(e-ISSN 2236-3122)
`Citrus Research & Technology, v. 37, n. 1, 2016
`http://dx.doi.org/10.4322/crt.ICC083
`
`Nota/Note
`
`Physical characteristics of insecticide spraying liquids with mineral oil
`and droplets formed on citrus leaves
`
`Jaqueline Franciosi Della Vechia1, Renata Thaysa da Silva Santos1, Daniel Junior de Andrade1
`& Marcelo da Costa Ferreira1
`
`SUMMARY
`
`The physical characteristics of a spray liquid are important in getting a good droplet formation
`and efficiency control over a target pest. These characteristics can be changed in various ways, the
`addition of mineral oil can be one of them. Thus, the aim of this study was to evaluate the physical
`characteristics of the surface tension of the diflubenzuron insecticide using different mineral oils in
`two concentrations and the interaction of droplets produced on the leaf surface of orange through the
`formed contact angle. Therefore, seven spraying liquids were prepared composed of diflubenzuron,
`often used in citrus for insect pest control, and three mineral oils (Argenfrut, OPPA and Nimbus)
`in two concentrations (0.25 e 0.5% v/v). Pendant droplets formed from these mixtures were measured
`to examine their impact on surface tension. Droplets were applied to the surface of orange leaves
`and the contact angle formed were measured. The addiction of the mineral oil to diflubenzuron
`reduce the surface tension and contact angles of droplets on leaf surfaces, resulting in a large surface
`area covered. Among the evaluated mineral oils, OPPA and Nimbus showed greater reduction in
`surface tension and smaller droplets contact angles on the orange leaf. Therefore, the application of
`the diflubenzuron with OPPA or Nimbus, at concentrations of 0.25 and 0.50%, provide a better
`spreadability of the sprayed droplets.
`Index terms: contact angle, surface tension, spreading.
`
`Características físicas de calda inseticida com óleo mineral e gotas formadas
`sobre folhas de citros
`
`RESUMO
`
`As características físicas de um líquido pulverizado são importantes afim de obter boa
`formação de gotas e eficiência de controle sobre um determinado alvo. Essas características podem
`ser alteradas de diversas formas, a adição de óleo mineral pode ser uma delas. O objetivo desse
`trabalho foi avaliar as características físicas da tensão superficial do inseticida diflubenzuron
`utilizando diferentes óleos minerais em duas concentrações, e a interação das gotas produzidas
`na superfície foliar de laranja através do ângulo de contato formado. Portanto, foram preparadas
`sete caldas fitossanitárias compostas pelo inseticida diflubenzuron, comumente utilizado em citros
`para o controle de insetos praga e três óleos minerais (Argenfrut, OPPA e Nimbus) em duas
`concentrações (0,25 e 0,5% v/v). Gotas pendentes formadas a partir dessas misturas foram medidas
`
`1 Universidade Estadual Paulista – UNESP, Jaboticabal, SP, Brazil
`Corresponding author: Jaqueline Franciosi Della Vechia, Universidade Estadual Paulista – UNESP, Via de Acesso Prof. Paulo Donato
`Castellane, s/n, CEP 14884-900, Jaboticabal, SP, Brazil. E-mail: jaque_dellavechia@hotmail.com
`
`SYNGENTA EXHIBIT 1018
`Syngenta v. UPL, PGR2023-00017
`
`

`

`Physical characteristics of insecticide spraying liquids…
`
`103
`
`em sua tensão superficial. Aplicaram-se gotas sobre a superfície de folhas de laranja e foi medido o ângulo de contato
`formado pela gota. A adição de óleo mineral ao diflubenzuron reduziu a tensão superficial e ângulo de contato
`das gotas com a superfície foliar, resultando em uma maior cobertura. Entre os óleos minerais avaliados, OPPA
`e Nimbus apresentaram maior redução na tensão superficial e ângulos de contato menores formados com a folha
`de laranja. Portanto, a aplicação de diflubenzuron com OPPA ou Nimbus, nas concentrações de 0,25 e 0,50%,
`proporciona uma melhor capacidade de espalhamento das gotas pulverizadas.
`Termos de indexação: ângulo de contato, tensão superficial, espalhamento.
`
`INTRODUCTION
`
`Brazilian citrus production is highly dependent on
`plant protection products due to the large amount of pests
`and diseases that occur in orchards. At that, farmers have
`adopted the chemical control (insecticides and acaricides)
`to reduce the population of the pests and decrease
`damages and harms, besides avoiding the transmission
`of phytopathogens (Yamamoto et al., 2009).
`The importance of pests in the citrus culture leads
`farmers to perform successive applications in the areas
`and with high volumes of application, elevating the final
`production cost, which shows the need for basic studies
`involving the aspects of the application technology
`(Barbosa et al., 2013).
`The diflubenzuron insecticide has been used to control
`Phyllocoptruta oleivora (Ashmead) (Acari: Eriophyidae),
`Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae)
`and Diaphorina citri Kuwayama (Hemiptera: Liviidae).
`The latter is the vector of huanglongbing (HLB, ex-greening),
`a disease that destroys citrus production. Diflubenzuron
`is a physiological insecticide/acaricide that belongs to
`the benzoylurea chemical group, acts through contact
`and intake and is formulated in concentrated suspension.
`The high volumes used in insecticide application,
`up to the point of runoff of the leaf, are often used.
`This means of application can cause serious economic
`and environmental issues. According to Taylor (2011),
`the spray retention is controlled by a series of factors,
`among them: the dynamic surface tension of the solution
`sprayed, the surface properties of the leaf and the contact
`angle of the droplet in the leaf surface, and the type of
`adjuvant and volume of application.
`Adjuvants are substances without phytosanitary
`properties added in a preparation to make the application
`easier, raise efficiency and reduce risks (Kissmann, 1998).
`The utilization of certain adjuvants can effectively improve
`the biological efficiency of insecticides. However, this
`improvement is not valid for all adjuvants – the product
`used and the biological target must be taken into account
`
`(Arrué et al., 2014). Adjuvants such as plant, mineral oils,
`or oil derivatives in the solution can raise the efficiency
`in the control of pests and diseases, since it protects the
`applied solution from unfavorable weather conditions, or
`improving the interaction between the solution and the
`target (Andrade Junior et al., 2010).
`Besides, adjuvants can help reduce the volume
`of application, since it is known that the use of oils
`provide decrease of the maximum amount of liquid that
`the leaves can retain, contributing to a reduction of the
`solution volume used in sprays in the citrus production
`(Barbosa et al., 2013). However, the use of smaller solution
`volumes raises the autonomy and the operational capacity
`of sprayers (Cunha et al., 2005), and consequently reduces
`the cost of application, generating economy to the farmers.
`One of the important factors that helped the retention of
`the solution in the target is the wetting, which is influenced
`by the surface tension. The surface tension of the droplets
`and its interaction with the target surface influence not
`only the wetting, but also the absorption process, what
`is fundamental for the effectiveness of the application
`(Cunha et al., 2017). The oils help the spreading and the
`absorption, reducing the degradation of active ingredients
`and the surface tension (Mendonça et al., 2007). On natural
`targets, the greatest wetting levels with water solutions
`were obtained through the smallest surface tensions and
`contact angles of the droplets (Iost & Raetano, 2010).
`Thus, the aim of this study was to evaluate the physical
`characteristics of the surface tension of the diflubenzuron
`insecticide using different mineral oils in two concentrations
`and the interaction of droplets produced on the leaf surface
`of orange through the formed contact angle.
`
`MATERIAL AND METHODS
`
`Seven different spraying liquids were prepared.
`The compositions of these spraying liquids were the
`insecticide diflubenzuron (Micromite) and three mineral
`oils (84.57 m/v - Argenfrut; 90.00% m/v - OPPA
`
`Citrus Research & Technology, v. 37, n. 1, p. 102-107, 2016
`
`

`

`104
`
`Della Vechia et al.
`
`and 42.80% m/v - Nimbus) in two concentrations
`(0.5 e 0.25% v/v).
`These different spraying liquids were analyzed on
`their physical characteristics when in contact with the
`adaxial surface of sweet orange of variety Valência
`[Citrus sinensis (L.) Osebeck cv. Valência] leaves and
`in contact with a comparatively smooth glass surface.
`Physiologically active citrus leaves were collected with
`the use of surgical gloves to avoid contact of skin oils
`with leaves.
`
`Assessment of the results
`
`The surface tension of the spraying liquids utilized in
`the experiment, as well as the contact angle by the applied
`droplets on the surface of citrus leaves and smooth glass,
`were assessed using a tensiometer equipment, Contact
`Angle System model OCA 15 EC/B, from Dataphysics
`enterprise. The tensiometer was equipped with a CCD
`high speed, high definition camera, which captures
`droplet formation with the aid of SCA20 software used
`for the automation of the equipment and handling of
`images obtained on a computer. For the surface tension
`analysis, pendant droplets were formed at the end of
`a needle (0.52 mm in external diameter) attached to a
`Hamilton syringe (graduated until 5 µL of volume)
`which in turn was attached to the tensiometer.
`For each spraying liquid, four pendant droplets were
`formed and analyzed by the software according to the
`Young-Laplace equation. Surface tension values expressed
`as mN.m-1 unit were then obtained. For the analysis of
`contact angle by droplets, the collected citrus leaves were
`cut into rectangles of about 5 cm2. These were set in a press
`in such a way so their adaxial surfaces were facing upward,
`before droplets of each spraying liquid were deposited.
`Images were captured every second for 60 seconds. On the
`smooth surface of glass, the variable of contact angle was
`also determined in relation to the application of droplets.
`An automatic device applied to the tensiometer determined
`movements on the syringe plunger that dispensed droplets
`both on the citrus leaves and the glass surface, so as to
`allow for the analysis of the contact angle. Once the whole
`droplet volume was dispensed on the surfaces, the syringe
`was rapidly retracted from the camera focus so the contact
`angle measurement could begin.
`For the contact angle analysis, droplets were dispensed
`in the fixed volume of 3 µL, while for surface tension
`analysis pendant droplets of 4 µL was used. These
`
`Citrus Research & Technology, v. 37, n. 1, p. 102-107, 2016
`
`volumes were selected in the experiment to provide better
`quality droplet images by the software camera, without
`influencing the spraying liquid’s characteristics. For all
`variables, values for the 5 seconds (5s), 30 seconds (30s)
`and 60 seconds (60s) were obtained and compared.
`
`Experimental design
`
`The analysis followed a randomized factorial design 7 × 3,
`representing 7 treatments (spraying liquids) in three
`different times (5s, 30 and 60s) with four replicates, for
`surface tension and contact angle variables, measured
`separately. The means of the variables were subjected
`to analysis of variance and compared using the multiple
`comparisons Tukey test to the level of 5% probability.
`
`RESULTS AND DISCUSSION
`
`Surface tension
`
`Significant differences were found between the
`treatments (F = 903.37; p < 0.0001) and the interaction of
`factors (F = 34.01; p < 0.0001) evaluated for the surface
`tension values obtained in the tensiometer. Pending droplets
`from the six treatments, composed by the combination
`of diflubenzuron and mineral oils, presented a difference
`regarding the control treatment (diflubenzuron without
`oil). The surface tension was higher for diflubenzuron and
`smaller for the combination of diflubenzuron and Nimbus
`in the two concentrations tested at five seconds (Table 1).
`At 30s, the highest surface tension observed was for
`diflubenzuron, while the smaller values were observed
`for the combinations of diflubenzuron and Nimbus and
`OPPA oils in both concentrations. At 60s, the treatments
`presented the same behavior than at 30s (Table 1).
`Comparing the surface tension values throughout the
`period evaluated, these were decreasing for all treatments.
`This surface tension variation throughout the 60s occurs
`due to the energy balance among solids, liquids and gases,
`tending to a balance of forces, and the use of adjuvants
`significantly affects this balance (Decaro Junior et al., 2015).
`The surface tension refers to the existing forces in
`the interface of non-mixable liquids, stopping them from
`mixing with each other (Azevedo, 2001). Based on the
`results observed, it can be inferred that the addition of
`mineral oil to the Diflubenzuron insecticide reduces the
`connection force among molecules, reflecting in smaller
`surface tension values.
`
`

`

`Physical characteristics of insecticide spraying liquids…
`
`105
`
`Table 1. Values in mN.m-1 of droplets surface tension from the different spraying liquids at different moments of
`measurement
`30s
`Spraying liquids
`52.72Bb
`Diflubenzuron + 0,5% Argenfrut
`47.92Cb
`Diflubenzuron + 0,25% Argenfrut
`36.01Db
`Diflubenzuron + 0,5% OPPA
`35.09Db
`Diflubenzuron + 0,25% OPPA
`35.30Dab
`Diflubenzuron + 0,5% Nimbus
`34.10Dab
`Diflubenzuron + 0,25% Nimbus
`65.54Ab
`Diflubenzuron
`3.09
`MSDb
`2.43
`MSDc
`43.81b
`Média
`0.92
`MSD
`3.16
`CV
`aMeans followed by the same lower case letter on the column and uppercase letter on the line does not differ by
`Tukey test (p>0.05). Minimum significant difference for columnsb and linesc.
`
`5s
`67.79Baa
`63.96Ca
`43.37Da
`42.36Da
`36.91Ea
`35.87Ea
`72.10Aa
`
`51.77a
`
`60s
`46.37Bc
`40.86Cc
`34.44Db
`33.49Db
`33.83Db
`33.08Db
`61.75Ac
`
`40.55c
`
`Table 2. Degree values of contact angle formed by droplets applied on adaxial citrus leaves surface, using the
`different spraying liquids at different moments of measurement
`30s
`Spraying liquids
`5s
`69.98ABb
`Diflubenzuron + 0,5% Argenfrut
`79.71ABaa
`63.39BCab
`Diflubenzuron + 0,25% Argenfrut
`70.25BCa
`52.33Db
`Diflubenzuron + 0,5% OPPA
`60.34DEa
`55.10CDb
`Diflubenzuron + 0,25% OPPA
`67.11CDa
`51.06Dab
`Diflubenzuron + 0,5% Nimbus
`58.81DEa
`52.28Dab
`Diflubenzuron + 0,25% Nimbus
`55.69Ea
`76.13Aa
`Diflubenzuron
`81.39Aa
`9.84
`MSDb
`7.76
`MSDc
`60.04b
`Média
`2.93
`MSD
`7.45
`CV
`aMeans followed by the same lower case letter on the column and uppercase letter on the line does not differ by
`Tukey test (p>0.05). Minimum significant difference for columnsb and linesc.
`
`60s
`66.41ABb
`59.57BCb
`51.17Db
`51.43CDb
`47.74Db
`44.72Db
`73.88Aa
`
`46.42c
`
`67.64a
`
`Foliar surface
`
`Contact angle
`
`Significant differences were found between the
`treatments (F = 59.16; p < 0.0001) and the evaluation
`times (F = 43.98; p < 0.0001). However, there was no
`interaction between the two factors (F = 0.61; p = 0.8224)
`for the contact angle values obtained regarding the citrus
`leaf. At 5s, diflubenzuron and diflubenzuron + Argenfrut
`at 0.5% had no difference and presented the highest values
`of contact angle formed with the leaf. The smallest values
`
`were obtained with the combination of diflubenzuron and
`Nimbus, in both concentrations, and diflubenzuron and
`OPPA in the larger concentration (Table 2).
`At 30s and 60s, the treatments presented the same
`behavior as presented at 5s (Table 2). The contact angle
`values of each treatment decreased throughout the
`evaluation, presenting higher values for the first 5s, except
`for diflubenzuron without mineral oil, which was stable
`throughout the evaluation.
`Droplets with smaller contact angles have their contact
`surface with the larger biological target, and consequently,
`higher coverage of this target (Queiroz et al., 2008).
`
`Citrus Research & Technology, v. 37, n. 1, p. 102-107, 2016
`
`

`

`106
`
`Della Vechia et al.
`
`According to Mendonça et al. (2007), the wetting area
`is correlated to the surface tension of the solution, to the
`type and to the dosage of the surfactant that composes
`the commercial product, in addition to the ultrastructure
`features (presence or absence of epicuticular wax) of the
`leaf surface.
`Moita Neto (2006) observed that droplets with
`contact angle smaller than 90º formed with the surface
`can characterize this surface as hydrophilic, that is, the
`surface got wet by the liquid. Therefore, the droplet
`applied is more widespread over the surface, and it may
`even form an uniform film (Iost & Raetano, 2010).
`Iost & Raetano (2010), aiming to evaluate the effect of
`surfactants in water solutions over the dynamic surface
`tension and contact angle of the droplets in artificial
`and natural surfaces, checked that in natural surfaces
`the highest levels of wetting with water solutions were
`obtained through smaller surface tensions and contact
`angles of the droplets.
`As observed in this experiment, oils with proportion of
`90.00% (OPPA) and 42.80% (Nimbus) in their formulation
`were the ones which provided better physical features to
`the droplets. It is known that commercial mineral oils have
`non-phytotoxic oil and surfactants in their formula, both
`of which have their proportions indicated on the labels
`of the products. However, companies do not indicate the
`type of adjuvant used as emulsifier in the formulation of
`these oils (Queiroz et al., 2008). Since these emulsifiers
`also determine some physical and chemical features of the
`spray solution, such as the surface tension, we cannot infer
`that, in this case, the proportion of oil in the formulations
`was the only factor that determined the physical features
`of the droplets – they could also be influenced by the
`surfactants used in the formulations.
`In summary, when adding mineral oil to the diflubenzuron
`solution, the surface tension decreases, the area covered
`by one droplet is larger, replacing a certain amount of
`smaller droplets that was formed by the solution without
`oil. Corroborating with the results from Decaro Junior et al.
`(2015), which observed that it would be necessary 40% less
`droplets from a profenofos solution with 12.50% of oil
`(863 mm2 per droplet) to completely cover the same
`surface area of a coffee leaf when only water is applied
`(1.42 mm2). Therefore, this ratio must be used to determine
`the application volume, because high volume applications
`commonly used in citrus culture could lead the coverage
`to the wetting level in the leaves. Barbosa et al. (2013),
`aiming to determine the retention capacity of the solution
`by citrus leaves, checked that, with the addition of mineral
`
`Citrus Research & Technology, v. 37, n. 1, p. 102-107, 2016
`
`oil to the solution, 0.09 mg i.a. m-2 of leaf area would
`be retained from the acaricide. If plant oil is added, the
`acaricide retention would be 0.19 mg i.a. m-2 of the leaf.
`If the first amount is enough to control a given pest,
`it can be admitted that in the last case scenario there
`will be a superdosage happening. On the other hand,
`if 0.09 mg i.a. m-2 is considered enough, the solution
`volume used could be reduced, avoiding waste.
`Xu et al. (2011) showed in a study that the use of
`adjuvants can significantly improve physical features of
`the sprayed solution and, consequently, raise the wet area
`in the surface of the target in question. These alterations of
`the physical features of the solution regarding the surface
`tension and contact angle of the droplet with the target
`result in economical and environmental benefits, since
`it allows the adoption of smaller application volumes,
`avoiding wastes (excessive volumes) and helping reduce
`environmental contamination.
`
`CONCLUSION
`
`Mineral oils mixed with diflubenzuron reduce the
`surface tension of the droplets and result in smaller contact
`angles of the droplets with the citrus leaves surface.
`The application of the diflubenzuron with OPPA or
`Nimbus, at concentrations of 0.25 and 0.5%, provide a
`better spreadability of the sprayed droplets.
`
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`Received: February 14, 2017
`Accepted: August 21, 2017
`
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