Aerial pesticide application is often used in pest eradication programmes, particularly when the pest is widespread or located in the tops of tree canopies. Spray treatments are most effective when there is good spray coverage throughout the canopy.

A research programme based at Scion and supported by Better Border Biosecurity (B3) has focused on several ways of improving the effectiveness of aerial spraying while minimising the associated risks.

First, the development of spray deposition models that are applied to a wide range of aerial spray application scenarios are helping scientists to understand how spray deposition and coverage varies with different application techniques. Linked to geographic information system software, the models produce maps that depict the result of the operation for various scenarios.

These results enable managers to plan operations to ensure that the required amount of active ingredient is deposited throughout the canopy and that the risks associated with spray drift are managed adequately.  The results can also assist with decision-making processes during an incursion response.

Scion’s General Manager of Forest Science, Dr Brian Richardson, says, “We have never stopped looking for ways to improve the cost-effectiveness and accuracy of aerial spray operations. Managing the risks around spray drift has been a strong driver of our research programme, and we have achieved significant results by working in collaboration with the U.S. Forest Service and Canadian Forest Service.”

In related work, B3 Scion researchers recently worked with Zespri® to test new aerial spray optimisation methods to assist with their battle against Psa (Pseudomonas syringae pv. Actinidia) in kiwifruit orchards. Data from the Zespri® and Kiwifruit Vine Health trial are being applied to improve existing aerial spray models especially for pergola-type canopies.

This work allowed for the quantification of the interaction between the aircraft wake under different operating conditions (combinations of helicopter type, release height, and flying speed) and the canopy structure. Helicopter wake turbulence can have a large influence on deposition and drift and B3 is seeking to understand how to use this to best advantage.

A third line of research has used actual data from successful campaigns to develop a new publicly available web-based application called the Swath Calibration tool (see for the beta version). It is designed to help spray applicators improve the chance of stopping the spread of unwanted organisms. Scion also offers a calibration service for those who require technical support.

The calibration process ensures that the specified pesticide dose is efficiently distributed across the target area at minimum cost. When material is released from an aircraft, it doesn’t land in a perfectly uniform spread, and this natural variation causes some degree of over-dosing and under-dosing within the target zone. Under-dosing is a particular concern for a pest eradication operation where survivors could re-establish the population.

Scion Research has proposed a new modelling approach for aircraft calibration that allows a more accurate understanding of the spray deposit variation likely to result from different operational specifications. With this knowledge it is possible to understand the tradeoffs between operational cost, practical considerations (such as how fast to fly and the distance between flight lines), and the probability that all pests in the target zone receive a lethal dose.

The new calibration protocol has been published in a peer reviewed, international science journal and has been presented to the Ministry of Primary Industries (formerly Ministry of Agriculture and Forestry) at a workshop. It is available for future incursion responses.

Contact: Tara Strand, Scion, email: [email protected]