It’s one of those rainy-day jobs when you’re itching to be powering up in the field. But that’s when spending a little time going over your sprayer will pay dividends, says Andrew Frankenfield, Penn State Extension agronomist. And the time is now.
• Step 1: Check all hoses, pumps and valves. Replace as needed. Remember, you’ll be running this sprayer over a lot of acres when downtime is extremely expensive.
• Step 2: Check the tank’s condition, including the straps holding it to the frame, for unusual wear. Then give it a spring cleaning with this common recipe:
First, flush it with water. Then add 25 gallons of fresh water plus 1 quart of household ammonia. Agitate the solution and run it through the sprayer for 2 minutes. Leave that solution in the sprayer and booms for at least 2 hours. Finally, flush the solution out and rinse with clean water.
• Step 3: Worn or partially clogged nozzles and dirty strainers will cause uneven spray distribution, which can lead to problems later this spring. Clean all nozzles and strainers with warm, soapy water.
• Step 4: Now it’s time to check nozzle output. “Relying on your pressure gauge, gear and tachometer settings from last year simply isn’t enough!” emphasizes Frankenfield. Here’s the procedure:
Using a calibration cup or a graduated container marked in ounces, catch each nozzle’s output for 20 seconds and write down the output ounces. Then add up the total ounces of all nozzles and divide by the number of nozzles to get average output per nozzle. If any nozzle puts out more than 10% above or below the average, clean or replace that nozzle.
Here’s the critical part: Recheck the output from any cleaned or replaced nozzle and use its output to figure a new average. If more than two nozzles have output rates 10% above or below the average, replace all of them, then repeat the process to ensure uniform flow rate.
• Step 5: Finally, you’re ready to calibrate spray rate. If the rate is too low, you risk product failure and will waste your time and money. If it’s too high, you waste chemical and money, may violate the label and risk pollution.
Use this boom calibration method
Frankenfield recommends using the 1/128th of an acre method to calibrate a boom sprayer. Use the accompanying table to find the distance you must travel to cover 1/128th of an acre per nozzle. Based on your boom nozzle spacing, measure off the distance needed.
Fill the tank half full with water (no pesticide). Mark off that distance in the field. Make sure your sprayer reaches full operating speed before reaching the first marker of the test course.
Make at least two runs over the marked distance with all the equipment to be used during the application. Use the gear and throttle settings that will be used during actual spraying. Obtain an average time in seconds the sprayer takes to travel that marked distance.
Park the tractor and adjust sprayer pressure to the level you’ll use for application. Now, using a calibration cup, catch the output from a single nozzle for the length of your average travel time. The ounces collected from one nozzle equals the gallons per acre output of your entire sprayer.
Compare the actual application rate with your intended rate. If the actual rate is more than 5% higher or lower than your intended rate, you must make adjustments.
How to adjust the rate
One way to adjust rate is to change the pressure. Lowering the spray pressure will reduce the spray delivered; higher pressure means more spray is delivered. Remember, do not vary from the manufacturer’s recommended nozzle pressure range.
Another way to correct application rate is to change your actual travel speed. Slower speeds mean more spray is delivered; faster speeds mean less is delivered.
If you’re running a relatively low pressure, it’s easiest to increase your pressure and maintain the same ground speed. If these changes don’t meet your desired rate, you may have to select a new set of nozzles with smaller or larger orifices.
Here’s an example based on the table’s 20-inch nozzle spacing. According to the table you need to calculate how long it takes to drive 204 feet.
Suppose it takes 28 seconds to drive 204 feet, and you’ve collected 20 ounces from one nozzle in 28 seconds. Your spray rate based on water is 20 gallons per acre.
But what if you’re spraying 28% UAN? You’ll need to adjust your sprayer because UAN is thicker or denser than water. The conversion factor is 1.13 for 28%-0-0. To apply 20 gallons per acre of 28%, you’ll need to calibrate your sprayer to apply 22.6 gpa of UAN (20 gpa x 1.13=22.6 gpa).
Source: Penn State Extension