Aspects of application technology, efficacy and selectivity of ACCase-inhibiting herbicides in chia cropAbstract
The research proposal was part of the evaluation of the application technology, control efficiency and selectivity of the chia crop (Salvia hispanica L.) subjected to sequential applications of herbicides inhibiting the enzyme ACCase. The experiment was conducted under field and in the laboratory conditions at the State University of the Midwestern Paraná State University (UNICENTRO), CEDETEG Campus, Guarapuava, Paraná, Brazil. The treatments consisted of the sequential application of clethodim (108 and 216 g ha-1), sethoxydim (184 and 368 g ha-1), tepraloxydim (200, 100 and 200 g ha-1), haloxyfop (48 and 96 g ha-1), fenoxaprop (110 and 220 g ha-1), quizalofop (120 and 240 g ha-1), fluazifop (250 and 500 g ha-1), weeded control and unweeded control. All herbicides were associated with the adjuvant mineral oil Assist™ (0.25 L ha-1) and sprayed with an application rate of 200 L ha-1. No significant differences were found between the treatments for the spray deposition of herbicides applied to crabgrass (Digitaria horizontalis). In chia, the average deposition of the treatments clethodim (216 g ha-1), sethoxydim (368 g ha-1), tepraloxydim, haloxyfop and fenoxaprop was 16.5% higher than the group of other herbicides. All herbicides were efficient for crabgrass, especially in sequential application, although they caused height reduction and more evident phytotoxicity symptoms in the crop in the second application (≤18%). However, only haloxyfop (48 and 96 g ha-1) and quizalofop (240 g ha-1) were not considered selective for sequential application in chia because they reduced grain yield by around 15.3% and 26.7%, respectively.
Keywords:
post-emergence; phytotoxicity; spray deposition; Salvia hispanica L
Resumo
A proposta de estudo se enquadrou na avaliação da tecnologia de aplicação, da eficiência de controle e seletividade da cultura da chia (Salvia hispanica L.) submetida a aplicações sequenciais de herbicidas inibidores da enzima ACCase. O experimento foi desenvolvido a campo e em laboratório na Universidade Estadual do Centro-Oeste, Campus CEDETEG, Guarapuava/PR. Os tratamentos foram constituídos pela aplicação sequencial de clethodim (108 e 216 g ha-1), sethoxydim (184 e 368 g ha-1), tepraloxydim (100 e 200 g ha-1), haloxyfop (48 e 96 g ha-1), fenoxaprop (110 e 220 g ha-1), quizalofop (120 e 240 g ha-1), fluazifop (250 e 500 g ha-1), controle mecânico das plantas daninhas e testemunha sem controle. Todos os herbicidas foram associados ao adjuvante óleo mineral Assist® (0,25 L ha-1), e pulverizados com taxa de aplicação de 200 L ha-1. Não foram encontradas diferenças significativas entre os tratamentos para a deposição dos herbicidas aplicados em capim-colchão (Digitaria horizontalis). Em chia, a deposição média dos tratamentos clethodim (216 g ha-1), sethoxydim (368 g ha-1), tepraloxydim, haloxyfop e fenoxaprop foi 16,5% superior ao grupo dos demais herbicidas. Todos os herbicidas foram eficientes para capim-colchão, principalmente em aplicação sequencial, apesar de causarem redução de altura e sintomas de fitointoxicação mais evidentes na cultura na segunda aplicação (≤18%). Entretanto, apenas haloxyfop (48 e 96 g ha-1) e quizalofop (240 g ha-1) não foram considerados seletivos para aplicação sequencial em chia por reduzirem a produtividade de grãos em torno de 15,3% e 26,7%, respectivamente.
Palavras-chave:
pós-emergência; fitointoxicação; depósito da aplicação; Salvia hispanica L
1. Introduction
Chia (Salvia hispanica L.), a seed crop belonging to the family Lamiaceae, originated in Mexico and northern Guatemala and has historically held nutritional importance for the peoples of Central America (Busilacchi et al., 2013). Its seeds contain several valuable compounds, including proteins, fiber, omega-3 fatty acids, and other lipids (Ayerza, 2010; Ayerza and Coates, 2011; Migliavacca et al., 2014; Knez Hrnčič et al., 2019). Chia is an annual plant that can reach up to 2 m in height. Its fruits are small (2 mm in length and 2 mm in diameter) and single-seeded. The seeds are characterized by variable coat color and irregular spots (Di Sapio et al., 2012). The plants have hollow stems and opposite, broad leaves. Low planting densities stimulate lateral branching, contributing to increased yield (Wojahn et al., 2018; Pereira et al., 2020).
This seasonal crop requires, on average, 800 to 900 mm of rainfall during the growth cycle. After establishment, it tolerates periods of water scarcity. Chia is considered a short-day plant, and temperatures should not exceed 33 °C to avoid compromising pollination. It is well-adapted to tropical and subtropical climates but sensitive to low temperatures, particularly frost (Ayerza and Coates, 2006; Jamboonsri et al., 2012; Pereira et al., 2020).
Given its valuable nutritional properties and growing use in food products in Brazil, the crop has gained importance in the state of Rio Grande do Sul, where it shows good adaptation to local climatic conditions (Zanatta et al., 2016). Weed management is a crucial practice in chia cultivation in the region. The first 45 days after crop establishment represent a critical period for preventing weed competition, as plant development is slow (Zavalia et al., 2011). However, chemical control of broadleaf and grass weeds remains challenging due to the crop's high sensitivity to post-emergence herbicides, which increases the risk of phytotoxicity. As a result, farmers either adopt higher planting densities to promote faster soil coverage and reduce weed infestation (Ayerza and Coates, 2006) or rely on manual weeding, which is costly and labor-intensive (Karkanis et al., 2018). This situation is aggravated by the scarcity of information on suitable herbicides for the crop. Studies have contributed to a better understanding of the biological factors influencing chia development (Schuelter et al., 2024).
Recent studies have contributed to expanding the knowledge regarding the adaptation and establishment of chia under Brazilian growing conditions. Costa et al. (2022) demonstrated that the physiological quality and germination performance of Salvia hispanica seeds can be influenced by strategies that mitigate water stress during the early stages of development.
The growing demand for sustainable agricultural systems has stimulated the adoption of biological technologies capable of improving plant performance and reducing dependence on conventional inputs. In this context, Nascimento et al. (2022) reported the potential of Trichoderma spp. as biological agents for promoting plant growth, enhancing nutrient utilization and contributing to disease suppression in agricultural systems.
In chia cultivation, weed interference can reduce both seed yield and quality. Despite the lack of technical information, chemical control may represent a viable strategy (Karkanis et al., 2018). For instance, herbicides that inhibit the enzyme acetyl-CoA carboxylase (ACCase) are promising candidates, as they are applied post-emergence, control grass species, and are selective for dicotyledonous crops (Vidal and Merroto Junior, 2001). Nevertheless, further studies are needed to better understand the efficiency and selectivity of ACCase-inhibiting herbicides, as well as to refine application technologies.
In light of these considerations, the objective of this study was to evaluate the application technology, weed control efficacy, and herbicide selectivity to chia (Salvia hispanica L.) following sequential applications of ACCase-inhibiting herbicides under edaphoclimatic conditions representative of southern Brazil.
2. Material and Methods
The experiment was conducted under field conditions in an experimental area of the Midwestern Paraná State University (UNICENTRO), CEDETEG Campus, Guarapuava, Paraná, Brazil (25°23′07.5″S 51°29′45.2″W, 1022 m a.s.l.) (Figure 1). The soil is classified as a typical dystrophic Brown Latosol with a clayey texture (Santos et al., 2025). Physicochemical analysis showed the following characteristics: pH in CaCl2 4.99, 4.93 cmolc dm-3 potential acidity (H+ + Al+3), 3.98 cmolc dm-3 Ca+2, 1.73 cmolc dm-3 Mg+2, 0.15 cmolc dm-3 K+, 2.99 mg dm-3 P (Mehlich), and 41.18 g dm-3 C. Texture analysis revealed that the soil contained 580 g kg-1 clay, 260 g kg-1 silt, and 160 g kg-1 sand. The climate is classified as humid subtropical mesothermal (Cfb) in the Köppen climate classification, being characterized by cool summers, winters with frequent and severe frosts, and no defined dry season (Aparecido et al., 2016). The mean annual maximum temperature is 23.5 °C, and the mean annual minimum temperature is 12.7 °C (Nitsche et al., 2019).
Location of the experimental site at the Midwestern Paraná State University (UNICENTRO). CEDETEG Campus. Guarapuava. Paraná. Brazil.
Climatological data were obtained from the UNICENTRO weather station located on the CEDETEG Campus, approximately 150 m from the experimental site (Figure 2).
Climatological data during the experimental period. UNICENTRO weather station. CEDETEG Campus. Midwestern Paraná State University (UNICENTRO). Guarapuava. Paraná. Brazil. 2018/2019.
The experimental design was a randomized block design consisting of 16 treatments with 10, 4, 4 and 5 replicates for the variables spray deposition, weed control, yield components of selectivity and physicochemical characteristics of herbicide solutions, respectively. The experimental units consisted of plots with a total area of 10.0 m2 (2.5 × 4.0 m). Border rows were excluded from analysis.
The treatments consisted of sequential application of the herbicides clethodim (108 and 216 g ha-1), sethoxydim (184 and 368 g ha-1), tepraloxydim (200, 100 and 200 g ha-1), haloxyfop-p-methyl (48 and 96 g ha-1), fenoxaprop-p-ethyl (110 and 220 g ha-1), quizalofop-p-tefuryl (120 and 240 g ha-1), fluazifop-p-butyl (250 and 500 g ha-1), weed control by mechanical weeding and without control. All herbicide applications were associated with the adjuvant mineral oil Assist™ (0.25 L ha-1), and carried out with the aid of a knapsack sprayer, equipped with ADGA110.015 nozzles and a spray volume of 200 L ha-1.
Chia was sown manually on November 18, 2018, following conventional soil preparation by plowing and harrowing. Row spacing was 0.5 m, with a density of 160,000 plants ha-1. Basal fertilization consisted of 300 kg ha-1 04-14-08 NPK fertilizer. Additionally, 100 kg ha-1 urea was applied at 25 days after emergence.
Herbicide applications were performed post-emergence using a backpack sprayer equipped with four ADGA 110.015 nozzles operated at 210 kPa, 3.6 km h-1, and 200 L ha-1. Meteorological conditions during the first (January 11, 2019, from 13h:10min to 13h:55min) and the second (February 1, 2019, from 16h:15min to 16h:50min) applications were recorded using a portable digital thermo-hygro-anemometer. Mean values were as follows: air temperature of 26.1 and 27.4 °C, relative humidity of 69.4% and 63.2%, and wind speed of 2.8 and 2.2 km h-1 for the first and second applications, respectively.
A tracer dye was added to the spray solution and subsequently recovered from two target plants. Evaluations were performed on one tiller of a control weed (Digitaria horizontalis, commonly known as crabgrass) and six fully expanded leaves of chia plants randomly selected in the upper and middle portions of the plant. At the first application, crabgrass had four tillers per plant and a density of 8 plants m-2. Following application, crabgrass and chia samples were washed separately with 20 and 60 mL of distilled water, respectively, in plastic bags under constant agitation for 20 seconds. The amount of deposited tracer was quantified by spectrophotometry. Absorbance was measured at 630 nm, and quantification (g L-1) was achieved against a standard curve, following the methods described by Souza et al. (2007) and Maciel et al. (2014a, b, 2019). The washed samples were then placed in paper bags and dried in a forced-air oven at 65 °C for 72 h. Deposition values are expressed as µL g-1 dry matter.
Phytotoxicity symptoms were evaluated in chia crops and the crabgrass control at 7, 14, 21, and 28 days after the first and second applications (DAA). Evaluations were performed using a visual rating scale according to the method described by the Brazilian Weed Science Society (SBCPD, 1995), in which 0% indicates absence of symptoms and 100% indicates plant death. In addition, the variables chlorophyll content (SPAD index) and electron transport rate (ETR; μmol m-2 s-1) in chia leaves were evaluated using a Y (II) fluorometer meter (OPTI-SCIENCES, Hudson, USA) at 7, 14, 21 and 28 days after the second application (DAA2) and a SPAD-502 chlorophyll meter (KONICA MINOLTA, Japan), at 14 and 28 days after the first application, and at 21 DAA2.
Plant height was measured at 14 and 28 days after the first application and at 28 days after the second application (DAA). Measurements were taken from the ground surface to the insertion point of the last fully expanded leaf. number of branches per plant (NB) and number of inflorescences per plant (NI), hundred seed weight (HSW) and seed yield (SY) were also determined. Seed yield is expressed as kg ha-1.
In the laboratory, physicochemical properties of herbicide spray solutions were also assessed, including pH, electrical conductivity and static surface tension, immediately after solution preparation. In the laboratory, the physicochemical properties of the herbicide solutions were also evaluated, immediately after preparation, using a completely randomized design, with 15 treatments and 3, 3 and 10 replications, respectively, for the variables hydrogen potential (pH), electrical conductivity and static surface tension. Static surface tension was measured according to the methodology described by Maciel et al. (2010; 2014b) and Hama et al. (2018), by weighing droplets formed at the tip of a burette positioned over an analytical balance (precision 0.001 mg) within 25-30 seconds. Solution pH and electrical conductivity were determined using digital pH and conductivity meters.
Data were tested for normality (Shapiro-Wilk) and homogeneity of variances (Hartley’s test). Analysis of variance (ANOVA) was performed using the F-test, and means were compared using the Scott-Knott clustering test (p ≤ 0.05) with the Sisvar™ software (Ferreira, 2011). Physicochemical properties, spray deposition, and electron transport rate (ETR) were also presented as bar charts with 95% confidence intervals (CI 95%) at p < 0.05. Treatments were considered statistically different when confidence intervals did not overlap (Cumming et al., 2004; Concenço et al., 2018).
3. Results and Discussion
3.1. Physicochemical characteristics of spray solutions
Regarding the physicochemical characteristics of the spray mixtures, all herbicide solutions, regardless of the dose, showed foam on the surface of the liquid after agitation, and the lowest amounts formed soon after preparation and that persisted in the solution for a longer time were observed for sethoxydim and haloxyfop-p-methyl (Figure 3a). Clethodim, tepraloxydim, fluazifop and quizalofop-p-tefuryl, especially in the highest doses, showed the highest amount and persistence of foam over the time of the evaluations. Foaming in herbicide mixtures is not a desirable characteristic, and can cause problems with overflows, dose errors, product waste and application failures, as well as prolong the preparation time of the mixture, when waiting for it to dissipate (Maciel et al., 2010).
Physicochemical characteristics of the foam volume evaluated between 0 to 30 minutes (min) after stirring the mixtures (a). static surface tension (ST) (b). potential of hydrogen (pH) and electrical conductivity (c) of the different doses of herbicides spray solutions with the adjuvant Assist™ (0.5 L ha-1). Bars represent 95% confidence intervals. Different letters represent significant differences by the Scott-Knott test (p ≤ 0.05) and CV% confidence interval. The numbers in parentheses represent the herbicide rate in g ai ha-1. Guarapuava. Paraná. Brazil.
All herbicides of the chemical group cyclohexanediones (clethodim, sethoxydim tepraloxydim), with the exception of sethoxydim (184 g ha-1) (pH 5.2), presented pH values of the solutions with average indices between 3.6 and 4.8, lower than the herbicides of the aryloxyphenoxypropionate group (haloxyfop-p-methyl, fenoxaprop-p-ethyl, quizalofop-p-tefuryl, ), which, with the exception of quizalofop-p-tefuryl (240 g ha-1) (pH 5.2), resulted in pH between 5.6 and 6.6 (Figure 3b). However, for the electrical conductivity of the solutions, this trend of grouping of results that occurred with pH was not observed. All higher doses provided a significant increase in electrical conductivity, and the herbicides that stood out with the highest values, regardless of the dose, were in decreasing order fenoxaprop-p-ethyl, quizalofop-p-tefuryl and tepraloxydim
It is important to note that based on the best chemical stability and leaf absorption/penetration of ACCase (Acetyl-CoA Carboxylase) inhibitor herbicides, the ideal pH range of the spray solution is generally slightly acidic, between 4.0 and 6.0 (Wills and McWhorter, 1989; Rodrigues and Almeida, 2018). In addition, Maciel et al. (2010) and Cunha et al. (2017) also demonstrated the potential to reduce the pH of the mineral oil solution used in this work, as well as other research results mentioning an increase or variations in the electrical conductivity of different aqueous solutions, depending on the adjuvant used (Cunha and Alves, 2009; Cunha et al., 2010).
For the surface tension of the solutions, no significant changes were observed among the herbicides, regardless of the dose, reaching average levels of 38.6 to 40.6 mN m-1, values only lower in relation to water (72.6 mN m-1) (Figure 3c). The reduction of surface tension and, consequently, of the angle of contact of the droplets with the surfaces, usually has a positive correlation with the scattering of the droplet, increasing the deposit and coverage of the target (Decaro Júnior et al., 2015, Costa et al., 2020).
3.2. Spray solution deposition on crabgrass and chia crop plants
No significant differences were observed among treatments of spray deposition on crabgrass (Figure 4a). Similarly, based on the confidence interval, no differences in spray deposition were detected between rates of the same herbicide for this species. By contrast, for chia (Figure 4b), two distinct groups of spray deposition were observed. Treatments with 216 g ha-1 clethodim, 368 g ha-1 sethoxydim, tepraloxydim (100 and 200 g ha-1), haloxyfop-p-methyl (48 and 96 g ha-1) or fenoxaprop-p-ethyl (110 and 220 g ha-1) showed higher deposition values than those based on 108 g ha−1 clethodim, 184 g ha-1 sethoxydim, quizalofop-p-tefuryl (120 and 240 g ha-1) or fluazifop-p-butyl (250 and 500 g ha-1). Comparison of confidence intervals between rates of the same herbicide revealed that only sethoxydim exerted a rate-dependent effect, with the low rate resulting in reduced deposition compared with the high rate.
Spray solution deposition on Digitaria horizontalis (a) and chia crop plants (b) following the first herbicide application. Bars represent 95% confidence intervals. Different letters represent significant differences by the Scott-Knott test (p ≤ 0.05) and CV% confidence interval. The numbers in parentheses represent the herbicide rate in g ai ha-1. Guarapuava. Paraná. Brazil.
According to Lost and Raetano (2010) and Godinho Junior et al. (2015), adjuvants modify the physicochemical properties and droplet dynamics of spray solutions. Therefore, when analyzing spray deposition, it is important to consider that target characteristics, as well as interactions between adjuvant and herbicide formulations, can distinctly influence deposition performance. Roman et al. (2007) and Azevedo (2011) reported that most ACCase-inhibiting herbicides applied post-emergence are recommended to be used in conjunction with agricultural oil to enhance their activity. Among the herbicides evaluated, only fluazifop-p-butyl (Fusilade™ 250 EW) does not technically require the addition of adjuvants (Rodrigues and Almeida, 2018), as it is formulated as an oil-in-water emulsion (EW). Due to its high stability, it is designed to be readily diluted in the spray mixture.
3.3. Crabgrass control
The control efficiency of crabgrass ranged from 30% to 38.5% at 7 days after the first application (DAA), with the best results obtained with haloxyfop-p-methyl (48 and 96 g ha-1) and fenoxaprop-p-ethyl (110 g ha-1) (Table 1). At 14 DAA, control levels remained unsatisfactory (≤64%). However, higher efficacy values, indicating faster herbicide activity, were again observed for haloxyfop-p-methyl (96 g ha-1) and fenoxaprop-p-ethyl (110 and 220 g ha-1). At 21 DAA, although most treatments achieved at least 64% control (minimum observed for clethodim at 108 g ha-1), the highest efficacy levels were obtained with haloxyfop-p-methyl (96 g ha-1), quizalofop-p-tefuryl (240 g ha-1), fluazifop-p-butyl (500 g ha-1), and sethoxydim (368 g ha-1), with control values of 79.0%, 74.0%, 73.5%, and 72.3%, respectively.
Control (%) of the weed crabgrass (D. horizontalis) at 7. 14. 21. and 28 days after the first (DAA) and second applications (DAA2) of the post-emergence herbicides on chia crops. Guarapuava. Paraná. Brazil.
At 28 DAA, haloxyfop-p-methyl (96 g ha-1), 240 g ha−1 quizalofop-p-tefuryl, fenoxaprop-p-ethyl (110 g ha-1), fluazifop-p-butyl (250 and 500 g ha-1), and sethoxydim (184 and 368 g ha-1) were highly effective in controlling crabgrass (≥95.3%), not differing significantly from the weeded control (Table 1). Additionally, 216 g ha-1 clethodim and 120 g ha-1 quizalofop-p-tefuryl provided satisfactory control (≥80.0%), according to SBCPD (1995) criteria. Barroso et al. (2010), in studying the efficacy of ACCase-inhibiting herbicides against Digitaria ciliaris, reported that only clethodim (84 g ha-1), tepraloxydim (100 g ha-1), haloxyfop-methyl (60 g ha-1), and fluazifop-p-butyl (500 g ha-1) achieved effective control (≥90%) at 29 days. On the other hand, clethodim + quizalofop-p-ethyl (48 + 40 g ha-1) and clethodim + fenoxaprop-p-ethyl (50 + 50 g ha−1) showed satisfactory control (≥80.0%).
At 7 days after the second application (DAA2), the same herbicide treatments that had shown high efficacy in controlling crabgrass at 28 days after the first application maintained their performance and did not differ from the weeded control, surpassing fenoxaprop-p-ethyl (220 g ha-1) and the other treatments, which achieved only satisfactory control. At 14 DAA2, almost all treatments reached high efficacy (≥93.5%) or complete weed control (Table 1), with only clethodim (108 g ha-1), tepraloxydim (100 g ha-1), and haloxyfop-p-methyl (48 g ha-1) performing satisfactorily (≥80.0%), according to SBCPD criteria (1995). At 21 DAA2, although all treatments showed high control efficiency, clethodim (108 g ha-1) and haloxyfop-p-methyl (48 g ha-1) still had slightly lower values (94.0% and 93.3%, respectively) in relation to the weeded control. All treatments achieved maximum control of crabgrass at the 28 DAA2.
3.4. Visual phytotoxicity, chlorophyll content and electrons transport rate of the chia plants
Mild symptoms of phytotoxicity were observed in chia plants at 7 DAA for all treatments, with quizalofop-p-tefuryl (240 g ha-1) and fluazifop-p-butyl (250 and 500 g ha-1) resulting in the highest levels of visual damage (5.8%) (Table 2, Figures 3 and Figure 5). From 14 DAA onward, no symptoms were observed for most herbicides, with only slight phytotoxicity (<4.0%) recorded for haloxyfop-p-methyl (96 g ha-1) and fluazifop-p-butyl (250 and 500 g ha-1). However, generalized chlorosis was observed at 7 DAA2, with injury levels ranging from 10% to 18%, particularly in the apical region (areas of active growth) and adjacent leaves. These symptoms were more intense along leaf margins. At 14 DAA2, chlorosis persisted at a lower intensity, without progression to tissue necrosis. The highest injury levels were observed for haloxyfop-p-methyl (48 and 96 g ha-1) and fluazifop-p-butyl (250 and 500 g ha-1). From 21 DAA2 onward, the phytotoxic symptoms were no longer observed in chia plants, except for the aforementioned treatments. Similar to the present study, Rojas (2013) reported chlorosis symptoms of up to 26% in chia plants subjected to post-emergence application of quizalofop-p-ethyl (130 g ha-1). In contrast, Cazares et al. (2015) did not observe phytotoxicity in chia subjected to fluazifop-p-butyl at doses of 750 and 1500 g ha-1.
Phytotoxicity symptoms in chia plants submitted to sequential application of ACCase inhibitor herbicides in the post-emergence of the crop at 7. 14. 21. and 28 days after the first (DAA) and second applications (DAA2). Guarapuava. Paraná. Brazil.
Phytotoxicity symptoms in chia crop plants of chia submitted to sequential application of ACCase inhibitor herbicides in the post-emergence of the crop. The numbers in parentheses represent the herbicide rate in g ai ha-1. Guarapuava. Paraná. Brazil.
The selectivity of the herbicides that act by inhibiting the ACCase enzyme (acetylcoenzyme A carboxylase) for dicotyledonous plants is due to the presence of prokaryotic (chloroplast) and eukaryotic (cytoplasm) ACCAse, unlike monocotyledons that only have eukaryotic ACCase, in the herbicide site of action (Sasaki et al., 1995; Shaner, 2014). Similar to the behavior of absence of injuries or only mild symptoms of discoloration/chlorosis, especially of the younger chia leaves, they have also been described in other annual eudicotyledon species, such as soybean, bean, castor bean and peanut (Barroso et al., 2010, Maciel et al., 2011; Dourado Neto et al., 2013; Marchioretto and Magro, 2017).
For the chlorophyll content (SPAD index) in chia leaves, significant reductions were observed at 7 DAA2 for all herbicides in relation to the controls, and this behavior was maintained only for haloxyfop-p-methyl (48 and 96 g ha-1), fenoxaprop-p-ethyl (110 and 220 g ha-1) and fluazifop-p-butyl (250 and 500 g ha-1) up to 7 DAA2 (Table 3). From the 21 DAA2 onwards, no significant differences were found between treatments for this variable.
Chlorophyll content (SPAD) and electrons transport rate (ETR) of chia plants submitted to sequential application of ACCase inhibitor herbicides in the post-emergence of the crop. Guarapuava. Paraná. Brazil.
Regarding the electron transport rate (ETR) in chia plants, significant reductions were observed at 14 days after the first application (DAA) for the grouping of treatments composed of the highest doses of clethodim and quizalofop, as well as the two doses of haloxyfop and fluazifop, which was on average 7.6% lower than the grouping constituted by the treatments belonging to the controls without application (Table 3). At 28 DAA, with the exception of the lowest doses of tepraloxydim (100 g ha-1) and quizalofop-p-tefuryl (120 g ha-1), which showed ETR similar to the controls, all the other herbicide treatments formed a group that, on average, was still characterized by a 12.7% reduction in photosynthetic activity. ETR levels were again evaluated at 21 DAA2 and identified only for clethodim (216 g ha-1), haloxyfop-p-methyl (48 and 96 g ha-1) and quizalofop-p-tefuryl (240 g ha-1) mean ETR values lower than the other treatments.
3.5. Plant height and production components of the chia plants
In general, herbicide treatments decreased plant height compared with the untreated control at 28 DAA and at 28 days after the second application (DAA2) (Table 4). Although height reduction was small at 28 days after the first application compared with the weeded control, this effect persisted up to 28 DAA2. Furthermore, it was generally more pronounced for fluazifop-p-butyl and tepraloxydim treatments, regardless of rate. Rojas (2013) also reported reduced plant height in chia following application of quizalofop-p-ethyl (130 g ha-1). By contrast, Karkanis et al. (2018) observed that post-emergence application of fluazifop-p-butyl (125 g ha-1) did not significantly affect plant height or biomass in experiments conducted at two locations in Greece.
Plant height and production components represented by branch number (BN). inflorescence number (IN). hundred seed weight (HSW) and seed yield (SY) of chia submitted to sequential application of ACCase inhibitor herbicides in the post-emergence of the crop. Guarapuava. Paraná. Brazil.
It is important to emphasize that, for the height of chia plants, regardless of the action of the herbicides, it was detected that the vegetative growth was expressive, reaching an average of 1.77 m at 28 DAA2, as well as values close to 2.00 m at harvest. Similar results were reported by Pereira et al. (2020) and Grigolo et al. (2025) in research carried out in the western and southwestern Paraná, unlike Wojahn et al. (2018), in research conducted in the northwest region of Rio Grande Do Sul, where the plants reached smaller stature.
Regarding branch number, all herbicide treatments and the weeded control differed from the non-weeded control, exhibiting 17.5% and 14.9% higher values, respectively (Table 3). For inflorescence number, only fluazifop-p-butyl (125 and 250 g ha−1) and the non-weeded control reduced this variable, by 20.5% and 45.5%, respectively, compared with the weeded control (Table 4). Similar results were reported by Rojas (2013), who observed that quizalofop-p-ethyl (130 g ha−1) did not negatively affect the number of nodes, branches, or inflorescences in chia plants compared with the weeded control.
No significant differences in hundred seed weight were observed among herbicide treatments and controls (Table 4). Haloxyfop-p-methyl (48 and 96 g ha−1) and quizalofop-p-tefuryl (240 g ha−1) significantly reduced seed yield, with mean reductions of 14.4%, 16.3%, and 26.7%, respectively, compared with the weeded control (Table 3). Similar reductions in chia yield were reported by Pozo (2010) and Rojas (2013) for haloxyfop-p-methyl and quizalofop-p-tefuryl.
It should be noted that, although the level of weed crabgrass (D. horizontalis) infestation was considered low (8 plants m−2), chia seed yield decreased by 24.9% in the presence of weeds under the soil and climate conditions of Guarapuava, Paraná, Brazil. This reduction underscores the need for effective weed management targeting species of Poaceae, as most of the ACCase-inhibiting herbicides evaluated here showed promise in chia cultivation.
4. Conclusions
No significant differences were observed in spray deposition on crabgrass among the herbicides. In contrast, in chia plants, treatments with clethodim (216 g ha−1), sethoxydim (368 g ha−1), tepraloxydim, haloxyfop-p-methyl, and fenoxaprop-p-ethyl resulted in an average spray deposition 16.5% higher than that observed for the group formed by the remaining herbicides.
All herbicides were effective in controlling crabgrass and also reduced plant height and caused some level of visual phytotoxicity in the crop (≤18%), particularly under sequential application.
Sequential application of haloxyfop-p-methyl (48 and 96 g ha−1) and quizalofop-p-ethyl (240 g ha−1) in chia was not considered selective, as grain yield was reduced by approximately 15.3% and 26.7%, respectively.
Acknowledgements
This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Finance Code 001) and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) - Process Nº 302923/2022-5 - Research productivity grant - Call CNPq Nº 09/2022.
Data Availability Statement
The research data is available upon prior request via email to the corresponding author.
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