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Rotorua, New Zealand

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.). Source

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. Source

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. Source

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. Source

Dorr G.J.,University of Queensland | Dorr G.J.,Queensland University of Technology | Forster W.A.,Plant Protection Chemistry NZ Ltd. | Mayo L.C.,Queensland University of Technology | And 7 more authors.
Crop Protection | Year: 2016

Retention of sprays on plants is a critical component influencing the effectiveness of agrichemical applications. Previous simulations of spray retention by plants gave poor agreement for hard-to-wet species when compared with actual measured retention. A new model is developed here that accounts for: species wettability, impaction angle, droplet bounce, partial retention on shatter, a variable time to shatter, and the number of daughter droplets produced. The aim of this study was to compare predictions from the new model with data obtained by spraying five mixtures via five nozzles onto easy-to-wet cotton (Gossypium hirsutum L.), and hard-to-wet wheat (Triticum aestivum L.) and fat hen (Chenopodium album L.). The new model correctly predicts retention to be highest on cotton and lowest on wheat. The trend in both measured data and the model predictions is for retention to decrease with increasing droplet size, on all three plant species. Formulation is correctly predicted to have little influence on retention by easy-to-wet cotton plants and to enhance retention by the harder-to-wet wheat and fat hen plants. The parameters that describe partial retention on shatter and variable time to shatter have a substantial influence on retention, as they affect primary or secondary droplet capture. A better understanding of the kinetic energy effects and the interactions between the formulation and the leaf surface are needed to refine their input values. © 2016 Elsevier Ltd. Source

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