Spray technology for optimum pesticide application in macadamias (MC00041)

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Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.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?

Spray application in macadamias could be considered a worst-case spraying scenario as trees were often grown on steep slopes and could reach heights of 8-10m with dense canopies. A huge range of equipment was available to spray such trees but their underlying mechanisms were poorly understood. The project investigated the appropriate spray volumes for high volume Dilute spraying and concluded that a spray volume of 6.0 L per 100 cubic metres of canopy was a safe, conservative estimate. This volume should be used as the basis for calculating the spray concentration for low volume Concentrate sprays. The project also assessed several air-assisted technologies and the effects of changes in sprayer calibration. The trials found that spray volume, air volume and tractor speed had little effect on coverage. The trials showed that it was almost impossible to achieve good coverage at 6 m height with a low-profile airblast with hollow cone jets. Fans on towers showed promise but droplet size and air ducting appeared critical. The trials suggested that for hollow cone jets air-displacement within the canopy was less important than the effects of drift. Changing the point of delivery of droplets and increasing the kinetic energy / momentum of droplets may have been ways to improve carriage to the top of the canopy. Such changes may have been achieved by increasing the use of solid cone or solid stream jets at 15-20 bar pressure targeting the top of the canopy. Given the difficulties of reaching and penetrating the top of the canopy more work needed to be done on the effects of top and side canopy pruning and within canopy spraying.