Abstract
Background
Glyphosate is the most effective herbicide to control the invasive and perennial Eragrostis plana in Southern Brazil. However, one application has not been sufficient to prevent the regrowth of plants.Objective: The aim of this research was to evaluate the efficacy of glyphosate sprayed alone or mixed with fluazifop-p-butyl or flumioxazin on E. plana control and to investigate 14C-glyphosate absorption and translocation.
Methods
Plants with 2-3 tillers were treated with glyphosate (700 g a.e. ha-1), fluazifop-p-butyl (47 g a.i. ha-1), flumioxazin (100 g a.i. ha-1), glyphosate + fluazifop-p-butyl (700 g a.e. ha-1 + 47g a.i. ha-1), glyphosate + flumioxazin (700 g a.e. ha-1 +100 g a.i. ha-1). Weed control was evaluated visually for 28 d after treatment (DAT) when plants were harvested for shoot dry biomass determination. 14C-glyphosate absorption and translocation were measured at 24 and 72 h after treatment.
Results
Glyphosate at 700 g a.e. ha-1 controlled E. plana plants at 2-3 tillers. The mixture with fluazifop-p-butyl or flumizin did not significantly increase the level of control (87 and 86% at 7 DAT, respectively) but increased 14C-glyphosate translocation to the roots.
Conclusions
Glyphosate is effective on E. plana. However, applied with fluazifop-p-butyl could improve the control of this weed, especially when perennial plants of E. plana dominate the field, preventing their fast regrowth.
14C-glyphosate; fluazifop-p-butyl; forage grass; invasive plant; tough lovegrass
1.Introduction
The structure and floristic richness of Southern fields of Brazilian rangelands in Rio Grande do Sul, Santa Catarina, and Paraná states are unique. Such diversity derives from a multitude of factors like climate, soil, and vegetation management (Boldrini, 2009Boldrini I. [The flora of the fields of Rio Grande do Sul State] In: Pillar VP, Müller SC, Castilhos ZMS, Jacques AVA. [Southern fields: conservation and sustainable use of biodiversity]. Brasília: Ministério do Meio Ambiente; 2009. p. 63-77. Portuguese.). More than 450 species belonging to the family Poaceae and more than 200 species belonging to the family Fabaceae are distributed in this region and are economically relevant, given their forage profile (Boldrini, 2009Boldrini I. [The flora of the fields of Rio Grande do Sul State] In: Pillar VP, Müller SC, Castilhos ZMS, Jacques AVA. [Southern fields: conservation and sustainable use of biodiversity]. Brasília: Ministério do Meio Ambiente; 2009. p. 63-77. Portuguese.). Despite the importance of and benefits from fields composing the “Pampa biome”, they have been degraded due to several factors, among them, intense grazing, burning (although forbidden), mechanized cultivation practices (Medeiros, Focht, 2007), and biological invasion of exotic species (Pivello et al., 1999Pivello VR, Shida CN, Meirelles ST. Alien grasses in Brazilian savannas: a threat to the biodiversity. Biodiv Conserv. 1999;8(9):1281-94. Available from: https://doi.org/10.1023/A:1008933305857
https://doi.org/10.1023/A:1008933305857...
) such as tough lovegrass (Eragrostis plana Nees). This species has caused a severe biodiversity loss in the region, which is of great environmental concern (Medeiros, Focht, 2007).
E. plana was introduced into Brazil in the 1950s as a putative high-quality forage, but the low digestibility and poor nutrient composition did not allow its use as expected (Kissmann, Groth, 1999). E. plana invasion in native rangelands has contributed to the declining abundance of native grasses, affecting pasture quality and causing animal losses (Medeiros et al., 2009Medeiros RB, Saibros JC, Focht T. [Invasion of annoni grass (Eragrostis plana Nees) in the Pampa Biome of Rio Grande do Sul]. In: Pillar VP, Müller SC, Castilhos ZMS, Jacques AVA, editors. [Southern fields: conservation and sustainable use of biodiversity]. Brasília: Ministério do Meio Ambiente; 2009. p. 319-30.), including teething wear of livestock due to its very fibrous leaves. Recently, it was observed that E. plana and E. pilosa, another invasive species from Africa, could compete with irrigated rice crop (Carloto et al., 2019Carloto B, Buriol G, Dorneles S, Trivisol V, Peripolli M. Morphological and phenological responses of Eragrostis plana Nees and Eragrostis pilosa (L.) P. Beauv. Plants subjected to different soil moisture conditions. Planta Daninha. 2019;37:1-7. Available from: https://doi.org/10.1590/S0100-83582019370100128
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). High allelopathic potential has been observed in field and laboratory studies and is known to facilitate E. plana establishment and displacement of native flora. A study evaluating leaf extracts from E. plana on clover seed germination confirmed its allelopathic effect (Scheffer-Basso et al., 2019Scheffer-Basso SM, Fiorentin F, Favaretto A. Influence of phenology and post-harvest processing of vegetal material on the allelopathy of annoni grass (Eragrostis plana) extracts. Planta Daninha. 2019;37:1-11. Available from: https://doi.org/10.1590/S0100-83582019370100013
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).
The best application timing for systemic herbicides, especially for the management of perennial weeds, corresponds to the stage where maximum basipetal translocation of carbohydrates occurs (Banks et al., 1977Banks PA, Kirby MA, Santelmann PW. Influence of postemergence and subsurface layered herbicides on horsenettle and peanuts. Weed Sci. 1977;25(1):5-8. Available from: https://doi.org/10.1017/S004317450003280X
https://doi.org/10.1017/S004317450003280...
). This change in the translocation pattern of photoassimilates usually takes place after flowering and allows phloem-mobile herbicides, such as glyphosate, to reach roots and rhizomes, optimizing herbicide activity. Glyphosate is considered the best herbicide for E. plana management (Goulart et al., 2012Goulart ICGDR, Nunes AL, Kupas V, Merotto Jr. A. [Interactions between herbicides and safeners to tough lovegrass control in natural pasture]. Cienci Rural. 2012;42:1722-30. Portuguese. Available from: https://doi.org/10.1590/S0103-84782012001000002
https://doi.org/10.1590/S0103-8478201200...
; Bastiani et al., 2021Bastiani MO, Roma-Burgos N, Langaro AC, Salas-Perez RA, Rouse CE, Fipke MV et al. Ammonium sulfate improves the efficacy of glyphosate on South African lovegrass (Eragrostis plana) under water stress. Weed Sci. 2021;69(2):167-76. Available from: https://doi.org/10.1017/wsc.2020.97
https://doi.org/10.1017/wsc.2020.97...
). During the E. plana life cycle, the full-tillering stage is when plants are least sensitive to glyphosate (Bastiani et al., 2021Bastiani MO, Roma-Burgos N, Langaro AC, Salas-Perez RA, Rouse CE, Fipke MV et al. Ammonium sulfate improves the efficacy of glyphosate on South African lovegrass (Eragrostis plana) under water stress. Weed Sci. 2021;69(2):167-76. Available from: https://doi.org/10.1017/wsc.2020.97
https://doi.org/10.1017/wsc.2020.97...
), the cause of reduced glyphosate translocation into different plant parts, especially in older tillers. Instead, minimum amounts are distributed across some tillers, which results in sublethal concentrations on a per-tiller basis, allowing several tillers to regrow. E. plana does not have rhizomes. Nevertheless, Favaretto et al. (2015)Favaretto A, Santos J, Carneiro CM, Basso SMS. The first anatomical and histochemical study of tough lovegrass (Eragrostis plana Nees, Poaceae). African Journal of Agricultural Research. 2015; 10: 2940-2947. Available from: https://doi.org/10.5897/AJAR2014.9145
https://doi.org/10.5897/AJAR2014.9145...
found starch accumulation in roots of E. plana, which can explain the fast regrowth observed in the field after unsuccessful glyphosate applications. Incomplete control of perennial grasses with herbicides is a common problem.
The mixture of active ingredients can be beneficial to slow the evolution of herbicide resistance and increase the spectrum of controlled weeds (Norris et al., 2001Norris JL, Shaw DR, Snipes CE. Weed control from herbicide combinations with three formulations of glyphosate. Weed Technol. 2001;15(3):552-8. Available from: https://doi.org/10.1614/0890-037X(2001)015[0552:WCFHCW]2.0.CO;2
https://doi.org/10.1614/0890-037X(2001)0...
). A herbicide mixture is synergistic when the effect is greater than the sum of both herbicides applied alone. However, if the observed effect of the mixture is lower than the sum of individual effects, it is classified as antagonistic (Colby, 1967Colby SR. Calculating synergistic and antagonistic responses of herbicide combinations. Weeds. 1967;15(1):20-2. Available from: https://doi.org/10.2307/4041058
https://doi.org/10.2307/4041058...
). The interaction is additive if the sum of isolated effects does not differ from the mixture effect (Staker, Oliver, 1998). An interesting example is the synergistic interaction between glyphosate and clethodim or haloxyfop described for Digitaria insularis (L.) Fedde. control (Barroso et al., 2014Barroso AAA, Albrecht AJP, Reis FC, Filho RV. Interaction among ACCAse inhibitors herbicides and different formulations of glyphosate on sourgrass control. Planta Daninha. 2014;32(3):619-27. Available from: https://doi.org/10.1590/S0100-83582014000300018
https://doi.org/10.1590/S0100-8358201400...
). Herbicide options for E. plana management are limited, and, in general, are not as efficient as glyphosate when applied by themselves (Goulart et al., 2012Goulart ICGDR, Nunes AL, Kupas V, Merotto Jr. A. [Interactions between herbicides and safeners to tough lovegrass control in natural pasture]. Cienci Rural. 2012;42:1722-30. Portuguese. Available from: https://doi.org/10.1590/S0103-84782012001000002
https://doi.org/10.1590/S0103-8478201200...
; Faleiro et al., 2021Faleiro, E. A, Lamego FP, Schaedler CE, Del Valle TA, Azevedo EB. Integrated management of tough lovegrass (Eragrostis plana Nees): associating chemical control tools and plant physiology. Ciência Rural. 2021;51Available from: https://doi.org/10.1590/0103-8478cr20210490
https://doi.org/10.1590/0103-8478cr20210...
). Therefore, farmers mostly rely on glyphosate mixtures to manage E. plana infestations. A commonly used partner for glyphosate - especially in soybean preplant burndown applications - is flumioxazin, a protoporphyrinogen oxidase (PROTOX) inhibitor. To a lower extent, glyphosate + fluazifop-p-butyl have also been used by farmers in Southern Brazil.
Similar to the E. plana case, several invasive plants worldwide have escaped cultivation or been introduced without a previous thorough evaluation (Nentwig et al., 2018Nentwig W, Bacher S, Kumschick S, Pyšek P, Vilà M. More than “100 worst” alien species in Europe. Biol Invasions. 2018;20:1611-21. Available from: https://doi.org/10.1007/s10530-017-1651-6
https://doi.org/10.1007/s10530-017-1651-...
). As a consequence, negative environmental impacts on native flora and fauna could occur if the species is not managed. Limited knowledge exists about herbicide behavior in E. plana plants during their life cycle, and additional research is needed to establish a correct management strategy. Knowledge about the absorption and translocation of glyphosate on E. plana is needed. Interestingly, Bastiani et al. (2021)Bastiani MO, Roma-Burgos N, Langaro AC, Salas-Perez RA, Rouse CE, Fipke MV et al. Ammonium sulfate improves the efficacy of glyphosate on South African lovegrass (Eragrostis plana) under water stress. Weed Sci. 2021;69(2):167-76. Available from: https://doi.org/10.1017/wsc.2020.97
https://doi.org/10.1017/wsc.2020.97...
found that the addition of ammonium sulfate to glyphosate increased translocation out of the treated leaf in E. plana. However, when associated with other herbicides, no information about glyphosate translocation is reported to manage this invasive plant.
Therefore, the objectives of this research were to: 1) evaluate glyphosate efficacy at 2-3 tiller stage when applied alone or in association with flumioxazin or fluazifop-p-butyl-p-butyl; and 2) evaluate the effect of these mixtures in glyphosate absorption and translocation.
2.Material and Methods
The experiments were carried out between December 2018 and January 2019 in a greenhouse and the Radioisotope Laboratory of Crop, Soil and Environmental Sciences Department da University of Arkansas (CSES/UARK), Fayetteville - AR, United States. Seeds of E. plana were collected in native pastures of the Federal University of Pelotas, Capão do Leão, RS, Brazil, in March 2018.
2.1 Glyphosate Efficacy
Experimental units were pots of 500 mL of field soil from the Arkansas Main Research Station at Fayetteville, CSES/UARK, United States. Seeds were sown, and seedlings were thinned to 1 plant per pot five days after emergence. E. plana plants were grown in a greenhouse maintained at 32/28 °C day/night temperature, with a 14 h light supplementation. When plants reached the 2- to 3-tiller stage, they were sprayed with one of the following herbicide treatments: glyphosate (700 g a.e. ha-1), fluazifop-p-butyl-p-butyl (47 g a.i. ha-1), flumioxazin (100 g a.i. ha-1), glyphosate + fluazifop-p-butyl-p-butyl (700 g a.e. ha-1 + 47 g a.i. ha-1) and glyphosate + flumioxazin (700 g a.e. ha-1 + 100 g a.i. ha-1). An untreated check was included. The experiment consisted of a completely randomized design, with four replicates (one replicate = 1 plant per pot). Two runs of the experiment were conducted simultaneously in two different greenhouses. Herbicides were applied at a constant pressure of 280 kPa in a spray chamber equipped with a 1-m spray boom with two flat-fan nozzles (Teejet TP 800067), spaced 0.5 m apart, and calibrated to deliver a spray volume of 187 L ha-1.
2.2 Absorption and translocation of glyphosate studies
E. plana plants were cultivated as previously described. At the 2- to 3-tiller stage, plants were sprayed with one of the herbicide treatments: glyphosate (700 g a.e. ha-1), glyphosate + fluazifop-p-butyl (700 g a.e. ha-1 + 47 g a.i. ha-1) and glyphosate + flumioxazin (700 g a.e. ha-1 + 100 g a.i. ha-1). The same application equipment and parameters were used. Immediately after herbicide application, plants were taken to the radioisotope laboratory, where 14C-glyphosate was applied. The radiolabeled herbicide was applied to the third youngest, fully expanded leaves using a microsyringe in four 1-µL droplets resulting in a total of 150,000 dpm of [14C] glyphosate applied per plant. Plants were harvested at 24 and 72 hours after treatment (HAT).
To recover the unabsorbed glyphosate, treated leaves were harvested and triple-rinsed in 10 mL of a 9:1 mixture of water and methanol. A composite sample was made by mixing 5 mL aliquots of each replicate, and 10mL of scintillation cocktail was added (Ultima GoldTM; PerkinElmer Inc., Waltham, MA, USA). Radiation was quantified using a liquid scintillation spectrometer (LSS, Packard Tri-Carb 2100TR; Packard Instrument Corp., Downers Grove, IL, USA). Glyphosate absorption was calculated as the percentage of total radioactivity recovered (rinsate + radioactivity the plant) as described by the following equation:
Glyphosate translocation was evaluated by dividing the treated plant into sections: treated leaf (TL), above TL, below TL, tillers, and roots, for each harvest time, which were dried at 60°C for 48 h. After that, they were oxidized in a biological oxidizer (OX500TM; R. J. Harvey Instrument Corp., Tappan, NY, USA). The 14CO2 evolved during sample combustion was trapped in a glass scintillation vial containing 15 mL of scintillation cocktail (Carbon-14 Cocktail; R. J. Harvey Instrument Corp.). It was quantified using the LSS, as previously described.
One plant from each harvest period and treatment was used to visualize herbicide translocation through autoradiographs. Plants were collected at 24 and 72 HAT and immediately pressed in absorbent paper. Leaves were placed to avoid the treated leaf contacting other parts of the plant. Plants were dried and, subsequently, exposed to a phosphorescent film for 48 h. After which they were scanned in Storm 820 PhosphorImagerTM (Molecular Dynamics Inc., Sunnyvale, CA, USA).
2.3 Statistical analysis
Herbicide effect was visually assessed using a 0 to 100% scale at four intervals: 7, 14, 21, and 28 days after treatment (DAT), where 0% represents the absence of symptoms, and 100% represents plant death (Sociedade Brasileira da Ciência de Plantas Daninhas, 1995Sociedade Brasileira da Ciência de Plantas Daninhas – SBCPD. [Procedures for installing, evaluating and analyzing herbicide experiments]. Londrina: Sociedade Brasileira da Ciência de Plantas Daninhas; 1995. Portuguese.). After the last visual assessment, shoots were harvested and dried at 60 °C to determine the final shoot dry mass. Data was checked for normality (Shapiro-Wilk), and an analysis of variance was performed considering run as fixed effect using the function lmer in the package lme4 (version 1.1-26), in R 4.0.3 (R Core Team, 2019R Core Team. R: a language and environment for statistical computing. Viena: R Foundation for Statistical Computing; 2019.). Because no significant effect was observed (p ≥ 0.05), data from both runs of the experiments were combined, and means were compared using the Tukey’s test (package ExpDes1.2.1). Statistical analyses were performed using R software (R Core Team, 2019R Core Team. R: a language and environment for statistical computing. Viena: R Foundation for Statistical Computing; 2019.).
3.Results and Discussion
E. plana control with glyphosate reached 95% at 7 DAT (Table 1), and 100%at 14 DAT. Glyphosate + fluazifop-p-butyl or flumioxazin provided control of 87% and 86% at 7 DAT, respectively, with means not differing from glyphosate applied alone. Fluazifop-p-butyl and flumioxazin applied by themselves were not different from each other. Only 32 and 30% control of E. plana at 7 DAT were observed for fluazifop-p-butyl and flumioxazin respectively. However, at 14 DAT, fluazifop-p-butyl provided better control than flumioxazin, 76% and 32%, respectively. The greatest control achieved with fluazifop-p-butyl by itself was observed at 28 DAT (88%), at which time flumioxazin provided 39% control of E. plana (Table 1). Glyphosate was efficient in controlling young plants of E. plana (2- to 3-tiller stage), which was not surprising considering that young plants have less biomass and higher herbicide absorption than old plants (Degreeff et al., 2018Degreeff RD, Varanasi A, Dille JE, Peterson D, Jugulam M. Influence of plant growth stage and temperature on glyphosate efficacy in common lambsquarters (Chenopodium album). Weed Technol. 2018;32(4):448-53. Available from https://doi.org/10.1017/wet.2018.38
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). In addition, the translocation patterns of photoassimilates can change considerably during the plant is life cycle, affecting herbicide activity (Fadin et al., 2018Fadin DA, Tornisielo VL, Barroso AAM, Ramos S, Reis FC, Monquero PA. Absorption and translocation of glyphosate in Spermacoce verticillata and alternative herbicide control. Weed Res. 2018;58(5):389-96. Available from: https://doi.org/10.1111/wre.12329
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).
In general, the addition of other herbicides does not affect the efficacy of glyphosate when it is applied at a stage when the weed is highly susceptible; however, glyphosate efficacy can be compromised by certain herbicide mixtures when applied at a suboptimal growth stage or during suboptimal environmental conditions. To illustrate this point, the addition of 2.4-D, chlorimuron, metolachlor, or cloransulam to glyphosate did not affect Spermacoce verticillata control, when plants were sprayed at the 2- to 4-leaf stage. At that stage, glyphosate alone or in combination provided high levels of control. However, when plants were sprayed at the 4- to 6-leaf stage, the glyphosate + cloransulam mixture was 40% more effective compared to glyphosate applied alone (Fadin et al., 2018Fadin DA, Tornisielo VL, Barroso AAM, Ramos S, Reis FC, Monquero PA. Absorption and translocation of glyphosate in Spermacoce verticillata and alternative herbicide control. Weed Res. 2018;58(5):389-96. Available from: https://doi.org/10.1111/wre.12329
https://doi.org/10.1111/wre.12329...
). Likewise, glyphosate alone or in combination with quizalofop or clethodim was equally effective in controlling D. insularis sprayed at the 4-leaf stage. However, these herbicides were synergistic when applied to bigger plants (3 to 4 tillers) (Barroso et al., 2014Barroso AAA, Albrecht AJP, Reis FC, Filho RV. Interaction among ACCAse inhibitors herbicides and different formulations of glyphosate on sourgrass control. Planta Daninha. 2014;32(3):619-27. Available from: https://doi.org/10.1590/S0100-83582014000300018
https://doi.org/10.1590/S0100-8358201400...
). While glyphosate alone provided 48% control, the addition of quizalofop or clethodim resulted in 79% and 81% control, respectively (Barroso et al., 2014Barroso AAA, Albrecht AJP, Reis FC, Filho RV. Interaction among ACCAse inhibitors herbicides and different formulations of glyphosate on sourgrass control. Planta Daninha. 2014;32(3):619-27. Available from: https://doi.org/10.1590/S0100-83582014000300018
https://doi.org/10.1590/S0100-8358201400...
).
The glyphosate + flumioxazin treatment was included in our study as it is commonly used by farmers in Southern Brazil, before to soybean cultivation in crop-livestock integration system areas. Farmers reported improved E. plana control in the field (personal communication), but we did not observe this in our test where glyphosate alone already provided highest control (>90%). A repetition of this study using older plants beyond four tillers, could be informative. As flumioxazin had very poor activity on E. plana control (< 39% at 28 DAT) (Table 1), we believe that its use by farmers mixed with glyphosate is justified by its residual soil activity (Oliveira et al., 1998Oliveira MF, Silva AA, Neves JCL. Influência do tamanho do agregado e do nível de umidade do solo na atividade do flumioxazin. Revista Ceres, v. 45, p. 81-87, 1998.; Carvalho, 2017)Carvalho FT. Efficacy of flumioxazin applied in the preharvest desiccation of soybean and residual effect on weed control in the winter maize. Rev Cienc Agron. 2017;26(4):683-93. Available from: https://doi.org/10.32929/2446-8355.2017v26n4p683-693
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, which would reduce the establishment of E. plana seedlings from the seed bank. This assumption needs further investigation. The mixture of glyphosate with other herbicides can have different results (Staker, Oliver, 1998). This research detected no visible improvement in glyphosate efficacy when mixed with fluazifop-p-butyl or flumioxazin herbicides.
The total amount of glyphosate absorbed by E. plana at 24 HAT reached 25% of the applied, 41% for glyphosate + fluazifop-p-butyl, and 28% for glyphosate + flumioxazin (Figure 1A). Hence, the addition of fluazifop-p-butyl to glyphosate favored its early absorption. Interestingly, flumioxazin enhanced glyphosate absorption at 72 HAT but limited its translocation: 60% of the absorbed herbicide remained in the treated leaf (TL) (Figure 1B). PROTOX-inhibitors have differential absorption by weeds, but in general, their translocation is limited (Vanstone, Stobbe, 1978; Ritter, Coble, 1981; Higgins et al., 1998; Unland et al., 1999Unland RD, Al-Khatib K, Peterson DE. Interactions between imazamox and diphenylethers. Weed Sci. 1999;47(4):462-6. Available from: https://doi.org/10.1017/S0043174500092080
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). Glyphosate isolated showed less total absorption and translocation than when mixed with fluazifop-p-butyl or flumioxazin. However, it was not observed difference on E. plana control (Table 1). Possibly, a synergistic effect explain this and need further investigation based on studies of the mixture of glyphosate with other herbicides (Staker, Oliver, 1998; Barroso et al., 2014Barroso AAA, Albrecht AJP, Reis FC, Filho RV. Interaction among ACCAse inhibitors herbicides and different formulations of glyphosate on sourgrass control. Planta Daninha. 2014;32(3):619-27. Available from: https://doi.org/10.1590/S0100-83582014000300018
https://doi.org/10.1590/S0100-8358201400...
).
Percentage of absorption and translocation of 14C-glyphosate at 24 (A) and 72 (B) hours after treatment: Total (absorption and translocation), treated leaf (TL), above treated leaf (ATL), below treated leaf (BTL), roots and plant tillers of Eragrostis plana. Herbicides applied at 2-3 tillers stage. Each plant received a total of 150,000 dpm of [14C] glyphosate. Different lowercase letters indicate statistical differences among plant parts by Tukey’s test (P ≤ 0.05). Bars represent the standard error. Fayetteville/AR, USA, 2018/19.
Perhaps the most interesting result of this research was that the addition of fluazifop-p-butyl to glyphosate increased glyphosate movement to the roots regardless of the evaluation timings. This was clearly seen in the autoradiographies. As mentioned before, we were not able to observe additive or synergistic effects because glyphosate alone provided excellent control of E. plana. However, the improved translocation to the roots indicates the mechanism through which fluazifop-p-butyl may enhance E. plana control under field conditions. Glyphosatetranslocation in plants goes in both directions, the root system and shoot, and follows the flow of carbohydrates from sources towards sinks (amphimobile). The herbicide has a tendency to accumulate in the apical meristems of leaves and roots (Chen et al., 2009Chen RF, Wang HH, Wang CY. Translocation and metabolism of injected glyphosate in lead tree (Leucaena leucocephala). Weed Sci. 2009;57(5):229-34. Available from: https://doi: 10.1614/WS-08-155.1
https://doi:...
; Reis et al., 2015Reis FCD, Tornisielo VL, Cason JB, Dias ACR, Freitas M, Sotomayor JF, Barroso AA, Filho RV. Uptake, translocation, and control of trumpet flower (Tecoma stans) with aminocyclopyrachlor. Journal of Environmental Science and Health, 2015;50: 727-733. Available from: https://doi.org/10.1080/03601234.2015.1048106
https://doi.org/10.1080/03601234.2015.10...
). Some E. plana features, such as high lignin concentration in leaves (Favaretto et al., 2015Favaretto A, Santos J, Carneiro CM, Basso SMS. The first anatomical and histochemical study of tough lovegrass (Eragrostis plana Nees, Poaceae). African Journal of Agricultural Research. 2015; 10: 2940-2947. Available from: https://doi.org/10.5897/AJAR2014.9145
https://doi.org/10.5897/AJAR2014.9145...
), and the possible interdependence mechanism between early tillers (Corrêa et al., 2014Corrêa EB, Silveira MCT, Morais SL, Trentin G, Perez NB, Natividade RS. [Characterization of the dynamics of annoni grass tillers regarding the translocation of the herbicide glyphosate]. In: Procedings of the 13th Congresso de Iniciação Científica; 2014; Pelotas, RS, Brasil. Pelotas: Universidade Federal de Pelotas; 2014. Portuguese.; Bastiani et al., 2021Bastiani MO, Roma-Burgos N, Langaro AC, Salas-Perez RA, Rouse CE, Fipke MV et al. Ammonium sulfate improves the efficacy of glyphosate on South African lovegrass (Eragrostis plana) under water stress. Weed Sci. 2021;69(2):167-76. Available from: https://doi.org/10.1017/wsc.2020.97
https://doi.org/10.1017/wsc.2020.97...
), tend to impair glyphosate translocation. The associated use of glyphosate with other herbicides capable of improving its translocation is an option to be considered for managing perennial species such as E. plana. However, further studies to assess the translocation of 14C-glyphosate/fluazifop-p-butyl at different invasive plant development stages are needed.
The knowledge generated in this research can be used to optimize a technique for E. plana control that is currently used in Southern Brazil. The equipment called Campo Limpo, developed in collaboration with Brazilian Agricultural Research Corporation (Empresa Brasileira de Pesquisa Agropecuária – Embrapa), selectively applies glyphosate on the target plants without exposing the desired forage to the herbicide (Perez, 2015Perez N. [Integrated method of pasture recovery (Mirapasto): grass-annoni focus]. Bagé: Embrapa; 2015. Portuguese.). However, weed control is many times unsatisfactory given the fact that plants are distributed in dense tussocks, which reduce herbicide translocation throughout the whole plant and lead to resprouting. In this sense, the addition of fluazifop-p-butyl to glyphosate may enhance Campo Limpo efficiency and practicality.
4.Conclusions
Glyphosate at 700 g a.e. ha-1 effectively controlled Eragrostis plana when applied at the 2- to 3-tiller stage.
Autoradiograph of Eragrotis plana with glyphosate (700 g e.a ha-1), glyphosate + fluazifop-p-butyl (700 g e.a + 47 g i.a ha-1) and glyphosate + flumioxazin (700 g e.a + 100 g i.a ha-1) added with 14C-glyphosate at 24 and 72 HAT. (A) pressed plant (B) translocation autoradiograph. Fayetteville/AR, USA, 2018/19.
The addition of fluazifop-p-butyl or flumioxazin to glyphosate does not improve E. plana control. However, the mixture with fluazifop-p-butyl increased 14C-glyphosate translocation in the invasive plant and may be useful for managing adult plants in highly infested fields.
Acknowledgements
We are thankful to the Brazilian Agricultural Research Corporation – Embrapa (Brazil), Federal University of Pelotas (UFPel), and the Weed Physiology Project, University of Arkansas Division of Agriculture, Arkansas (United States), for funding this research. The student and research were also supported by the Coordination for the Improvement of Higher Education Personnel (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Capes), and the National Council for Scientific and Technological Development (Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq) through a scholarship to the first author and fellowship to the last author (grant: CNPq 305816/2016-0).
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Publication Dates
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Publication in this collection
11 Nov 2022 -
Date of issue
2022
History
-
Received
4 Apr 2022 -
Accepted
26 Sept 2022