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Herbicide selectivity and weed control in gladiolus cultivation

Seletividade de herbicidas e controle de plantas daninhas no cultivo de gladíolo

Abstract

The objective of this work was to evaluate the selectivity of pre- and post-emergent herbicides and their efficiency in weed control, as well as the growth and quality of floral stems, in a gladiolus (Gladiolus x grandiflorus) crop in two growing seasons. The experiments were carried out in the field, where the planted gladiolus received the application of pre- and post-emergent herbicides, with and without mechanical weed control. At 7, 14, 21, and 28 days after emergence (DAE), monocotyledon and eudicotyledon control and phytotoxicity to gladiolus plants were evaluated. At 28 DAE, the shoot dry matter of weeds and gladiolus plants was also evaluated. The s-metolachlor and diuron pre-emergent herbicides and the haloxyfop-p-methyl post-emergent herbicide are selective to gladiolus plants in both seasons, which allows of the production of floral stems with commercial quality. The s-metolachlor and haloxyfop-p-methyl herbicides also promote an efficient control of monocotyledons regardless of the growing season. Although, when applied, saflufenacil and 2,4-D cause phytotoxicity in the vegetative phase of gladiolus, they do not affect the production of floral stems and control satisfactorily eudicotyledons in the second season.

Index terms:
Gladiolus x grandiflorus; floriculture; phytotoxicity; post-emergence; pre-emergence; quality standard

Resumo

O objetivo deste trabalho foi avaliar a seletividade de herbicidas pré e pós-emergentes e a sua eficiência no controle de plantas daninhas, bem como o crescimento e a qualidade de hastes florais, na cultura do gladíolo (Gladiolus x grandiflorus), em duas épocas de cultivo. Os experimentos foram conduzidos a campo, onde os gladíolos plantados receberam a aplicação de herbicidas pré e pós-emergentes, com e sem controle mecânico das plantas daninhas. Aos 7, 14, 21 e 28 dias após a emergência (DAE), avaliaram-se o controle de monocotiledôneas e eudicotiledôneas, além da fitotoxicidade no gladíolo. Aos 28 DAE, também foi avaliada a massa seca da parte aérea das plantas daninhas e dos gladíolos. Os herbicidas pré-emergentes s-metolacloro e diuron e o pós-emergente haloxifope-p-metílico são seletivos ao gladíolo, em ambas as épocas de cultivo, o que possibilita a produção de hastes florais com qualidade comercial. Os herbicidas s-metolacloro e haloxifope-p-metílico também promovem controle eficiente de monocotiledôneas independentemente da época de cultivo. Embora, quando aplicados, saflufenacil e 2,4-D causem fitotoxicidade na fase vegetativa do gladíolo, não afetam a produção de hastes florais e controlam satisfatoriamente as eudicotiledôneas no segundo cultivo.

Termos para indexação:
Gladiolus x grandiflorus; floricultura; fitotoxicidade; pós-emergência; pré-emergência; padrão de qualidade

Introduction

Gladiolus (Gladiolus x grandiflorus Hort.) is a plant belonging to the family Iridaceae that is propagated by corms and used as a cut flower with a high acceptance in the flower market (Schwab et al., 2015SCHWAB, N.T.; STRECK, N.A.; BECKER, C.C.; LANGNER, J.A.; UHLMANN, L.O.; RIBEIRO, B.S.M.R. A phenological scale for the development of Gladiolus. Annals of Applied Biology, v.166, p.496-507, 2015. DOI: https://doi.org/10.1111/aab.12198.
https://doi.org/10.1111/aab.12198....
; Tomiozzo et al., 2019TOMIOZZO, R.; UHLMANN, L.O.; BECKER, C.C.; SCHWAB, N.T.; STRECK, N.A.; BALEST, D.S. How to produce gladiolus corms? Ornamental Horticulture, v.25, p.299-306, 2019. DOI: https://doi.org/10.1590/2447-536x.v25i3.2048.
https://doi.org/10.1590/2447-536x.v25i3....
). The species stands out for being easy to grow, having a low production cost, and for the elegance of its florets, which present a diversity of colors and formats, good post-harvest durability, and added value, resulting in a quick financial return (Tomiozzo et al., 2018TOMIOZZO, R.; PAULA, G.M. de; STRECK, N.A.; UHLMANN, L.O.; BECKER, C.C.; SCHWAB, N.T.; MUTTONI, M.; ALBERTO, C.M. Cycle duration and quality of gladiolus floral stems in three locations of Southern Brazil. Ornamental Horticulture, v.24, p.317-326, 2018. DOI: https://doi.org/10.14295/oh.v24i4.1237.
https://doi.org/10.14295/oh.v24i4.1237....
; Bosco et al., 2021BOSCO, L.C.; STANCK, L.T.; SOUZA, A.G. de; ROSSATO, O.B.; UHLM ANN, L.O.; STRECK, N.A. Quantitative parameters of floral stems of gladiolus plants grown under minimum tillage system in Santa Catarina, Brazil. Revista Caatinga, v.34, p.318-327, 2021. DOI: https://doi.org/10.159 0/1983-21252021v34n 208rc.
https://doi.org/10.159...
). Because of these agronomic and ornamental characteristics, the gladiolus is the most important species of a project, called Flores para Todos (flowers for all), aiming to stimulate flower production and, consequently, provide income for more than 150 families of family farmers from Northern to Southern Brazil (Uhlmann et al., 2019UHLMANN, L.O.; BECKER, C.C.; TOMIOZZO, R.; STRECK, N.A.; SCHONS, A.; BALEST, D.C.; BRAGA, M. dos S.; SCHWAB, N.T.; LANGNER, J.A. Gladiolus as an alternative for diversification and profit in small rural property. Ornamental Horticulture, v.25, p. 200-08, 2019. DOI: https://doi.org/10.14295/oh.v25i2.1541.
https://doi.org/10.14295/oh.v25i2.1541....
; Streck & Uhlmann, 2021STRECK, N.A.; UHLMAN N, L.O. Flowers for all; bridging the gap between science and society. Chronica Horticulturae, v.61, p.32-34, 2021.).

Gladiolus plants are usually cultivated using the conventional system, characterized by soil turning and bed preparation (Bosco et al., 2021BOSCO, L.C.; STANCK, L.T.; SOUZA, A.G. de; ROSSATO, O.B.; UHLM ANN, L.O.; STRECK, N.A. Quantitative parameters of floral stems of gladiolus plants grown under minimum tillage system in Santa Catarina, Brazil. Revista Caatinga, v.34, p.318-327, 2021. DOI: https://doi.org/10.159 0/1983-21252021v34n 208rc.
https://doi.org/10.159...
). However, according to these same authors, the soil is continuously exposed throughout cultivation because of the high frequency of soil mobilization and the low population density and lanceolate leaves of this crop, creating favorable conditions for the germination and emergence of weeds, which can negatively interfere with plant development and floral stem quality due to the low weed control in gladiolus (Forte et al., 2018FORTE, C.T.; GALON, L.; BEUTLER, A.N.; REICHERT JR., F.W.; MENEGAT, A.D.; PERIN, G.F.; TIRONI, S.P. Cultivation systems, vegetable soil covers and their influence on the phytosocyology of weeds. Planta Daninha, v.36, e018176776, 2018. DOI: https://doi.org/10.1590/S0100-83582018360100099.
https://doi.org/10.1590/S0100-8358201836...
; Martins et al., 2019MARTINS, D.; MARTINS, C.C.; SILVA JR., A.C. Weed management and herbicide selectivity in or namental plants. Planta Daninha, v.37, e019216908, 2019. DOI: https://doi.org/10.1590/S0100-83582019370100155.
https://doi.org/10.1590/S0100-8358201937...
). In that system, soil turning also causes alterations in the environment that can lead to propagule dispersal and the increase in weed germination (Schneider, 2007SCHNEIDER, A.A. A flora naturalizada no estado do Rio Grande do Sul, Brasil: herbáceas subespontâneas. Biociências, v.15, p. 257-268, 2007.).

Even under conditions considered unfavorable for most cultivated plants, weeds show a high competitive ability, attributed to their rapid growth and initial development, efficient reproduction and dispersion mechanisms, and adaptability, which increase their potential to access limited resources of the environment, such as nutrients, light, and water (Fahad et al., 2015FAHAD, S.; HUSSAIN, S.; CHAUHAN, B.S.; SAUD, S.; WU, C.; HASSA N, S.; TANVEER, M.; JAN, A.; H UANG, J. Weed g row th and crop yield loss in wheat as influenced by row spacing and weed emergence times. Crop Protection, v.71, p.101-108, 2015. DOI: https://doi.org/10.1016/j.cropro.2015.02.005.
https://doi.org/10.1016/j.cropro.2015.02...
; Caratti et al., 2016CARATTI, F.C.; LAMEGO, F.P.; SILVA, J.D.G.; GARCIA, J.R.; AGOSTI NETTO, D. Partitioning of competition for resources between soybean and cor n as competitor plant. Planta Daninha, v.34, p.657-665, 2016. DOI: https://doi.org/10.1590/S0100-83582016340400005.
https://doi.org/10.1590/S0100-8358201634...
). This competition negatively affects the growth and development of ornamental plants, reducing the quality and final yield of floral stems or corms, which are the propagation material of gladiolus plants (Manuja et al., 2005MANUJA, S.; RAM, R.; SINGH, R.D.; MUKHERJEE, D. Evaluation of different herbicides for protection of gladiolus (Gladiolus spp.) crop from weeds. Crop Protection, v.24, p.921-926, 2005. DOI: https://doi.org/10.1016/j.cropro.2005.01.019.
https://doi.org/10.1016/j.cropro.2005.01...
; Martins et al., 2019MARTINS, D.; MARTINS, C.C.; SILVA JR., A.C. Weed management and herbicide selectivity in or namental plants. Planta Daninha, v.37, e019216908, 2019. DOI: https://doi.org/10.1590/S0100-83582019370100155.
https://doi.org/10.1590/S0100-8358201937...
).

In ornamental crops, weed control is commonly carried out using the mechanical method, through weeding or uprooting, whose required labor increases production costs and may cause quality loss in the final product due to physical damage (Queiroz et al., 2016QUEIROZ, J.R.G.; SILVA JR., A.C.; MARTI NS, D. Herbicide selectivity in tropical ornamental species. Planta Daninha, v.34, p.795-801, 2016. DOI: https://doi.org/10.1590/S0100-83582016340400020.
https://doi.org/10.1590/S0100-8358201634...
). The chemical method is an alternative for that type of production system, being one of the most applied in agriculture because it is easy to use and has a fast action on the target (Harker & O’Donovan, 2013HARKER, K.N.; O’DONOVAN, J.T. Recent weed control, weed management, and integ rated weed management. Weed Technology, v.27, p.1-11, 2013. DOI: https://doi.org/10.1614/WT-D-12-00109.1.
https://doi.org/10.1614/WT-D-12-00109.1....
).

Up to date, only two active ingredients are registered for weed control in gladiolus: sethoxydim, an acetyl-coenzyme A carboxylase inhibitor herbicide, indicated to be applied post-emergence for the control of monocotyledon weeds; and trifluralin, a microtubule assembly inhibitor to be applied pre-emergence for the control of mono- and eudicotyledon weeds (Agrofit, 2022AGROFIT: Sistema de Agrotóxicos Fitossanitários. Available at: <https://agrofit.agricultura.gov.br/>. Accessed on: Oct. 10 2022.
https://agrofit.agricultura.gov.br/...
). Therefore, studies are still necessary to determine the efficiency and selectivity of herbicides and to recommend possible chemical alternatives for weed management in this crop.

The objective of this work was to evaluate the selectivity of pre- and post-emergent herbicides and their efficiency in weed control, as well as the growth and quality of floral stems, in a gladiolus crop in two growing seasons.

Materials and Methods

Two field experiments were carried out in 2018 and 2019, in the winter-spring and summer-autumn growing seasons, respectively, in the experimental area of the Department of Phytosanitary Defense of Universidade Federal de Santa Maria, located in the municipality of Santa Maria, in the state of Rio Grande do Sul, Brazil (29°42'S, 53°43'W, at an altitude of 96 m). According to Köppen-Geiger’s classification, the climate is Cfa, warm and wet subtropical, with no defined dry season. The values registered for the main climatic variables are: 1,830 mm average annual precipitation; 14.7 and 25.2°C minimum and maximum average temperatures, respectively; 77% relative humidity; and 16.4 MJ m-1 per day solar radiation (Wrege et al., 2012WREGE, M.S.; STEINMETZ, S.; REISSER JÚNIOR, C.; ALMEIDA, I.R. de. (Ed.). Atlas climático da Região Suldo Brasil: est ados do Paraná, Santa Catarina e Rio Grande do Sul. 2.ed. Brasília: Embrapa, 2012. 333p.). The soil of the experimental area is classified as an Argissolo Vermelho distrófico arênico (Santos et al., 2018SANTOS, H.G. dos; JACOMINE, P.K.T.; ANJOS, L.H.C. dos; OLIVEIRA, V.A. de; LUMBRERAS, J.F.; COELHO, M.R.; ALMEIRA, J.A. de; ARAUJO FILHO, J.C. de; OLIVEIRA, J.B. de; CUNHA, T.J.F. Brazilian Soil Classification System. 5th ed. rev. and exp. Brasília: Embrapa, 2018.), i.e., a Paleaudalf (Soil Survey Staff, 2014SOIL SURVEY STAFF. Keys to soil taxonomy. 12th ed. Washington: USDA, 2014. 360p.).

According to Instituto Nacional de Meteorologia (INMET, 2022INMET. Instituto Nacional de Meteorologia. Available at: <https://tempo.inmet.gov.br/TabelaEstacoes/A001>. Accessed on: June 1 2022.
https://tempo.inmet.gov.br/TabelaEstacoe...
), specifically during the experimental period, in the first growing season, total precipitation was 499.6 mm and average temperature was 17.1°C, with minimum and maximum temperatures of 1.0 and 35.1°C, respectively (Figure 1 A). In the second season, total precipitation was 572.8 mm and average temperature was 20.5°C, with minimum and maximum temperatures of 7.9 and 36.3°C, respectively (Figure 1 B).

Figure 1
Meteorological data of minimum temperature, maximum temperature, and precipitation during the experimental periods in the winter-spring (A) and summer-autumn (B) growing seasons of 2018 and 2019, respectively, in the municipality of Santa Maria, in the state of Rio Grande do Sul, Brazil. The arrows represent the time of application of the pre- and post-emergent herbicides.

Gladiolus corms of the Jester cultivar were planted on July 18 in the winter-spring of 2018 and on February 22 in the summer-autumn of 2019, in beds with paired rows spaced at 0.40 m, with 0.20 m between plants in the row, at a depth of 10 to 15 cm, totaling 40 corms per plot. The experimental design was randomized complete blocks with four replicates, in which the experimental units consisted of the plots with 4.0 m of length and 1.0 m of width (4.0 m2).

After planting, the average date of emergence was determined by monitoring plant emergence, considered when 50% of the plants in the plots were visible above soil surface. As plant emergence stabilized, thinning was carried out weekly, maintaining one seedling per corm aiming at a standardized production of a single stem. When gladiolus plants were between the V3 and V4 stages (three and four leaves, respectively), 350 kg ha-1 urea (45% N) were applied as topdressing in all experimental plots. The other management practices were planned using the PhenoGlad model (Uhlmann et al., 2017UHLMANN, L.O.; STRECK, N.A.; BECKER, C.C.; SCHWAB, N.T.; BENEDETTI, R.P.; CHARÃO, A.S.; RIBEIRO, B.S.M.R.; SILVEIRA, W.B.; BACKES, F.A.A.L.; ALBERTO, C.M.; MUTTONI, M.; PAULA, G.M. de; TOMIOZZO, R.; BOSCO, L.C.; BECKER, D. PhenoGlad: a model for simulating development in Gladiolus. European Journal of Agronomy, v.82, p.33-49, 2017. DOI: https://doi.org/10.1016/j.eja.2016.10.001.
https://doi.org/10.1016/j.eja.2016.10.00...
), which calculates the phenology of gladiolus plants based on meteorological temperature data. The phenological stages of the gladiolus plants were observed according to the scale proposed by Schwab et al. (2015)SCHWAB, N.T.; STRECK, N.A.; BECKER, C.C.; LANGNER, J.A.; UHLMANN, L.O.; RIBEIRO, B.S.M.R. A phenological scale for the development of Gladiolus. Annals of Applied Biology, v.166, p.496-507, 2015. DOI: https://doi.org/10.1111/aab.12198.
https://doi.org/10.1111/aab.12198....
.

After the application of the treatments, the number of leaves of six gladiolus plants from the center of each plot was counted up to the final leaf number (FLN). The daily thermal time (STd, °C day) from emergence to FLN, corresponding to the vegetative phase, was calculated using the following equation: STd = [(Tmax + Tmin)/2 - Tb], where Tmax and Tmin are the daily maximum and minimum air temperatures (°C), respectively, measured at the main climatological station of INMET, located approximately 1.5 km from the experimental area; and Tb is the base temperature of the crop, which is 2°C (Arnold, 1960ARNOLD, C.Y. Maximum-minimum temperature as a basis for computing heat units. Proceedings of the American Society for Horticultural Science, v.76, p.682- 692, 1960.; Uhlmann et al., 2017UHLMANN, L.O.; STRECK, N.A.; BECKER, C.C.; SCHWAB, N.T.; BENEDETTI, R.P.; CHARÃO, A.S.; RIBEIRO, B.S.M.R.; SILVEIRA, W.B.; BACKES, F.A.A.L.; ALBERTO, C.M.; MUTTONI, M.; PAULA, G.M. de; TOMIOZZO, R.; BOSCO, L.C.; BECKER, D. PhenoGlad: a model for simulating development in Gladiolus. European Journal of Agronomy, v.82, p.33-49, 2017. DOI: https://doi.org/10.1016/j.eja.2016.10.001.
https://doi.org/10.1016/j.eja.2016.10.00...
). The accumulated thermal time (STa, °C day) was calculated by the equation: STa = Σ STd. The phyllochron in each plant, defined as the time interval between the appearance of two successive leaves (°C day per leaf), was calculated by the inverse of the slope of the linear regression between leaf number and STa (Xue et al., 2004XUE, Q.; WEISS, A.; BAENZIGER, P.S. Predicting leaf appearance in field grown winter wheat: evaluating linear and non-linear models. Ecological Modelling, v.175, p.261-270, 2004. DOI: https://doi.org/10.1016/j.ecolmodel.2003.10.018.
https://doi.org/10.1016/j.ecolmodel.2003...
).

Both experiments were composed of ten treatments (T1 to T10) each. T1–T3 and T4–T8, respectively, consisted of the following pre- and post-emergent herbicides: T1, diclosulam (42 g a.i. ha-1); T2, s-metolachlor (1,440 g a.i. ha-1); T3, diuron (200 g a.i. ha-1); T4, glyphosate (1,350 g a.i. ha-1); T5, haloxyfop-p-methyl (120 g a.i. ha-1); T6, saflufenacil (49 g a.i. ha-1); T7, 2,4-D (1,005 g a.i. ha-1); and T8, imazapyer + imazapic (70.5 + 24.5 g a.i. ha-1). T9 and T10 were the control treatments without herbicide application, with (weeded check) and without (untreated check) mechanical weed control, respectively.

In the winter-spring and summer-autumn growing seasons, the pre-emergent herbicides were applied seven and five days after planting, respectively, and the post-emergent herbicides when the plants were in the V3 stage, which is the recommended time for the application of N topdressing (Schwab et al., 2015SCHWAB, N.T.; STRECK, N.A.; BECKER, C.C.; LANGNER, J.A.; UHLMANN, L.O.; RIBEIRO, B.S.M.R. A phenological scale for the development of Gladiolus. Annals of Applied Biology, v.166, p.496-507, 2015. DOI: https://doi.org/10.1111/aab.12198.
https://doi.org/10.1111/aab.12198....
). Herbicides were applied using a CO2-pressurized backpack sprayer equipped with six TeeJet XR 110.015 flat fan nozzles (TeeJet Technologies, Glendale Heights, IL, USA), spaced at 0.5 m, which was also the height of the target, and calibrated to provide an application volume of 150 L ha-1. The time of application was under the climatic conditions recommended by the manufacturer. For the plots corresponding to the treatment with mechanical weed control, weeding was carried out approximately every 15 days with the aid of a hoe, maintaining the crop free from the negative interference of weeds.

The control of monocotyledons and eudicotyledons and their phytotoxicity to gladiolus plants were evaluated at 7, 14, 21, and 28 days after emergence (DAE) for pre-emergent herbicides and after the application of treatments (DAT) for post-emergent herbicides. For this, a visual scale ranging from 0 to 100% was used, representing the absence of injuries and the complete death of the plants, respectively (Frans et al., 1986FRANS, R.; TALBERT, R.; MARX, D.; CROWLEY, H. Experimental design and techniques for measuring and analyzing plant responses to weed control practices. In: CAMPER, N.D. ( Ed.). Research methods in weed science. 3rd ed. Champaign: Southern Weed Science Society, 1986. p.29-45.). In 2018, there was no emergence of eudicotyledon weeds in the area treated with pre-emergent herbicides; therefore, only the control of monocotyledons was evaluated. To determine the predominant weeds, sampling was carried out using a 0.25 m2 quadrat frame placed in two locations per plot.

In addition, the shoot dry matter (DM) of the weeds and gladiolus crop was evaluated, respectively, using weed plant material from within a 0.25 m2 frame and two plants per plot collected at 28 DAE for pre-emergent herbicides and at 28 DAT for post-emergent herbicides. The weeds and gladiolus plants were placed, separately, in a forced-air circulation oven, at 60ºC, for 72 hours until reaching constant mass, and then weighed; the obtained value was converted to 1.0 m2 for weeds and to gram per plant for gladiolus.

For gladiolus, maximum leaf area (LA) was determined at the R2 stage (harvesting point of the flower stem) by measuring the length and width of each leaf of the two plants collected per plot. The leaf area index (LAI) was calculated by dividing the sum of the LA of all leaves of the plant by the soil area occupied by each plant (800 cm2), using the equation described by Schwab et al. (2014)SCHWAB, N.T.; STRECK, N.A.; REHBEIN, A.; RIBEIRO, B.S.M.R.; ULHMANN, L.O.; LANGNER, J.A.; BECKER, C.C. Dimensões lineares da folha e seu uso na determinação do perfil vertical foliar de gladíolo. Bragantia, v.73, p.97-105, 2014. DOI: https://doi.org/10.1590/brag.2014.014.
https://doi.org/10.1590/brag.2014.014....
: LA = 0.644 (L.W), where L and W correspond to the length and width of the leaves, respectively. Furthermore, the quantitative parameters indicative of floral stem quality – such as stem length, spike length, stem diameter, and number of florets – were measured. However, the LAI and the quality parameters of the floral stem were not determined for the treatments with 2,4-D and imazapyr+imazapic in 2018 and with glyphosate in 2018 and 2019 since these herbicides caused the death of gladiolus plants and/or damaged the floral stems after being applied.

Variable data for all treatments were analyzed together, except those for the DM of weeds and gladiolus because they were collected at different times. The data were subjected to the analysis of variance using the F-test, at 5% probability, and, when statistical significance was observed, means were compared by the Scott-Knott test, also at 5% probability, using the R software (R Core Team, 2020R CORE TEAM. R: a language and environment for statistical computing. Vienna: R Foundation for Statistical Computing, 2020.). Data without statistical significance by the F-test was not considered.

Results and Discussion

The analysis of variance showed statistical significance for phytotoxicity (Table 1) and the control

Table 1
Phytotoxicity to gladiolus (Gladiolus x grandiflorus) plants at 7, 14, 21, and 28 days after crop emergence when pre-emergent herbicides were applied or after the application of post-emergent herbicides in the winter-spring and summer-autumn growing seasons of 2018 and 2019, respectively, in the municipality of Santa Maria, in the state of Rio Grande do Sul, Brazil(1).

(Table 2) at 7, 14, 21, and 28 DAE or DAT, as well as for the stem length, phyllochron, and FLN growth variables in the two growing seasons (Table 3). However, the LAI and floral stem quality were significant only in the second season for pre- and post-emergent herbicides. Regarding the DM of weeds and gladiolus plants, significance was observed only in the treatments with post-emergent herbicides in the first season and both in the treatments with pre- and post-emergent herbicides in the second (Table 4). The results are presented separately according to the growing season.

Table 2
Control of monocotyledon weeds in gladiolus (Gladiolus x grandiflorus) at 7, 14, 21, and 28 days after crop emergence when pre-emergent herbicides were applied or after the application of post-emergent herbicides in the winter-spring and summer-autumn growing seasons of 2018 and 2019, respectively, in the municipality of Santa Maria, in the state of Rio Grande do Sul, Brazil(1).
Table 3
Final leaf number (FLN), phyllochron (PHYL), leaf area index (LAI), and stem length (SL) of gladiolus (Gladiolus x grandiflorus) as a function of pre- and post-emergent herbicide application in the winter-spring and summer-autumn growing seasons of 2018 and 2019, respectively, in the municipality of Santa Maria, in the state of Rio Grande do Sul, Brazil(1).
Table 4
Dry matter (DM) of eudicotyledon and monocotyledon weeds and of gladiolus (Gladiolus x grandiflorus) at 28 days after crop emergence when pre-emergent herbicides were applied or after the application of post-emergent herbicides in the winter-spring and summer-autumn growing seasons of 2018 and 2019, respectively, in the municipality of Santa Maria, in the state of Rio Grande do Sul, Brazil(1).

In the first season, the haloxyfop-p-methyl herbicide presented the lowest phytotoxicity to the crop at 7 and 14 DAT, with values lower than 5% throughout the experimental period (Table 1). This herbicide is among those that inhibit the enzyme acetyl-coenzyme A carboxylase, promoting the destruction of the meristems of species of the family Poaceae; however, species from other families are frequently tolerant to it (Oliveira Júnior, 2011OLIVEIRA JÚNIOR, R.S. Mechanisms of action of herbicides. In: OLIVEIRA JÚNIOR, R.S.; CONSTANTIN, J.; INOUE, M.H. (Ed.). Biology and weed management. Curitiba: Omnipax, 2011. p.141-192.; Leal et al., 2020LEAL, J.F.L.; SOUZA, A. dos S.; RIBEIRO, S.R. de S.; OLIVEIRA, G.F.P.B.; ARAUJO, A.L.S.; BORELLA, J.; LANGARO, A.C.; MACHADO, A.F.L.; PINHO, C.F. de. 2,4-Dichlorophenoxyacetic-N-methylmethanamine and haloxyfop-P-methyl interaction: sequential and interval applications to effectively control sourgrass and fleabane. Agronomy Journal, v.112, p.1216 -1226, 2020. DOI: https://doi.org/10.1002/agj2.20018.
https://doi.org/10.1002/agj2.20018....
), which may explain the selectivity to gladiolus of the family Iridaceae. Queiroz et al. (2016)QUEIROZ, J.R.G.; SILVA JR., A.C.; MARTI NS, D. Herbicide selectivity in tropical ornamental species. Planta Daninha, v.34, p.795-801, 2016. DOI: https://doi.org/10.1590/S0100-83582016340400020.
https://doi.org/10.1590/S0100-8358201634...
also found phytotoxicity values lower than 5% due to the application of fluazifop-p-butyl, quizalofop-p-ethyl, and sethoxidim at 28 DAT when evaluating the selectivity of different herbicides to the Alpinia purpurata (Vieill.) K.Schum., Strelitzia reginae Aiton, and Heliconia psittacorum L.f. ornamental monocotyledons. In general, the s-metolachlor, diuron, and diclosulam pre-emergent herbicides resulted in a low phytotoxicity to gladiolus, with values at 28 DAE similar to those of haloxyfop-p-methyl after 28 DAT and of the controls without herbicides (Table 1). Therefore, these pre-emergent herbicides could be considered selective to the gladiolus crop.

In the second season, the saflufenacil herbicide caused a phytotoxicity above 80% throughout the experimental period, whereas glyphosate, imazapyr+imazapic, and 2,4-D led to an intermediate phytotoxicity above 30% at 21 and 28 DAT (Table 1). Since the commercially acceptable phytotoxicity limit for gladiolus is 10%, the application of these herbicides is not recommended in this growing season (Richardson & Zandstra, 2006RICHARDSON, R.J.; ZANDSTRA, B.H. Evaluation of flumioxazin and other herbicides for weed control in gladiolus. Weed Technology, v.20, p.394-398, 2006. DOI: https://doi.org/10.1614/WT-05-031R2.1.
https://doi.org/10.1614/WT-05-031R2.1....
).

The control of monocotyledon weeds was above 90% at 28 DAT or DAE with the application of the haloxyfop-p-methyl, diclosulam, and s-metolachlor herbicides, but was slightly lower, 80% at 28 DAE, with that of diuron (Table 2). The DM obtained with the post-emergence application of glyphosate, imazapyr+imazapic, and haloxyfop-p-methyl did not differ in relation to that of the weeded check and was even similar to that of gladiolus plants when the latter herbicide was used (Table 4).

The predominant weed species were Lolium multiflorum Lam., Anagallis arvensis L., and Ipomoea triloba L. in the first season and I. tr iloba and Raphanus sativus L. in the second. In the untreated check in the second season, the DM of the monocotyledon species, mainly of L. multiflorum, was higher than that of the eudicotyledons (Table 4). Therefore, knowing the weed flora in each growing season is important for the production of floral stems, especially for All Souls’ Day, one of their main peaks of demand in Brazil (Becker et al., 2020BECKER, C.C.; STRECK, N.A.; UHLMANN, L.O.; SILVEIRA, W.B. Scheduling optimum planting window for gladiola based on El Niño Southern Oscillation. Scientia Agricola, v.77, e20180336, 2020. DOI: https://doi.org/10.1590/1678-992X-2 018-0336.
https://doi.org/10.1590/1678-992X-2...
). In this scenario, farmers should decide on the use of pre- and post-emergence herbicides that are selective to gladiolus, registered, and that exert control over this weed class.

In general, the tested post-emergent herbicides, except haloxyfop-p-methyl, promoted a superior control of eudicotyledon species compared with the weeded check (Table 5). This result confirms that found for the DM of eudicotyledons, whose lowest values were obtained with the application of saflufenacil, 2,4-D, glyphosate, and imapazyr+imazapic, which did not differ f rom each other and from the weeded check (Table 4). Freitas et al. (2007)FREITAS, F.C.L.; GROSSI, J.A.S.; BARROS, A.F.; MESQUITA, E.R.; FER REIR A, F.A.; BA RBOSA, J.G. Controle químico de brilhantina (Pilea microphylla) no cultivo de orquídeas. Planta Daninha, v.25, p.589-593, 2007. DOI: https://doi.org/10.1590/S0100-83582007000300019.
https://doi.org/10.1590/S0100-8358200700...
concluded that oxyfluorfen showed an effective control of 90% of the target species Pilea microphylla L., being selective to two orchid species – Epidendrum ibaguense Kunth and Dendrobium sp. This result is an indicative that, in addition to saflufenacil, other protoporphyrinogen oxidase inhibitors should be tested in gladiolus plants cultivated under Brazilian conditions in order to better understand the selectivity of these herbicides to the crop.

Table 5
Control of eudicotyledon weeds in gladiolus (Gladiolus x grandiflorus) at 7, 14, 21, and 28 days after crop emergence when pre-emergent herbicides were applied or after the application of post-emergent herbicides in the winter-spring and summer-autumn growing seasons of 2018 and 2019, respectively, in the municipality of Santa Maria, in the state of Rio Grande do Sul, Brazil(1).

In addition to their low phytotoxicity (Table 1), haloxyfop-p-methyl and the pre-emergent herbicides did not interfere with the growth and development of gladiolus plants, since no differences were observed between these treatments and the controls without herbicide application for FLN, phyllochron, and stem length (Table 3). However, further studies should be carried out using different rates and sites to confirm the results obtained both for phytotoxicity to gladiolus and the DM of the crop, important indicators of plant growth and development.

Contrastingly, the glyphosate, imazapyr+imazapic, and 2,4-D herbicides paralyzed the growth of gladiolus plants, stabilizing the FLN at approximately four leaves (Table 3) and, consequently, leading to higher phyllochron values, i.e., a longer interval between the appearance of sequential leaves on the stem. Moreover, the application of saflufenacil and glyphosate caused plant death and that of 2,4-D and imazapyr+imazapic, the deformation of leaves and floral stems, which made it impossible to evaluate the LAI and quality of floral stems at the R2 stage. These results are an indicative that these herbicides cannot be used in the management of weeds in the gladiolus crop.

Haloxyfop-p-methyl caused the lowest phytotoxicity to gladiolus at 7 and 14 DAT, with total plant recovery from this period onwards, not differing from the controls without herbicide application (Table 1). The diuron and s-metolachlor pre-emergent herbicides were also highly selective to gladiolus, showing a phytotoxicity of less than 5% at 28 DAE (Table 1), whereas glyphosate was not, causing a phytotoxicity above 80% at 28 DAT. Manuja et al. (2005)MANUJA, S.; RAM, R.; SINGH, R.D.; MUKHERJEE, D. Evaluation of different herbicides for protection of gladiolus (Gladiolus spp.) crop from weeds. Crop Protection, v.24, p.921-926, 2005. DOI: https://doi.org/10.1016/j.cropro.2005.01.019.
https://doi.org/10.1016/j.cropro.2005.01...
, however, found that Gladiolus spp. plants with chlorotic spots at 7 DAT due to the application of glyphosate completely recovered from this phytotoxic effect at 21 DAT. These different results could be attributed to the time of application of glyphosate, which was at 90 days after planting in Manuja et al. (2005)MANUJA, S.; RAM, R.; SINGH, R.D.; MUKHERJEE, D. Evaluation of different herbicides for protection of gladiolus (Gladiolus spp.) crop from weeds. Crop Protection, v.24, p.921-926, 2005. DOI: https://doi.org/10.1016/j.cropro.2005.01.019.
https://doi.org/10.1016/j.cropro.2005.01...
, when plants were more developed than at 50 days after planting in the present study.

The diclosulam and s-metolachlor pre-emergent herbicides and the glyphosate, imazapyr+imazapic, and haloxyfop-p-methyl post-emergent herbicides showed a control of monocotyledon weeds above 80% at 21 and 28 DAT or DAE, in both growing seasons (Table 2). For eudicotyledons, diclosulam, saflufenacil, 2,4-D, glyphosate, and imazapyr+imazapic stood out at 21 and 28 DAT, showing a control above 85% for this weed spectrum and not differing from the weeded check (Table 5). Of the herbicides with action on eudicots, diuron exerted the weakest control, which was below 40% at 28 DAE.

In the second growing season, eudicotyledon species were predominate in the untreated check, evidenced by their higher DM values compared with those of monocotyledons (Table 4). Therefore, chemical weed management in gladiolus plants between late summer and early autumn should prioritize selective pre- or post-emergent herbicides for the control of broad-leaved weeds.

Diclosulam and s-metolachlor caused greater reductions in the DM of monocotyledon and eudicotyledon weeds, not differing from the weeded check, which is in alignment with the results obtained for the control (Table 4). Regarding the post-emergent herbicides, saflufenacil, 2,4-D, glyphosate, and imazapyr+imazapic led to a lower DM of eudicot yledon weeds, whereas glyphosate, imazapyr+imazapic, and haloxyfop-p-methyl decreased the DM of monocotyledons, also not differing from the weeded check.

The application of imazapyr+imazapic and diclosulam resulted in a slower plant vegetative growth, evidenced by a longer phyllochron, lower FLN, and shorter stem length, as well as in a worse quality of floral stems, confirmed by a shorter spike length and lower final floret number compared with the weeded check (Tables 3 and 6). Saflufenacil and 2,4-D, however, did not differ from the weeded check regarding phyllochron, FLN, stem length, final floret number, and spike length, meaning that the initial phytotoxicity observed did not cause a greater damage to the production of floral stems. Furthermore, haloxyfop-p-methyl, diuron, and s-metolachlor did not affect plant growth since the values obtained for DM, FLN, phyllochron, and the LAI did not differ from those of the weeded check, allowing of the production of floral stems with an adequate quality for commercialization (Tables 3 and 4).

Table 6
Spike length (SPL), stem diameter (SD), and final floret number (FFN) of gladiolus (Gladiolus x grandiflorus) as a function of pre- and post-emergent herbicide application in the summer-autumn growing season of 2019, in the municipality of Santa Maria, in the state of Rio Grande do Sul, Brazil(1).

The LAI showed a positive linear relationship with the quality parameters of gladiolus flowers. The herbicide treatments that promoted higher values of this index were those that resulted in a longer stem length, a longer spike length, and a wider stem diameter (Table 3). Therefore, the lower values obtained for the LAI with the application of diclosulam and imazapyr+imazapic were related to a shorter stem length, shorter spike length, and narrower stem diameter, evidencing the importance of maintaining the leaf area for the growth and production of gladiolus flower stems and also of choosing selective herbicides that do not interfere negatively in this characteristic (Table 6). According to Silva et al. (2016)SILVA, D.F. da; PIO, R.; SOARES, J.D.R.; NOGUEIRA, P.V.; PECHE, P.M.; VILLA, F. The production of Physalis spp. seedlings grown under different-colored shade nets. Acta Scientiarum, v.38, p.257-263, 2016. DOI: https://doi.org/10.4025/actasciagron.v38i2.27893.
https://doi.org/10.4025/actasciagron.v38...
and Trachta et al. (2020)TRACHTA, M.A.; ZANON, A.J.; ALVES, A.F.; FREITAS, C.P. de O. de; STRECK, N.A.; CARDOSO, P. de S.; SANTOS, A.T.L.; NASCIMENTO, M. de F. do; ROSSATO, I.G.; SIMÕES, G.P.; AMARAL, K.E.F. do; STRECK, I.L.; RODRIGUES, L.B. Leaf area estimation with nondestructive method in cassava. Bragantia, v.79, p.472-484, 2020. DOI: https://doi.org/10.1590/1678-4499.20200018.
https://doi.org/10.1590/1678-4499.202000...
, larger leaf areas allow of a greater interception of solar radiation, favoring the production, through photosynthesis, of photoassimilates that are, then, allocated to the vegetative and reproductive organs of the plants, enabling their growth and development. Therefore, any factor that interferes with leaf area can affect plant yield, whether in the form of grains as commodities or floral stems as ornamental plants.

In addition to the plant protection products registered for gladiolus, the obtained results are an indicative that there are other active ingredients selective to the species and with a good efficiency in weed management. Although the active ingredients tested in the present study are not recommended specifically for gladiolus, these findings may support future work aiming to include this crop in the label of other products. However, further research needs to be carried out to confirm the behavior of the evaluated herbicides.

Conclusions

  1. The s-metolachlor and diuron herbicides applied at pre-emergence and haloxyfop-p-methyl at post-emergence are selective to gladiolus (Gladiolus x grandiflorus) regardless of the growing season and do not hinder crop growth and floral stem quality.

  2. S-metolachlor and haloxyfop-p-methyl promote an efficient control of monocotyledon weeds at pre-and post-emergence, respectively, in the winter-spring and summer-autumn cultivation of gladiolus plants.

  3. For cultivation in summer-autumn, the application of saflufenacil and 2,4-D causes phytotoxicity to gladiolus but does not affect the production of floral stems, controlling eudicotyledon weeds.

Acknowledgment

To Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), for financial support (process number 308942/2020-5).

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Publication Dates

  • Publication in this collection
    13 Mar 2023
  • Date of issue
    2023

History

  • Received
    02 June 2022
  • Accepted
    08 Nov 2022
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