Plant Protection Chemistry NZ Ltd.

Rotorua, New Zealand

Plant Protection Chemistry NZ Ltd.

Rotorua, New Zealand
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Tredenick E.C.,Queensland University of Technology | Farrell T.W.,Queensland University of Technology | Forster W.A.,Plant Protection Chemistry NZ Ltd | Psaltis S.T.P.,Queensland University of Technology
Frontiers in Plant Science | Year: 2017

The agricultural industry requires improved efficacy of sprays being applied to crops and weeds in order to reduce their environmental impact and deliver improved financial returns. Enhancedfoliar uptake is one means of improving efficacy. The plant leaf cuticle is known to be the main barrier to diffusion of agrochemicals within the leaf. The usefulness of a mathematical model to simulate uptake of agrochemicals in plant cuticles has been noted previously in the literature, as the results of each uptake experiment are specific to each formulation of active ingredient, plant species and environmental conditions. In this work we develop a mathematical model and numerical simulation for the uptake of hydrophilic ionic agrochemicals through aqueous pores in plant cuticles. We propose a novel, nonlinear, porous diffusion model for ionic agrochemicals in isolated cuticles, which extends simple diffusion through the incorporation of parameters capable of simulating: plant species variations, evaporation of surface droplet solutions, ion binding effects on the cuticle surface and swelling of the aqueous pores with water. We validate our theoretical results against appropriate experimental data, discuss the key sensitivities in the model and relate theoretical predictions to appropriate physical mechanisms. Major influencing factors have been found to be cuticle structure, including tortuosity and density of the aqueous pores, and to a lesser extent humidity and cuticle surface ion binding effects. © 2017 Tredenick, Farrell, Forster and Psaltis.


Dorr G.J.,University of Queensland | Wang S.,China Agricultural University | Mayo L.C.,Queensland University of Technology | McCue S.W.,Queensland University of Technology | And 3 more authors.
Experiments in Fluids | Year: 2015

This paper combines experimental data with simple mathematical models to investigate the influence of spray formulation type and leaf character (wettability) on shatter, bounce and adhesion of droplets impacting with cotton, rice and wheat leaves. Impaction criteria that allow for different angles of the leaf surface and the droplet impact trajectory are presented; their predictions are based on whether combinations of droplet size and velocity lie above or below bounce and shatter boundaries. In the experimental component, real leaves are used, with all their inherent natural variability. Further, commercial agricultural spray nozzles are employed, resulting in a range of droplet characteristics. Given this natural variability, there is broad agreement between the data and predictions. As predicted, the shatter of droplets was found to increase as droplet size and velocity increased, and the surface became harder to wet. Bouncing of droplets occurred most frequently on hard-to-wet surfaces with high-surface-tension mixtures. On the other hand, a number of small droplets with low impact velocity were observed to bounce when predicted to lie well within the adhering regime. We believe this discrepancy between the predictions and experimental data could be due to air layer effects that were not taken into account in the current bounce equations. Other discrepancies between experiment and theory are thought to be due to the current assumption of a dry impact surface, whereas, in practice, the leaf surfaces became increasingly covered with fluid throughout the spray test runs. © 2015, Springer-Verlag Berlin Heidelberg.


Dorr G.J.,Queensland University of Technology | Kempthorne D.M.,Queensland University of Technology | Mayo L.C.,Queensland University of Technology | Forster W.A.,Plant Protection Chemistry NZ Ltd. | And 5 more authors.
Ecological Modelling | Year: 2014

Pesticides used in agricultural systems must be applied in economically viable and environmentally sensitive ways, and this often requires expensive field trials on spray deposition and retention by plant foliage. Computational models to describe whether a spray droplet sticks (adheres), bounces or shatters on impact, and if any rebounding parent or shatter daughter droplets are recaptured, would provide an estimate of spray retention and thereby act as a useful guide prior to any field trials.Parameter-driven interactive software has been implemented to enable the end-user to study and visualise droplet interception and impaction on a single, horizontal leaf. Living chenopodium, wheat and cotton leaves have been scanned to capture the surface topography and realistic virtual leaf surface models have been generated. Individual leaf models have then been subjected to virtual spray droplets and predictions made of droplet interception with the virtual plant leaf. Thereafter, the impaction behaviour of the droplets and the subsequent behaviour of any daughter droplets, up until re-capture, are simulated to give the predicted total spray retention by the leaf. A series of critical thresholds for the stick, bounce, and shatter elements in the impaction process have been developed for different combinations of formulation, droplet size and velocity, and leaf surface characteristics to provide this output.The results show that droplet properties, spray formulations and leaf surface characteristics all influence the predicted amount of spray retained on a horizontal leaf surface. Overall the predicted spray retention increases as formulation surface tension, static contact angle, droplet size and velocity decreases. Predicted retention on cotton is much higher than on chenopodium. The average predicted retention on a single horizontal leaf across all droplet size, velocity and formulations scenarios tested, is 18, 30 and 85% for chenopodium, wheat and cotton, respectively. © 2013 Elsevier B.V.


Schou W.C.,Scion Research | Forster W.A.,Plant Protection Chemistry NZ Ltd. | Mercer G.N.,Australian National University | Teske M.E.,Continuum Dynamics, Inc. | Thistle H.W.,U.S. Department of Agriculture
Transactions of the ASABE | Year: 2012

AGDISP uses canopy structure and collection efficiency to model canopy interception but assumes droplets that intercept a leaf surface are retained at that point and do not bounce or shatter. This behavior is not the case for many plant species, particularly species that are moderately to very difficult to wet, for which canopy deposition would be overestimated with this assumption. This article summarizes the initial implementation of process-based models for spray droplet bounce and shatter within an experimental build of AGDISP in order to predict spray retention within plant canopies. Spray simulations were run for formulations ranging in surface tension, applied to three species (wheat, canola, and capsicum) with different wettabilities and leaf orientations, and using the AGDISP ground model with and without the retention model, to evaluate the impact of the retention model on canopy deposition within AGDISP. The model outputs were also compared to previously determined tracksprayer results. The current AGDISP canopy deposition (interception) model was unable to fully account for differences in retention due to the spray formulation used or species studied. Incorporation of the process-driven models for bounce and shatter allowed these differences to be predicted. Over the three species and four formulations studied, there was good agreement (Pearson's correlation coefficient = 0.9308, p = 0.0000, indicating an almost certain correlation) between predicted and experimentally determined retention. Considerable work is still required to make this approach practical. However, this article illustrates that the ability to model retention is important for many crops (and weeds) and that the approach outlined herein is an effective adjunct to the current AGDISP interception model. © 2012 American Society of Agricultural and Biological Engineers.


Forster W.A.,Plant Protection Chemistry NZ Ltd. | Mercer G.N.,Australian National University | Schou W.C.,Scion Research
New Zealand Plant Protection | Year: 2012

The retention and distribution of spray droplets within the plant canopy have a crucial effect on the biological efficacy of pesticides. To maximise spray retention, droplets that impact a leaf must remain on the plant. Three outcomes are possible when a droplet impacts a leaf surface: adhesion, bounce or shatter. Those droplets that bounce or shatter can continue their journey through the canopy, depositing at lower levels in the canopy or on the ground. Mathematical models based on the physical processes involved in the bounce/adhesion and shatter of droplets have been developed, improved and described. These process-based retention models have recently been implemented within an experimental build of the spray application simulation software AGDISP. This has allowed differences in total spray retention to plants, due to the spray formulation used or vegetative species studied, to be predicted. This paper discusses these new tools, illustrates the effect different spray formulations and application parameters have on predicted retention, and compares model predictions with measured retention. © 2012 New Zealand Plant Protection Society (Inc.).


Forster W.A.,Plant Protection Chemistry NZ Ltd | Kimberley M.O.,Scion Research
Pest Management Science | Year: 2015

BACKGROUND: The objective of the present study was to determine the contribution of the active ingredient (AI) and surfactant, and their concentrations, to the foliar uptake of agrichemicals, and to examine the physical properties that would need to be included in a model for foliar uptake. RESULTS: All spray formulation component variables significantly affected uptake, explaining 73% of the deviance. The deviance explained by each factor ranged from 43% (AI concentration nested within AI) to 5.6% (surfactant). The only significant interaction was between AI and surfactant, explaining 15.8% of the deviance. Overall, 90% of the deviance could be explained by the variables and their first-order interactions. CONCLUSIONS: Uptake increased with increasing lipophilicity of the AI at concentrations below those causing precipitation on the leaf surface. AI concentration had a far greater (negative) effect on the uptake of the lipophilic molecule epoxiconazole. The uptake of 2-deoxy-D-glucose (DOG) and 2,4-dichlorophenoxyacetic acid (2,4-D) increased with increasing hydrophile-lipophile balance (HLB) of the surfactant, the effect of HLB being far greater on the hydrophilic molecule DOG. However, the differences observed in epoxiconazole uptake owing to the surfactant were strongly positively related to the spread area of the formulation on the leaf surface. For all AIs, uptake increased in a similar manner with increasing molar surfactant concentration. © 2014 Society of Chemical Industry.


Nairn J.J.,Plant Protection Chemistry NZ Ltd. | Forster W.A.,Plant Protection Chemistry NZ Ltd. | van Leeuwen R.M.,Plant Protection Chemistry NZ Ltd.
Weed Research | Year: 2013

The adhesion of a spray droplet upon initial contact with a leaf surface is extremely important to spray efficacy and is dependent on dynamic interactions between droplets (formulation, size, velocity) and leaf (micro-topography, surface chemistry, veininess, hairiness and orientation). A 'universal' spray droplet adhesion model has previously been developed, using 50% aqueous acetone contact angles as a measure of leaf surface properties; this model satisfactorily predicts initial adhesion over a range of formulation surface tensions, droplet sizes and velocities. However, it failed to fit data from hairier leaves. This study investigates initial spray droplet adhesion on hairy leaves. Two categories of hairy leaves were identified by how the droplets penetrate the leaf hairs, Wenzel (hairy) and Cassie-Baxter (super hairy). For the Wenzel-type, a simple constant accounted for the increased droplet shatter caused by the hairs. For the Cassie-Baxter-type, a cushioning factor was introduced to account for the absorption of kinetic energy at impact by the hair mat. The cushioning factor was estimated by measuring the relative height of the hair mat. By including these two parameters, the new model successfully predicted the mean adhesion of non-hairy, hairy and super-hairy plants (R2 = 0.96). This model and the underlying principles determining hairy leaf adhesion developed in this article will help develop spray formulations effective at targeting hairy-leaved weed and crop species. © 2013 European Weed Research Society.


Nairn J.J.,Plant Protection Chemistry NZ Ltd. | Forster W.A.,Plant Protection Chemistry NZ Ltd.
New Zealand Plant Protection | Year: 2015

Pyranine, a water soluble fluorescent tracer, has been used in spray drift studies, yet there is limited information regarding analytical methods, and conflicting information on the rapidity and extent to which the pyranine may degrade. This study assessed the suitability of pyranine as a tracer for drift studies. While pyranine did decompose when exposed to sunlight whilst in solution, spray droplets dry in minutes and photodecomposition appears to be significantly slower in the solid phase. Droplet residues showed minimal photodecomposition after exposure to sunlight for 2 h. Pyranine samples could be stored in cool, dark conditions, as dried deposits or in solution, for over 2 weeks without significant degradation. Pyranine is a suitable tracer for spray drift determinations as there is no significant degradation over the time required to collect, process and measure samples allowing residues to be accurately quantified, provided liquid extracts are suitably buffered. © 2015 New Zealand Plant Protection Society (Inc.).


Nairn J.J.,Plant Protection Chemistry NZ Ltd | Forster W.A.,Plant Protection Chemistry NZ Ltd | van Leeuwen R.M.,Plant Protection Chemistry NZ Ltd
Pest Management Science | Year: 2011

Background: Spray droplet adhesion is dependent not only on formulation and droplet parameters but also on the surface properties (physical and chemical) of the leaf. Quantifying these leaf surface properties would aid understanding and modelling of adhesion, helping to optimise spray formulations. Fractal dimensions (FDs) were used to quantify the relative leaf surface roughness of ten plant species. Static droplet contact angles were measured on each leaf surface, and wetting tension was calculated. Chemical profiles of the leaf surfaces were developed by evaluating contact angle behaviour relative to solution dielectric constants. Results: The FDs of Cryo-SEM micrographs taken at 300× magnification gave the best correlation with adhesion. The wetting tension intercept had a strong relationship with mean adhesion, and successfully accounted for the wettability of the outlier species. Conclusions: The microroughness of the leaf surface, as revealed by Cryo-SEM, can be quantified by fractal dimension analysis. However, the wetting tension intercept is a more useful universal measure of the surface properties of the leaf (including roughness) as they pertain to adhesion. The slope of the wetting tension versus dielectric constant plot allowed preliminary quantification of the chemical contribution of leaf surface dielectric behaviour to adhesion. © 2011 Society of Chemical Industry.


PubMed | Plant Protection Chemistry NZ Ltd
Type: Journal Article | Journal: Pest management science | Year: 2016

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.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.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.

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