How do you know how much product you are putting out if you haven't calibrated your sprayer??

At the recent ARS field days in Froid and here in Sidney, I did a session on calibrating spraying equipment.  While there has already been a good portion of pesticides applied in the county, a little reminder about applying the right amounts never hurts. 

It used to be that calibrating a sprayer was a long, difficult, drawn out process that seemed like a person needed a degree in mathematics to do, but that is not the case anymore.  Now, calibration of both boom sprayers and hand-held sprayers can be done easily with very little math involved.  When applying pesticides, whether it be with a large boom sprayer or a hand-held sprayer, it is important to know how much product (in gallons per acre) is being applied.  Here is how to do that.

With a boom sprayer, this is done in 4 easy steps; 

 1.       Determine the length of the course that you need to drive.  This is done by dividing 340 by the nozzle spacing (in feet) of your boom.  For example, if the nozzles on your boom are 18 inches apart, the equation would be 340÷1.5 which equals 227.  So your course would be 227 feet.

2.       Time how long it takes you to drive the course at a constant spray speed.  You should make sure you are up to speed prior to starting the course and should travel it 2-3 times and take an average.

3.       Collect liquid from a nozzle at a constant RPM/pressure for the amount of time found in step 2.  Prior to doing this, you should make sure that your nozzles are putting out the same amount of product by averaging all nozzles on the boom and either cleaning or replacing those that are putting out product at 10% above or below the average.

4.       Determine Gallons Per Acre (GPA) by converting ounces of liquid obtained in step 3 into GPA.  If 20 ounces where obtained then you would be putting out 20 GPA.

For handheld or backpack sprayers, the process is essentially the same, just done on a smaller scale.

1.       Measure an area 18.5’ by 18.5’.  This represents 128^th of an acre.

2.       Time how long it takes you to walk and spray (at as much of a constant pressure as you can) the 18.5’ by 18.5’ course.  Just like with the boom sprayer, you will want to do this a couple of times to determine an average.

3.       Spray liquid (water) into a measuring container for the length of time determined in step 2.  Again, you will want to try as best as you can to maintain a constant pressure.


4.       Determine GPA by converting the ounces collected in step 3 directly to GPA.
Now this may appear to be time consuming but it really does not take too long and may help in the long run financially as you may not need to add as much product as you thought.
I would suggest visiting http://msuextension.org/publications/AgandNaturalResources/MT200915AG.pdf for more information about calibrating different types of sprayers and determining nozzles.  I also have a couple of digital readers that I am happy to let you borrow that will tell you how many gallons per minute your sprayer is putting out and makes it a little easier to get a good recording.