1.Introduction

Soybean (Glycine max L. Merrill) has been the main crop to contribute to the increase in area and grain production in Brazil and worldwide. Projections from the U.S. Department of Agriculture (USDA, 2024) estimate a total production of 399 million tons for the 2023/2024 global harvest. In Brazil, the production is estimated to reach 157 million tons (USA, 2024). One of the main factors that can reduce soybean productivity is the presence of weeds, among which horseweed (Conyza bonariensis) stands out. Field experiments conducted in Brazil indicated that just one C. bonariensis plant m^-2 can reduce soybean productivity by up to 25.9%, depending on the cultivar used (Agostinetto et al., 2017).

Horseweed belongs to the Asteraceae family and is a monoecious weed propagated exclusively by seeds. It presents closed capitula during pollination, with an average of 4% cross-pollination (Shields et al., 2006). It has an annual or biannual cycle, and can produce more than 200 thousand seeds per individual (Bhowmik, Ekech, 1993). The small seeds are composed of papillus, which facilitate their dispersal, and can reach more than 550 kilometers away from the mother plant (Shields et al., 2006). Once in the soil, the horseweed seeds can remain viable for up to three years, ensuring multiple emergency flows throughout different crops and growing season. This germination depends on the seed burial depth and soil and climate conditions (Vargas et al., 2018). Preventing the production and germination of weed seeds is a viable strategy for reducing the spread of difficult-to-control species (especially herbicide-resistant), frequently used in integrated pest management (Schaeffer et al., 2020).

Plants from this genus have become one of the main problems linked to weed management in Brazil and worldwide, due to their high aggressiveness and seed production (Bajwa et al., 2016). Furthermore, some horseweed species present biotypes that are herbicide-resistant to different mechanisms of action, such as: inibitors of the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPs), acetolactate synthase (ALS), photosystems I and II (PSI and PSII) and Protoporphyrinogen Oxidase inhibitors (PPO); in addition to biotypes that have multiple resistance to EPSPs+ALS, EPSPs+ALS+PSI and EPSPs+PSI+PPO+PSII+auxin inhibitors (Heap, 2024).

Herbicide-resistant horseweed plants, once uncontrolled in the field, will be able to complete their life cycle, replenishing the seed bank, and possibly resulting in the propagation of these genotypes in future crops and adjacent areas. Therefore, strategies aiming at reducing the feeding process of soil seed bank are crucial for preventing the spread of herbicide-resistant genotypes (Schaeffer et al., 2020; Heap, 2024). This process can occur via a reduction in the production of new seeds or by making their germination unfeasible. In Australia and the United States of America, a non-chemical strategy has been used in recent years, which consists of the mechanical destruction of seeds during harvest (Walsh et al., 2013). Alternatively, the reduction in seed production and viability can also be achieved through the use of herbicides, when applied at the correct time in the weed’s life cycle (Piasecki et al., 2019). However, as the flowering of the weed community occurs after the crop emergence, there is limited availability of herbicides to be used, being restricted to the product’s selectivity to the crop.

The transgenic event DAS-44406-6 (Enlist E3™, Corteva^® Agriscience), which was recently launched in Brazil (Silva et a., 2021), guarantee glyphosate-, glufosinate- and 2,4-D-tolerance to soybean plants. This process is conferred by a double mutation in the enzyme 5-enolpyruvylshikimate- 3-phosphate synthase (2MEPSPS – for glyphosate-tolerance), phosphinothricin acetyltransferase (PAT – for glufosinate-tolerance) and aryloxyalkanoate dioxy-genase-12 (AAD-12 – for 2,4-D-tolerance) (Lepping et al., 2013). With the development of soybean cultivars tolerant to auxinic herbicides (dicamba and 2,4-D), there will be the possibility of applying molecules with these mechanisms of action in the crop’s post-emergence.

Therefore, we hypothesize that horseweed biotypes exposed to these herbicides will reduce seed production and/or germination. Furthermore, mixing these herbicides with glyphosate will possibly enhance this inhibitory effect on horseweed plant seeds. Thus, the objective of this research was to evaluate the production, germination and morphological characteristics of seeds from different horseweed biotypes, which were subjected to the application of auxinic herbicides, alone or in mixture with glyphosate, at different phenological stages.

2.Material and Methods

2.1 Greenhouse experiment

Two experiments were conducted under semi-controlled conditions (one for each horseweed biotype), in a greenhouse, at the Federal University of Paraná – UFPR, located in Curitiba-PR (25º24’44.75”S and 49º14’52.42”W). Inside the greenhouse, the light incidence with a 12-hour photoperiod was guaranteed by the presence of high-pressure metal vapor lamps. Both experiments were carried out without water restrictions, with daily irrigation. To this end, horseweed (C. bonariensis) seeds were collected in an environmental protection area free from the application of herbicides at the Canguiri Experimental Farm (biotype Canguiri hereafter; collection carried out in June 2020), located in Pinhais-PR (25º23’13.9” S and 49º07’36.01” W). Another seed collection was carried out in a commercial grain production area located in Palotina-PR (24º20’03.55” S and 53º49’23.69” W) (biotype Palotina hereafter; collection carried out in June 2021), with reports of failure in weed control using glyphosate. After collection, the seeds were stored in paper bags at room temperature. The collected seeds were deposited in a mixture of soil and horticultural substrate (Plantmax^®) in a 1:1 ratio in germination trays. When the plants had approximately three leaves, each seedling was singularly transplanted into a five-liter pot containing soil with the following chemical characteristics: pH in water = 4.8; Ca = 8.4 cmol_c dm^-3; Mg = 4.9 cmol_c dm^-3; Al = 0.1 cmol_c dm^-3; H+Al = 8.4 cmol_c dm^-3; CEC = 21.62 cmol_c dm^-3; SMP pH = 5.3; P resin = 7.0 mg dm^-3; K = 0.12 cmol_c dm^-3 and base saturation (%BS) of 61%, with physical characteristics of humic dystrophic Red-Yellow Latosols with clayey texture. In both experiments, a completely randomized experimental design was used, organized in a 10x3 factorial scheme, with 4 replications. The first factor consisted of the application of four auxinic herbicides, alone or in mixture with glyphosate, a treatment with glyphosate alone (Glizmax^®, 648 g L^-1 ae, Corteva^® Agriscience, São Paulo) at a dose of 648 g ha^-1 ae, and a control without herbicide application. The herbicides used were: 2,4-D (DMA^® 806 BR, 670 g L^-1 ae, Corteva^® Agriscience, São Paulo) at a dose of 806 g ha^-1 ae; dicamba (Atectra^®, 480 g L^-1 ae, Basf^® S.A., São Paulo), at a dose of 480 g ha^-1 ae; triclopyr (Triclon^®, 480 g L^-1 ae, UPL^® do Brasil, Itupevara), at a dose of 480 g ha^-1 ae; and halauxifen-methyl+diclosulam (Paxeo^®, 110.33 g kg^-1 ae + 580 g kg^-1 ae, Corteva^® Agriscience LLC, United States) at a dose of 44 g ha^-1 ae. The herbicide Paxeo^® was used even though it had diclosulam in its commercial formulation, as there was no disponibility of isolated halauxifen-methyl in Brazil when the first experiment took place (June 2020). The second factor consisted of different stages of plant development at the time of application, as follows: ~6 leaves (early vegetative hereafter); ~20 leaves (late vegetative hereafter); and ~40 leaves with the beginning of the reproductive stage (early reproductive hereafter), marked by the emission of floral buds, prior to anthesis.

For both experiments, herbicide applications were carried out in an open area, using a backpack sprayer with constant pressure (CO₂), equipped with a one meter bar and two spray tips (AIXR 11002VP, TeeJet^® Technologies) regulated to a tank volume of 150 L ha^-1. After the applications, visual assessments of horseweed plant control were conducted at 42 days after application (DAA), using a scale from 0 to 100%, where 0% represented plants without symptoms and 100% represented plant death (SBCPD, 1995). Horseweed plants that reached physiological maturity had their seeds collected manually over 42 days (considering the cycle of the biotypes used, the first collection began approximately 150 days after transplanting the seedlings into the pots). These seeds were stored in paper bags at a controlled temperature of 4 °C for 60 days to overcome dormancy and then used to evaluate seed production per plant and seed germination.

2.2 Experiment at field conditions

A third experiment was conducted in field conditions, at the Campos Gerais Agricultural Experimental Station – EEACG, located in Palmeira-PR (25º25’40.33”S and 50º03’17.21”W) in January 2021, with the occurrence of horseweed (C. bonariensis) (Palmeira biotype hereafter). The area had a history of grain cultivation, with crop rotation of soybeans, corn and beans. The climate is humid subtropical, according to the Köppen classification. The average temperatures and precipitation during the experiment are shown in Figure 1.

A completely randomized experimental design was used, organized in a 10x2 factorial scheme, with 4 replications, in plots with 2 x 2 meters. The first factor consisted of treatments with the same herbicides that were used in the greenhouse experiments. The second factor consisted of two stages of horseweed development: ~10 leaves (late vegetative hereafter); and ~70 leaves with the beginning of the reproductive stage (early reproductive hereafter), marked by the emission of floral buds, prior to anthesis. For each plot, four plants were selected (according to the growth stage), marked with tape, and manually isolated by removing surrounding plants with a hoe immediately before herbicide application. For the application of herbicides, the visual assessment of plant control, seeds collection and storage, were conducted using the same methodologies previously described.

2.3 Analysis of seed production and germination

For all three experiments, 60 days after seed collection, samples from each horseweed plant (different days of collection) were homogenized, cleaned and weighed to determine the total seeds weight, after weighing on an precision analytical balance. Then, the weight of one thousand seeds (WTS) was determined and the number of seeds produced per plant was estimated. The WTS was obtained through the random counting of 1,000 horseweed seeds (4 x 250), using a magnifying glass with forty times magnification and tweezers, followed by determining the weight on a precision scale (Piasecki et al., 2019).

For the germination tests, 100 horseweed seeds were used (4 replications of 25 seeds), randomly selected, with the aid of a magnifying glass with a forty-fold magnification and tweezers. Prior to sowing, horseweed seeds were soaked for 24 hours in distilled water at room temperature. In the test, the seeds were distributed on two sheets of germitest paper, placed in a germination box (12 cm x 12 cm) with the sheets moistened with distilled water equivalent to 1.5 times their dry weight. The evaluations were carried out in a BOD (Biochemical Oxygen Demand) germination chamber, with a 24-hour photoperiod of light, at 25 °C with a luminous flux of 1,300 lux. These conditions were determined based on previous studies (data not shown). Two germination counts were carried out; one at 7 and another at 14 days after the test had started, for determining the total percentage of germination in each count. Then, the calculation of reduction in germination was carried out in relation to the control without application. The extrusion of the radicle and/or coleoptile was considered to be a germinated seed (Ministério da Agricultura, Pecuária e Abastecimento, 2009).

2.4 Statistical analysis

The data were subjected to analysis of variance (ANOVA) using the F test, at a 5% probability level (p<0.05) using the PROC GLM procedure in SAS (version 9.3, SAS Institute, Cary, NC). When significant, orthogonal contrasts (p<0.05) were used to compare mixtures and groups of herbicides for each phenological stage of horseweed, separately. The groups of treatments chosen for the comparison between the contrasts were based on soybean genotypes resistant to the herbicides 2,4-D and dicamba, recently commercialized.

3.Results and Discussion

3.1 Control efficacy

In the experiments with the Canguiri and Palotina horseweed biotypes, herbicide applications at the early vegetative stage resulted in 100% plant control, regardless the herbicides used (Tables 1 and 2). At the late vegetative stage for the Canguiri biotypes, glyphosate alone showed higher control efficacy (90%) compared to the auxinic herbicides alone (43.2%) (Table 1). However, the combination of glyphosate with auxinic herbicides provided higher control (94.1%) when compared to glyphosate alone (Table 1). For horseweed plants at advanced stages of development, auxinic herbicides applied alone did not provide satisfactory control, but the additive effect of glyphosate enhanced the efficacy of auxinic herbicides (Table 1), which was also reported by Soares et al. (2012). The average control provided by 2,4-D and dicamba was higher than the one provided by triclopyr and halauxifen-methyl; however, all auxinic treatments alone showed control levels equal to or below 50% (Table 1). The combination with glyphosate increased horseweed control to at least 87.7% (Table 1).

For the Palotina biotype at the late vegetative stage (Table 2), control with glyphosate alone was lower (35%) compared to the auxinic herbicides (59.6%), opposingly to results obtained with the Canguiri biotype. This difference can be attributed to the genetic diversity of horseweed plants, as biotypes from different locations may exhibit different responses to the selection pressures imposed by herbicides, and consequently, the plants may show differential responses to the herbicides (Paula et al., 2017; Schneider et al., 2020). Auxinic herbicides applied in combination with glyphosate were more effective when compared to auxinic herbicides applied alone, with control values increasing from 59.2% to 81.5% (Table 2). Similarly, the addition of glyphosate increased the control of 2,4-D and dicamba from 51.2 to 83.7%, but did not affect halauxifen-methyl and triclopyr (Table 2). Despite some differences in control scores between treatments with glyphosate and auxinic herbicides for the early reproductive stage (Table 2), all treatments resulted in unsatisfactory control levels (lower than 76.2%), especially when compared to the scores obtained in the early vegetative stage (Table 2). The sensitivity of plants to the herbicide glyphosate can be influenced by the stage of development (Santos et al., 2014). The lower control at more advanced stages in Conyza spp. can be explained by reduced absorption due to the plant having a thicker cuticle, limited translocation, and a greater ability to metabolize the herbicide (Koger, Reddy, 2005; Sen et al., 2023). These results indicate that the plant stage is a crucial factor when applying herbicides and the chemical control of horseweed should be preferably carried out on plants in early development stages to not compromise the control effectiveness (Tables 1-3). However, in an integrated weed management strategy, in which replenishment of the soil seed bank must be considered (Schaeffer et al., 2020), the assessment of the quantity and quality of the seeds produced should be also carried out, as shown in the topics below.

Considering the experiment conducted under field conditions (Palmeira biotype – Table 3), at the late vegetative and early reproductive stages, higher control was achieved by applying auxinic herbicides in combination with glyphosate (99.3%), compared to glyphosate isolated (47.5%) and also to auxinic herbicides alone (88.6%) (Table 3). The mixture of auxinic herbicides with glyphosate aimed at controlling glyphosate-tolerant or resistant plants is especially necessary for horseweed plants at later development stages (Osipe et al., 2017). Treatments with triclopyr and halauxifen-methyl were more efficient than treatments with 2,4-D and dicamba. However, it is important to note that the addition of diclosulam to Paxeo^® may also have contributed to the greater control efficacy of halauxifen-methyl compared to 2,4-D and dicamba alone (Table 3). Although the herbicides 2,4-D, dicamba, triclopyr, and halauxifen-methyl are classified as auxinic herbicides, the difference in control observed among these herbicide molecules in this study may be also related to the mechanism of action of each molecule within the plant, such as their cellular transport. Transport proteins are likely the first selective target sites for auxin found by exogenous auxins, like auxinic herbicides. The main auxin influx carrier, AUX1, which is the dominant pathway for absorbing indole-3-acetic acid (IAA) into plant cells, has a high affinity for the herbicide 2,4-D but no activity with the herbicides dicamba, triclopyr, and halauxifen-methyl, as these molecules are not transported by AUX1 (Hoyerova et al., 2018). In this sense, Walsh et al. (2006) reported that AFB5 mutants of Arabidopsis thaliana are resistant to halauxifen-methyl, suggesting that this molecule preferentially binds to AFB5 over TIR1 (Lee et al., 2014). On the other hand, the TIR1 mutants are resistant to dicamba and 2,4-D, which means that these herbicides have affinity for TIR1 (Gleason et al., 2011). These differential responses may result in changes in horseweed metabolism due to the difference in herbicide affinity for auxin receptors (McCauley, Young, 2019). Therefore, this may be a possible explanation for the difference between the treatments tested in this study, regarding the control efficacy and formation of horseweed seeds (Tables 1-5 and Figure 2).

3.2 Horseweed (Conyza bonariensis) seed production in response to herbicide application

Considering plants’ seeds production, the non-treated horseweed plants produced almost 22,000 seeds per plant, considering the mean of all three experiments. On the other hand, the application of any herbicides in both vegetative stages (early and late vegetative) completely inhibited seed production in greenhouse experiments, for Palotina and Canguiri biotype, even with the maintenance of vegetative tissue on some occasions (data not shown). This is probably due to the fact that plants’ seed production potential can be negatively affected by prolonged stress conditions during the vegetative growth period (Takeno, 2016), as occurred by the exposure to herbicides. As a result of the chemical stress caused by herbicides, there may be a low reserves accumulation in the stem, which can severely harm the reproductive development of plants, reducing the amount of metabolic products that would be sent to the flowers and seeds during their formation (Barnabás et al., 2008; Takeno, 2016). For the flower formation, sugars, nutrients and an adequate hormonal balance are required. Thus, a possible imbalance of these substances, as a result of herbicide exposure, could result in an increase in ethylene synthesis, inhibiting the morphogenesis and differentiation of the apical meristems, making the plant to remain in the vegetative stage. Consequently, flowers and seeds were not formed (Takeno, 2016).

Herbicide applications at the early reproductive stage caused a significant reduction in the number of seeds produced (Table 4). When fruit production occurs induced by the application of exogenous auxins, there is no ovule fertilization (Meng et al., 2023). As a result, the ovary develops into a fruit, with or without the formation of seeds. If seeds are produced, they will not have an embryo, making seeds unviable, resulting in reduced germination.

For the Palmeira biotype, the application of glyphosate at the late vegetative stage reduced the number of horseweed seeds by approximately 95%, being more effective compared to the early reproductive (Table 5). Opposingly, Piasecki et al. (2019) showed that the application of glyphosate to glyphosate-resistant horseweed in the vegetative stage reduced the number of seeds by 68.4%; but when applied at the early reproductive stage, a total inhibition in seed production was observed. This difference observed in both studies may be related to the fact that resistant and susceptible biotypes have different capacities for herbicides metabolism, absorption and/or translocation (Palma-Bautista et al., 2020; 2021; Torra et al., 2024). On the other hand, the mix of auxinic herbicides with glyphosate were more efficient than glyphosate sprayed alone, causing a 95% reduction in horseweed seed production for the Canguiri biotype (Table 4). Scruggs et al. (2020) reported similar results, as the herbicides glyphosate, 2,4-D and 2,4-D+glyphosate provided a reduction in Amaranthus palmeri seeds production of 66, 95 and 97%, respectively.

Considering the auxinic herbicides isolated, the reduction in seed production was higher at both stages of Palmeira biotype compared to the glyphosate alone (Table 5). The herbicides 2,4-D and dicamba can be used in the post-emergence of tolerant soybean cultivars, therefore, invariably, horseweed plants can be exposed to the application of these herbicides at different stages of development in the crop post-emergence. Therefore, our results suggest that the use of these auxinic herbicides may be a viable option for enhancing the inhibition of seed production in glyphosate-resistant horseweed biotypes, being a viable alternative to be adopted in producing areas in the near future.

For the Palotina biotype, glyphosate applied alone reduced seed production by 83%, reaching higher values compared to the isolated auxinic herbicides (Table 4). On the other hand, the Palmeira biotype produced seeds when glyphosate was applied alone in both growth stages, as the control scores reached only 47.5% (Table 3), being less efficient in reducing seed production when compared to the auxinic herbicides alone (Table 5). This variation between the biotypes observed here suggest that this response may also be biotype-dependent.

3.3 Seeds germination and morphological traits

Considering seeds collected from Palmeira biotype, there was a 36% reduction in the germination of horseweed seeds at 7 DAS, when the plants were treated with glyphosate; on the other hand, the auxinic herbicides alone and in mixture with glyphosate achieved a 100% reduction in germination (Table 6). For the other biotypes tested, all herbicide treatments reduced 100% of seeds viability regardless of the application stage (data not shown). This is possibly due to the fact that stress conditions can contribute to the formation of seeds with low reserves and limited accumulation of enzymes active in the germination process, which leads them to have low physiological quality (Cohen et al., 2021). In soybean cultivation, subdoses of 2,4-D (5.16 to 41.5 g ha^-1) and dicamba (3.7 to 29.8 g ha^-1) reduced seeds productivity and physiological quality (Silva et al., 2018). In another study, Shuai et al. (2017) reported that the application of exogenous auxins delayed seed coat rupture, repressed root protrusion and decreased gibberellin synthesis from soybean seeds. Similarly, Roth et al. (2021) showed that the application of glyphosate and triclopyr to Alliaria petiolata plants, at an early stage of fruit development (still green), resulted in 74% and 64% reduction in seed production, respectively. The authors also reported that there was a reduction in the seeds viability up to 95%, demonstrating the effectiveness of these herbicides for this purpose.

Horseweed’s seed germination data showed that the treatments were not only effective in controlling seed production, but also effective in inhibiting the production of viable seeds (except for glyphosate applied alone – Table 6). Thus, based on our results, it is estimated that from a total of 22,000 seeds produced by a plant without herbicides application (mean of all three experiments – data not shown), there is the potential for germination of more than 21 thousand new plants, as the control plants reached germination percentage values of 97% (data not shown). Applying herbicides even at advanced stages of plant development (late vegetative or early reproductive), the germination potential can be reduced to almost zero (Table 6), which could be highly effective in the integrated management of this species. However, given that Conyza spp. will flower during the late development stages of soybean, the recommendation of auxinic herbicide application before soybean reaches physiological maturity could affect the presence of herbicide traces in the seeds, as previously reported for glyphosate (Arregui et al., 2003; Duke et al., 2003). Despite the fact that both non–auxin resistant soybean and 2,4-D-resistant soybean (Enlist^®) have the capacity to metabolize 2,4-D as early as 14 DAA (Zaccaro-Gruener et al., 2023; Mueller et al., 2024), further studies are needed to evaluate the presence of these herbicides in the grains, in order to enable the insertion of this management in commercial areas, without the presence of herbicide residues in the seeds.

Through morphological analyses, we observed that the seeds from the non-treated control (which showed 97% germination – data not shown) showed the formation of hairy papillus and achene (Figure 3A). Furthermore, the following characteristics were noted: straight and slightly longitudinally curved achenes, oblanceolate and wider at the apex; papillus uniseriate, hairy, with 20-25 silky, denticulated, yellowish-white hairs; basal insertion; narrow base with small white carpopodium; pericarp with a membranous texture, and fibrous rib, with a slightly shiny translucent surface, amber or yellowish in color; embryo axial, spatular and straight (Kissmann, Groth, 1999). Seeds from plants treated with herbicides were dark in color, had damaged achenes and papillae, and did not have embryos; especially in response to auxinic herbicides mixed with glyphosate (Figure 3G-J). The application of herbicides alone caused a lower level of apparent morphological damage (Figure 3B-F), when compared to those in mixture (Figure 3G-J). Despite this, it is worth highlighting that in both cases, germination was reduced by 100% (Table 6).

The production of viable weed seeds is the main mechanism for supplying the soil seed bank, in addition to playing an essential role in the reproduction, dispersal and succession of species (Carpio et al., 2020). In productive areas, the soil seed bank is the main responsible for the maintenance of weed community infestation in future crops, presenting a high potential for interfering with productivity, especially due to the fact that they remain viable in the soil for long periods (Agostinetto et al., 2017). Specifically for horseweed, Wu et al. (2007) reported that its seeds can remain viable for approximately three years. Thus, studies aiming for ways to make the production and germination of weed seeds unfeasible can provide important information for reducing the weed community in commercial areas worldwide, also contributing to the reduction of the dispersion of herbicide-resistant biotypes (Piaseck et al., 2019).

Our results showed that the application of auxinic herbicides and glyphosate are capable of inhibiting the production and germination of horseweed seeds (Tables 4-6). In field situations, this result would prevent the replenishment of the soil seed bank, culminating in two major benefits to the crop production system, namely: 1) decreased competition due to the reduction in the density of weeds that would be present in the field in the following crop years; and 2) delaying the evolution of weed resistance, due to the reduction in the dissemination of seeds of resistant biotypes, which would also act in the preservation and maintenance of existing herbicide technologies (Schaeffer et al., 2020). This strategy must be planned in the medium- and long-term and integrated with different management practices. Variation in the horseweed development stage may also occur due to the emergence of seeds staggered throughout the year. Thus, the results obtained here, that the herbicides used reduce seed production and germination at any stage of plant development, provide the basis for a more variable application strategy throughout the crop cultivation. Despite this, it is important to highlight that variations in sensitivity between different horseweed populations may occur, due to the genetic diversity that the species presents due to its hybridization (Paula, Pinto-Maglio, 2015; Paula et al., 2017).

4.Conclusions

It is concluded that the auxinic herbicides 2,4-D, dicamba, triclopyr and halauxifen-methyl, applied alone or in association with glyphosate, reduced horseweed seeds production and germination, regardless of plant growth stage (early and late vegetative, or early reproductive). Herbicides application caused morphological changes in the seeds and the absence of embryos. For plants that produced seeds, there was a 100% reduction in germination, emphasizing that the application of these herbicides can be a viable strategy in the integrated management of this species.

Acknowledgements

We are grateful for the financial support provided by The National Council for Scientific and Technological Development (CNPq, grant #132546/2020-5) to the first author.

References

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