Advancements in spray application

The key takeaways from the most recent international Workshop on Spray Application and Precision Technology in Fruit Growing. By Anna Mouton.

The value of new spray-application technology depends on the grower’s perspective, said Dr Gideon van Zyl, crop-protection specialist at agricultural consultancy ProCrop. He was reporting on the most recent SuproFruit workshop, which he attended as part of his involvement in the Hortgro industry leadership programme.

SuproFruit is aimed at a small group of international experts. Van Zyl shared a photo of field-day participants viewing an advanced sprayer.

“Researchers from the Netherlands asked about its drift-reduction potential,” he said. “The Poles asked about its cost, the Germans about its efficacy, the UK about whether it will solve their labour issues.

“But the Spanish asked the most important question — is it practical to implement at the farm level?”

Van Zyl elaborated that spray-application advancements cluster in five areas: spray deposition and efficacy, drift reduction, logistics, practicality, and cost. “It doesn’t matter how cool the technology is,” he said. “These are the factors deciding if growers implement new technology.”

He believes the advancements most applicable to South African growers are those that can improve sprayer selection, enable faster throughput without compromising deposition, and prepare our industry for drift mitigation.

“The most important advancement we’ve made is understanding and implementing canopy-adapted spraying,” said Van Zyl.

“This was one of the main topics of the SuproFruit workshop. Experts talked about how we can have all the technology we want, but if we can’t get canopy-adapted spraying right, there’s no point in new technology.”

Sprayer selection

Canopy-adapted spraying matches the forward speed, air output, and water volume to the canopy. “We want to maximise the droplets we put on and minimise the droplets not hitting the target — lost through drift, blow-off and blow-through,” said Van Zyl.

He emphasised that canopy-adapted spraying starts with sprayer selection. “Our mission is to load droplets into the air stream and carry them effectively to the target. The sprayer shouldn’t remove droplets from the tree. It should place them there and leave them there.”

The air profile must match the tree profile. Van Zyl observed that South African orchards tend to have high trees. Low-profile sprayers can’t reach the tops without high air volumes and speeds, resulting in blow-through and blow-off at the bottom of the canopy and increased spray drift.

A mismatch between sprayers and canopies is particularly problematic in high-density orchards.

Van Zyl would like growers to have better information about sprayer performance. “In Europe, many farmers are protected by systems for sprayer evaluation,” he said.

Performance Pulvé is the French sprayer-performance project. Participation is voluntary. Manufacturers submit their equipment to standardised, controlled deposition and efficacy tests, and drift-potential assessment. The results are displayed on the sprayer and published on a website.

The German system maps the air-profile speed and volume and spray-volume distribution and publishes the data, as well as a whitelist of fan types suited to three-dimensional crops. Test results include diesel consumption, CO₂ emissions, and drift-reduction potential.

“The dream is to have a South African system one day,” said Van Zyl, “in which we classify sprayers to protect growers — to make sure they choose the correct sprayer from the beginning.”

Spray by numbers

Van Zyl highlighted three aspects of canopy-adapted spraying that growers can adjust immediately: forward speed, air volume, and spray volume.

When the forward speed is too slow and the air volume too high, the spray blows through the canopy. When the forward speed is too fast and the air volume too low, the spray doesn’t penetrate the canopy.

“Depending on the orchard floor and row width, the faster you drive with higher air volumes, the better the air column will bend into the canopy,” said Van Zyl.

He used the example of a third-leaf, high-density Gala block on M.9 to illustrate that the traditional low-profile axial fans are ill-suited to modern orchards. These fans produce 48 200 m³ at 540 rpm, translating into a tractor speed of nearly 8 km per hour.

“Is this realistic?” asked Van Zyl. “And you would be blowing through a lot of the active ingredient. This is becoming a big issue in high-density orchards, especially with dormant sprays, where you’re coating the next row.”

Besides adjusting forward speed, air volume can be tweaked through gear selection and PTO manipulation. As a last resort, the fan blade pitch can be changed.

Van Zyl also discussed spray volumes and nozzle selection. For the details, view his presentation on the Hortgro YouTube channel.

Precision tools

While new technologies don’t replace the need for correct sprayer calibration, Van Zyl touched on several advances that can help growers practice canopy-adapted spraying.

These include ultrasonic or LiDAR (light detection and ranging) canopy sensors, which measure the canopy position and contour. The sprayer adjusts nozzle delivery accordingly, either by sprayer pressure adaptation or individual nozzle selection.

“A LiDAR-based system is currently available in South Africa,” said Van Zyl. “It’s expensive, but it can add value if set up correctly depending on within-orchard variation.”

Pulse-width modulation technology, increasingly popular in grain and broadacre crops, may be on the horizon for tree crops. In pulse-width modulation, the delivery of individual nozzles is controlled by opening and closing solenoid valves, not by manipulating system pressure as in conventional nozzles. This can enhance deposition uniformity and quality.

At an orchard level, application rates can be varied based on vigour maps generated from satellite imagery. The sprayer switches between nozzle options as it moves from one zone to another.

Another existing system adjusts pressure during spraying to allow for variable forward speed. “If you’re running at high speeds on the inside of the orchard, but you need to exit the orchard at a slower speed, this system will regulate the flow rate automatically,” explained Van Zyl.

In conclusion, Van Zyl returned to the topic of canopy-adapted spraying. “Canopy-adapted spraying will increase work rates, reduce the risks of operator exposure, drift, noise pollution, and bystander conflict, and potentially reduce fuel consumption and cost inputs,” he said. “And you can do it immediately.”

This article is based on a presentation at the 2024 Hortgro Technical Symposium. Go to the Hortgro YouTube channel to watch Van Zyl and other speakers at this event.