms at 35 DAT even for 1047 g·ha–1 dose (Table 2). GALON et al. (2015)GALON, L.; CASTOLDI, C.T.; FORTE, C.T.; KUJAWISKI, R.; DAVID, F.A.; PERIN, G,F.; RADÜNZ, A.L.; AGAZZI, L.R.; ROSSETTI, J.; RADÜNZ, L.L. Efficacy and phytotoxicity of herbicides applied for the handling of weeds that infest wheat. Revista Brasileira de Herbicidas, Londrina, v.14, n.2, p.128-140, 2015. https://doi.org/10.7824/rbh.v14i2.405
https://doi.org/10.7824/rbh.v14i2.405...
when evaluating the efficacy and phytotoxicity of herbicides applied for weed management in wheat, found low phytotoxicity in Quartzo cultivar with application of 2,4-D herbicide, maximum phytotoxicity obtained was 4.5% at 7 DAT , at 21 DAT there were no more symptoms.

Applications before tillering are considered early and can cause phytotoxicity, with symptoms like ear retention in the stem being very common, remaining distorted due to the attachment of the apex to the stem by the awns (ROMAN et al., 2006ROMAN, E.S.; VARGAS, L.; RODRIGUES, O. Manejo e controle de plantas daninhas em trigo. (Embrapa Trigo. Documentos Online, 63). Passo Fundo: Embrapa Trigo, 2006. Available from: https://www.infoteca.cnptia.embrapa.br/bitstream/doc/852518/1/pdo63.pdf. Acessed on: 6 June 2020.
https://www.infoteca.cnptia.embrapa.br/b...
). Comparing the increase in 2,4-D doses, it was observed high phytotoxicity symptoms in all development stages of wheat crop, and all evaluations were adjusted to a linear equation (Fig. 1). There was a decrease in wheat phytotoxicity at each evaluation performed, this for all doses, at 35 DAT the maximum symptoms were 5%. These symptoms are caused by the effect of auxin on the inducing signals, the hormones when perceive the auxin of herbicide, interrupt the natural signals; as a consequence, there are torsions in the leaves and other deformations (IONESCU; PENESCU, 2015IONESCU, N.; PENESCU, A. Aspects of winter wheat physiology treated with herbicides. Agriculture and Agricultural Science Procedia, Amsterdam, v.6, p.52-57, 2015. https://doi.org/10.1016/j.aaspro.2015.08.037
https://doi.org/10.1016/j.aaspro.2015.08...
).

Figure 1
Phytotoxicity (%) evaluated at 7 (a), 14 (b), 21 (c), 28 (d) and 35 (e) DAT in ‘ORS Vintecinco’ wheat as a function of application of 2,4-D doses and development stages.

For the physiological parameters of wheat crop, such as Gs, Ci, A, UEA, and EC, there was no difference between application stages (Table 3). It is noteworthy that the visual phytotoxicity at 28 DAT did not exceed 7%, indicating recovery of wheat plants (Table 2). In view of this fact, it is noteworthy that the herbicide, object of the study, did not change physiological characteristics of the crop, possibly due to low phytotoxicity or even to metabolization by wheat crop to a non-toxic product. In work carried out by ALTERMAN; NEPTUNE (1977)ALTERMAN, M.K.; NEPTUNE, A.M.L. Efeito do ácido 2,4-diclorofenoxiacético (2,4-D) na absorção do fósforo (32p) pelo trigo (Triticum aestivum., L) e a sua distribuição na planta. Anais da Escola Superior de Agricultura Luiz de Queiroz, São Paulo, v.34, p.541-550. https://doi.org/10.1590/S0071-12761977000100042
https://doi.org/10.1590/S0071-1276197700...
, they found that wheat can metabolize 2,4-D to a nontoxic product and, thus, not affect plant’s physiology or absorption of essential resources for its growth and development.

Table 3
Effect of 2,4-D herbicide applied in crop in several doses and different stages on stomatal conductance (Gs), internal CO2 concentration (Ci), photosynthetic activity (A), efficient water use (UEA) and carboxylation efficiency (EC) of ‘ORS Vintecinco’ wheat.

Regarding comparisons between 2,4-D doses, the evaluated physiological variables did not show any alteration for the moment in which the evaluation was carried out, and there was no adjustment of the data to the tested models (Fig. 2). For photosynthesis, in addition to herbicide action, there may be other factors that cause its alteration such as; light, water stress, soil characteristics, crop management, plant characteristics, and others (MATOS et al., 2013MATOS, C.C. de; FIALHO, C.M.T.; FERREIRA, E.A.; SILVA, D.V.; SILVA, A.A. da; SANTOS, J.B. dos; FRANÇA, A.C.; GALON, L. Características fisiológicas do cafeeiro em competição com plantas daninhas. Bioscience Journal, Uberlândia, v.29, n.5, p.1111-1119, 2013.). The carboxylation efficiency is directly related to photosynthetic activity, what occurs because of stomata, which close and open, regulating the CO2 entry into the plant (TAIZ et al., 2017TAIZ, L.; ZEIGER, E.; MOLLER, I.M.; MURPHY, A. Fisiologia e Desenvolvimento Vegetal. 6. ed. Porto Alegre: Artmed, 2017.). Based on this and considering that evaluation time was distant from the applications, plant may have recovered its metabolism, degrading the herbicide to a non-toxic product and thus not showing differences for physiological parameters, as explained above.

Figure 2
Effect of 2,4-D herbicide doses, applied at different crop development stages, on stomatal conductance (a), internal CO2 concentration (b), photosynthetic activity (c), efficient water use (d) and carboxylation efficiency (e) of ‘ORS Vintecinco’ wheat.

Regarding grain yield components, it was observed that number of spikes.m–2, spikes length and thousand grain mass were not affected by the application of 2,4-D, as there was no significant difference between application stages, for neither herbicide doses (Table 4, Fig. 3). This fact is due to wheat plant was able to metabolize the herbicide, even when it was applied outside the recommended stage. Similar results regarding the number of spikes·m–2 were found by RODRIGUES et al. (2006)RODRIGUES, O.; MARCHESE, J.A.; VARGAS, L.; VELLOSO, J.A.O.; RODRIGUES, R.C.S. Efeito da aplicação de herbicida hormonal em diferentes estádios de desenvolvimento de trigo (Triticum aestivum L. Cvs. Embrapa 16 e BR 23). Revista Brasileira de Herbicidas, Londrina, v.5, n.1, p.19-29, 2006. https://doi.org/10.7824/rbh.v5i1.41
https://doi.org/10.7824/rbh.v5i1.41...
when evaluating effect of hormonal herbicide application at different stages of wheat development.

The number of full grains per ear showed a difference for application stages in each doses evaluated, having a negative effect for the treatments where the herbicide was applied before tillering and at booting. The application before tillering generated the greatest number of sterile grains per ear, directly influencing grain yield (Table 4). Increasing 2,4-D doses linearly decreased the number of grains per ear (Fig. 4a) and increased the number of sterile grains, possible due to the increase in grain sterility (Fig. 4b). IONESCU; PENESCU (2015)IONESCU, N.; PENESCU, A. Aspects of winter wheat physiology treated with herbicides. Agriculture and Agricultural Science Procedia, Amsterdam, v.6, p.52-57, 2015. https://doi.org/10.1016/j.aaspro.2015.08.037
https://doi.org/10.1016/j.aaspro.2015.08...
, when working with different herbicides in wheat, including 2,4-D, observed that number of full grains per spikes also decreases, but thousand grain mass was not changed when applied 2,4-D isolated. RODRIGUES et al. (2006)RODRIGUES, O.; MARCHESE, J.A.; VARGAS, L.; VELLOSO, J.A.O.; RODRIGUES, R.C.S. Efeito da aplicação de herbicida hormonal em diferentes estádios de desenvolvimento de trigo (Triticum aestivum L. Cvs. Embrapa 16 e BR 23). Revista Brasileira de Herbicidas, Londrina, v.5, n.1, p.19-29, 2006. https://doi.org/10.7824/rbh.v5i1.41
https://doi.org/10.7824/rbh.v5i1.41...
found similar results with applications of the auxinic herbicide dicamba, resulting in a reduction in the number of full grains per spikes, which caused a loss of up to 60% in wheat grain yield.

Table 4
Grain·m–2, spike length (cm), full and sterile grain·spike–1, hectoliter weight (kg·hL–1), thousand grain mass (g) and yield (kg·ha–1) as a function of 2,4-D herbicide doses applied at several development stages in ‘ORS Vintecinco’ wheat.
Figure 3
Effect of 2,4-D herbicide doses, applied at different crop development stages; (a) on number of spikes (m–2) and (b) length of spikes (cm) of ‘ORS Vintecinco’ wheat.
Figure 4
Effect of 2,4-D herbicide doses, applied at different crop development stages, on full (A) and sterile (B) number of grains per spikes of wheat crop.

For hectoliter weight (kg·hL–1) and thousand grain mass no differences were observed between the application stages (Table 4) and no data adjustments were found for the models tested with increasing doses of 2,4-D (Fig. 5). In relation to thousand grain mass, RODRIGUES et al. (2006)RODRIGUES, O.; MARCHESE, J.A.; VARGAS, L.; VELLOSO, J.A.O.; RODRIGUES, R.C.S. Efeito da aplicação de herbicida hormonal em diferentes estádios de desenvolvimento de trigo (Triticum aestivum L. Cvs. Embrapa 16 e BR 23). Revista Brasileira de Herbicidas, Londrina, v.5, n.1, p.19-29, 2006. https://doi.org/10.7824/rbh.v5i1.41
https://doi.org/10.7824/rbh.v5i1.41...
found similar results when applying dicamba, having no effect on this variable.

Figure 5
Effect of 2,4-D herbicide doses, applied at different crop development stages, on hectoliter weight (A) and thousand-grain weight (B) of ‘ORS Vintecinco’ wheat.

Regarding grain yield, there was a difference between the stages in which the herbicide 2,4-D was applied, but only for doses 698, 1047 and 1396. 2,4-D use in the tillering and in the first node showed higher productivity than other stages. Early applications, such as before tillering, and later as in booting, caused decreases in wheat grain yield (Table 4). Similar results were found by TOTTMAN (1977)TOTTMAN, D.R. The identification of growth stages in winter wheat with reference to the application of growth regulator herbicides. Annals of Applied Biology, London, v.87, n.2, p.213-224, 1977. https://doi.org/10.1111/j.1744-7348.1977.tb01877.x
https://doi.org/10.1111/j.1744-7348.1977...
where early application of 2,4-D and 2-methyl-4-chlorophenoxyacetic acid affected the morphology of the plant, causing changes in leaves and ears, due to interfering in the distribution of new leaves and in the beginnings of spikelets.

With increasing doses, there was a linear decrease in grain yield for all stages in which 2,4-D was applied (Fig. 6). When comparing the application of the highest 2,4-D dose (1396 g·ha–1) against the lowest (0 g·ha–1), there was a reduction of 27.6, 18.8, 17.6, and 27.0% using the herbicide before tillering, at tillering, at the first node and at booting, respectively. This decrease may be linked to the effect of auxin on cell division, elongation and vascular differentiation, which in adequate doses can stimulate these processes, but in high concentrations, they affect plant growth processes and cause damage to the crop (WOODWARD; BARTEL, 2005WOODWARD, A.W.; BARTEL, B. Auxin: regulation, action, and interaction. Annals of Botany, Oxfordshire, v.95, n.5, p.707-735, 2005.).

Figure 6
Effect of 2,4-D herbicide doses, applied at different crop development stages, on grain yield (kg·ha–1) of ‘ORS Vintecinco’ wheat.

CONCLUSIONS

The best stages to apply 2,4-D are tillering and at the first node, the application before tillering and booting resulted in grain yield losses in ‘ORS Vintecinco’ wheat. Neither one of the doses and application stages of 2,4-D affect the characteristics related to wheat physiology of ‘ORS Vintecinco’ wheat. Increasing the doses of 2,4-D herbicide, the application reduces yield of ‘ORS Vintecinco’ wheat, regardless the application stage.

ACKNOWLEDGEMENTS

Not applicable.

  • Peer Review History: Double-blind Peer Review.
  • AVAILABILITY OF DATA AND MATERIAL

    The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.
  • FUNDING

    Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul
    Grants No: 19/2551-0000874-0 and 842-25.51/13-4
    Universidade Federal da Fronteira Sul
    Grant No: PES-2019-0592
    Conselho Nacional de Desenvolvimento Científico e Tecnológico
    Grants No: 406221/2016-2 and 306927/2019-5
  • ETHICAL APPROVAL

    Not applicable.

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Edited by

Section Editor: Silvia Galleti

Publication Dates

  • Publication in this collection
    09 Jan 2023
  • Date of issue
    2022

History

  • Received
    26 June 2020
  • Accepted
    31 Oct 2022
Instituto Biológico Av. Conselheiro Rodrigues Alves, 1252 - Vila Mariana - São Paulo - SP, 04014-002 - São Paulo - SP - Brazil
E-mail: arquivos@biologico.sp.gov.br