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It’s time to calibrate

published: April 21st 2017
by: Caitlin Richards

Frequent showers and greening pastures mean one thing – spring is here. For many producers and landowners the spring season is also spraying season. Most producers are pulling out their spraying rigs, if they haven’t already, to start the spring task of spraying. 

Just as synonymous as showers and greening pastures are with spring, so should sprayer calibration be with the start of spraying season. Texas A&M Agri Life Extension Service Range Specialist in Uvalde Bob Lyons shares how to calibrate spray rigs and explains why it is important. 
“Calibration is really, very easy,” Lyons said. “It doesn’t take a lot of time, but it is really important.” 
Taking the time to calibrate your sprayer is vital to save time and money in the long run. A sprayer should be calibrated at least once a year to ensure the right amount of chemical is being applied at the correct rate. 
“That way you don’t waste money by applying too much, or not enough and not get the desired effect,” Lyons said. “It is going to save you money and make your applications more effective.” 
Every chemical, whe-ther it is an insecticide, herbicide or fertilizer, has a recommended rate for spraying in order to get a desired effect. Lyons has illustrated in figure 1 (page 8) to show the effects of under and overestimating spray volume from not calibrating a sprayer. 
For example, underestimating spray-volume by mixing for a ten gallon per acre expected spray-volume, but actually spraying 30 gallons results in applying herbicide at three times the herbicide’s recommended rate. 
“We have recommended herbicide rates for a reason,” Lyons said. “Those are the rates that we know work. So there is no use in applying more.”
On the other hand, overestimating spray-volume by mixing for a 30-gallon per acre expected spray-volume and actually spraying ten gallons results in applying only about one-fourth of the recommended herbicide rate. 
“Herbicides have a maximum use rate per acre,” Lyons said. “So, if you underestimate your volume you could be exceeding your maximum rate, which would be basically a violation of the label, and therefore the law.” 
Sprayer calibration is just as much about saving time and money as it is being a responsible producer. The spraying rates that are in place are also there to protect the environment from harmful overuse.
“If we want to be good stewards, part of being a good steward is applying these herbicides and insecticides properly,” Lyons said. “That goes back to calibration. There is no way we can do it properly if we don’t calibrate.” 
Luckily, calibration is easy to get done and should take at most 30 minutes. Calibration should occur on a day where the conditions are ideal for spraying and on moderate terrain. Windy days and extremely smooth terrain, like a road, are not days or the place to calibrate. 
The principle behind calibration is the same whether it is a boom type sprayer or a boom-less type sprayer. Calibration will measure the amount of liquid being dispersed from the sprayer over a given distance going a set speed. 
The given distance will be the calibration course, which directly correlates with the nozzle and swath spacing. The nozzle spacing distance on boom sprayers and the swath width on boom-less sprayers determine the length of the calibration course.
Texas A&M AgriLife Extension Service Exten-sion Forage Specialist, Larry Redmon, Ph.D. put together a sprayer calibration document to help guide producers in the calibration process. In the document, Redmon outlined calibration course distances that correspond with the nozzle spacing and swath width. See figures 2 and 3 (below).
After determining the length of the course, measure and stake off the course distance. Next, drive the course in the same gear and rpm that you plan to drive when spraying, and record the time in seconds. It is recommended to do this step twice and then take the average time. 
Now, it is time to drive the course and catch the liquid to determine if the output rate is correct, thus calibrating the sprayer. To do this, the liquid being sprayed out – Lyons suggests using water- needs to be caught. 
“The boom type model sprayers are easy, because you put the container that is going to catch the output right underneath the nozzle,” Lyons said. “The boom-less models are a little different and a little  harder to do.”
Any container would do for a boom sprayer, like a measuring cup or bucket. Lyons recommends attaching a trash bag or soda bottle to the boom-less models. 
Once the course has been driven and timed how long it takes to drive it, park the sprayer, turn it on and catch the liquid from a nozzle for the same number of seconds it took to drive the course. The amount of liquid caught determines the spray volume, which is how much the sprayer dispersed. 
With boom models, the number of ounces caught equals the number of gallons per acre. The number of pints caught from a boom-less model equals the number of gallons per acre. For example, ten ounces caught from a boom model means the output rate is ten gallons per acre. 
“If they want to put out 20 gallons per acre when they only caught ten, what that tells them is they need to slow down and run the course again at a slower RPM,” Lyons said. “It is the same if they catch too much, -- they then need to speed up. It is just a matter of adjusting their speed to put out the volume that they want.”
Depending on the chemical, there is a target spray volume per acre a producer wants to hit. The way it is achieved is by setting the tractor to the correct RPMs, which is determined through calibration. Typically, producers are looking for a ten to 20 gallon per acre spray volume.
“It is really that simple,” Lyons said. “You run the course a couple of times. Time yourself how many seconds it took, and catch the spray-volume. Then make your adjustments from there.” 
It is also recommended to check all of the nozzles. The flow rate should not vary more than 10% among all of the nozzles. Nozzles that do not fall into this range should be replaced. 
With nearly everything being automated today by sensors and warning lights, producers and all people get out of the habit of manual checks. Sprayer calibration is just that though, a manual check to ensure effectiveness. 
“The biggest thing that is overlooked is producers just don’t do it,” Lyons said. “They assume they are putting out enough, but they are not calibrating. So they really don’t know.” 
In the long run, 30 minutes spent calibrating can save producers time and money. Reapplying chemical is sometimes needed for producers due to other general factors. Don’t let faulty calibration be the cause, though.
“Before you start your sprayer season it is good to calibrate,” Lyons said. “If you calibrate before you start your spray season, it is something you won’t forget.”

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