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Mechanics Corner: Calibrating your sprayer for top performance

Andy Overbay Published on 11 June 2014

I know am I preaching to the choir when I tell you that making the most of every input is paramount to the success of a farming operation today. Folks that cannot control costs (at least those outside of government) simply don’t last too long in the business world, whether their business is farming or not.

Chemical costs, like any other input in your cropping operation, can get out of control in a hurry, especially if you are inadvertently over-applying or under-applying. Proper sprayer calibration and maintenance will help your profit margin by minimizing waste and also help you avoid the most costly chemical cost of all … the application that doesn’t work.

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Proper sprayer application depends on the combination of six basic properties:

  • Sprayer design
  • Nozzle type
  • Boom height
  • Boom pressure
  • Agitation
  • Ground speed

Chemicals will be applied correctly when these six components are used in the right combination and chemicals have been properly mixed. Dr. Bobby Grisso, extension engineer at Virginia Tech, adds that pre-season visual checks are not adequate to ensure an accurate application – nor is the fact that the equipment or nozzles are new.

Since calibrating and re-calibrating a sprayer over the growing season may be very necessary, it is helpful to have a quick way to check and re-check the sprayer’s functionality.

There are many variables as outlined briefly above that affect spray performance, but nozzles seem to cause the greatest variance in that performance. For the remainder of this article, we will hone in on how to quickly check your nozzles and make sure they are doing the job intended.

It should also be noted that many chemicals now state on their labels a recommended nozzle to use when applying that particular product. So as a reminder: The label is the law. If an off-target application results in a loss by a neighbor, you may be liable if you didn’t follow all label directions.

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There are also many ways to calibrate or check nozzles. There are handheld models that check individual nozzles which can be very accurate, but their costs may make them less attractive to all users.

One method that anyone can use is outlined in the VCE publication #442-453, “ Fine Tuning a Sprayer with ‘Ounce’ Calibration Method .” This handy guide, authored by Dr. Grisso along with Mike Weaver, Kevin Bradley, Scott Hagood and Henry Wilson, is available online. If you cannot find it, email me and I’ll send it to you.

The ounce method is really a calculation of how much spray one is placing on 1/128 of an acre. Since there are 128 ounces in a gallon, the ounces emitted by the nozzle over a determined amount of time equals the amount in gallons applied per acre.

Knowing the gallons per acre will help you quickly determine the amount of chemical to add to your sprayer in order to meet your goals. The table will help you determine the distance and time needed to collect your nozzles.

First, using the spacing of your nozzles, select a distance needed to travel and mark that distance off using flags or any object you choose. The distance may be permanent so you don’t have to re-measure. The terrain should mimic the area you are going to spray. Tractors usually gain or lose 10 percent of their ground speed while traveling up or down slopes.

Second, drive the distance and time the sprayer in seconds. You need to use the speed you will be travelling in the field, so be sure you are running at that speed when you enter the designated area. Timing needs to be as exact as possible, so you may want to make more than one run to build some data.

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One trick I use is placing an empty drink can at the beginning and end of the run where my tire will run over it. Upon hearing the pronounced “crunch” of the can, I start and stop my timing. It is also advised to have the tank one-half to two-thirds full so the weight of the sprayer is more like actual conditions.

Third, in a stationary position, bring the sprayer up to your operating throttle setting and correct boom pressure. Catch the nozzle discharge for the time determined in step two and measure that amount in ounces.

If you have more than one nozzle per row, catch all of them and add them together. Remember to use only clean water for this step and wear the proper personal protection clothing regardless. The ounces collected from the nozzle will give you the gallons per acre applied by your sprayer.

Let’s say you collected 20 ounces from your nozzle over the allotted time and your product chosen for application calls for 2.5 ounces per acre for a given target. Your sprayer has a 500-gallon tank and at 20 gallons per acre (converted from 20 ounces collected), that means you can spray 25 acres with each tank mix.

Therefore, to get the proper application of product, multiply 2.5 ounces per acre by 25 acres and you will find you need to add 75 ounces of product to your tank to properly apply your spray to the target pest.

Finally, check all the nozzles for equal output. If you have discrepancies, change them out with new nozzles. If you choose to clean nozzles, use only tools and techniques recommended by the manufacturer. Using wires, screwdrivers or pocket knives are good ways to guarantee an inaccurate spray pattern. PD

Andy Overbay holds a Ph.D. in ag education and has more than 40 years of hands-on dairy and farming experience.

andrew overbay

Andy Overbay
Extension Agent
Virginia Cooperative Extension

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