Droplet evaporation and spread on waxy and hairy leaves associated with type and concentration of adjuvants

Comparison of off-target pesticide drift in paddy fields from unmanned aerial vehicle spraying using cellulose deposition sampler

Off-target pesticide drift in paddy fields following unmanned aerial vehicle (UAV) spraying was evaluated using cellulose deposition samplers (CDSs). An analytical method for quantifying ferimzone Z and E isomers deposited on CDSs was developed using LC-MS/MS. The suitability of the CDS method was confirmed by comparing deposition patterns on CDSs with residue levels in rice plant samples. To assess pesticide deposition in paddy fields, CDSs were strategically placed at varying distances from target areas, followed by UAV spraying. The fungicide agrochemicals were applied with and without adjuvants, and wind direction affected the drift trajectory for all treatment groups. Adjuvants, particularly soy lecithin as the major component, significantly enhanced pesticide deposition within the spray pathway while reducing drift rates relatively by 47.9-68.0 %. Higher wind speeds were found to exacerbate drift, but adjuvant-treated sprays showed less variability in deposition patterns under these conditions. Pesticide residues in harvested brown rice were found to be below the maximum residue limits (MRLs), ensuring safety for consumption. These findings highlight the importance of selecting appropriate adjuvants in UAV-based pesticide applications to optimize deposition efficiency and minimize environmental contamination.

Understanding dilution effects on particle-containing pesticide droplets deposition on rice leaf via developing CFD-VOF-DPM model

BACKGROUND

Pesticide dilution is one of the essential aspects of plant protection. However, the effect of dilution on the deposition characteristics of pesticide droplets containing particulate additives on crop leaf surfaces remains unclear and warrants further research. Herein, a validated computational fluid dynamics (CFD)-volume of fluid (VOF)-discrete phase model (DPM) numerical model was developed to analyze the influence of particle content on the deposition behavior of droplets on the leaf surface comparatively, taking into account the particle content of different diluted thifluzamide solutions. Additionally, the study aimed to analyze further the kinetic behavior of pesticide droplets landing on rice leaves across different dilution conditions.

RESULTS

Pesticide droplets diluted 100-fold had a lower retraction rate during spreading than particle-free droplets, so the solution is more easily deposited in the leaves. Moreover, the low dilution (high concentration) increased the critical adhesion rate between droplets and rice leaves, inhibiting the bouncing of droplets on the leaf surface, thus promoting their effective deposition on the surface. In addition, low dilution (high concentration) is not conducive to spreading droplets when the impact velocity is high, and it also results in a large amount of pesticide use.

CONCLUSION

The actual application process can be through understanding the dilution factor of the configured pesticide solution, and reasonable adjustment of the nozzle pressure can effectively improve the utilization rate of pesticides and reduce the pollution brought by pesticides to the environment. These results provide an essential reference for studying pesticide droplet deposition characteristics, including rice plant protection and spraying technology. © 2024 Society of Chemical Industry.

Relationship between Salmonella enterica attachment and leaf hydrophobicity, roughness, and epicuticular waxes: a focus on 30 baby-leaf salads

BACKGROUND

The first step in the contamination of leafy vegetables by human pathogens is their attachment to the leaf surface. The success of this is influenced strongly by the physical and chemical characteristics of the surface itself (number and size of stomata, presence of trichomes and veins, epicuticular waxes, hydrophobicity, etc.). This study evaluated the attachment of Salmonella enterica to 30 baby-leaf salads and tested whether the differences found among them were related to the following leaf traits: hydrophobicity, roughness, and epicuticular waxes.

RESULTS

Differences in susceptibility to contamination by S. enterica were found between the 30 baby-leaf salads investigated. The lowest attachment was found in wild lettuce (Lactuca serriola L.) and lamb's lettuce 'Trophy F1' (Valerianella locusta [L.] Laterr.), with values of 1.63 ± 0.39 Log(CFU/cm2) and 1.79 ± 0.54 Log(CFU/cm2), respectively. Attachment was correlated with hydrophobicity (measured as contact angle) (r = -0.39) and epicuticular waxes (r = -0.81) but not with roughness (r = 0.24). The most important wax components for attachment were alcohols and, in particular, the three-dimensional (3D) wax crystals of C26 alcohol, but fatty acids probably also had a role. Both these compounds increased hydrophobicity. The presence of thymol, whose antimicrobial properties are well known, was found in lamb's lettuce.

CONCLUSIONS

The findings of this study can help to predict and control the attachment and contamination of leafy salads by enterobacteria. They also provide useful information for breeding programs aiming to develop cultivars that are less susceptible to human pathogens, enhancing the food safety of vegetables. © 2024 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Elucidating Factors Contributing to Dicamba Volatilization by Characterizing Chemical Speciation in Dried Dicamba-Amine Residues

Dicamba is a semivolatile herbicide that has caused widespread unintentional damage to vegetation due to its volatilization from genetically engineered dicamba-tolerant crops. Strategies to reduce dicamba volatilization rely on the use of formulations containing amines, which deprotonate dicamba to generate a nonvolatile anion in aqueous solution. Dicamba volatilization in the field is also expected to occur after aqueous spray droplets dry to produce a residue; however, dicamba speciation in this phase is poorly understood. We applied Fourier transform infrared (FTIR) spectroscopy to evaluate dicamba protonation state in dried dicamba-amine residues. We first demonstrated that commercially relevant amines such as diglycolamine (DGA) and n,n-bis(3-aminopropyl)methylamine (BAPMA) fully deprotonated dicamba when applied at an equimolar molar ratio, while dimethylamine (DMA) allowed neutral dicamba to remain detectable, which corresponded to greater dicamba volatilization. Expanding the amines tested, we determined that dicamba speciation in the residues was unrelated to solution-phase amine pKa, but instead was affected by other amine characteristics (i.e., number of hydrogen bonding sites) that also correlated with greater dicamba volatilization. Finally, we characterized dicamba-amine residues containing an additional component (i.e., the herbicide S-metolachlor registered for use alongside dicamba) to investigate dicamba speciation in a more complex chemical environment encountered in field applications.

The key factors of solid nanodispersion for promoting the bioactivity of abamectin

Solid nanodispersion (SND) is an important variety of nanopesticides which have been extensively studied in recent years. However, the key influencing factors for bioactivity enhancement of nanopesticides remain unclear, which not only limits the exploration of relevant mechanisms, but also hinders the precise design and development of nanopesticides. In this study, we explored the potential of SND in enhancing the bioactivity of nanopesticides, specifically focusing on abamectin SND prepared using a self-emulsifying-carrier solidifying technique combined with parameter optimization. Our formulation, consisting of 8% abamectin, 1% antioxidant BHT (2,6-di-tert-butyl-4-methylphenol), 12% complex surfactants, and 79% sodium benzoate, significantly increased the pseudo-solubility of abamectin by at least 3300 times and reduced its particle size to a mere 15 nm, much smaller than traditional emulsion in water (EW) and water-dispersible granule (WDG) forms. This reduction in particle size and increase in surface activity resulted in improved foliar adhesion and retention, enabling a more efficient application without the need for organic solvents. The inclusion of antioxidants also enhanced photostability compared to EW, and overall stability tests confirmed SND's resilience under various storage conditions. Bioactivity tests demonstrated a marked increase in toxicity against diamondback moths (Plutella xylostella L.) with abamectin SND, which exhibited 3.7 and 7.6 times greater efficacy compared to EW and WDG, respectively. These findings underscore the critical role of small particle size, high surface activity, and strong antioxidant properties in improving the performance and bioactivity of abamectin SND, highlighting its significance in the design and development of high-efficiency, eco-friendly nanopesticides and contributing valuably to sustainable agricultural practices.

Quantifying the effect of non-ionic surfactant alkylphenol ethoxylates on the persistence of thiabendazole on fresh produce surface

BACKGROUND

Understanding the role of adjuvants in pesticide persistence is crucial to develop effective pesticide formulations and manage pesticide residues in fresh produce. This study investigated the impact of a commercial non-ionic surfactant product containing alkylphenol ethoxylates (APEOs) on the persistence of thiabendazole on apple and spinach surfaces against the 30 kg m-3 baking soda (sodium bicarbonate, NaHCO3 ) soaking, which was used to remove the active ingredient (AI) in the cuticular wax layer of fresh produce through alkaline hydrolysis. Surface-enhanced Raman scattering (SERS) mapping method was used to quantify the residue levels on fresh produce surfaces at different experimental scenarios. Four standard curves were established to quantify surface thiabendazole in the absence and presence of APEOs, on apple and spinach leaf surfaces, respectively.

RESULTS

Overall, the result showed that APEOs enhanced the persistence of thiabendazole over time. After 3 days of exposure, APEOs increased thiabendazole surface residue against NaHCO3 hydrolysis on apple and spinach surfaces by 5.39% and 10.47%, respectively.

CONCLUSION

The study suggests that APEOs led to more pesticide residues on fresh produce and greater difficulty in washing them off from the surfaces using baking soda, posing food safety concerns. © 2023 Society of Chemical Industry.

Computational fluid dynamics simulation analysis of the effect of curved rice leaves on the deposition behaviour of droplets

BACKGROUND

Although previous studies on the droplet deposition behaviour of rice leaves have modelled the leaves as flat surface structures, their curved surface structures actually have a significant effect on droplet deposition.

RESULTS

In this paper, the statistical distribution of the coordinate parameters of rice leaves at the elongation stage was determined, computational fluid dynamics (CFD) simulation models of droplet impact on rice leaves with different curvature radii were built, and the effect of leaf curvature radius on the deposition behaviour and spreading diameter of droplets on rice leaves was studied using validated simulation models. The results showed that the average relative errors of the CFD simulation models were in the range of 2.23-9.63%. When the droplets struck the rice leaves at a speed of 4 m/s, the 50 μm droplets did not bounce within the curvature radii of 25-120 cm, the maximum spreading diameters of 200 and 500 μm droplets that just adhered to the leaves were 287 and 772 μm, respectively. The maximum spreading diameters of 50, 200, and 500 μm droplets that just split were 168, 636, and 1411 μm, respectively. As the curvature radii of the leaves increased, the maximum spreading diameter of the droplets gradually decreased, and droplet bouncing was more likely to occur. However, a special case in which no significant change in the maximum spreading diameter arose when 50 μm droplets hit a leaf with a curvature radius exceeding 50 cm.

CONCLUSION

Splitting generally occurred for large droplets with a small curvature radius and small tilt angle; bouncing generally occurred for large droplets with a large curvature radius and large tilt angle. When the droplet was small, the deposition behaviour was mostly adhesion. The change in spreading diameter after stabilisation was similar to the change in maximum spreading diameter, where the spreading diameter after stabilisation greatly increased after droplet splitting. This paper serves as a reference for the study of pesticide droplet deposition and its application in rice-plant protection.

Effect of adjuvants on physicochemical properties of lime sulfur on flower/paraffin and application on flower thinning

Introduction

Adjuvants can effectively enhance the utilization rate of pesticides, but the application of adjuvants in plant growth regulators is rarely studied.

Methods

This work explored the effects of adjuvants dioctyl sulfosuccinate sodium salt (AOT) and methyl oleate (MO) on lime sulfur (LS), especially the drop behavior on flower and paraffin surface.

Results

The results showed that the addition of AOT and AOT+MO can significantly reduce the static and dynamic surface tension of LS from 72mN/m to 28mN/m and 32mN/m respectively, and increase the spreading factor from 0.18 to 1.83 and 3.10 respectively, reduce the bounce factor from 2.72 to 0.37 and 0.27 respectively. The fluorescence tracer test showed that the addition of adjuvants could promote the spreading and permeation of droplets. The field test results revealed that the flower thinning rate of adjuvant and non-adjuvant were 80.55% and 54.4% respectively, and the flower thinning effect of adding adjuvant was the same as that of artificial which the flower thinning rate was 84.77%. The quality of apples treated with adjuvants was similar to that treated with artificial, and the weight of single fruit increased by 24.08% compared with CK (spray water).

Discussion

The application of tank-mixture adjuvant could reduce the dosage of LS for thinning agent application, improve apple's quality, and decrease labor cost and improve the economic benefits of fruit planting and the environmental benefits of plant growth regulators.

Measuring the photostability of agrochemicals on leaves: understanding the balance between loss processes and foliar uptake

BACKGROUND

Photostability is an important property in agrochemicals, impacting their biological efficacy, environmental fate and registrability. As such, it is a property that is routinely measured during the development of new active ingredients and their formulations. To make these measurements, compounds are typically exposed to simulated sunlight after application to a glass substrate. While useful, these measurements neglect key factors that influence photostability under true field conditions. Most importantly, they neglect the fact that compounds are applied to living plant tissue, and that uptake and movement within this tissue provides a mechanism to protect compounds from photodegradation.

RESULTS

In this work, we introduce a new photostability assay incorporating leaf tissue as a substrate, designed to run at medium throughput under standardized laboratory conditions. Using three test cases, we demonstrate that our leaf-disc-based assays provides quantitatively different photochemical loss profiles to an assay employing a glass substrate. And we also demonstrate that these different loss profiles are intimately linked to the physical properties of the compounds, the effect that those properties have on foliar uptake and, thereby, the availability of the active ingredient on the leaf surface.

CONCLUSIONS

The method presented provides a quick and simple measure of the interplay between abiotic loss processes and foliar uptake, supplying additional information to facilitate the interpretation of biological efficacy data. The comparison of loss between glass slides and leaves also provides a better understanding of when intrinsic photodegradation is likely to be a good model for a compound's behaviour under field conditions. © 2023 Society of Chemical Industry.

Investigation of factors enhancing droplets spreading on leaves with burrs

Introduction

Spread effect is one of the aspects on deposition quality evaluation of pesticide droplets. It could be affected by many factors such as the microstructure of the target plant leaf surface, physical features of the droplets, and the concentration of spray additives.

Methods

In this study, using a high-speed photography system, 2.3% glyphosate ammonium salt solution with different concentration of the additive was applied to investigate the impact process of single droplet deposition on the plant leaf surface with burrs. Effect of droplet sizes and velocities on spreading area and dynamic deposition procedure was analyzed using image processing programs.

Results

The diffusion factor in the process of droplet spreading was changed over time. The occurrence of bubbles in the droplets was observed in the results. With the bubble generation, the droplet diameter expands and a better diffusion effect is obtained. As a result, better spreading effect was obtained as the droplet diameter was expanded with the generation of bubbles. The significant effects of each physical property of droplets on droplet spreading and the interaction effects between the influencing factors were analyzed. A significant correlation was found between additive concentration, droplet impact velocity, droplet diameters and droplet spreading area. All interactions of concentration:velocity, concentration:diameter, velocity:diameter, and concentration:velocity:diameter had a significant effect on the spreading area of droplets. The study of the factors influencing the process of pesticide droplet impact on the leaf surface contributes to the efficient use of pesticides. Thus, the consumption of pesticides and the resulting impact on the environment can be reduced.

A new laboratory method to study the impact of leaf texture on pesticide dislodgeable foliar residues (DFR)

Pesticides are vital in meeting the challenge of feeding the rapidly increasing world population. However, it is crucial that they are used in a way that does not compromise the safety of humans or the environment. Non-dietary worker risk assessments consider the amount of residue which can be transferred from plant foliage to the skin or clothes, known as dislodgeable foliar residues (DFRs). DFR data scarcity due to the costly and seasonal characteristics of DFR studies is an obstacle to the extrapolation of DFR data to different crops/leaves. This paper validates a new proof-of-concept technique to investigate factors that may affect DFR (leaf texture) using the fungicide difenoconazole EC 10% as an example on various leaves (i.e., French bean, soybean, tomato, oilseed rape, and wheat). DFR was the lowest in the case of oilseed rape (31.0 ± 3.4%) and the highest in French beans (82.0 ± 2.9%). This significant difference in DFR in the findings of this study sheds light on the importance of the leaf surface as a major factor affecting DFR and supports the application of the laboratory method for more extensive data generation. More data generation would enable the extrapolation saving money and resources.

Understanding the impact of a non-ionic surfactant alkylphenol ethoxylate on surface-enhanced Raman spectroscopic analysis of pesticides on apple surfaces

Pesticide active ingredients (AIs) are often applied with adjuvants to facilitate the stability and functionality of AIs in agricultural practice. The objective of this study is to investigate the role of a common non-ionic surfactant, alkylphenol ethoxylate (APEO), on the surface-enhanced Raman spectroscopic (SERS) analysis of pesticides as well as its impact on pesticide persistence on apple surfaces, as a model fresh produce surface. The wetted areas of two AIs (thiabendazole and phosmet) mixed with APEO were determined respectively to correct the unit concentration applied on apple surfaces for a fair comparison. SERS with gold nanoparticle (AuNP) mirror substrates was applied to measure the signal intensity of AIs with and without APEO on apple surfaces after a short-term (45 min) and a long-term (5 days) exposure. The limit of detection (LOD) of thiabendazole and phosmet using this SERS-based method were 0.861 ppm and 2.883 ppm, respectively. The result showed that APEO decreased the SERS signal for non-systemic phosmet, while increased SERS intensity of systemic thiabendazole on apple surfaces after 45 min pesticide exposure. After 5 days, the SERS intensity of thiabendazole with APEO was higher than thiabendazole alone, and there was no significant difference between phosmet with and without APEO. Possible mechanisms were discussed. Furthermore, a 1% sodium bicarbonate (NaHCO₃) washing method was applied to test the impact of APEO on the persistence of the residues on apple surfaces after short-term and long-term exposures. The results indicated that APEO significantly enhanced the persistence of thiabendazole on plant surfaces after a 5-day exposure, while there was no significant impact on phosmet. The information obtained facilitates a better understanding of the impact of the non-ionic surfactant on SERS analysis of pesticide behavior on and in plants and helps further develop the SERS method for studying complex pesticide formulations in plant systems.

Herbicides Harm Key Orchard Predatory Mites

The phytoseiid mites Galendromus occidentalis and Amblydromella caudiglans are critical for conservation biological control of pest mites in Washington State, U.S.A. apples. While the non-target effects of insecticides on phytoseiids are well described, research on herbicide effects is limited. Using laboratory bioassays, we examined lethal (female mortality) and sublethal (fecundity, egg hatch, larval survival) effects of seven herbicides and five adjuvants on A. caudiglans and G. occidentalis. The effects of mixing herbicides with recommended adjuvants were also tested to determine if the addition of an adjuvant increased herbicide toxicity. Glufosinate was the least selective herbicide tested, causing 100% mortality in both species. Paraquat caused 100% mortality in A. caudiglans and 56% mortality in G. occidentalis. Sublethal effects were significant for both species when exposed to oxyfluorfen. Adjuvants did not cause non-target effects in A. caudiglans. The non-ionic surfactant and methylated seed oil increased mortality and decreased reproduction in G. occidentalis. The high toxicity of glufosinate and paraquat for both predators is concerning; these are the primary "burn down" herbicide alternatives to glyphosate, which is decreasing in use due to consumer toxicity concerns. Field studies are needed to determine the extent to which herbicides disrupt orchard biological control, focusing on glufosinate, paraquat, and oxyfluorfen. Consumer preferences will need to be balanced with natural enemy conservation.

Achieving High Efficacy and Low Safety Risk by Balancing Pesticide Deposition on Leaves and Fruits of Chinese Wolfberry (Lycium barbarum L.)

Pesticide residue has become the main technical barrier that restricts the export of Chinese wolfberry. Can we achieve high efficacy and low safety risk by balancing pesticide deposition on the leaves and fruits of Chinese wolfberry? In this research, the structural characteristics and wettability of leaves and fruits of Chinese wolfberry at different growth stages were studied. The adaxial and abaxial surfaces of leaves were hydrophobic, whereas the fruit surfaces were hydrophilic. Adding spray adjuvant could increase the retention of droplets on the leaf surfaces of Chinese wolfberry by 52.28-97.89% and reduce the retention on the fruit surfaces by 21.68-42.14%. A structural equation model analysis showed that the adhesion tension was the key factor affecting the retention of the solutions among various interface behaviors. When the concentrations of Silwet618, AEO-5, Gemini 31551, and 1227 were 2-5 times higher than their CMCs, the retention of pesticide solutions (pyraclostrobin and tylophorine) on Chinese wolfberry leaves significantly increased, and the control efficacies on aphids and powdery mildew also dramatically improved (65.90-105.15 and 41.18-133.06%, respectively). Meanwhile, the retention of pesticides on the fruit of Chinese wolfberry was reduced. This study provides new insights into increasing the utilization of pesticides in controlling pests and improving food safety.

Biological, surface, and wetting behavior of bio-surfactants tank-mixed with trifloxysulfuron-sodium on Sorghum halepense

BACKGROUND

There is a public interest in developing bio-surfactants due to their low toxicity and high biodegradation potential. However, their biological, surface, and behavior to use with agrochemicals has not been investigated.

RESULTS

Critical micelle concentrations (CMCs) for the synthetic surfactant dioctyl sodium sulfosuccinate (DOSS), the bio-surfactant rhamnolipid (RL), and the bio-surfactant surfactin (SF) were 1200, 50, and 50 mg L^-1 , respectively. Based on the ability of the surfactants to reduce the surface tension of trifloxysulfuron-sodium spray solution at 0.25 to 1× CMC, they are ranked SF > RL > DOSS, while at 1.5 to 4× CMC, they are ranked SF = RL > DOSS. Without surfactant, trifloxysulfuron-sodium at 10.04 g ha^-1 reduced johnsongrass growth up to 50% (ED₅₀ ). At best, SF at 1 to 4× CMC halved ED₅₀ . Unlike DOSS, which increased ED₅₀ (12.89 g ha^-1 ) due to a phytotoxic effect, SF and RL at 4× CMC decreased ED₅₀ (5.19 and 6.50 g ha^-1 , respectively) without a phytotoxic effect. A 5-μl droplet containing SF dried faster due to greater spread on the leaf surface than other surfactants. Although the wetted area of the leaf with the droplet containing RL was wider than that of DOSS, it took longer to dry. This observation contradicts the previous theory.

CONCLUSION

In terms of dosage, safety, and efficacy, the RL and SF were comparable to DOSS in other tank-mix with trifloxysulfuron-sodium. It seems that RL also works as a humectant, while SF likely works as a wax solubilisant. © 2023 Society of Chemical Industry.

Eco-Oriented Formulation and Stabilization of Oil-Colloidal Biodelivery Systems Based on GC-MS/MS-Profiled Phytochemicals from Wild Tomato for Long-Term Retention and Penetration on Applied Surfaces for Effective Crop Protection

Vegetable oils as hydrophobic reserves in oil dispersions (OD) provide a practical approach to halt bioactive degradation for user and environment-efficient pest management. Using biodegradable soybean oil (57%), castor oil ethoxylate (5%), calcium dodecyl benzenesulfonates as nonionic and an-ionic surfactants, bentonite (2%), and fumed silica as rheology modifiers, we created an oil-colloidal biodelivery sytem (30%) of tomato extract with homogenization. The quality-influencing parameters, such as particle size (4.5 μm), dispersibility (97%), viscosity (61 cps), and thermal stability (2 years), have been optimized in accordance with specifications. Vegetable oil was chosen for its improved bioactive stability, high smoke point (257 °C), coformulant compatibility, and as a green build-in-adjuvant by improving spreadability (20-30%), retention and penetration (20-40%). In in vitro testing, it efficiently controlled aphids with 90.5% mortalities and 68.7-71.2% under field-conditions without producing phytotoxicity. Wild tomato-derived phytochemicals can be a safe and efficient alternative to chemical pesticides when combined wisely with vegetable oils.

Effect of aerial application of adjuvants on pepper defoliant droplet deposition and efficacy of defoliation sprayed by unmanned aerial vehicles

Defoliant spraying is an important aspect of the mechanized processing of pepper harvesting. Complete and uniform spraying of defoliant could improve the quality of defoliation and reduce the impurity content in processing pepper. In this study, we assessed the effect of aerial spraying of adjuvants on physicochemical properties of defoliant solution and droplet deposition when using an unmanned aerial vehicle (UAV) for defoliation spraying. The results showed that Puliwang was a better aerial spray adjuvant suitable for spraying defoliants for processing pepper using UAVs, with a higher defoliation rate and better droplet deposition. Although the YS-20 adjuvant had a higher droplet deposition amount (0.72 μg/cm²) in the middle layer, its performance was poor in droplet size, density, and coverage. The size and density of the droplets added with the Manniu were basically the same as the Puliwang, even the distribution uniformity was better (the CV of the upper canopy layer was only 33.6%), but the coverage rate was poor. In the treatment with AS-901N, there was no marked increase in droplet size, so evaporation and drift were not improved, eventually resulting in a lower defoliation rate. Puliwang had the highest comprehensive score, followed by AS-910N, YS-20, and Manniu.

Effect of Adjuvant, Concentration and Water Type on the Droplet Size Characteristics in Agricultural Nozzles

One of the goals of adding adjuvants to agricultural spray solutions is to enhance the droplet size characteristics of this spray. Droplet size, in turn, has an influence in the deposited spray quality, in addition to the drift and losses of spray to off-target places. The aim of this research was to evaluate the effect of adding adjuvants to two types of water from different sources on the droplet size characteristics. Two types of adjuvants were employed in the tests: the active substance content of the first adjuvant was a 50% aqueous solution of sodium salt of alkylbenzenesulfonic acid—10% (HY), whereas the second was from rapeseed oil (natural origin)—85% (OL). Both adjuvants were tested in two concentrations: the first was with the concentration recommended by the manufacturer (100%), whereas the second concentration was 50% of the recommended dose. Two types of water from different sources were used in the tests: the first was from a village in the eastern part of Poland (WS), whereas the second was tap water from the city of Lublin, Poland (WUP). Dv0.1, Dv0.5, or volume median diameter (VMD), Dv0.9, Sauter mean diameter (SMD), relative span (RS), and the droplet size distribution were measured and calculated as characteristics of the droplet size. Results showed that the source of water affected the influence of adding adjuvant to the spray solution. Water from the WS source with adjuvant resulted in a numerical decrease in the Dv0.5 values in the percentage of droplet size range below 150 µm, whereas water from the WUP source resulted in an increase in these values (except when adding the HY adjuvant at 50% concentration). Adjuvant concentration significantly (p < 0.05) influenced the features of Dv0.9, SMD, and RS. Adding the OL adjuvant type numerically decreased the percentage of droplet size below 150 µm, and the Dv0.5 values, but only when the WS water source was used.

Effects of tank-mix adjuvants on physicochemical properties and dosage delivery at low dilution ratios for unmanned aerial vehicle application in paddy fields

BACKGROUND

Unmanned aerial vehicles (UAVs) have been developed to improve the efficiency of pesticide applications, and they are now widely utilized in Asia. The deposition and retention periods of pesticides on plant surfaces present serious challenges for modern precision agriculture, as these factors directly affect pesticide bioavailability, efficacy, and loss. Tank-mix adjuvants have been utilized to improve pesticide performance, but their effects on physicochemical properties and dosage delivery at low dilutions are not well understood.

RESULTS

We found that different tank-mix adjuvants affected droplet impact behavior, the wetting and spreading of spray dilutions, and pesticide deposition on rice leaves by changing the physicochemical properties of spray dilutions. The adjuvant methyl oxirane polymer with oxirane, mono (3,5,5-trimethylhexyl) ether (adjuvant c) significantly reduced the dynamic surface tension of the spray dilution and inhibited the rebound of large droplets (D₀  = 2 ± 0.2 mm) and spray droplets (0.2 MPa with a LU-01 nozzle) on rice leaves, and improved the wetting and spreading performance of the spray dilution on rice leaves. Field tests showed that adjuvant c could significantly increase the deposition of chlorantraniliprole on rice leaves.

CONCLUSION

Overall, the use of appropriate tank-mix adjuvants at low dilution ratios for UAV application in paddy fields can improve the performance of spray dilutions, increase the effective deposition and wetting spread of pesticides on rice leaves, further reduce the dosage of pesticide products and improve pesticide utilization. © 2022 Society of Chemical Industry.

Plant Material as a Novel Tool in Designing and Formulating Modern Biostimulants-Analysis of Botanical Extract from Linum usitatissimum L

Nowadays, researchers are looking into next-generation biostimulants that can be designed as a dedicated agronomic tool based on plant materials. The aim of the present study was to develop a novel biostimulating product, based on plant material in the form of linseed aqueous extracts. The scope of the research included the physicochemical characterization of the product and identification of its biostimulating potential. The study has confirmed that the plant biostimulant derived from L. usitatissimum can be used as a viable agronomic tool for growing soybean. The designed and produced biostimulant is rich in bioactive compounds, including amino acids, free fatty acids, carbohydrates, and micro- and macroelements. The tested biostimulant showed significantly lower values of surface tension in relation to water and a commercial biostimulant. The soybean crops responded to the application of the preparation by improvements in agronomic and morphological levels. The linseed macerates were effective in terms of soybean yields and profitability. Our findings serve as preliminary evidence for the viability of designing and developing novel biostimulants derived from plant materials. This comprehensive approach to designing and formulating novel bioproducts necessitates more extensive and targeted research to fully explain the mechanisms behind the improvements observed in the soybean cultivation.

Surface properties of Tetranychus urticae Koch (Acari: Tetranychidae) and the effect of their infestation on the surface properties of kidney bean (Phaseolus vulgaris L.) hosts

BACKGROUND

The wettability of the target surfaces affects the wetting and deposition of pesticides on them. The properties of leaf surfaces change after infestation by Tetranychus urticae Koch. Studying the surface wettability of T. urticae and the changes in leaf wettability after infestation is important to guide the use of acaricides.

RESULTS

The body surface of T. urticae is an ellipsoidal crown covered with dense cuticle striations and hairs arranged in different directions, which makes the surface of T. urticae rough and hydrophobic. The abaxial surfaces of the leaves are rougher and more hydrophobic than the adaxial surfaces. After infestation by T. urticae, the faded spots were sunken on the adaxial surface and raised on the abaxial surface, where they had formed new wide peaks and valleys. The adaxial surface became obviously rougher and more hydrophobic, while the roughness of the abaxial surface became slightly larger, and the change in hydrophobicity was not obvious. The contact angles of the studied commercial acaricide on these surfaces were greater than 65° and were affected by the infestation. Reducing the surface tension can allow for better wetting of these surfaces and eliminate changes in leaf wettability.

CONCLUSION

The surfaces of kidney bean leaves became more hydrophobic after infestation by T. urticae with hydrophobic surface. The wettability of the acaricide solution should be adjusted according to the changes in leaf wettability. This study has important theoretical guiding significance for improving effective deposition of acaricide.

Efficient pesticide formulation and regulation mechanism for improving the deposition of droplets on the leaves of rice (Oryza sativa L.)

BACKGROUND

The effective deposition of pesticide droplets on the target leaf surface is critical for improving the utilization of pesticides. We proposed a new way to enhance the droplet deposition on the target leaf surface by changing the properties of pesticide formulation, and this formulation can be sprayed directly or at a low dilution. In addition, it is a simple method to select a suitable concentration and formulation by evaluating the interfacial dilational rheological properties of pesticide droplets.

RESULTS

The wetting behavior of two types of pesticide formulations prepared by oil-based solvent on the rice leaf surface was investigated based on the surface free energy, surface tension, contact angle, adhesion tension, and adhesion work. The interfacial dilational rheological properties of different pesticide solutions were measured as a function of concentration. This study clearly demonstrates the fact that water-in-oil emulsion has a better wettability than oil-in-water emulsion, especially with the increase of the concentration of the solution, the droplets can be wetted and spread faster on the leaves. Compared with vegetable oil (methyl oleate), mineral oil (solvent oil No. 200) has smaller dilational modulus and surface tension, showing excellent wetting properties.

CONCLUSION

The water-in-oil emulsion prepared with solvent oil No. 200 has the smallest dilational modulus, and the spray droplets spread rapidly to the maximum wetting area on the rice leaves, which can be used in an ultra-low volume spray. The results provide new insights into how to increase the deposition of droplets on superhydrophobic leaf surfaces by screening formulations and concentrations. © 2021 Society of Chemical Industry.

Different leaf-mediated deposition, absorbed and metabolism behaviors of 2,4-D isooctyl ester between Triticum aestivum and Aegilops tauschii Coss

Tausch's goatgrass (Aegilops tauschii Coss.), is a major weed species, infesting wheat (Triticum aestivum) fields in China. 2,4-D isooctyl ester is widely used for broadleaf weed control and selected as a tool to study the differences between, A. tauschii and T. aestivum. In this study, we measured the growth responses of these species to 2,4-D isooctyl ester and found that T. aestivum was more sensitive to the herbicide than A. tauschii. To clarify the reasons for this difference, we measured the leaf-mediated deposition, absorption and metabolism of 2,4-D isooctyl ester and the expression of auxin receptor transport inhibitor response (TIR1) gene in T. aestivum and A. tauschii. The results indicated that the deposition of 2,4-D isooctyl ester droplets may be lower on A. tauschii than on T. aestivum, because of the increased contact angle and greater density of trichomes on the leaves of the former. A distinct increase in 2,4-D isooctyl ester uptake was detected in T. aestivum during the entire experimental period, and the rate was 2.2-fold greater than that in A. tauschii at 6 h after treatment. Compared with A. tauschii, T. aestivum exhibited a greater accumulation of primary metabolite 2,4-D in plants, which may be responsible for the different responses of the two species. Additionally, the absolute expression level of TIR1 was clearly greater in T. aestivum than that in A. tauschii. These data will be helpful to further understand the differences between T. aestivum and A. tauschii, which may provide a unique perspective for the development and identification of new target compounds that are effective against this weed species.

Relationship of contact angle of spray solution on leaf surfaces with weed control

The weeds are important in agricultural and livestock areas because these plants can cause several damages, especially in the yield. The herbicide pulverization for weed control is the most used, but the efficiency of the control can be dependent the several factors, for example, the correct chose the herbicide and the mixture or not with adjuvant. This study aimed to evaluate the contact angle of herbicide solution droplets associated with adjuvant when deposited on the leaf surface of different weed species and their relationship with chemical control. For the contact angle experiment, the design was completely randomized, with four repetitions, while for the control experiment, a randomized block design was used, both experiments were arranged in a factorial (4 × 2 + 1) design. Factor A corresponded to four spray solutions containing the herbicide no addition of adjuvants and herbicide associated with adjuvants (vegetable oil, mineral oil, and lecithin), factor B to two herbicide dosages, and additional treatment corresponded to water. The contact angle was determined in six weed species: Crotalaria incana, Lantana camara, Ipomoea grandifolia, Asclepias curassavica, Sida obtusifolia, and Ricinus communis, on the adaxial and abaxial surface of each species, and an artificial surface. For the weed control experiment was used two weed species: C. incana and L. camara. The multivariate analysis allowed the understanding of the behavior of the contact angle of the different groups on the natural and artificial surfaces, due to the formation of factors. For all plants, except for the abaxial surface of I. grandifolia and the adaxial surface of A. curassavica, the association of herbicide and adjuvants reduced contact angle on the surfaces. The chemical control resulted in an indirect relation with contact angle, where smaller contact angles of the herbicide solution resulted in a higher percentage of plant intoxication. Therefore, for this situation, it is recommended to use the herbicide aminopyralid + fluroxypir associated with lecithin.

Impact of the equilibrium relationship between deposition and wettability behavior on the high-efficiency utilization of pesticides

BACKGROUND

Often, due to the occurrence of powdery mildew, cucumber leaf surfaces is changed into a more hydrophobic surface, which affects wetting and spreading of liquid pesticides, reducing their efficiency. The wetting and deposition behavior of liquid pesticides can be improved by adding surfactants to pesticides. Added surfactants affect the spray volume of the pesticide, which can lead to waste and a low utilization rate of the pesticide. It is important to further balance the relationship between deposition and wettability of pesticide liquid on the surfaces of healthy leaves and powdery mildew leaves of cucumber.

RESULTS

This study evaluated the deposition and wettability of hexaconazole (Hexa) with surfactants on the surfaces of healthy leaves and powdery mildew leaves of cucumber. The deposition rates of Hexa with surfactants were lower than that of Hexa due to the loss of solution in conventional spray volume (750 L ha^-1 ). The deposition rate of Hexa did not necessarily increase with increasing spray volume, and the deposition rate did not increase again after the spray volume increased to a certain level. Under the condition that the prevention and control effect were not reduced, we found that the volume of solution spray with added Silwet618 or AEO-5 should be adjusted to half of the normal volume, while the volume of solution spray with added 1227 or rosin-based quarternary ammonium should be adjusted to two-thirds of the normal volume to increase the deposition rate by approximately 30%. Regarding the wetting parameters, the results showed that the wettability of Hexa with Silwet618 was the best, but their combination was not ideal according to the composite index and deposition. By analyzing all the parameters, it was found that the spray volume reduction of Hexa with surfactant was approximately equal to the solution surface tension reduction, compared with the parameters of Hexa.

CONCLUSION

The equilibrium relationship between deposition rate and wetting parameters was determined to provide guidance for the application of surfactants and to lower the dosage of pesticides to increase their efficiency and reduce their application. © 2021 Society of Chemical Industry.

Copper-fixed quat: a hybrid nanoparticle for application as a locally systemic pesticide (LSP) to manage bacterial spot disease of tomato

The development of bacterial tolerance against pesticides poses a serious threat to the sustainability of food production. Widespread use of copper (Cu)-based products for plant disease management has led to the emergence of copper-tolerant pathogens such as Xanthomonas perforans (X. perforans) strains in Florida, which is very destructive to the tomato (Solanum lycopersicum) industry. In this study, we report a hybrid nanoparticle (NP)-based system, coined Locally Systemic Pesticide (LSP), which has been designed for improved efficacy compared to conventional Cu-based bactericides against Cu-tolerant X. perforans. The silica core-shell structure of LSP particles makes it possible to host ultra-small Cu NPs (<10 nm) and quaternary ammonium (Quat) molecules on the shell. The morphology, release of Cu and Quat, and subsequent in vitro antimicrobial properties were characterized for LSP NPs with core diameters from 50 to 600 nm. A concentration of 4 μg mL^-1 (Cu): 1 μg mL^-1 (Quat) was found to be sufficient to inhibit the growth of Cu-tolerant X. perforans compared to 100 μg mL^-1 (metallic Cu) required with standard Kocide 3000. Wetting properties of LSP exhibited contact angles below 60°, which constitutes a significant improvement from the 90° and 85° observed with water and Kocide 3000, respectively. The design was also found to provide slow Cu release to the leaves upon water washes, and to mitigate the phytotoxicity of water-soluble Cu and Quat agents. With Cu and Quat bound to the LSP silica core-shell structure, no sign of phytotoxicity was observed even at 1000 μg mL^-1 (Cu). In greenhouse and field experiments, LSP formulations significantly reduced the severity of bacterial spot disease compared to the water control. Overall, the study highlights the potential of using LSP particles as a candidate for managing tomato bacterial spot disease and beyond.

Evaporating droplets on inclined plant leaves and synthetic surfaces: Experiments and mathematical models

HYPOTHESIS

Evaporation of surfactant droplets on leaves is complicated due to the complex physical and chemical properties of the leaf surfaces. However, for certain leaf surfaces for which the evaporation process appears to follow the standard constant-contact-radius or constant-contact-angle modes, it should be possible to mimic the droplet evaporation with both a well-chosen synthetic surface and a relatively simple mathematical model.

EXPERIMENTS

Surfactant droplet evaporation experiments were performed on two commercial crop species, wheat and capsicum, along with two synthetic surfaces, up to a 90° incline. The time-dependence of the droplets' contact angles, height, volume and contact radius was measured throughout the evaporation experiments. Mathematical models were developed to simulate the experiments.

FINDINGS

With one clear exception, for all combinations of surfaces, surfactant concentrations and angles, the experiments appear to follow the standard evaporation modes and are well described by the mathematical models (modified Popov and Young-Laplace-Popov). The exception is wheat with a high surfactant concentration, for which droplet evaporation appears nonstandard and deviates from the diffusion limited models, perhaps due to additional mechanisms such as the adsorption of surfactant, stomatal density or an elongated shape in the direction of the grooves in the wheat surface.

Eco-friendly Water-Based λ-Cyhalothrin Polydopamine Microcapsule Suspension with High Adhesion on Leaf for Reducing Pesticides Loss

Recently, innovations of nano/microcarrier formulations have been focused on improving application efficiencies and retention time. In this study, a water-based 2.5% λ-cyhalothrin (LC) microcapsule suspension (CS) was developed by orthogonal test with biodegradable and adhesive polydopamine (PDA) microcapsules (MCs) as carriers. The obtained LC-PDA CS had good suspension properties, flow behavior, storage stability, and rheological properties. LC-PDA CS had higher retention, wettability, and decreased rainwater washing out on the leaves than commercial CS. LC-PDA CS displayed higher insecticidal activity against Lipaphis erysimi compared to commercial CS. LC-PDA CS reduced the toxicity of LC to the aquatic organism Danio rerio compared to LC. The above results demonstrated that LC-PDA CS would be eco-friendly water-based pesticides carrier system for prolonging the retention time on target leaf and reducing toxicity to aquatic organisms.

Fungicide Formulations Influence Their Control Efficacy by Mediating Physicochemical Properties of Spray Dilutions and Their Interaction with Target Leaves

In this study, three types of pyraclostrobin formulations (including emulsifiable concentrate (EC), suspension concentrate (SC), and microcapsules (MCs)) were used to control cucumber anthracnose. Pyraclostrobin EC had the highest inhibitory activity against Colletotrichum orbiculare in vitro. Much different from the bioactivity in vitro, pyraclostrobin MCs exhibited the highest control efficacy on cucumber anthracnose both in pot and field experiments. The physicochemical properties (particle size, surface tension) of the spray dilution, their interaction with target leaves (contact angle, adhesional tension, work of adhesion, retention, crystallization) and dissipation dynamic of the active ingredient were found to be highly potential factors that would significantly influence the control efficacy of pesticide formulations. Results showed that the control efficacies of different formulations of pyraclostrobin were determined mainly by the final behavior of the pesticides at the target interface, namely, the retention, crystallization, and dissipation dynamics of active ingredients. This study had revealed crucial factors that would influence the efficacy of different formulations of pyraclostrobin and thus could guide the rational and efficient use of different formulations of pesticides on target crops.

Evaluation of Residue Levels of Imidacloprid and Thiamethoxam After Foliar Application to the Citrus Varieties Lane Late, Valencia Late, Rohde Summer, and Nules

Neonicotinoids are used to protect citrus trees against pests. Dissipation and persistence of neonicotinoids in pollen and nectar of citrus trees after foliar applications and their potential exposure to pollinators have not been well characterized. Field studies were conducted using three orange and one mandarin varieties to compare the imidacloprid and thiamethoxam residue levels and their decline in pollen and nectar after treatments in pre-bloom close to flowering period and their persistence 1 yr after treatment. The possible risk to honeybees was assessed. In nectar, thiamethoxam and imidacloprid residues were between 61 and 99% lower than in pollen, depending on the citrus variety or/and the days after treatment when applied close to blooming. At the end of the flowering period, imidacloprid in pollen and nectar was not detected in the mandarin variety after treatment in pre-bloom, whereas for thiamethoxam, no residues were detected in nectar but 10 ng/g was detected in pollen. There were no quantifiable levels of residues for either neonicotinoids in pollen or nectar during the flowering period of the following year. Neonicotinoid residue levels and their decline in nectar and pollen in citrus depended on the timing of applications relative to flowering and on the citrus variety. The absence of neonicotinoid residues 1 yr out after foliar applications in all varieties assayed demonstrated that none of the neonicotinoids tested were persistent. The results could be different in other citrus varieties, and therefore, also the exposure assessment for managed pollinators.

Effect of addition of adjuvants on physical and chemical characteristics of Bt bioinsecticide mixture

Bacillus thuringiensis (Bt) is the main bacterium used in the formulation of bioinsecticides because it produces toxins and spores that are toxic to several orders of insects. The efficacy of Bt bioinsecticide is influenced by the quality of its application. The association with other crop protection products, such as adjuvants, can affect the physical and chemical parameters of the mixture. This study evaluated the physical and chemical parameters, volume median diameter (VMD), uniformity coefficient of droplets (SPAN), percentage of volume in drift droplets (%V <100 µm), contact angle, surface tension, potential of hydrogen (pH) and electrical conductivity (E.C.) of Bt bioinsecticides in concentrated suspension (SC), and wettable powder (WP) formulations associated with adjuvants. The largest droplet diameter and smallest values of drift droplets were found in the WP formulation with lower drift potential. The addition of mineral oil and surfactant to the mixtures of bioinsecticide reduced contact angle values and surface tension of the droplets, resulting in greater spreading of droplets in leaves. The addition of lecithin and propionic-acid-based adjuvants lowered the pH in both formulations. The adjuvants used in this study affected the physical and chemical characteristics of the mixtures, improving or impairing the quality of Bt bioinsecticide applications.

Role of Adjuvants in the Management of Anthracnose-Change in the Crystal Morphology and Wetting Properties of Fungicides

The hydrophobic wax layer of pepper fruit (Capsicum frutescens L.) increases the importance of selecting adjuvants that improve the wetting property of droplets on the target organism and increase the effective utilization of fungicides. In this study, the effect of adjuvants including nonionic, cationic, organosilicone, and oils on the wettability of fungicides was determined. The critical micelle concentrations for S903 (organosilicone), 1227 (cationic), AEO-5 (nonionic), GY-Tmax (oil), and XP-2 (oil) were 25, 1000, 100, 200, and 500 mg/L, respectively. Interface behaviors and in vivo tests suggested that adjuvants at appropriate concentrations (S903, 2.5 mg/L; 1227, 100 mg/L; AEO-5, 1 mg/L; GY-Tmax, 50 mg/L; and XP-2, 5 mg/L) resulted in optimum efficiency. Adjuvants significantly increased the inhibitory activity of pyraclostrobin against the mycelial growth, spore germination, and germ tube elongation of Colletotrichum scovillei by 41.3-58.8%, 28.2-44.6%, and 27.8-39.8%, respectively. Pyraclostrobin amended with S903 and XP-2 showed higher efficacy against anthracnose than the fungicide alone on pepper fruit. The increased efficacy may have resulted from the changed crystal morphology (ellipses of similar sizes), improved wettability, and rainfastness. A structural equation model indicated that surface tension and retention play the most important roles in the application properties of fungicide. In field experiments, the efficacy of pyraclostrobin with adjuvants showed no significant difference with pyraclostrobin alone, which indicated that, except for adjuvants, other spraying technologies are important for improving the field performance of fungicides. These results provide a foundation for the synthesis of highly efficient fungicides based on crystal structure and for the sustainable management of pepper anthracnose.

Oil Adjuvants Enhance the Efficacy of Pyraclostrobin in Managing Cucumber Powdery Mildew (Podosphaera xanthii) by Modifying the Affinity of Fungicide Droplets on Diseased Leaves

Adding adjuvants improved the affinity of fungicide droplets to cucumber leaves infected with powdery mildew (Podosphaera xanthii) and subsequent efficacy of fungicide treatments in reducing the disease. The affinity of oil adjuvants was quantified by adhesional tension and "work of adhesion". Oil adjuvant-fungicide mixtures were applied to plants in field experiments to evaluate their effectiveness in disease prevention. Both the adhesional tension and work of adhesion of the adjuvants at selected concentrations increased on powdery-mildew-infected cucumber leaves more than on healthy cucumber leaves. The adjuvant GY-Tmax (GYT) displayed the best surface activity or "surfactivity" in enhancing the affinity and adherence of droplets to powdery-mildew-infected cucumber leaves, while epoxidized soybean oil (ESO), methyl oleate, and biodiesel exhibited much lower effects in terms of the surface tension, contact angle, adhesional tension, and work of adhesion. Field experiments determined that the combination of GYT at 1,000 mg liter^-1 and pyraclostrobin (150 g a.i. ha^-1) was most effective (91.52%) in controlling cucumber powdery mildew. Pyraclostrobin with ESO was also highly effective (ranging from 77.54 to 89.65%). The addition of oil adjuvants, especially GYT and ESO, to fungicide applications can be an effective strategy to enhance the efficacy of pesticides in controlling plant diseases by modifying the affinity of fungicide droplets to symptomatic leaves.

Influence of Multiple Factors on the Wettability and Surface Free Energy of Leaf Surface

The wettability of plant leaves directly reflects leaf hydrophilicity, which is the key factor that influences the adhesion of liquid pesticide as well as affects plant protection products (PPP) efficacy. Generally, the wettability of leaf surface is quantified by the contact angle and surface free energy (SFE), which are mainly dependent on leaf surface properties, liquid properties and other spraying parameters. Therefore, the aim of this paper was to investigate the SFE of rice and rape leaves with the variation of leaf status, leaf surface, and probe liquid as well as the influence of droplet falling height, solid surface, and PPP concentration on the wettability. The results showed that: (1) the dispersive components of SFE of rice and rape account for a large proportion which are closely related to their hydrophobicity—the abaxial of rape new leaf and the adaxial of rape old leaf are easier to wet comparing with rice and rape leaves in other statuses; (2) the increase of droplet falling height had a significant effect on improving the wettability between wax surface and adjuvant solution, while it had little improving effect on the wettability between wax surface and water; (3) the wettability of different solid surface varied greatly, and the order of wettability from good to bad is water-sensitive paper (WSP), wax, rape leaf, and rice leaf; (4) the effect of PPP concentration on the leaf surface wettability is significant, the contact angle decreased with the increase of PPP concentration, and the wettability of microemulsion is better than that of suspending agent and wettable powder. In conclusion, the SFE and wettability of crop leaf surface determine the suitable type of PPP, studying the influence of multiple factors on leaf surface wettability can provide a reliable reference for providing scientific guidance as well as improving the effective utilization of PPP.

Comparison of Spray Deposition, Control Efficacy on Wheat Aphids and Working Efficiency in the Wheat Field of the Unmanned Aerial Vehicle with Boom Sprayer and Two Conventional Knapsack Sprayers

As a new low volume application technology, unmanned aerial vehicle (UAV) application is developing quickly in China. The aim of this study was to compare the droplet deposition, control efficacy and working efficiency of a six-rotor UAV with a self-propelled boom sprayer and two conventional knapsack sprayers on the wheat crop. The total deposition of UAV and other sprayers were not statistically significant, but significantly lower for run-off. The deposition uniformity and droplets penetrability of the UAV were poor. The deposition variation coefficient of the UAV was 87.2%, which was higher than the boom sprayer of 31.2%. The deposition on the third top leaf was only 50.0% compared to the boom sprayer. The area of coverage of the UAV was 2.2% under the spray volume of 10 L/ha. The control efficacy on wheat aphids of UAV was 70.9%, which was comparable to other sprayers. The working efficiency of UAV was 4.11 ha/h, which was roughly 1.7–20.0 times higher than the three other sprayers. Comparable control efficacy results suggest that UAV application could be a viable strategy to control pests with higher efficiency. Further improvement on deposition uniformity and penetrability are needed.

Natural green-peel orange essential oil enhanced the deposition, absorption and permeation of prochloraz in cucumber

Pesticides have long been used in agricultural production and will continue to be used long into the future. Enhancing their efficient use in agricultural production is an effective method to avoid their loss to non-target areas, such as soil, water and air. Here natural green-peel orange essential oil (GOEO) was used as a spray adjuvant to improve the efficient use of pesticides. A comparative study between a conventional formulation and a conventional formulation with GOEO was conducted. Conventional formulations of prochloraz were chosen as control groups. It was obvious that the concentrations of prochloraz and its metabolite in cucumber leaves treated by conventional formulations with GOEO were much higher than those treated without GOEO. The data also showed, for both emulsifiable concentrate (EC) and suspension concentrate (SC), that the spreading and penetration performance were improved when GOEO was used as a spray adjuvant, but with SC the impact was more significant. GOEO improved the deposition, absorption and degradation performance of prochloraz on cucumber leaves. It was more applicable to those pesticide formulations without a good wetting and spreading effect, such as SC. As a plant source extract, GOEO is much safer for crops and more friendly to the environment than other synthetic adjuvants. The application of GOEO as a spray adjuvant has great potential to increase the pesticide utilization rate.

Natural green-peel orange essential oil was used as a spray adjuvant to improve the efficient use of pesticides.

Mathematical Modeling of Diffusion of a Hydrophilic Ionic Fertilizer in Plant Cuticles: Surfactant and Hygroscopic Effects

The agricultural industry requires improved efficacy of sprays being applied to crops and weeds to reduce their environmental impact and increase financial returns. One way to improve efficacy is by enhancing foliar penetration. The plant leaf cuticle is the most significant barrier to agrochemical diffusion within the leaf. The importance of a mechanistic mathematical model has been noted previously in the literature, as each penetration experiment is dictated by its specific parameters, namely plant species, environmental conditions such as relative humidity and spray formulation including adjuvant addition. A mechanistic mathematical model has been previously developed by the authors, focusing on plant cuticle diffusion of calcium chloride through tomato fruit cuticles including pore swelling, ion binding and evaporation, along with the ability to vary the active ingredient concentration and type, relative humidity and plant species. Here we further develop this model to include adjuvant effects as well as the hygroscopic nature of deliquescent ionic solutions with evaporation on the cuticle surface. These modifications to a penetration and evaporation model provide a novel addition to the literature and allow the model to be applied to many types of evaporating ionic hygroscopic solutions on many types of substrates, not just plant cuticles. We validate our theoretical model results against appropriate experimental data, discuss key sensitivities and relate theoretical predictions to physical mechanisms. The important governing mechanisms influencing surfactant enhanced penetration of ionic active through plant cuticles were found to be aqueous pore radius, pore density, cuticle thickness and initial contact angle of the applied droplet; ion binding, relative humidity and evaporation including hygroscopic water absorption parameters for point of deliquescence. The sensitivity analysis indicated surfactants increase penetration by changing the point of deliquescence of a solution, which alters the water absorption and the initial contact angle, which alters the number of pores under the droplet. The results of the validation and sensitivity analysis imply that this model accounts for many of the mechanisms governing penetration in plant cuticles.

Assessment of ethylene glycol diacetate as an alternative carrier for use in agrochemical emulsifiable concentrate formulation

The conventional emulsifiable concentrate (EC) formulation contains a large amount of aromatic solvents, which causes adverse effects to both the environment and human health due to the toxicity of the solvents. Here, we developed a 2.5% lambda-cyhalothrin EC formulation with ethylene glycol diacetate (EGDA) as the solvent, and the developed formulation serves as an environmental-friendly alternative to overcome the adverse effects of aromatic solvents. The physicochemical characterizations, wettability properties, phytotoxicity and bioassays of the EGDA-EC formulation were systematically investigated and compared with that of the EC formulation with xylene as the solvent. The results showed that both EC formulations had excellent emulsion properties and storage stabilities. Additionally, the EGDA-EC formulation possessed a higher flash point (96 °C), indicating safer production, storage and transport. The retentions of the EGDA-EC sample on leaves were 1.22-1.46-fold higher than that of the xylene-EC sample, and the EGDA-EC also exhibited lower surface tensions and contact angles, which would benefit decreasing drift-off and improving utilization. Furthermore, the bioassays demonstrated that the EGDA-EC formulation had lower acute toxicity to aquatic organisms and higher control efficacy to target insects compared with the xylene-EC formulation. Therefore, EGDA is a promising carrier for oil-soluble agrochemicals to improve their application performance and reduce their adverse effects.

Wettability of pear leaves from three regions characterized at different stages after flowering using the OWRK method

BACKGROUND

A better understanding of leaf surface wettability is critical to improve the adhesion of liquid pesticides. Leaf surface wettability is dependent on the property of the liquid as well as the physical and chemical properties of the leaf, which vary with climate and growth stage. The aim of this study was to characterize the wettability of pear leaves from three different climatic regions at different stages after flowering.

RESULTS

The contact angles of different test liquids were measured on both adaxial and abaxial pear leaf surfaces and the Owens-Wendt-Rabel-Kaelble (OWRK) method was used to calculate surface free energy (SFE) and its polar and non-polar components. The results demonstrated that the SFE of both the adaxial and abaxial surface of the pear leaf, and the proportion of polar component, increased with increasing time after flowering. At early growth stages, pear leaves were highly hydrophobic, similar to a polytetrafluoroethylene surface, whereas at later growth stages, pear leaves were hydrophobic, more similar to a polymethylmethacrylate surface. Also, the SFE differed with climatic region. Factors influencing these changes are discussed.

CONCLUSION

Changes in contact angles and SFE correlated with the change of the leaf surface wettability. Leaves became easier to wet (higher SFE), with an overall increasing polar component to the surface, with increasing age after flowering. As expected, changes in wettability were found in pear leaves at different stages after flowering and in different regions (P < 0.05). Pear leaves from Yuanping were easier to wet than leaves from Yuci and Linyi, and adaxial surfaces were easier to wet than abaxial surfaces. These results provide beneficial information for the application of agrochemicals for improved wetting and spreading behavior. © 2018 Society of Chemical Industry.

Evaporation kinetics of surfactant solution droplets on rice (Oryza sativa) leaves

The dynamics of evaporating sessile droplets on hydrophilic or hydrophobic surfaces is widely studied, and many models for these processes have been developed based on experimental evidence. However, few research has been explored on the evaporation of sessile droplets of surfactant or pesticide solutions on target crop leaves. Thus, in this paper the impact of surfactant concentrations on contact angle, contact diameter, droplet height, and evolution of the droplets' evaporative volume on rice leaf surfaces have been investigated. The results indicate that the evaporation kinetics of surfactant droplets on rice leaves were influenced by both the surfactant concentrations and the hydrophobicity of rice leaf surfaces. When the surfactant concentration is lower than the surfactant CMC (critical micelle concentration), the droplet evaporation time is much longer than that of the high surfactant concentration. This is due to the longer existence time of a narrow wedge region under the lower surfactant concentration, and such narrow wedge region further restricts the droplet evaporation. Besides, our experimental data are shown to roughly collapse onto theoretical curves based on the model presented by Popov. This study could supply theoretical data on the evaporation of the adjuvant or pesticide droplets for practical applications in agriculture.

Foliar penetration enhanced by biosurfactant rhamnolipid

With recent environmental and health concerns, biosurfactants have obtained increasing interest in replacing conventional surfactants for diverse applications. In agriculture, the use of surfactant in stimulating foliar uptake is mainly for wetting leaf surface, resisting deposition/evaporation, enhancing penetration across cuticular membrane (CM) and translocation. This paper aimed to address the improved foliar uptake by rhamnolipid (RL) in comparison with the currently used alkyl polyglucoside (APG). As found, compared with APG at 900mg/L (1×critical micellar concentration, CMC), RL at a much lower concentration of 50mg/L (1×CMC) showed much better wettability and surface activity, indicative of its high effectiveness as surfactants. Its performance on resistance to deposition and evaporation was at least as same as APG. Moreover, RL could significantly improve the penetration of herbicide glyphosate and other two small water-soluble molecules (phenol red and Fe(2+)) across CM at an equivalent efficiency as APG at 1×CMC. Finally, the greatly enhanced herbicidal actitivity of glyphosate on greenhouse plants confirmed that RL and APG could both enhance the foliar uptake including translocation. Overall, RL should be more applicable than APG in agriculture due to its more promising properties on health/environmental friendliness.

Effect of solution and leaf surface polarity on droplet spread area and contact angle

BACKGROUND

How much an agrochemical spray droplet spreads on a leaf surface can significantly influence efficacy. This study investigates the effect solution polarity has on droplet spreading on leaf surfaces and whether the relative leaf surface polarity, as quantified using the wetting tension dielectric (WTD) technique, influences the final spread area. Contact angles and spread areas were measured using four probe solutions on 17 species.

RESULTS

Probe solution polarity was found to affect the measured spread area and the contact angle of the droplets on non-hairy leaves. Leaf hairs skewed the spread area measurement, preventing investigation of the influence of surface polarity on hairy leaves. WTD-measured leaf surface polarity of non-hairy leaves was found to correlate strongly with the effect of solution polarity on spread area.

CONCLUSIONS

For non-polar leaf surfaces the spread area decreases with increasing solution polarity, for neutral surfaces polarity has no effect on spread area and for polar leaf surfaces the spread area increases with increasing solution polarity. These results attest to the use of the WTD technique as a means to quantify leaf surface polarity. © 2015 Society of Chemical Industry.

Measuring Leaf Penetration and Volatilization of Chlorothalonil and Epoxiconazole Applied on Wheat Leaves in a Laboratory-Scale Experiment

Estimation of pesticide volatilization from plants is difficult because of our poor understanding of foliar penetration by pesticides, which governs the amount of pesticide available for volatilization from the leaf surface. The description of foliar penetration is still incomplete because experimental measurements of this complex process are difficult. In this study, the dynamics of leaf penetration of C-chlorothalonil and C-epoxiconazole applied to wheat leaves were measured in a volatilization chamber, which allowed us to simultaneously measure pesticide volatilization. Fungicide penetration into leaves was characterized using a well-defined sequential extraction procedure distinguishing pesticide fractions residing at different foliar compartments; this enabled us to accurately measure the penetration rate constant into the leaves. The effect of pesticide formulation was also examined by comparing formulated and pure epoxiconazole. We observed a strong effect of formulation on leaf penetration in the case of a systemic product. Furthermore, the penetration rate constant of formulated epoxiconazole was almost three times that of pure epoxiconazole (0.47 ± 0.20 and 0.17 ± 0.07, respectively). Our experimental results showed high recovery rates of the radioactivity applied within the range of 90.5 to 105.2%. Moreover, our results confirm that pesticide physicochemical properties are key factors in understanding leaf penetration of pesticide and its volatilization. This study provides important and useful parameters for mechanistic models describing volatilization of fungicides applied to plants, which are scarce in the literature.

MALDI-MS Imaging Analysis of Fungicide Residue Distributions on Wheat Leaf Surfaces

Improved retention and distribution of agrochemicals on plant surfaces is an important attribute in the biological activity of pesticide. Although retention of agrochemicals on plants after spray application can be quantified using traditional analytical techniques including LC or GC, the spatial distribution of agrochemicals on the plants surfaces has received little attention. Matrix assisted laser desorption/ionization (MALDI) imaging technology has been widely used to determine the distribution of proteins, peptides and metabolites in different tissue sections, but its application to environmental research has been limited. Herein, we probed the potential utility of MALDI imaging in characterizing the distribution of three commercial fungicides on wheat leaf surfaces. Using this MALDI imaging method, we were able to detect 500 ng of epoxiconazole, azoxystrobin, and pyraclostrobin applied in 1 μL drop on the leaf surfaces using MALDI-MS. Subsequent dilutions of pyraclostrobin revealed that the compound can be chemically imaged on the leaf surfaces at levels as low as 60 ng of total applied in the area of 1 μL droplet. After application of epoxiconazole, azoxystrobin, and pyraclostrobin at a field rate of 100 gai/ha in 200 L water using a track sprayer system, residues of these fungicides on the leaf surfaces were sufficiently visualized. These results suggest that MALDI imaging can be used to monitor spatial distribution of agrochemicals on leaf samples after pesticide application.

Characterization of droplet impact and deposit formation on leaf surfaces

BACKGROUND

Elucidation of droplet dynamic impact and deposit formation on leaf surfaces would assist in modifying application strategies potentially to improve biological control efficiency and minimize pesticide waste.

RESULTS

The mechanics of the three-dimensional droplet impact and formation process on hydrophilic and hydrophobic leaf surfaces was investigated with a system that independently controlled droplet diameter, impact speed and impact angle. Spray solutions were made with a nonionic surfactant in distilled water. Water-only droplets rebounded or splashed on hydrophobic leaves of Euphorbia pulcherrima and Zea mays, but not on hydrophilic Dracaena deremensis leaves. Droplet spread areas on D. deremensis at 5.0 m s(-1) impact speed increased 1.9-fold when the droplet diameter was increased from 175 to 481 µm. Similarly, spread areas of 306 µm water-only droplets increased 2.0-fold when the impact speed was increased from 3.5 to 7.0 m s(-1) . At surfactant concentrations of 0, 0.25, 0.50 and 0.75% (v/v), percentages of droplets that either splashed or bounced off Z. mays were 56, 37, 2 and 0% respectively.

CONCLUSION

Microscopic measurements of droplet impact clarified the effectiveness of surfactants in enhancing droplet retention on hydrophobic leaves and also revealed that water droplets did not rebound or splash on hydrophilic leaves. © 2014 Society of Chemical Industry.

Leaf structures affect predatory mites (Acari: Phytoseiidae) and biological control: a review

Because of their size, small arthropods can be highly affected by characteristics of the leaf surface. Leaf surfaces have various structures, such as trichomes and domatia, which add to the complexity of the microenvironment experienced by arthropods. Plant structure can affect the retention and performance of predators and parasitoids and it has been proposed that phylloplane characteristics be modified to improve the utility of these organisms as biological control agents. Phytoseiids have a long history as biological control agents of pest mite species in agricultural systems. In the past 30 years, extensive research has shown that trichomes and domatia influence phytoseiid populations and performance. Various reasons have been proposed to explain this relationship, including increased pollen capture for use as a food source, escape from predation, avoidance of adverse abiotic conditions, and increased/decreased ease of prey capture. There is potential for the manipulation of crops to improve biological control by phytoseiids, but incorporating beneficial traits into plants is likely to have lower priority than other breeding characteristics. The objectives of this review are to summarize the evidence for the relationship between phytoseiids and leaf surface structures, discuss possible hypotheses to explain this relationship, examine the potential of altering current crop varieties for the purpose of increasing phytoseiid populations or performance, and conduct a meta-analysis to quantify the effects of plant surface structures on phytoseiid and phytophagous mite densities.

Intrusive trichome bases in the leaves of silverleaf nightshade (Solanum elaeagnifolium; Solanaceae) do not facilitate fluorescent tracer uptake

PREMISE OF THE STUDY

Solanum elaeagnifolium (silverleaf nightshade), having originated in the Americas, is now a serious summer-growing, perennial weed in many countries, including Australia. Most surfaces of the plants have a dense covering of trichomes, giving them a silvery-white appearance, hence the common name. We aimed to identify structural and functional properties of its leaves, especially the trichomes, that may affect the uptake of foliar-applied tracer dyes.

METHODS

The structure of leaves of Solanum elaeagnifolium was examined by light and scanning electron microscopy. The potential for transport of materials between trichomes and veins was studied with symplastic (carboxyfluorescein diacetate) and apoplastic (lucifer yellow) tracer dyes.

KEY RESULTS

Mature leaves had a dense covering of complex, stellate trichomes on both surfaces, particularly the abaxial. The basal cells of Solanum elaeagnifolium trichomes penetrated into the underlying palisade mesophyll layers. The innermost lobes of these basal cells sometimes contacted the bundle sheath of the veins, but were not observed to directly contact the xylem or phloem. We found that neither symplastic nor apoplastic dyes were transferred between the basal cells of the trichomes and the vascular tissues. The trichome layer repelled water-based tracer dyes, while one of four adjuvants tested facilitated entry of both symplastic and apoplastic dyes.

CONCLUSIONS

Our results did not support a transport function for the trichomes. The trichomes may protect the mesophytic leaves from invertebrate herbivory, while also probably decreasing radiation absorbed resulting in cooler leaves in this summer-growing species.

The mechanism of methylated seed oil on enhancing biological efficacy of topramezone on weeds

Methylated seed oil (MSO) is a recommended adjuvant for the newly registered herbicide topramezone in China and also in other countries of the world, but the mechanism of MSO enhancing topramezone efficacy is still not clear. Greenhouse and laboratory experiments were conducted to determine the effects of MSO on efficacy, solution property, droplet spread and evaporation, active ingredient deposition, foliar absorption and translocation of topramezone applied to giant foxtail (Setaria faberi Herrm.) and velvetleaf (Abutilon theophrasti Medic.). Experimental results showed that 0.3% MSO enhanced the efficacy of topramezone by 1.5-fold on giant foxtail and by 1.0-fold on velvetleaf. When this herbicide was mixed with MSO, its solution surface tension and leaf contact angle decreased significantly, its spread areas on weed leaf surfaces increased significantly, its wetting time was shortened on giant foxtail but not changed on velvetleaf, and less of its active ingredient crystal was observed on the treated weed leaf surfaces. MSO increased the absorption of topramezone by 68.9% for giant foxtail and by 45.9% for velvetleaf 24 hours after treatment. It also apparently promoted the translocation of this herbicide in these two weeds.