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20190604 Fresh Quarterly Issue 5 13 Save Money With Scientific Dosing
Issue FiveJuly 2019

Save money with scientific dosing

The MABO Dosing Model. By Engela Duvenage.

Using more effective application methodologies to apply pesticide sprays, such as faster driving speeds, reduced air assistance and lower spray volumes, could potentially save apple producers up to 40% in working costs. Such vast savings are possible when using the MABO dosing model, according to Philip Rebel, a MSc student at Stellenbosch University.

“Current models work when applying pesticide sprays, but we can be more efficient. We need to consider new models,” Rebel asserted. Pest and disease control can tally up to a third of a successful apple farm’s preharvest overheads.

Rebel explained that the Unrath tree-row-volume model currently used in high-density South African orchards originated in the 1980s. Current application volumes range on average between 650 and 2 000 litres of spray volume per hectare, and tractor driving speeds between 3.5 and 4.5 kilometres per hour.

The Unrath model was developed four decades ago on much larger, open, vase-shaped tree canopies that are not seen in orchards today. Rebel noted that over the years tree architecture and orchard structure in South Africa have been changing to higher density plantings of more trees per hectare, with tall spindle-shaped apple trees and smaller tree canopy volumes.

Rebel conducted a series of trials using the MABO — Marktgemeinschaft Bodenseeobst —extended tree-row-volume dosing model. It was shown to be a more cost-effective and easier-to-use alternative to the conventional Unrath tree-row-volume model, when used in local high-density apple orchards at spray volumes of 750 litres or more per hectare and tractor speeds of 4.5 kilometres per hour.

MABO was developed in Germany and Austria in tall spindle-shaped canopied, high-density orchards with between 1 500 and 4 500 trees per hectare.

“In South Africa, MABO would be suitable for orchards with a row width of four metres or less,” Rebel said.

MABO in practice

Rebel explained that the MABO model uses the orchard with the largest filter area as a reference orchard. This determines a constant spray-machine calibration and tank concentration for the whole farm. All other orchards on the farm are then treated as a fraction of the reference orchard. Spray volumes for these orchards are manipulated by tractor speed and air assistance. For example, if an orchard has a smaller filter area than the reference orchard, spray volume and air assistance for that orchard will be adjusted by increasing the forward speed or reducing power-take-off speed.

The revolutions per minute of the power take-off change the air assistance produced. As a start, Rebel suggested that gear selection to the nearest speed indicated by the MABO model might be a better option to manipulate the air column, since changes to revolutions per minute can be detrimental if not done correctly or with the correct sprayer.

Rebel’s experiments showed no significant differences in the spray deposition parameters of pesticides in trials conducted in orchards with a row width of four metres, when comparing conventional tree-row-volume and MABO models. There was however a significant drop in costs with the MABO model in terms of the work rate per hectare, and savings in water, fuel, and time in the orchard.

“There is definitely a place for low-volume concentrate sprays and lower volumetric airflow rates in high-density South African orchards. The MABO model could be a good and easy alternative for the way in which we spray in South Africa,” Rebel concluded.

His research was supervised by Prof. Adéle McLeod of the Department of Plant Pathology at Stellenbosch University, and Bekker Wessels and Dr Gideon van Zyl from the agricultural consultancy firm ProCrop. The project was funded by Hortgro Pome.

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