Calibrating helps you get the most out of your sprayer, and the material you’re applying. But the first tool that should come to mind when you contemplate spraying should be a simple calculator. That’s because calibrating your sprayer is essential to protecting your turf and getting the most out of the materials you’re applying.

Sprayer calibration is frequently skipped over, says Dr. Casey Reynolds, turfgrass specialist with the Texas A&M AgriLife Extension Service. “The thing I see frequently is that people are intimidated by it, and they overthink it and think it’s complicated. And I understand that, because when I started spraying, I felt the same way,” says Reynolds. “But you can’t spray without understanding calibration.”

From park and rec complexes to high-end professional fields, most sports turf managers are using fixed-boom sprayers, observes Reynolds, who frequently gives presentations on sprayer calibration. There are multiple ways to calibrate different sprayers, but when it comes to fixed-boom sprayers Reynolds prefers the “5940 method.”

Dr. Casey Reynolds, turfgrass specialist with the Texas A&M AgriLife Extension Service, says that many turf professionals are intimidated by the prospect of calibrating their sprayers. But fine-tuning the spray process through proper calibration offers many benefits, he emphasizes.
Photo by Kay Ledbetter/Texas A&M AgriLife Extension Service.

This method involves a relatively simple equation:

Gallons Per Acre = (Gallons Per Minute x 5940) x (Miles Per Hour x Nozzle Spacing in Inches)

While this is the most commonly used formula, it’s also possible to change the equation around if it’s necessary to calculate gallons per minute:

Gallons Per Minute = (Gallons Per Acre x Miles Per Hour x Nozzle Spacing in Inches) x 5940

While some turf pros are worried about doing the math incorrectly, Reynolds says, “The most common mistake I see is people not even trying to calculate. They’ll buy a sprayer and the sales rep will tell them that it’s set up for 40 gallons per acre, and they go with that.”

While the factory setup may be accurate, it may or may not be appropriate for the material being applied, he notes. For example, a new sprayer that’s set up to apply 40 gallons per acre at a certain speed will obviously apply a different volume if that speed is increased or decreased out in the field. “Or if you change your pressure, your spray volume changes. Or if in the future you change your nozzles, your spray volume changes,” he explains. “So there are a lot of factors that can change your spray volume, but the 5940 method accounts for all of them.”

Reynolds recommends replacing nozzles once a year, and calibrating sprayers at least once per year. One good reason to replace those old nozzles: Reynolds says the biggest change in spray equipment in recent years has been in the area of nozzle technology. “You can buy nozzles now that just give you better coverage and performance than some of the older ones,” he states. “One way that I think many people have the opportunity to improve the performance of their sprayers is by updating with new pumps and new nozzles, because they just perform so much better.”

For those spraying different materials, it might make sense to buy more than one type of nozzle. “I really encourage people to change their nozzles based on what they are applying. That’s where I think a lot of sports turf managers miss the potential to improve the performance of their products,” Reynolds says.

For example, when spraying a broadleaf herbicide, a low spray volume is likely sufficient because the weed is right up at the surface of the grass plant. “All you’re trying to do is coat the surface of that leaf, so 30 gallons per acre might be plenty,” he notes. The same would be true when spraying a foliar fertilizer product.

On the other hand, if you’re spraying a wetting agent to combat hydrophobic dry spots in your soil, then the goal is much different. Instead of just being concerned about coating the surface, your goal is to get the wetting agent 6 inches down into the rootzone. “So 30 gallons per acre isn’t going to do it,” Reynolds says. “The same is true if you’re trying to spray an herbicide that’s systemic and you need to get it down to the crown or the root of the plant to help protect those parts of the plant. Again, 30 gallons isn’t going to do it – you need to bump up to 90 or 100 gallons per acre.”

Since different materials require different spray volumes to be maximally effective, the easiest and most accurate way to achieve those different volumes is by changing nozzles depending on what’s being applied, Reynolds advises. The information needed will be right on the nozzle; for example, an “8003” nozzle will have an 80 degree spray angle and apply 0.3 gallons per minute at 40 psi.

“Many newer sprayers have rotating carousels that have two or three different nozzle configurations,” adds Reynolds. “So you may have one nozzle set up that sprays 30 gallons per acre that you spray all of your foliar fertilizers with, and another set up at 90 gallons per acre that you spray all your systemic fungicides or wetting agents with. Once you get calibrated using the 5940 method, it’s a really easy flip of the nozzle.”

Using this approach, the nozzle alters the volume being applied, so speed and pressure don’t need to be tinkered with.

However, it’s not necessary to change nozzles. “Some guys will calibrate and calculate that at 30 gallons they’re going 3 mph, so they’ll just slow down to 1 mph when they want 90 gallons per acre. It’s just personal preference. But I feel you’re better always keeping your speed and pressure constant, and then all you have to do to alter your spray volume is switch out your nozzles,” says Reynolds. “Just like any math equation, the more things you can keep constant, the less chance for error.”

When you need to slow down it will take longer to get the job done, and crew members might forget to change speeds or adjust pressure. Establishing standard settings for speed and pressure removes some potential for human error to occur out in the field, he notes. Even on a sprayer without a built-in nozzle carousel, swapping nozzles takes just minutes, and they can be color-coded to distinguish between the different spray volumes to be used with different products.

While a rough estimate may work when spraying, fine-tuning the process through calibration will likely be better for the turf, and for the bottom line. Reynolds cites the example of one expensive fungicide that comes with label instructions to apply the material at a minimum spray volume of 87 gallons per acre. “If you go out and spray a $400-per-pound product like that at too low of a spray volume, all of that fungicide will land on the leaf, while the disease is on the crown and in the root. So even if you put out the right amount, you sprayed it in the wrong spray volume,” he emphasizes.

The way to get chemicals down into the root zone is to increase the spray volume so the product is put in enough water that it will flush down through the leaves and the canopy to get where it’s actually supposed to go, he explains. Another example would be when spraying insecticides for grubs, cutworms or other insects that live down in the soil. Reynolds says, “It does you no good to spray that insecticide up on top of the canopy; you have to get that product in contact with the insect for it to be effective.”

Conversely, it’s less of a problem when too much spray volume is used; most herbicides come with labels that allow for a wide range – say 20 to 240 gallons per acre – while still being effective. “The same is true with fertilizers; yes, you’re trying to coat the leaf, but if you go at too high of a spray volume, some of the material is still going to land on the leaves and be taken up by the roots,” says Reynolds. But, he points out, spraying at a higher volume than is specified does come with a cost in terms of added time spent spraying and extra trips to refill the tank. So, again, taking the time to calibrate the sprayer and select the right nozzles will make the application process as efficient as possible.

Once calibration is complete, Reynolds recommends double-checking to ensure that the sprayer is performing the way it should according to the calculations. “It’s always a good idea to turn your sprayer on and make sure you’re getting the right gpm. If your nozzle tells you you’re supposed to get 0.4 gallons per minute at 40 psi, then just take five or 10 minutes to turn your sprayer on, set it to whatever pressure you’re going to spray at, and hold a container under one of the nozzles to see how many gallons you actually get in a minute.”

For those who manage sports turf and use fixed-boom sprayers, the “5940 method” can simplify the calibration process and increase spraying efficiency and effectiveness.
Photo by Kay Ledbetter/Texas A&M AgriLife Extension Service.

If the numbers don’t match up, it could be a sign that the pressure is correct at the pump, but has dropped slightly by the time it reaches the nozzle. “If you end up catching 0.35 gpm instead of 0.4, then you just plug that new number into the formula,” he explains. The beauty of the 5940 method is that it can take all of these variables into account.

Like anything in life, calibrating becomes easier after you’ve done it several times. Reynolds says, “Once you spray a few times, and a week or two goes by and you see the weeds dying and your turf is fine, that’s when you get the confidence to say, ‘Wow, I did calibrate correctly.’ And, eventually, it just becomes second nature.”