Bunch spray technology
About the trial
To support growers transition from bunch dusting to bunch spraying, the DPI extension team have investigated alternative bunch spray systems that deliver good coverage for controlling banana rust thrips.
The trial consisted of three different air assisted systems and three different hydraulic systems, comparing their effectiveness in controlling banana rust thrips. Also recorded, was the average time for each system to deliver 50-60mL of spinetoram solution to a bunch. In accordance with the product label, the solution was mixed at the specified label rate and was applied after the bunch cover had been placed on the bunch. All bunches were covered with a liner and 40 μm plastic bunch cover tied with flues (opening left in top of bag).
Assessments for banana rust thrips damage was undertaken at harvest, with all fingers in a bunch assessed for damage.
Hydraulic systems - delivering 28psi with 12v pump
Treatment 1 – Spray wand from underneath the bag
Teejet grey adjustable nozzle (38720-PPB-X8)
Spray applied via the flue at the top of the bunch cover for 2 seconds. Then applied underneath the bunch cover and liner from top hand to the bottom in a zig-zag motion for 3-4 seconds.
Treatment 2 – Spray wand from underneath and top of bag
Teejet grey adjustable nozzle (38720-PPB-X8)
Spray applied from underneath the bunch cover and liner. Spraying from the top hand to the bottom in a zig-zag motion for 5-6 seconds.
Treatment 3 – Spray ring prototype
3 x 0.75 (BETE FF028-145) nozzles
Spray ring was slid underneath the liner and bunch cover and spray was applied from top hand to bottom hand for 3-3.5 seconds. *Note, the ring was difficult to get up underneath the liner and bunch cover and was not easy to place around the fruit in an efficient time.
Air-assisted systems - delivering 28psi with 12v air compressor
Treatment 4 – Aeropro spray gun
2.5mm nozzle opened half of a turn
Spray applied from reaching under the bunch cover and liner, spraying up at a 45-degree angle as far around the bunch and down to the bottom hands in a zig zag motion for 5-6 seconds.
Treatment 5 – Star S-770 spray gun
1.2mm nozzle opened one and a half turns
Spray applied from reaching under the bunch cover and liner, spraying up at a 45-degree angle as far around the bunch and down to the bottom hands in a zig-zag motion for 4-5 seconds.
Treatment 6 – Prototype air sprayer
using 12v air compressor and 12v pump
Spray applied from just underneath the bunch cover and liner, spraying from the bottom of the bag pointing upwards for 3-3.5 seconds.
Key findings
All air-assist and hydraulic chemical spray treatments provided good control of banana rust thrips (Figure 1).
Greater than 96% of all fingers in bunches across all treatments recorded no damage. This compared to 47% of fingers in the water control.
Positioning the spray ring (treatment 3) underneath the liner and bunch cover was difficult and the time taken would not make it commercially feasible.
Growers that have previously dusted can easily modify their current compressed air system to trial the air-assisted options.
The DPI extension team in collaboration with banana grower Mark McAvoy put together a demonstration video of the spray gun system Mark uses on his farm for bunch spraying.
For more information on this trial contact the DPI extension team:
betterbananas@dpi.qld.gov.au
This research has been undertaken as part of the National Banana Development and Extension Program (BA19004), which is funded by Hort Innovation, using the banana industry research and development levies and contributions from the Australian Government. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture. The Queensland Government has also co-funded the project through the Department of Primary Industries.
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