Wind-tunnel research tests spraying rules

Key points

  • Centre tests new and existing chemical formulations and equipment
  • Wind tunnel can generate wind speeds up to 150 knots to simulate ground and aerial spray applications
  • Researchers control and manipulate factors that influence spray drift and efficacy, such as weather, wind speed and direction, nozzle size, atmospheric stability, tank mix, boom height and boom stability
  • Testing a new low-drift formulation in the wind tunnel has helped a US chemical company secure a five-fold reduction in the buffer zone for its product 

High-tech testing of spray-drift-reduction technologies, such as new chemical formulations and nozzles, is helping manufacturers develop new products while providing industry with the data needed to test or challenge regulations

In early September, restrictions were put in place in South Australia to stop crop-protection chemicals from drifting onto, and potentially damaging, sensitive crops, such as those in the Barossa Valley’s vineyards.

For many of the region’s grain growers it created confusion and concern. After a wet winter, some growers had delayed sowing and, with that, plans for broadleaf weed control. With restrictions also dictating the climatic conditions under which spraying could occur, many grain growers were left unsure about if and when spraying could occur.

For Dr Andrew Hewitt, the situation unfortunately provided the perfect example of what he, fellow researchers and members of the GRDC-supported National Working Party on Pesticide Application (NWPPA) hoped to avoid.

Photo of Dr Andrew Hewitt, Queensland Centre for Pesticide Application and Safety

Dr Andrew Hewitt leads the University of Queensland’s Centre for Pesticide Application and Safety, which tests new and existing chemical formulations and equipment to provide important information on spray drift.

Dr Hewitt heads the University of Queensland’s Centre for Pesticide Application and Safety. Based at the university’s Gatton campus, the centre tests new and existing chemical formulations and equipment, providing important information on spray drift.

With the NWPPA, Dr Hewitt, who has a long history in spray-drift mitigation, is hoping to shift regulators’ attitudes from a ‘no-spray’ approach to one where buffer zones are directional and flexible, giving growers spraying choices.

“Instead of a ‘no-spray’ approach, we want to identify risky and non-risky spraying conditions, allowing the grains industry to negotiate its position,” he says.

The NWPPA was established three years ago following the Australian Pesticides and Veterinary Medicines Authority’s new guidelines on buffer zones, which, among other rules, require drift restraint statements and mandatory no-spray zones.

Dr Hewitt says the guidelines and subsequent restrictions are based on worst-case scenarios: “We want to be able to push back with data.”

Central to this task is information gathering and this is where the centre’s wind tunnel comes in.

The wind tunnel is housed in its own building and has an electric turbine capable of generating wind speeds from a few knots up to 150 knots to simulate ground and aerial spray applications. Spray droplets and their scatter pattern are captured for computer analysis and simulation. Spray drift models are developed for the chemical registration process.

“The wind tunnel is a hugely valuable tool. It allows us to test in a controlled, cost-effective and timely way,” Dr Hewitt says.

“It measures the spray dynamics of droplet size, velocity, drift, the amount of spray on crops and their efficacy. We can screen out 500 tests in the tunnel and take just the best five into the field, saving time and money.”

The tunnel lets researchers control and manipulate the factors that influence spray drift and effectiveness, such as weather, wind speed and direction, nozzle size, atmospheric stability, tank mix, boom height, boom stability and Delta T (how temperature and humidity affect evaporation).

The centre is building a comprehensive list of chemicals and nozzle combinations and their spray drift measures.

“We are measuring real sprays and real nozzles and from that we can tell what sort of drift the mixture and sprays will produce. The information gives growers a choice – what nozzle and spray can I use to manage risk?”

Dr Hewitt also aims to incorporate all the information into a smartphone app so growers can make spraying decisions ‘on the go’. He is talking to manufacturers about publishing quick response (QR) codes on pesticide labels.

Photo of a wind tunnel

Calculating spray droplet size is helped by this section of the wind tunnel, where droplets are measured.

These codes are a matrix barcode that contains product information. Smartphones can scan the codes and obtain information, which could help the grower to decide nozzle size, boom spray height or a range of other factors influencing safe and effective spraying.

The information being collated also arms the NWPPA with data for regulators so that buffer zones or other restrictions can be challenged – work that is already paying dividends. Dr Hewitt says that perhaps the group’s biggest success so far has been its work with a major US-based chemical company.

Through extensive field trials with Dr Hewitt, the company tested a new low-drift formulation, work that was linked with new models partly developed at Gatton.

With results to show regulators, the company was able to secure a five-fold reduction in the buffer zone for its product in the US.

“Regulators in the US regard our facility as the world’s best, so the company’s results were valued. The chemical company is now working with Australian regulators on a similar buffer zone reduction. It’s going to benefit Australian grain growers too.”

The centre has demonstrated similar reductions in spray drift by optimising links between nozzles and spray adjuvants. The work offers applicators more choice by effectively turning higher-drift chemicals into lower-drift chemicals.

Photo of smiling man

Postdoctoral research fellow Chris O’Donnell tests new and existing chemical formulations and equipment for spray drift using the wind tunnel at the University of Queensland’s Gatton campus.

PHOTO: Sarah Jeffrey

Dr Hewitt says regulators are reviewing this work and he expects a positive outcome.

The centre is also testing long-held beliefs about spraying, such as spraying at night.

Although growers have always been told not to spray at night, Dr Hewitt believes this may change, with wind-tunnel and field work showing it could in fact be the best time to spray, depending on droplet size.

He explains that stable conditions at night usually mean there is little or no wind and small droplets of spray may ‘hang’ in the air and not disperse well – or if they do move as drift, they are concentrated and could potentially cause crop or other damage.

But research is showing that this problem could be avoided by using larger droplets. “Night-time could prove to be the best time to spray, with cooler temperatures and reduced wind speeds a bonus. Our work will find out.”

Dr Hewitt says this research is an example of the centre’s multifaceted work, which aims to bring together chemical companies, nozzle manufacturers and regulators to benefit growers and the environment.

More information:

Dr Andrew Hewitt,
0427 025 354,


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