How to calibrate an airblast sprayer operator

Checking coverage on water-sensitive paper with some of the Grape Growers of Ontario members in 2012

Checking coverage on water-sensitive paper with some of the Grape Growers of Ontario members in 2012

When an extension worker, equipment retailer or consultant is asked to calibrate an airblast sprayer, they would be well advised to calibrate the sprayer operator as well.

Consider this: you and the operator are each investing three hours (average) to optimize the sprayer for a specific set of circumstances; the crop shape, size, phenology, and the weather conditions at the time of calibration. Depending on the reason for the calibration, you may even account for coverage requirements that reflect the product(s) mode of action and the pest location. This means that once you leave, the circumstances will change and the benefits of your efforts will quickly diminish.

Calibrations, like milk, have an expiry date.

There are three possible outcomes from a single, stand-alone calibration:

  1. The operator manages efficacious applications throughout the season because the variability in weather, crop and pest isn’t significant. This is generally not sustainable.
  2. Not recognizing that sprayer settings need constant adjustments (or being unable to make the changes) the operator experiences only modest results and decides calibration isn’t worthwhile.
  3. The operator experiences failures and lays the fault with you (as the last person the touch the sprayer) and/or the agrichemical rep that sold the chemical. Few sprayer operators blame timing or spray coverage.
Explaining how to place water-sensitive paper and ribbons in an apple tree

Explaining how to place water-sensitive paper and ribbons in an apple tree

The solution lies in the proverb “Give a man a fish and you feed him for a day; teach a man to fish and you feed him for a lifetime.” It is the sprayer calibrator’s responsibility to involve the sprayer operator and ensure they understand what is being done, why it is being done, and how to do it when you leave. Otherwise, expect to calibrate that sprayer again… soon.

In my experience, I have had the most success educating and empowering spray operators to make their own seasonal adjustments based on this approach:

  1. If you’re working at a large operation, try to have both the manager and the operators there at the same time. If you teach the manager, they might not effectively communicate the lessons to their operators. Likewise, if you teach the operators, they may not be able to convince the manager to let them spend money, or time, on making changes to the sprayer program. Get everyone on the same page, at the same time!
  2. Perform a pre-calibration inspection of the equipment with the sprayer operator. They know their equipment and can tell you about usage, history and maintenance. It also opens a dialogue between you and helps the operator to relax. Remember: from their perspective they may feel they are being judged and they will take criticisms and corrections personally. Do your best to reassure them during this phase that you are trying to make a good thing better – not to correct failings.
  3. With the operator, perform the basic calibration. Specifically, confirm sprayer ground speed, evaluate pressure gauge accuracy and evaluate nozzles. Explain what you are doing, and ask the operator questions. This is where you learn about their attitude – are they open-minded about changing how they do things? How has their efficacy been in the past? Will they spring for new parts? Do they need convincing that this process must be repeated regularly? Keeping the sprayer operator involved is critical. Do not let them wander away to answer cell phones, or get distracted by employees. Otherwise, you are on a service call and are not really doing them any favours.
  4. Demonstrating how deflectors aim air, and spray, into the target using some scrap wood.

    Demonstrating how deflectors aim air, and spray, into the target using some scrap wood.

    With the sprayer in the crop, have the operator tie wind-indicator ribbons in the canopy. Explain what they are doing and why. Tell them these ribbons should be monitored, maintained and replaced season-long.

  5. Discuss where water-sensitive papers should go, and how they should face. Have the operator tie flagging tape in key locations based on their experience with pest pressure. Give the operator a latex glove and while you write on the back of each card (position and trial number) have them clip them in place. Tell them how much they cost, where to buy them and the benefits of using them regularly.
  6. Have the operator spray the target crop using their typical set-up (i.e.. ground speed, pressure, rate, air settings, etc.) Have them watch the ribbons as they pass by and have them spray from both sides.
  7. The operator will be very surprised to learn they have drenched or missed the papers. They may or may not be surprised to have seen the ribbons stood straight out (indicating too much air). If you like, you can even set up papers in the next alley (or alleys) to show how much spray blew through the target. When the papers are dry enough, collect them and store them somewhere safe for later comparison. Explain that they can (potentially) save a lot of money and refill time by improving their efficiency. Get them on-board for the big change to come.
  8. Optimize sprayer ground speed, air direction (i.e. deflectors) and air speed/volume (i.e. fan speed). Then re-nozzle the sprayer using brass disc and core tips to reduce output in areas that were drenched or increase output in areas of sparse coverage. Quite often, I turn off the top and/or bottom nozzle positions. A piece of water-sensitive paper at the top and bottom of the canopy will confirm the wisdom in this. Label a new set of papers and have the grower position them in the same locations. Have them spray again.
  9. Tying flagging tape in trees to indicate prevailing wind and to calibrate airblast air settings.

    Tying flagging tape in trees to indicate prevailing wind and to calibrate airblast air settings.

    The goal is 85 medium droplets per square centimetre and 10-15% coverage for most insecticides and fungicides. If there are still drenches or misses, or if you’ve gone too far in a few positions, correct them and try once more. Make sure the sprayer operator will not be spraying in particularly hot or windy conditions, or your calibration at the top of the target can be compromised. Once you are both satisfied, work out the new sprayer output per area (e.g. US gpa or L/ha). You will have to discuss whether the operator plans to concentrate the tank to maintain the labelled “per area” rate (not recommended by me) or will continue to mix the tank as always and simply drive further on it (recommended by me). The later is called “Crop-Adapted Spraying“. It is their livelihood, and therefore their choice.

  10. The final step relies on how well you’ve earned the sprayer operator’s trust throughout this process. Once you have an output and spray distribution that you are both happy with, the operator should invest in moulded ceramic tips that emit similar rates to replace the brass disc-core. Then, they must be willing to repeat the process on any crops that are significantly different to ensure they have the right settings. Sometimes only modest changes are required between blocks. Further, they may have to revisit these settings as the season progresses to compensate for denser and/or larger canopies.

The following figures illustrate three airblast calibrations in apple orchards from spring 2014. Some required one attempt; others required a few trial settings before we achieved reasonable coverage. In all three cases, the sprayer operators reduced per-area rates, bought new nozzles and planned to buy water-sensitive paper. Further, they indicated they would continue to monitor ribbons (as long as they could be seen) and would review coverage after petal-fall.

Several nozzles shut off, spray re-distributed. Targets still drenched in two locations with a 24% savings in spray mix.

Several nozzles shut off, spray re-distributed. Targets still drenched in two locations with a 24% savings in spray mix.

Three successive re-calibrations were required. Output was reduced in the first trial, but poor coverage in position 3. Top nozzles turned off and spray re-distributed in trial 2, but a gust of wind reduced coverage at the top of the tree. Bottom nozzles turned off and spray redistributed to top nozzles for a 40% savings in spray mix.

Three successive re-calibrations were required. Output was reduced in the first trial, but poor coverage in position 3. Top nozzles turned off and spray re-distributed in trial 2, but a gust of wind reduced coverage at the top of the tree. Bottom nozzles turned off and spray redistributed to top nozzles for a 40% savings in spray mix.

Output reduced in all nozzle positions and sprayer fan speed reduced. The high humidity greatly reduced droplet evaporation and increased the spread on the papers. In this case, it was decided not to reduce output any further to account for anticipated growth and the high humidity. There was a 27% savings in spray mix.

Output reduced in all nozzle positions and sprayer fan speed reduced. The high humidity greatly reduced droplet evaporation and increased the spread on the papers. In this case, it was decided not to reduce output any further to account for anticipated growth and the high humidity. There was a 27% savings in spray mix.

 

So, the next time you calibrate an airblast sprayer, be sure to teach the sprayer operator what you are doing and why. Involve and engage them. Answer their questions. Encourage them to perform the same calibration for each significantly different block and make mid-season changes. With luck they will only call back to report success and savings, and not to condemn your efforts, or worse: to ask you to re-calibrate their sprayer!