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The application of pesticides to grape bunches

Grape and Wine Research and Development Corporation

Industry contacts:

• Mr Kieran Murphy, Food Science Australia (kieran.murphy@foodscience.afisc.csiro.au)
• Ms Alison Macgregor, Victorian Department of Natural Resources and the Environment (alison.macgregor@nre.vic.gov.au)

MISG moderator: Dr Steven Barry (s-barry.adfa.edu.au)

Background

Pesticides are applied to bunches of grapes throughout the growing season to protect them from fungal and insect attack. A variety of machine types are used with the most common being those that produce droplets using hydraulic nozzles and entraining the droplets within a high volume, low velocity air carrier. Air-shear nozzle technology has gained favour within Australian viticulture because of the high work rates possible when applying with this machine type. This machinery atomizes the spray mixture into relatively finer droplets than hydraulic systems and can therefore be used to apply the pesticides in lower volumes of water. The atomising and carrier air is comparatively low volume, high velocity in nature.

The capture of droplets changes throughout the growing season as the targets change. Three critical stages within the growing season for bunch applications include 80% capfall, pre-bunch closure and veraison.

The problem

Bunch structure

• Components of the bunch alter in size and shape with growth (flowers - berries).
• Bunch architecture and berry compactness is variable between varieties.

Bunch position

Bunches may be:

• exposed on the surface of the canopy within a well-defined zone
• obscured by foliage and other bunches, within a well-defined zone
• not heavily obscured by foliage, but distributed across the entire canopy
• crowded around the inner section of canopy, heavily obscured by foliage

Pesticide action

• Some pesticides must coat all green tissue to be effective, and remain on the surface, including the stalks of the bunch.
• Some pesticides must penetrate the tissue, particularly in and around wound sites (e.g. cap wound at flowering).

The machinery

• Use large droplets and high volumes of liquid containing dilute pesticide concentrations to deliver the chemical to the target sites. Thorough wetting of all of the surfaces is necessary to achieve dosage and coverage.

OR

• Use small droplets to deliver low volumes of concentrate spray mixture (1 - 5 times concentrated).

The question

Can the chemical application process be modeled, prioritizing the variables listed below at each of the three critical growth stages of 80% capfall, pre-bunch closure and veraison?

Some variables to consider are:

• Liquid volume applied
• Pesticide concentration
• Droplet spectrum produced
• Air qualities: volume, velocity, direction, turbulence
• Liquid properties (surface tension)

Outcome

Provide a decision framework for optimizing chemical application to grape bunches at the three critical growth stages of 80% capfall, pre-bunch closure and veraison.

Photographs

(These small images are linked to larger images. Photographs by Kerryn Hart, © Agriculture Victoria.)

	Grape bunch pre-flowering. The bunch is very loose and bunch parts are very small.
	Grape bunch at flowering. The flowering bunch becomes a massive surface of very fine flowering parts.
	Close-up of a cluster of flowers.
	Chardonnay bunch at berry set.
	Sultana bunch at berry set.
	Chardonnay bunch after bunch closure, with berries at their final size and density. This variety typically has a very tight bunch.
	Sultana bunch with berries at their final size and density. This variety typically has a loose bunch.

References

Xu, Z. G., Walklate, P. J., Rigby, S. G. & Richardson, G. M. 1998, Stochastic Modelling of turbulent spray dispersion in the near-field of orchard sprayers, Journal of Wind Engineering and Industrial Aerodynamics vol. 74-76 pp. 295-304.

Walklate, P. J., Weiner, K. L. & Parkin, C. S. 1996, Analysis of and Experimental Measurements Made on a Moving Air-Assisted Sprayer with Two-Dimensional Air-Jets Penetrating a Uniform Crop Canopy, Journal of Agricultural Engineering Research vol. 63, pp. 365-378.

May, Peter 2000, From bud to berry, with special reference to inflorescence and bunch morphology in Vitis vinifera L., Australian Journal of Grape and Wine Research vol. 6, pp. 82-98.

Pedras, M. H. J. & de Lemos, M. J. S. 2001, Macroscopic turbulence modeling for incompressible flow through undeformable porous media, International Journal of Heat and Mass Transfer, vol. 44, no. 6, pp. 1081-1093.

Reynolds, A. M., Reavell, S. V. & Harral, B. B. 2000, Flow and dispersion through a closed-packed fixed bed of spheres, Physical Review E vol. 62, no. 3, pp. 3632-3639.

Walklate, P. J., Richardson, G. M., Cross, J. V. & Murray, R. A. 2000, Relationships between orchard tree crop structure and performance characteristics of an axial fan sprayer, Aspects of Applied Biology vol. 57, pp. 285-292.