Improving spraying and management of spotting bugs in avocados (AV06001)

This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

Spotting bugs were major native pests of avocados along the east coast of Australia.
Spotting bugs had many alternate hosts from which they migrated into crops during spring and summer. Monitoring for the presence of spotting bugs in the crop allowed growers to apply targeted sprays to eliminate the pest and reduce fruit damage. However most growers continued to apply sprays on a calendar or ad-hoc basis because of the perceived need to apply protective fungicides.

This series of eleven workshops in New South Wales, Queensland and Western Australia aimed to give growers the knowledge and skills to monitor pests like spotting bug and make decisions on the appropriate actions for their individual situation. At the time the management of spotting bugs still often relied on effective spraying with broad-spectrum insecticides.

Spraying large canopies, such as avocados, was a complex process. In the past extension efforts had highlighted the importance of canopy air displacement to transport droplets to their target. The workshops focused instead on the importance of droplet kinetic energy and drift as major processes for spraying tall trees and on the appropriate calculation of Concentrate chemical rates.

The practical on-farm workshops demonstrated the effects of tractor speed, air volume and spray volume on coverage within the canopy. The flexible demonstrations, using an innovative system of placement of water-sensitive papers within the canopy, highlighted the ease of spraying the bottom of the canopy and difficulty in spraying the tops with hollow cone jets. The successful use of solid cone and solid stream jets to increase recovery in the tops was confirmed.

The steps involved in calculation of Concentrate rates based on an estimate of the Dilute spray volume and Dilute rate were presented and worked through. All participating growers were offered a free desktop assessment of their own sprayer’s calibration and received a comprehensive sprayer calibration manual to complement the field program.

The workshops were designed to give growers greater confidence in the calibration of their own sprayers and this was likely to result in improved coverage and control with reduced off-target impacts.