2,4-D and glyphosate drift interfere with the growth and initial development of rubber trees

ABSTRACT

The herbicides glyphosate and 2,4-D are widely used to control weeds in various crops. The rubber tree crop is exposed to these molecules, which can interfere with its establishment. This study aimed to assess the effects caused by the drift of glyphosate, 2,4-D, and the combination of both, in different proportions corresponding to 0, 4, 8, 16, 32, and 64% of the recommended dose (1,440 and 804 g a·e·ha^-1 of glyphosate and 2,4-D, respectively). The characteristic symptoms when 2,4-D was present in the drift began with wilting and shriveling of young leaves and, at the highest doses, quickly progressed to chlorosis, shoot epinasty, and edge necrosis, while mature leaves showed a brown color, culminating in a high rate of fall. The effects of glyphosate were intensified after leaf flushing, which occurred 120 days after its application and resulted in long, narrow, twisted leaves in a spiral shape and deformed shoots. Drift above 32% from the combination of glyphosate and 2,4-D resulted in a high mortality rate, while 16% damaged growth and resulted in the death of some plants. The results indicate that drift from the combination of glyphosate and 2,4-D intensifies the symptoms of phytotoxicity in rubber trees, with drift above 8% being harmful. For the herbicides applied alone, there was full recovery of the plants in the drift of up to 16%, so it is important to avoid the drift of these herbicides in the management of weeds in the rubber tree crop.

Key words
phytotoxicity; tolerance; sprout; necrosis; Hevea brasiliensis

Introduction

The rubber tree (Hevea brasiliensis) is the main source of natural rubber in the world (Nair 2021). Despite being originally from Brazil, there is a very large deficit between national rubber production and consumption, requiring importing a large part of what is consumed in the country. In this context, as a business opportunity, rubber plantations have grown significantly in last years (IBGE 2024; MAPA 2024).

Adequate initial development resulting in a uniform plant stand is a determining factor in achieving high levels of latex yield. Weed interference stands out among the factors influencing plant growth at this stage. These plants compete with the main culture for growth factors and possible allelopathic effects, resulting in a longer time for production to begin (Rabbani et al. 2011). The presence of weeds also increases the incidence of diseases due to the favorable microclimate that forms at the base of the stem (Pereira et al. 1999).

From planting to canopy closure, weed control should be conducted in the strip between the rows using cultural, chemical, or mechanical control. Currently, weed control is mostly conducted using herbicides due to their effectiveness and labor scarcity.

In the rubber tree culture weed control strips were evaluated monthly established by glyphosate applications at 1.08 kg.ae.ha^-1, complementing with hand-weeding if necessary, from planting up to 720 days (two years) after planting. The critical width of the weed control strip for establishment of a rubber tree plantation was in 100 cm (Guzzo et al. 2014). However, this control when carried out with non-selective herbicides can cause damage to the crop. This drift can occur both from use in the culture and from other cultures in adjacent areas. The herbicides 2,4-D and glyphosate are widely used to manage weeds in various crops. Glyphosate is applied post emergence, while 2,4-D can be applied post- or pre-emergence, depending on the selectivity of the non-target crop and the weed species to be controlled (Rodrigues and Almeida 2018). Chemical control can cause damage to non-target crops through drift, affecting production and plant morphology (Pereira et al. 2010). The damage caused by drift depends on some factors, such as the species affected, the action mode, the amount of product that reaches the plant, and the susceptibility of the species to a given product, among others (Yamashita and Guimarães 2005). Auxin herbicides such as 2,4-D are prone to volatilization and can be carried hundreds of meters by wind to non-target environments (Brochado et al. 2022).

Spraying in inadequate meteorological conditions of relative humidity, high temperatures and especially situations with high wind speed present a high risk of drift. Carlsen et al. (2006) findings supported that it is the physical properties of the spray and the conditions of application (i.e., equipment and meteorology) that are the primary determinants of primary drift rather than the chemical property of the pure active ingredients.

One aspect to consider is that, although introducing herbicide tolerant crops has provided producers with new options for managing weeds, the widespread adoption of these herbicides has increased the risk of drift to non-target plants (Vieira et al. 2020).

According to Gandolfo et al. (2012), the application of the herbicides 2,4-D and glyphosate in combination produces more drift than when applied alone, and the drift of each herbicide applied alone showed no statistical differences.

There are reports in the literature of damage caused by the drift of both glyphosate and 2,4-D on various crops, such as Conilon coffee (Yamashita et al. 2013), tomatoes (Fagliari et al. 2005), eucalyptus (Pereira et al. 2011), but scientific reports of the effects on rubber trees under field conditions are scarce.

This study aimed to assess the effects caused by simulated drift of glyphosate, 2,4-D, and the combination of both, at different concentrations, on the initial development of the rubber tree crop.

Material and methods

Location and characterization of the experimental area

The research was conducted at Instituto Agronômico – Centro APTA de Seringueira e Sistemas Agroflorestais, in Votuporanga, SP, Brazil (latitude 20°20’S, longitude 49°58’W, and altitude of 510 m), from March 2017 to June 2018. Data on minimum, average, and maximum temperature, rainfall (mm), and minimum and maximum relative air humidity were recorded (Figs. 1a and 1b).

Figure 1
Data on temperature, rainfall, and relative air humidity. (a) Minimum, average, and maximum air daily temperature. (b) Daily rainfall (Rain) and minimum (RHmin) and maximum (RHmax) daily relative air humidity, Votuporanga, SP, Brazil (Centro APTA de Seringueira e Sistemas Agroflorestais).

Experimental design

The experimental design used was randomized blocks, with four replications, in a 3 × 6 factorial scheme. The first factor consisted of the herbicide glyphosate, 2,4-D, and a combination of both. The second factor consisted of six doses of the herbicide glyphosate (0.00, 57.60, 115.20, 230.40, 460.80, and 921.60 g a.e.ha^-1); six doses of the herbicide, 2,4-D (0.00, 32.16, 64.32, 128.64, 257.28, and 514.56 g a.e.ha^-1), and six doses of the combination of both (0.0+0.0, 57.6+32.16, 115.2+64.32, 230.4+128.64, 460.8+257.28, and 921.6+514.56 g a.e.ha^-1), corresponding to 0, 4, 8, 16, 32, and 64% of the recommended doses (1,440 and 804 g a.e.ha^-1 of glyphosate and 2,4-D, respectively). Each experimental unit consisted of three plants, totaling 216 plants.

Setting up and conducting the experiment

The plants were transplanted to the field on March 17, 2017. Furrows were dug in rows spaced 1.5 m apart, with 1 m spacing between plants, followed by irrigation on the planting day. Budded plants with one mature leaf whorl of “GT1” as rootstock and “RRIM 600” as clone were used in all trials. When necessary, phytosanitary treatments were conducted according to the official recommendations (Gonçalves et al. 2014).

The treatments were applied on May 24, 2017, in budded plants with one mature leaf whorl. At the time of application, the weather conditions were recorded, with a wind speed of 0.5 m.s^-1, relative humidity of 67%, and an air temperature of 26°C.

The treatments were applied using a CO₂-pressurized backpack sprayer at a constant working pressure of 175 kPa, a 0.5 m wide boom, and two fan nozzles (TT 110:02), operating at the height of 0.4 m from the target, with a 1-m wide deposition band, providing a spray volume of 155 L.ha^-1.

Evaluations conducted

A scale of symptom scores was used to assess phytotoxicity, varying according to visual damage, as proposed by Deuber (1992) (Table 1). Evaluations were conducted at 2, 5, 9, 21, 42, 120, and 180 days after the application (DAA) of the treatments. The first and second leaf flushing appeared in the evaluations at 120 and 180 DAA.

Table 1
Scale of phytotoxicity scores.

Class	% of Damage	Damage
I	0–10	null
II	11–20	minimum
III	21–30	very weak
IV	31–40	weak
V	41–50	sensitive
VI	51–60	medium
VII	61–70	intense
VIII	71–80	severe
IX	81–90	very severe
X	91–100	total

• Source: Deuber (1992).

At 45 DAA, the total height of the plants and the length of the lesion on the stem of the rubber plants were measured to check the percentage of lesions on the stem. In addition, the number of leaves on the plants was counted to quantify the percentage of leaf fall.

Live plants were quantified at 90 and 400 DAA to calculate the plant survival rate.

Plant height, measured from the graft to the top, and stem diameter, measured 10 cm above the graft, were assessed at 0, 30, 90, 150, 200, and 400 DAA. Using this data, the percentage of plant growth was calculated.

Statistical analysis

The data was subjected to the preliminary normality test and transformed into (√x + 0.5), and then the analysis of variance was conducted. The significance of the mean squares obtained in the analysis of variance was tested using the F test at a 5% probability level, and the means were compared using the t test at a 5% probability level. The data was subjected to regression analysis for the herbicide dose factor, fitting models with a high R² and biological explanation.

Results and discussion

There was no interaction between herbicides and doses for neither the percentage of growth in stem diameter in the periods from 0 to 30 and 91 to 150 DAA nor for the percentage of growth in height in the intervals from 0 to 30 and 151 to 200 DAA.

In the initial evaluations (2 and 5 DAA), the herbicide 2,4-D showed increasing phytotoxicity from 8% of the recommended dose. The drift of the combination of herbicides showed no phytotoxicity up to 4% of the dose, promoting a peak in the evolution of phytotoxicity at 8%, maintaining this level even at the highest doses. Glyphosate applied alone showed no symptoms of phytotoxicity (Figs. 2a and 2b). According to Monquero et al. (2004), the mechanisms of tolerance to glyphosate depend on the species and may be due to differential absorption, metabolism of the herbicide by the plant, or even less translocation of the herbicide.

For the evaluations at 9, 21, and 42 DAA, the treatments showed increased phytotoxicity rates. According to the regression equation, at 42 DAA, the herbicide glyphosate showed 31.8% phytotoxicity at the highest dose, which is therefore considered weak. The treatment with 2,4-D showed increasing phytotoxicity as the doses increased, being very weak up to 8%, medium at 16%, and severe at 32 and 64% of the recommended dose. The combination of herbicides showed greater phytotoxicity than those applied alone, with weak phytotoxicity at 4%, comparable to the highest dose of glyphosate. However, from 32%, the difference was very small between 2,4-D applied alone or in combination with glyphosate, and at 64% of the recommended dose they were similar (Figs. 2c, 2d, and 2e).

Figure 2
Phytotoxicity percentage of rubber tree plants subjected to simulated drift of glyphosate, 2,4-D, and the combination of both herbicides at (a) two, (b) five, (c) nine, (d) 21, and (e) 42 days after application (DAA). The vertical bars represent the standard error of the treatments.

In evaluating the effects of applying glyphosate and 2,4-D alone and combined on forest species up to 28 DAA, it was found that, during the evaluations, phytotoxicity became more evident (Yamashita et al. 2009).

Concerning symptoms, at five DAA the plants the testify plants presented normal developing of leaves (Fig. 3a). The ones subjected to 2,4-D drift, as well as the combination of herbicides from 8% of the recommended dose, showed obvious symptoms of phytotoxicity, such as wilting and wrinkling of young leaves and mature leaves with a brownish color (Fig. 3b), and at doses from 32% onwards. In addition to these symptoms, they also showed chlorosis, shoot epinasty, and necrosis of the edges of young leaves.

Figure 3
Symptomatology of phytotoxicity of rubber tree plants subjected to drift from the combination of glyphosate and 2,4-D, assessed five (a and b) and nine (c and d) days after application. (a) 0%, no herbicide; (b) 8% of the recommended dose; (c and d) 32% of the recommended dose.

At nine DAA, the first symptoms appeared on the glyphosate treated plants, which increased as the dose increased, but in low intensity, while the treatments containing 2,4-D showed an increase in symptom intensity. The plants subjected to glyphosate drift showed wrinkling and wilting of the young leaves, similar to the initial symptoms of 2,4-D drift at low doses (two DAA), and showed no symptoms on the mature leaves. The most characteristic symptoms of glyphosate appeared only after the first leaf flushing at 120 DAA of the herbicide, resulting in plants with long, narrow, twisted leaves in a spiral shape. In addition, at the highest doses, shoots deformed along the stem and over-sprouting in the apical meristem of the plants. However, the plants in the 2,4-D treatment and the combination of 2,4-D and glyphosate at 64% and above 32% of the recommended dose, respectively, had completely necrotic mature leaves with a greyish brown color (Figs. 3c and 3d) and a brittle appearance, and the shoots were also necrotic.

The action of 2,4-D on the plant induces metabolic and biochemical changes, as it alters the metabolism of nucleic acids and the plasticity of the cell wall, consequently interfering with protein synthesis. There is an intense induction of cell proliferation in the tissues and an interruption of the phloem, stopping the movement of photoassimilates from the leaves to the roots. There is also a reduction in the rigidity of the cell wall due to an increase in the synthesis of the enzyme cellulase and a decrease in the osmotic potential of the cells caused by the accumulation of proteins. As a result of these effects, there is epinasty of the leaves, twisting of the stem, and thickening of the terminal buds, causing the death of the plant in a few days or weeks (Silva et al. 2007).

Glyphosate drift did not cause leaf fall; only the fall considered natural for the species was observed (Fig. 4). In their assessment of drift in the forest species Ceiba pentandra, Yamashita et al. (2009) observed that in plants treated with glyphosate at the lowest dose (180 g a.ae.ha^-1), the number of leaves remained significantly similar to that of the control.

Figure 4
Percentage of leaf fall of rubber trees subjected to drift from 2,4-D, glyphosate, and the combination of both herbicides at 45 days after application (DAA). The vertical bars represent the standard error of the treatments.

When the herbicides were combined at 8%, mature leaves fell, and young leaves wilted and twisted with no signs of necrosis. 2,4-D applied alone and in combination with glyphosate, at doses of 32 and 16%, respectively, resulted in plants mostly with mature leaves completely necrotic, shoots with epinasty and necrotic leaf edges, but some plants did not show severe symptoms as at higher doses.

The increase in leaf fall with the combination of herbicides began between 8 and 16% of the recommended dose (Fig. 4). At the 16% dose, there was over 90% leaf fall with the combination of herbicides and approximately 55% with 2,4-D applied alone, showing a synergistic effect of the combination in the suppressive effect on the rubber tree. However, from 32% of the recommended dose, 2,4-D alone and the combination of herbicides were equivalent, with high percentages of leaf fall. There was 100% leaf fall at the 64% dose and 94.8 and 99.5% at the 32% dose for the drift of 2,4-D and the combination of herbicides, respectively.

Oliveira Júnior et al. (2007) found that sub-doses of 2,4-D in grape cultivation resulted in leaf epinasty and deformation of young branches and leaves. These symptoms were predominantly evident in the young growing parts (leaves and green branches). As the sub-doses and severity of the symptoms increased, the phytointoxication observed progressed to necrosis, leaf fall, and deformations in the branches and stems.

Although there are reports of 2,4-D antagonism for some species, reducing glyphosate absorption and (to a lesser extent) translocation (Li et al. 2020), there was a synergistic effect of up to 32% of the recommended dose in this study.

Concerning the percentage of plant survival, assessed at 90 DAA, the drift resulting from the combination of 2,4-D and glyphosate, considering 16, 32, and 64% of the recommended dose, resulted in the death of 33.3, 66.7, and 66.7% of the rubber tree plants, respectively. When 2,4-D was applied alone, at doses of 32 and 64%, 25 and 58.3% of the plants died, respectively. Glyphosate drift did not result in plant death at any of the doses evaluated. The results show that 2,4-D applied alone or in combination with glyphosate can reduce the crop stand and thus increase the problems of competition with the weed community. In the evaluation at 400 DAA, the death of plants subjected to glyphosate doses above 32% was observed, while for the other treatments there were no new plant losses compared to the previous evaluation at 90 DAA. The death of these plants is probably related to the inhibition of root development, which, combined with the period of water deficiency, from the second half of April, resulted in the death of these plants due to the low availability of water during this period (Fig. 5).

Figure 5
Percentage survival of rubber tree plants subjected to simulated drift of 2,4-D, glyphosate (glyph), and the combination of both herbicides assessed at (a) 90 and (b) 400 days after application.

When the combination of herbicides was used, evaluations of damage to the rubber tree stems showed lesions reaching approximately 70% of the stem at the highest doses. The drift of 2,4-D applied alone showed stem damage from 32% of the recommended dose, reaching values similar to those observed for the associated herbicides at the highest dose. Glyphosate drift alone did not cause stem necrosis (Fig. 6).

Figure 6
Percentage of lesions on the stems of rubber trees subjected to simulated drift of 2,4-D, glyphosate, and the combination of both herbicides assessed 45 days after application (DAA). The vertical bars represent the standard error of the treatments.

The necrosis and consequent leaf fall may be associated with hormonal balance, which can be caused by both 2,4-D and glyphosate, altering ethylene biosynthesis and causing the leaves to fall (Vidal 1997). Necrosis in the stem is also due to the hormonal imbalance and accumulation of auxin in the plants as a result of 2,4-D drift so that the cells break because they do not follow the signaling of this hormone, resulting in cracks and necrosis in the stem (Oliveira Júnior and Constantin 2001).

Figure 7 shows the extent of the damage to the stems of the plants: plants that did not suffer any stem damage (Fig. 7a), plants that suffered some stem damage, but recovered (Fig. 7b), and plants that suffered total stem damage and consequent death (Fig. 7c).

Figure 7
Symptomatology on the rubber tree stems (a) in the control treatment, (b) in plants subjected to 2,4-D drift, and (c) in the combination of glyphosate and 2,4-D at 45 days after application.

At the time of the first leaf flushing after applying the treatments (120 DAA), the plants that had survived 2,4-D showed no symptoms of phytotoxicity and had recovered from the symptoms caused by the herbicide. The herbicide glyphosate showed increasing phytotoxicity from the 16% dose onwards, with very weak symptoms at this dose and severe symptoms at higher doses, showing over-sprouting and reduced or paralyzed growth. For the combination of herbicides, there was a similar trend to glyphosate alone, but with greater intensity of phytotoxicity (Fig. 8a).

Figure 8
Phytotoxicity percentage in rubber tree plants subjected to simulated drift of glyphosate, 2,4-D, and the combination of both herbicides assessed at (a) 120 days after application (emission of the first leaf flushing) and (b) 180 days after application (emission of the second leaf flushing). The vertical bars represent the standard error of the treatments.

At the time of the second leaf flushing (180 DAA), the combination of herbicides showed a similar phytotoxicity trend to the previous period (120 DAA), but with less intensity at 16 and 32% of the recommended dose. For the drift of glyphosate alone, there was reduction in phytotoxicity at the 16 and 32% doses, while at 64% of the recommended dose the plants did not recover from the previous evaluation. Most of the plants that received 64% of the recommended dose of glyphosate showed over-sprouting in the apical meristem and consequent growth paralysis. A few plants that did not have their growth paralyzed showed less vigor in the emission of leaf flushing, with their shortening (Fig. 8b).

The action of glyphosate on the plant affects the synthesis of secondary metabolites due to the shikimic acid pathway blocking. Some of the effects that can be affected by the action of the herbicide are the synthesis of indoleacetic acid (IAA) and other plant hormones, chlorophyll synthesis, protein synthesis, respiration, photosynthesis, and others. In the plant, the synthesis of the growth promoter (IAA) is inhibited because the precursors of its biosynthesis are inhibited by the action of glyphosate, resulting in a reduction of IAA in the plant (Yamada and Castro 2007).

The reduction of IAA in the plant affects the biosynthesis of another important plant bioregulator, a precursor to gibberellin synthesis (GA). The concentration of IAA and GA, in greater or lesser quantities in the shoots of tree species, affects cambial differentiation, favoring the formation of xylem or phloem (Yamada and Castro 2007).

Thus, the change in the concentration of the hormones IAA and GA, among other secondary metabolisms, resulting from the application of glyphosate, may be one of the main factors promoting plant growth paralysis, either due to the reduction in growth promoters, the reduction in photoassimilates resulting from the reduction in chlorophyll synthesis, or other factors.

The treatments did not affect height growth between 0 and 30 DAA (Fig. 9a). Height growth between 31 and 90 DAA was influenced in doses equal to or higher than 32% of the recommended dose. There was null growth in the combination of herbicides due to plant death.

Figure 9
Height growth percentage of rubber tree plants subjected to simulated drift of glyphosate, 2,4-D, and the combination of both herbicides at the intervals of (a) 0 to 30, (b) 31 to 90, (c) 91 to 150, (d) 151 to 200, (e) 201 to 400, and (f) 0 to 400 days after application (DAA). Vertical bars represent the standard error of the treatments.

The drift of the isolated herbicides reduced growth at doses of 32%, and for 64% of the recommended dose the growth of the plants that received the 2,4-D drift was null, also due to the death of the plants, while for glyphosate the plant growth was little reduced at the 32% of the recommended dose (Fig. 9b).

Plant growth was slow in the 91 to 150 DAA interval, with a slight difference from the previous interval (Fig. 9c). For the 151 to 200 DAA interval, there was no interaction between herbicides and doses, but there was less growth from 16% of the recommended dose onwards (Fig. 9d). No differences were observed in the growth period between 201 to 400 DAA up to 16% of the recommended dose (Fig. 9e). Considering the periods from 201 to 400 DAA and 0 to 400 DAA (Fig. 9e), there was the same growth trend, with no difference up to 16% of the recommended dose and reduction in growth as the doses increased.

Table 2 shows the main effects of the herbicides in the periods in which there was no interaction between doses and herbicides (0 to 30 DAA and 151 to 200 DAA for height and 0 to 30 DAA and 91 to 150 DAA for stem diameter). Among the herbicides, glyphosate resulted in lower stem diameter growth between 0 to 30 DAA, and the combination of herbicides reduced height growth between 151 to 200 DAA.

Table 2
Plant height growth percentage from 0 to 30 and from 151 to 200 days after application (DAA). Stem diameter growth percentage from 0 to 30 and 91 to 150 DAA of rubber tree plants subjected to simulated drift of glyphosate, 2,4-D, and the combination of both herbicides^*.

Herbicides	Plant height			Stem diameter
	DAA
	0–30	151–200		0–30	91–150
	%
2,4-D	2.10 a	9.68 a		6.59 a	3.03 a
Glyphosate	1.76 a	10.95 a		4.81 b	3.32 a
2,4-D + Glyphosate	2.33 a	7.21 b		7.68 a	2.60 a
Mean	2.06	9.28		6.36	2.98
C.V. (%)	30.13	25.02		23.18	30.92

• ^*
  Means followed by the same letter in the column do not differ by the t test at 5% probability;
• C.V.: coefficient of variation.

Concerning stem diameter growth, the treatments had no effect in the 0 to 30 DAA interval (Fig. 10a). The drift of 2,4-D and the combination of 2,4-D and glyphosate caused a similar reduction in stem diameter growth between 31 to 90 DAA, but the combination of herbicides resulted in less growth than 2,4-D, with null growth at 32% of the recommended dose. However, 2,4-D reduced growth to null only at 64% of the recommended dose. No differences were observed between the glyphosate doses in this interval (Fig. 10b). Between 91 to 150 DAA, regardless of the herbicide used, stem diameter growth was reduced at doses equal to or higher than 8% of the recommended dose (Fig. 10c).

Between 151 to 200 DAA, the combination of herbicides resulted in a slight decrease in stem diameter growth up to 16% of the recommended dose, with null growth at the highest doses. 2,4-D showed a linear decrease in stem diameter as the doses increased. Glyphosate reduced growth from the 16% dose onwards (Fig. 10d). It is important to note that, in the initial phytotoxicity evaluations, glyphosate had little effect, so, although the plant did not appear to be under the effect of the herbicide, this negative interference appeared later with the new leaf flushings.

From 201 to 400 DAA, there was a significant increase in stem diameter, showing an intense growth phase for the crop, with 43.1% growth at the 0 dose. There was a negative impact on growth from 16% of the recommended dose of the herbicides, which was more significant with the combination of herbicides, which showed null growth at a dose of 32%, while at the same dose 2,4-D showed 33% and glyphosate 22.9% growth in stem diameter (Figs. 10e and 10f).

Reduced growth in plant height and stem diameter can lead to a reduction in the plants ability to compete for environmental factors such as water, light, and nutrients, resulting in the formation of less vigorous plants (Yamashita et al. 2013) with a consequent increase in the frequency of dominated plants in the area, which results in a rubber tree plantation with less yield potential.

The drift of the associated herbicides proved more damaging than if they were applied alone. Some studies have shown a synergistic effect between the 2,4-D and glyphosate mixture, increasing weed control compared to herbicides alone (Takano et al. 2013). On the other hand, the effects of the drift of the mixture of these herbicides were also potentiated in the crop, with the combination of herbicides potentiating the initial effect, increasing stem injury and plant mortality, while the late effect of glyphosate was similar to those observed in the isolated application. According to Oliveira et al. (2021), adding glyphosate to the herbicides 2,4-D and dicamba reduces the surface tension and pH of the solution. Cobb and Reade (2010) point out that these synthetic auxins are weakly acidic herbicides that are absorbed better in slightly acidic environments due to the non-dissociation of the molecules, which facilitates absorption by the lipophilic cuticle.

In a study with forest species, Yamashita et al. (2009) recommended applying these herbicides in a directed jet to avoid damaging plant growth.

Figure 10
Stem diameter growth percentage of rubber tree plants subjected to simulated drift of glyphosate, 2,4-D, and the combination of both herbicides at intervals of (a) 0 to 30, (b) 31 to 90, (c) 91 to 150, (d) 151 to 200, (e) 201 to 400, and (f) 0 to 400 days after application (DAA). Vertical bars represent the standard error of the treatments.

Conclusion

The combination of glyphosate and 2,4-D intensifies the symptoms of phytotoxicity in rubber trees, with drift above 8% being harmful.

For the herbicides applied alone, there was full recovery of the plants in the drift of up to 16%.

ACKNOWLEDGMENTS

To Centro de Seringueira e Sistemas Agroflorestais for support during the research.

• How to cite: Zoz, A., Hirata, A. C. S., Scaloppi Júnior, E. J., Borges, W. L. B., Araújo, T. A. N. and Freitas, R. S. (2025). 2,4-D and glyphosate drift interfere with the growth and initial development of rubber trees. Bragantia, 84, e20240151. https://doi.org/10.1590/1678-4499.20240151
• FUNDING
  Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
  Finance Code 001
  Conselho Nacional de Desenvolvimento Científico e Tecnológico
  Grant No.: DT2

DATA AVAILABILITY STATEMENT

Data may be made available upon request to the corresponding author.

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Edited by

• Section Editor:
  Gabriel Constantino Blain https://orcid.org/0000-0001-8832-7734

Publication Dates

• Publication in this collection
  17 Jan 2025
• Date of issue
  2025

History

• Received
  09 July 2024
• Accepted
  29 Oct 2024