Targeting spray application

Comprehensive research looking at how best to use spray systems for pest and disease control in the vineyard is starting to bear fruit.

Data from two years of intensive work are now coming in and the University of Queensland research team, led by senior research fellow Dr Andrew Hewitt and senior research scientist Chris O’Donnell, has begun developing best practice models for use in Australian conditions.

The Wine Australia-funded project, titled A generic approach to improving spray coverage, was established to help growers maximise coverage while reducing environmental risks associated with agricultural plant-protection products and machines.

Much of the work is being carried out at Treasury Wine Estates’ Lake Cullulleraine vineyards in North-Western Victoria.

An important early finding is how targeted sprayers can both help reduce spray drift and increase canopy deposition, which in turn leads to more accurate dosing of chemical. Targeted sprayers include ducted sprayers, multi fan sprayers and others that can be adjusted to direct spray at the vine canopy.

‘Unlike a traditional airblast sprayer, targeted sprayers aim the spray directly at the target canopy, not at the ground or above the canopy where it can be caught in the wind and move off target’, Dr Hewitt said.

‘Targeting spray is achieved by adjusting fans or air outlets to aim the spray directly into the canopy.’

As part of the research, three sprayers were evaluated: a typical non-targeted airblast sprayer (Figure 1) and two targeted sprayers – a twin row multihead fan sprayer (Figure 2) and a pneumatic-electrostatic sprayer (Figure 3).

A key aim of the research was to understand how much spray was lost to drift (ground and air) during a typical spray application.

This is important information as spray drift can remain airborne and travel long distances with potentially significant consequences to other crops and people.

In airborne drift testing, an airblast was able to generate drift up to 15 meters into the air. The canopy height was just 2.5 metres high, resulting in significant off-target spray drift and wasted chemical.

The multihead fan sprayer and electrostatic sprayer also overshot the top of the canopy, but far less than the airblast sprayer.

‘The results show the concentration of drift at 0 to 2 metres (from the ground to the top of the canopy) were highest for the electrostatic sprayer, followed by the airblast sprayer.

‘This means many droplets passed through the canopy and up into the air’, Dr Hewitt said.

‘Given this observation, it is very important with these types of sprayers to only spray in toward the vineyard block to avoid off-site spray drift onto adjacent blocks, neighbours, roads or other sensitive areas.’

It is also important to adjust air speed to suit the vine canopy size.

Early research results demonstrate how well-targeted spray application increases deposition rates and achieve higher dosing of chemical on the canopy.

The airblast sprayer places significantly more agrochemical onto the lower canopy, compared to other sprayers tested, as it sprays mostly from below. While the airblast has less deposition onto the upper canopy, it produced the most off-target spray drift as only a fraction of the spray was intercepted by the canopy.

The design of the electrostatic and multihead fan sprayer resulted in much more even spray coverage on the upper and lower canopy.

Figure 1: The illustration shows the typical direction of air output by an airblast sprayer. A large fraction of the spray is forced upward and if it is not intercepted by the canopy, it can easily drift off-target.

Figure 2: A twin-row multihead fan sprayer which targets the canopy of each row with three fans and an array of nozzles. It has the benefit of converging airflows and each fan can be aimed for more precise targeting. By aiming all the airflows together in the row, much more of the spray is contained in and deposits on the canopy.

Figure 3: An electrostatic sprayer produces positively charged, ultra-fine droplets emitted from air outlets mounted to a boom to focus spray into the canopy.

Figure 4: Off-target spray deposit data collected in the air for three sprayers applying spray mix to a fully developed canopy.

Figure 5: A comparison of average amounts of agrochemical deposited onto leaves in upper and lower halves of the vine canopy when applied by three sprayer types

Pictures courtesy Mark Ledebuhr, Application Insight LLC