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Introduction
The repetitive use of the same herbicide can generate risks to the sustainability of agri cultural systems, as it causes important changes in the composition of the weed community present in agricultural areas. The emergence of herbicide-resistant weed biotypes is among the main concerns related to plant protection globally 5,14.
Due to the large-scale adoption of Roundup Ready® (RR®) technology, which gives plants tolerance to glyphosate, postemergence applications of this herbicide have become quite frequent in large crops such as soybeans 17. This fact significantly contributed to the increase in the population of weed species tolerant 13 to this herbicide in the cultivated areas, in addition to accelerating the selection of resistant biotypes. This change in the weed community has led to the need to complement chemical control, especially with the appli cation of latifolicides in soybean crops 1.
The association among herbicides with different modes of action has become an important strategy for the control of a wider spectrum of weed species 21, in addition to mitigating the occurrence of weed resistance to herbicides 18. Currently, ALS (e.g., imazethapyr, chlorimuron) and PPO (e.g., fomesafen, lactofen) inhibitors are among the most widely used herbicides in postemergence soybean crops and are used mainly in asso ciation with glyphosate. Despite showing satisfactory control for several weed species, especially broadleaves, these herbicides can cause injuries to soybean plants, with internal chlorosis and leaf tissue necrosis as the most frequent visual symptoms, which can nega tively affect crop yield 2.
In a study by Alonso et al. (2011), it was observed that the use of glyphosate isolated and in association with other postemergence herbicides provided visual symptoms of injuries in RR® soybean plants, causing a reduction in crop yield components. The most common symptom caused by the isolated application of glyphosate on RR® soybean is the chlorosis of the trifoliated leaves positioned in the upper portion of the plants; however, other negative effects were observed in studies with this herbicide, such as reduced nutrient absorption and plant growth 6,22.
The postemergence herbicide applications in soybean crops are more effective in weed control when carried out at the early stages of development. Fornazza et al. (2011) reported that some combinations of herbicides applied in the initial postemergence of soybean can affect the grain yield due to the low selectivity observed for some cultivars. The selectivity of herbicides for soybean cultivars, mainly related to the use of these products in associations, is an aspect to be carefully observed, mainly due to the current use in Brazil of genotypes with great phenotypic variation, highlighting relevant aspects, such as maturation groups, growth types, leaflet area, leaf inclination angle, and pubescence. The correct choice of soybean cultivars can avoid losses in grain yield resulting from low tolerance to herbicides.
In this context, the objective was to study the selectivity of latifolicides in association with glyphosate applied in the postemergence period of three RR® soybean cultivars in the Midwest region of Brazil.
Materials and methods
Three experiments were carried out in the field in the same plot located in the munici pality of Rio Verde (Goiás State), Brazil (17°52’05”S and 50°55’36”W; altitude: 741 m), from November 18th, 2020 to March 18th, 2021. In each experiment, the selectivity of herbicides applied postemergence to a soybean cultivar of indeterminate growth type and with great representation in terms of cultivated area in the Midwest region of Brazil was evaluated. The evaluated cultivars were M7110 IPRO® (maturity group - MG: 6.8), Focus IPRO® (MG: 7.2), and Bônus IPRO® (MG: 7.9).
According to Köppen’s classification, the climate of the municipality where the exper iments were carried out is of the Aw type, which is called “tropical with the dry season”, characterized by more intense rainfall in summer than in winter. In Figure 1, there are clima tological data related to temperature and relative humidity of the air, luminosity, and rainfall during the period of conducting the experiments.
Source: INMET - Instituto Nacional de Meteorologia. Collection station: Rio Verde (Goiás State).
Fuente: INMET - Instituto Nacional de Meteorología. Estación de recolección: Rio Verde (Estado de Goiás).
Figure 1: Data on temperature and relative air humidity, luminosity and rainfall during the period of conducting the experiments. Rio Verde (Brazil), 2020/2021. Figura 1: Datos sobre temperatura y humedad relativa del aire, luminosidad y precipitación durante el período de realización de los experimentos. Rio Verde (Brasil), 2020/2021.
Before the installation of the experiments, the analysis of soil samples collected at depths from 0 to 20 cm was carried out, which revealed the following physicochemical properties: pH in CaCl2 of 4.8; 5.0 cmolc dm-3 of H+ + Al+3; 2.78 cmolc dm-3 of Ca 2+; 1.09 cmolc dm-3 of Mg+2; 0.11 cmolc dm-3 of K+; 4.3 mg dm-3 of P; 30.2 g dm-3 organic matter; 42% sand; 7% silt and 51% clay (sandy clay texture). Before sowing, the weeds present in the experimental area received two herbicide applications (burndown desiccation), the first being carried out ten days before sowing (November 8th, 2020) with the application of glyphosate (720 g a.e. ha-1) and the second on the day of sowing (November 18th, 2020), with the application of glyphosate + flumioxazin (900 + 20 g a.i. ha-1) in association with the addition of Joint Oil® (0.5% V/V).
Soybean sowing was carried out mechanically, adopting a spacing of 0.5 m between rows. Twenty-two, 16, and 10 seeds of soybean were distributed per linear meter for the cultivars M7110 IPRO®, Foco IPRO®, and Bônus IPRO®, respectively. The seeds used in the exper iments received industrial treatment with fungicides and insecticides. Fertilization was carried out at sowing time, with application in the furrow of the equivalent of 400 kg ha-1 of 02-20-28 (N-P-K). The emergence of soybean seedlings of the three cultivars occurred on November 25th, 2020.
In all experiments, a randomized complete block design was used, evaluating eight treatments with four replications. The treatments consisted of the evaluation of herbicide associations applied in the postemergence period of soybean (Table 1).
Table 1: Treatments evaluated in post-emergence applications of soybean cultivars. Rio Verde (Brazil), 2020/2021. Tabla 1: Tratamientos evaluados en aplicaciones de post-emergencia de cultivares de soja. Rio Verde (Brasil), 2020/2021.
1/ For glyphosate 1176 g of active ingredient (a.i.) ha-1 corresponds to 960 g of acid equivalent (a.e.) ha-1. 2/ EPSPs = 5- enolpyruvylshikimate- 3-phosphate synthase; PSII = photosystem II; PPO = protoporphyrinogen oxidase; ALS = acetolactate synthase.
1/ Para el glifosato 1176 g de ingrediente activo (i.a.) ha-1 corresponde a 960 g de ácido equivalente (e.a.) ha-1. 2/ EPSPs = 5-enolpiruvilshikimato- 3-fosfato sintase; PSII = fotosistema II; PPO = protoporfirinógeno oxidase; ALS = acetolactato sintase.
It is worth noting that no adjuvants were added to the application of any of the treatments; this criterion was adopted because all the associations contained a glyphosate-based product in their compo sition. The experimental units consisted of six sowing lines, with a length of 5.0 m (15.0 m2). Only the four central lines of each experimental unit were considered useful areas for the evaluations, excluding 0.5 m from each end.
The treatments application in the three experiments was carried out on December 18th. 2020 (23 days after emergence- DAE). On this occasion, the soybean plants were at stage V5 (5 trifoliated leaves) for the cultivars M7110 IPRO® and Foco IPRO® and at V4 (4 trifoliated leaves) for the Bônus IPRO® cultivar, with plant height varying between 15 and 18 cm. At the time of application, the soil was wet, the temperature and relative humidity, minimum and maximum, were 23.1 and 25.1 °C and 60 and 64%, respectively, and the sky had the presence of few clouds and wind speed at values close to 1.2 km h-1. The applications were carried out using a CO2 pressurized back sprayer equipped with a boom fitted with 6 fan-type spray tips XR-110.015 spaced 50 cm apart and regulated to a pressure of 0.24 MPa. These application conditions provided an application rate equivalent to 150 l ha-1.
To ensure that the soybean plants were only exposed to the effect of herbicide treat ments, manual weeding of the species that made up the weed community of all experimental units was carried out throughout the entire crop cycle. In addition, during the development of soybean, cultural practices were carried out following the recommendations of Embrapa (2013), to control pests and diseases without letting them negatively influence the devel opment of the crop. All phytosanitary applications, except for the herbicide treatments that were the object of evaluation, were carried out using a tractor sprayer machine, adopting an application rate equivalent to 150 l ha-1.
Injury level evaluations of soybean cultivars were carried out at 7 and 28 days after herbicide application (DAA), using for this evaluation the scale proposed by the SBCPD (1995), which presents grades ranging from 0% to 100%, where 0% means the absence of symptoms and 100% represents the death of all plants present in the useful area. Plant height assessments (cm) were carried out at 50 DAE and at harvest time with the aid of a graduated measuring tape, measuring the distance from the soil surface to the apex in 5 plants per experimental unit. In addition, at the time of harvest, an evaluation of the plant stand was carried out, counting the number of plants present in a 3 m row, with the data for this variable presented as the number of plants per linear meter (plants m-1).
Additionally, in harvest, the yield components, number of pods per plant, and mass of 100 grains were evaluated. To evaluate the number of pods per plant, the count of pods present in 5 plants per experimental unit was performed. In the evaluation of 100 grain masses, 100 grains were counted and weighed on a precision scale, correcting the humidity content to 13%. To determine the grain yield, all plants present in the useful area of each experimental unit were plucked manually (M7110 IPRO® and Foco IPRO®, harvested on March 13th, 2021; Bônus IPRO®, harvested on March 18th, 2021), where this material was later submitted to threshing, packaging, identification, weighing and grain humidity correction processes to 13%.
Statistical analyses were performed using SISVAR software (2011). Data from all exper iments were submitted to analysis of variance by the F test (p≤0.05), and when there was a significant effect, the Scott‒Knott mean grouping criterion (p≤0.05) was applied.
Results and discussion
Experiment I: Selectivity of herbicide associations applied postemergence to the soybean cultivar M7110 IPRO®
Observing the phytotoxicity results for the cultivar M7110 IPRO® at 7 DAA, it can be seen that the levels of injuries caused by the herbicides varied from 11.25 and 14.50%, with no significant difference among the herbicide treatments; however, all differed from the control without herbicide application (Table 2).
Table 2: Injury level of soybean (cultivar: M7110 IPRO®) after application of post-emergence herbicide associations. Rio Verde (Brazil), 2020/2021. Tabla 2: Fitointoxicación de la soja (cultivar: M7110 IPRO®) después de la aplicación de asociaciones de herbicidas de postemergencia. Rio Verde (Brasil), 2020/2021.
a.i. = active ingredient; DAA = days after application. * Significant by F test (p≤0.05). Means followed by different letters in the column differ from each other by the Scott-Knott test (p≤0.05).
i.a. = ingrediente activo; DAA = días después de la aplicación. * Significativo por prueba F (p≤0,05). Medias seguidas de letras diferentes en la columna difieren entre sí por la prueba de Scott-Knott (p≤0,05).
Furthermore, it is worth emphasizing that, in this evaluation, the latifolicides associated with glyphosate postemergence did not enhance injury levels compared to the application of glyphosate isolated.
In the evaluation carried out at 28 DAA, the highest percentages of injury levels were seen in soybean plants that received postemergence applications of the association’s glyphosate + chlorimuron and glyphosate + lactofen, which presented values of 8.25% and 7.50%, respectively (Table 2). In a study by Alonso et al. (2010), it was observed that the association glyphosate + lactofen did not present selectivity for the soybean cultivar CD 214 RR®. In this final evaluation, except for the treatments mentioned above, no differences were observed between the other treatments and the control without herbicide application in terms of injury levels, which demonstrates the crop’s ability to recover from the negative effects caused by these herbicides.
The evaluation of plant height showed a direct relationship with the results of injury levels, since the treatments that provided higher percentages of injuries promoted a reduction in soybean size at 50 DAE (Table 3, page 91).
Table 3: Height and stand of soybean plants (cultivar: M7110 IPRO®) after application of post-emergence herbicide associations. Rio Verde (Brazil), 2020/2021. Tabla 3: Altura y soporte de plantas de soja (cultivar: M7110 IPRO®) después de la aplicación de asociaciones de herbicidas de postemergencia. Rio Verde (Brasil), 2020/2021.
a.i. = active ingredient; DAE = Days after emergence. * and ns Significant and non-significant, respectively, by the F test (p≤0.05). Means followed by different letters in the column differ from each other by the Scott-Knott test (p≤0.05).
i.a. = ingrediente activo; DAE = Días después de la emergencia. * y ns Significativo y no significativo, respectivamente, por la prueba F (p≤0,05). Medias seguidas de letras diferentes en la columna difieren entre sí por la prueba de Scott-Knott (p≤0,05).
On this occasion, the combination of glyphosate + chlorimuron and glyphosate + lactofen directly affected the plant size of this cultivar, providing reductions of 9.66% and 6.02%, respectively, for the height values measured in the control without herbicides. The low levels of foliar injuries found in the last phytotoxicity evaluation in the other treatments were not able to induce a reduction in the growth of soybean plants, since the height values were similar to the control without herbicide application.
At harvest, the PPO inhibitor herbicides fomesafen and lactofen and the ALS inhibitor chlorimuron, all in association with glyphosate, promoted significant reductions in plant height compared to the control without herbicide (Table 3). The average reduction in height value imposed by these treatments reached values of 4.81%, with no differences among these three herbicide treatments. The other herbicide treatments did not differ from the control regarding the final plant height. It is noteworthy that the height of plants can influence certain parameters of the soybean crop, such as the potential for plant lodging or yield losses in the mechanized harvesting operation due to the presence of pods at lower heights concerning the height work of the harvester cutting deck 8.
None of the herbicide treatments applied postemergence resulted in decreases in the range of plants evaluated at harvest (Table 3). In general, when the herbicide is registered for use in the crop and its positioning is followed correctly, it is unlikely that the plants will die, causing reductions in the final population of the crop. Regarding the evaluations of yield components, as well as soybean grain yield, there were no significant differences among treatments (Table 4).
Table 4: Number of pods per plant (NPP), the mass of 100 grains (M100G), and soybean grain yield (cultivar: M7110 IPRO®) after application of post-emergence herbicide associations. Rio Verde (Brazil), 2020/2021. Tabla 4: Número de vainas por planta (NPP), masa de 100 granos (M100G) y rendimiento de grano de soja (cultivar: M7110 IPRO®) después de la aplicación de asociaciones de herbicidas de postemergencia. Rio Verde (Brasil), 2020/2021.
a.i. = active ingredient. ns Not significant by the F test (p≤0.05).
i.a. = ingrediente activo. ns No significativo por la prueba F (p≤0,05).
In this sense, it is observed that the occurrence of foliar injuries asso ciated with the reduction in the size of plants caused by some herbicide treatments was not enough to affect the productive response of soybean cultivar M7110 IPRO®.
This fact can be explained by the regular rainfall in the months after spraying the treat ments (Figure 1, page 88), which may have promoted greater crop recovery capacity after light foliar stresses caused by the herbicides used in the experiment, preserving the yield components (number of pods per plant and mass of 100 grains), as well as grain yield. Work carried out by Alonso et al. (2010, 2011, 2013) also demonstrated the selectivity of these herbicides to soybean crops. Despite this, selectivity studies are always necessary, since genetic variations of cultivars are one of the main factors influencing the greater or lesser tolerance of plants to a particular active ingredient 19.
Based on the results obtained in the study with this cultivar, it is evident that all herbicide associations applied postemergence showed selectivity for M7110 IPRO® at the doses and application stage in which they were used. In addition, it appears that the cultivar M7110 IPRO® has good adaptability to cultivation in the region where the experiment was conducted since it presented high yield levels.
Experiment II: Selectivity of herbicide associations applied postemergence to the soybean cultivar Foco IPRO®
Cultivar Foco IPRO® showed differential susceptibility to the variable injury level, with significant differences among herbicide treatments and the control without application (Table 5).
Table 5: Injury level of soybean (cultivar: Foco IPRO®) after application of post-emergence herbicide associations. Rio Verde (Brazil), 2020/2021. Tabla 5: Fitointoxicación de la soja (cultivar: Foco IPRO®) después de la aplicación de asociaciones de herbicidas de postemergencia. Rio Verde (Brasil), 2020/2021.
a.i. = active ingredient; DAA = Days after application. * Significant by F test (p≤0.05). Means followed by different letters in the column differ from each other by the Scott-Knott test (p≤0.05).
i.a. = ingrediente activo; DAA = días después de la aplicación. * Significativo por prueba F (p≤0,05). Medias seguidas de letras diferentes en la columna difieren entre sí por la prueba de Scott-Knott (p≤0,05).
In the evaluation carried out at 7 DAA, glyphosate in association with lactofen, as well as in association with ALS-inhibitors herbicides, imazethapyr, chlorimuron, and cloran sulam, provided the highest percentage of injuries to soybean plants, at levels ranging from 8,75 to 12.50%. The application of glyphosate isolated and the associations of this herbicide with bentazon or fomesafen at 7 DAA resulted in lower levels of intoxication than the other herbicide treatments but were still higher than the control.
Regarding the results obtained in the evaluation carried out at 28 DAA, the association of glyphosate with imazethapyr provided the highest level of injury for this cultivar (10.00%) (Table 5), with leaf chlorosis being the main observed visual symptom. Following the treat ments with higher levels of injuries, lactofen, chlorimuron, and cloransulam were all applied in association with glyphosate. Furthermore, in this evaluation, the ability of the cultivar Foco IPRO® to recover from the phytotoxicity caused by these previously mentioned herbi cides inhibiting PPO and ALS was evident. According to Oliveira Jr. et al. (2008), the effects of applying glyphosate to soybeans with RR® technology may vary according to the genotype, the time of application, and the dose of herbicide used.
The data referring to the evaluations of plant height (50 DAE and harvest) and plant stand at harvest are presented in Table 6 (page 93).
Table 6: Height and stand of soybean plants (cultivar: Foco IPRO®) after application of post-emergence herbicide associations. Rio Verde (Brazil), 2020/2021. Tabla 6: Altura y soporte de plantas de soja (cultivar: Foco IPRO®) después de la aplicación de asociaciones de herbicidas de postemergencia. Rio Verde (Brasil), 2020/2021.
a.i. = active ingredient; DAE = Days after emergence. * and ns Significant and non-significant, respectively, by the F test (p≤0.05). Means followed by different letters in the column differ from each other by the Scott-Knott test (p≤0.05).
i.a. = ingrediente activo; DAE = Días después de la emergencia. * y ns Significativo y no significativo, respectivamente, por la prueba F (p≤0,05). Medias seguidas de letras diferentes en la columna difieren entre sí por la prueba de Scott-Knott (p≤0,05).
Regarding the evaluation of plant height, the herbicide treatments did not cause changes in the plant height of soybean (cultivar Focus IPRO®) in both evaluations, with no significant differences from the control without application. With the above, there is a quick recovery of the stresses promoted by the herbicides applied postemergence, detected in the visual evaluations of injury levels, allowing that the vegetative growth of the plants was not negatively affected.
The final stand of the plants was also not affected by the herbicide treatments (Table 6), which demonstrates, once again, the safety regarding the use of these herbicides for the soybean cultivar Foco IPRO®. The evaluated herbicides did not influence yield components (number of pods per plant and weight of 100 grains) or grain yield, not showing significant differences from the control without application (Table 7).
Table 7: Number of pods per plant (NPP), mass of 100 grains (M100G) and soybean grain yield (cultivar: Focus IPRO®) after application of post-emergence herbicide associations. Rio Verde (Brazil), 2020/2021. Tabla 7: Número de vainas por planta (NPP), masa de 100 granos (M100G) y rendimiento de grano de soja (cultivar: Focus IPRO®) después de la aplicación de asociaciones de herbicidas de postemergencia. Rio Verde (Brasil), 2020/2021.
a.i. = active ingredient. ns Not significant by the F test (p≤0.05).
i.a. = ingrediente activo. ns No significativo por la prueba F (p≤0,05).
Marchi et al. (2013) reported that the association of glyphosate (1176 g a.i. ha-1) with chlorimuron (10 g a.i. ha-1) applied to soybean plants at stage V2-V3 resulted in a significant reduction in the mass of 100 grains but without an impact on the grain yield. Regular and expressive rainfall observed mainly in the months of January and February favored the cultivar Foco IPRO® in the aspect of reestab lishing foliar intoxication initially promoted by the herbicides, favoring the demonstration of herbicide selectivity. The cultivar Foco IPRO® presented, regardless of the herbicide treat ments, yields ranging from 3,510 to 4,067 kg ha-1, which demonstrates its good adaptability to the southwestern region of Goiás State.
Experiment III: Selectivity of herbicide associations applied postemergence to the soybean cultivar Bônus IPRO®
The injury level caused by the herbicide treatments for the Bônus IPRO® soybean cultivar is shown in Table 8.
Table 8: Injury level of soybean (cultivar: Bônus IPRO®) after application of post-emergence herbicide associations. Rio Verde (Brazil), 2020/2021. Tabla 8: Fitointoxicación de la soja (cultivar: Bônus IPRO®) después de la aplicación de asociaciones de herbicidas de postemergencia. Rio Verde (Brasil), 2020/2021.
a.i. = active ingredient; DAA = Days after application. * Significant by F test (p≤0.05). Means followed by different letters in the column differ from each other by the Scott-Knott test (p≤0.05).
i.a. = ingrediente activo; DAA = días después de la aplicación. * Significativo por prueba F (p≤0,05). Medias seguidas de letras diferentes en la columna difieren entre sí por la prueba de Scott-Knott (p≤0,05).
As seen for the other cultivars, more accentuated levels of phytotox icity occurred in the first evaluation (7 DAA), with a partial or complete recovery of most soybean plants in the later evaluation (28 DAA).
At 7 DAA, the PPO and ALS inhibitors lactofen and chlorimuron, respectively, both asso ciated with glyphosate, presented the highest percentages of injury levels to the soybean cultivar Bônus IPRO®, with averages of 13.75% and 16,25%, respectively, differing signifi cantly from the other treatments and the control without herbicide application. These data corroborate the results presented by Alonso et al. (2010), who verified that the association of herbicides with PPO and ALS modes of action to glyphosate present symptoms of foliar phytotoxicity to soybean plants superior to other tested mixtures in evaluations carried out at 7 and 15 DAA.
The initial leaf symptoms observed after the application of these herbicides were similar to those described by Alonso et al. (2013), including chlorimuron chlorosis followed by necrosis in the apical leaves and chlorosis with subsequent necrosis and wrinkling for lactofen. Even at 7 DAA, the associations of glyphosate with cloransulam, imazethapyr, or fomesafen showed intermediate levels of injuries, with phytotoxicity varying from 10.75 to 12.50%, not differing from each other. The PSII inhibitor bentazon, in association with glyphosate, promoted mild injury symptoms (6.25%), characterized by small and few chlo rotic and necrotic spots on the leaves.
At 28 DAA, the soybean plants of the Bônus IPRO® cultivar already showed good recovery from the symptoms of injuries; however, higher levels of injuries were observed in treatments involving the association of glyphosate with lactofen, chlorimuron, and cloransulam, where the levels were in the range of 5.00 to 10.00%. The other herbicide treatments evaluated did not show significant differences among them, with a maximum percentage of injuries of 3.75%, and were statistically equivalent to the control, which was without application.
At 50 DAE, a significant reduction was observed in the soybean plant size of the Bônus IPRO® cultivar that received a postemergence application of the association glyphosate + chlorimuron, with an average decrease of 18.31% in plant height when compared to the control without herbicide application (Table 9, page 95).
Table 9: Height and stand of soybean plants (cultivar: Bônus IPRO®) after application of post-emergence herbicide associations. Rio Verde (Brazil), 2020/2021. Tabla 9: Altura y soporte de plantas de soja (cultivar: Bônus IPRO®) después de la aplicación de asociaciones de herbicidas de postemergencia. Rio Verde (Brasil), 2020/2021.
a.i. = active ingredient; DAE = Days after emergence. * and ns Significant and non-significant, respectively, by the F test (p≤0.05). Means followed by different letters in the column differ from each other by the Scott-Knott test (p≤0.05).
i.a. = ingrediente activo; DAE = Días después de la emergencia. * y ns Significativo y no significativo, respectivamente, por la prueba F (p≤0,05). Medias seguidas de letras diferentes en la columna difieren entre sí por la prueba de Scott-Knott (p≤0,05).
The glyphosate + imazethapyr and glyphosate + lactofen treatments also resulted in a lower plant height of soybean, but at a lower magnitude, with an average reduction of 7.42%. All other herbicide treatments did not significantly affect the size of soybean plants when compared to the control without herbicide application. Of the morphological variables, plant height was the most affected by herbicides applied postemergence and is an important parameter for measurement in selectivity experiments 12.
At harvest, plants of the cultivar Bônus IPRO® recovered for the variable height, with no more differences among the glyphosate + imazethapyr and glyphosate + lactofen asso ciations and the control without herbicide application (Table 9). Only the glyphosate + chlorimuron treatment provided a lower final plant height, with an average reduction of 9.56%, compared to the average height of soybean plants present in the control treatment plots without herbicides. Correia and Durigan (2007), evaluating the selectivity of eight commercial formulations of glyphosate-based products to two RR® soybean cultivars, found that none of the herbicides influenced the plant height.
The final stand of plants for the Bônus IPRO® cultivar remained statistically the same for all treatments, with no significant reduction occurring among the experimental units that received the herbicides and the control (Table 9). This result consolidates the results found for the cultivars M7110 IPRO® and Foco IPRO®, where it is verified that the evaluated herbicide treatments did not reduce the plant stand. For the variables number of pods per plant and mass of 100 grains, negative changes were not verified in the soybean plants of the cultivar Bônus IPRO® due to the application of postemergence herbicides (Table 10, page 96).
Table 10: Number of pods per plant (NPP), mass of 100 grains (M100G) and soybean grain yield (cultivar: Bônus IPRO®) after application of post-emergence herbicide associations. Rio Verde (Brazil), 2020/2021. Tabla 10: Número de vainas por planta (NPP), masa de 100 granos (M100G) y rendimiento de grano de soja (cultivar: Bônus IPRO®) después de la aplicación de asociaciones de herbicidas de postemergencia. Rio Verde (Brasil), 2020/2021.
a.i. = active ingredient. * and ns Significant and non-significant, respectively, by the F test (p≤0.05). Means followed by different letters in the column differ from each other by the Scott-Knott test (p≤0.05).
i.a. = ingrediente activo. * y ns Significativo y no significativo, respectivamente, por la prueba F (p≤0,05). Medias seguidas de letras diferentes en la columna difieren entre sí por la prueba de Scott-Knott (p≤0,05).
This result differs from the study carried out by Alonso et al. (2011), where it was verified that the association of glyphosate and lactofen promoted a significant reduction in the mass of 100 grains.
Regarding grain yield, the treatments isolated glyphosate, glyphosate + lactofen, and glyphosate + imazethapyr provided significant reductions in this parameter of 8.99%, 6.62%, and 9.67%, respectively, compared to the grain yield recorded in the control without herbicide application (Table 10, page 96). These results demonstrate the lack of selectivity of these herbicide treatments for use in production areas that use this cultivar. According to Constantin et al. (2016), the attenuation of negative effects, such as foliar injuries, caused by the herbicide glyphosate in genetically modified soybean cultivars (RR®) can be mini mized, maintaining the crop’s yield potential through the use of biostimulant products. The other herbicide treatments did not damage the grain yield of the cultivar Bônus IPRO®, which presented yields ranging from 3,288 to 3,903 kg ha-1, regardless of the evaluated herbicide treatments.
Conclusion
The stand of plants at harvest of soybean cultivars M7110 IPRO®, Foco IPRO®, and Bônus IPRO® was not decreased by postemergence applications of glyphosate, either isolated or in association with bentazon, fomesafen, lactofen, imazethapyr, chlorimuron, and cloransulam.
None of the evaluated herbicide treatments caused a reduction in the grain yield of cultivars M7110 IPRO® and Foco IPRO®; however, the herbicides lactofen and chlorimuron, in association with glyphosate, were the ones that caused the highest levels of phytotox icity to M7110 IPRO®, and the combination of glyphosate with imazethapyr caused greater phytotoxicity in the cultivar Foco IPRO®.
Post-emergence application of glyphosate was isolated, and the associations of glyphosate + lactofen and glyphosate + imazethapyr decreased the grain yield of the Bônus IPRO® soybean cultivar.
The results of the present work reinforce the need for care in choosing the soybean cultivar and the selection of the herbicides to be applied postemergence, as the genetics of the material are decisive for the response in terms of sensitivity to the applied herbicides.
