Good to the last droplet

Keys to calibrating your sprayer to get more bang for your buck



A miscalibrated sprayer is like a box of chocolates – you never know what you’re going to get. Maybe you’ll get proper coverage or maybe it’ll be lost to drift.

Accurate calibration is the only way to know how much chemical is being applied to your field. Even with the current use of electronics to monitor and control the application of crop protection products, a thorough sprayer calibration procedure is essential to ensure against misapplication. Failure to calibrate a sprayer can injure your crop, cause pollution and worst of all waste money.

“The sprayer itself needs to be operating as efficiently as possible,” says Bob Wolf, K-State extension application technology specialist. “Especially the first time out in the spring, you need to make sure your sprayer is all tuned up. That there are no leaks, the pump works properly, nothing is plugged and every component is functioning properly including electronics.” While that may cover the basics Wolf says there’s more to the calibration process.

“Take into account what kind of coverage the chemical will need and pick the right nozzle type to maximize it’s impact,” Wolf says. “Applicators need to consider what type of activity the chemical has, whether it needs contact area or if it will translocate through the plant, then calibrate for the system to best deliver the proper amount on the target.”

When it comes to selecting nozzles, there’s certainly a plethora of choices these days but no singular silver bullet says application technology research scientist with Syngenta, Dan Kidder. He finds nozzle manufacturer catalogs and the pesticide product labels very helpful in making this decision. “It’s tempting to try to make one set of nozzles work for all products by changing your sprayer pressure and ground speed,” Kidder says. “But with the diversity of products typically used on today’s state-of-the-art farms this strategy will almost always result in less than optimum application of some of the products. Less than optimum coverage requires higher product use rates and may cause unnecessary environmental loading. It pays to invest in several sets of nozzles for your different products. And better yet, install swivel style multiple nozzle bodies on your boom so you can change spray tips with just a flick-of-the-wrist.”

Some nozzles also produce a broader spectrum of droplet sizes, another important aspect of in terms of crop protection application. “Droplet size impacts coverage and droplet size impacts drift,” Wolf says. “Somewhere we have to find the happy medium because the common thought is smaller droplets means better coverage but we come against some things in the environment that prevent that. Smaller droplets will drift easier and some applicators overlook the evaporation concern. Especially in the Kansas and Nebraska areas that can have wind and dry conditions it’s definitely something to keep in mind.”

An adopted standard specifies a droplet size spectrum broken down into six categories; very fine, fine, medium, coarse, very coarse and extra coarse. Product labels are now featuring the recommended droplet size to improve application performance.

“Applicators are getting more and more focused on droplet size because we are learning that certain types of targets require different kinds of coverage and droplet size aspects than others and the sprayer must be set up for it,” Wolf says. “It’s going to require applicators to have a pretty good knowledge on the type of nozzles they are using and relate that to the product recommendation for droplet size.”

But how much difference does size really make? A drop is a drop, right? Not when talking about spray application, where every drop counts. “A change in droplet size has a huge effect on the number of droplets applied per square inch,” Kidder says. “For instance, reducing droplet size by half increases the number of droplets applied per square inch by eight times. Large droplets drift less than small droplets so spray losses are minimized. Large droplets also penetrate crop canopies better to reach the lower leaves; which is important for some fungicide applications. But smaller droplets cover the upper canopy better and are also better at providing some coverage on the underside of leaves.”

Kidder also suggests applicators match droplet size to spray volume. “If you’re lowering spray volume to save time, reduce droplet size to maintain quality. Higher water volumes result in higher operating cost due to more time and energy traveling to and from the refill site and soil compaction is sometimes a consideration when hauling high volumes of water back and forth across the field.”

Spray application is not what it use to be. For good reasons growers seem more focused than ever on reducing costs and optimizing sprays. “Producers pretty much know how to calibrate to get the right orifice size to deliver the right gallons per acre,” Wolf says. “But now there’s more to it, they have this droplet size spectrum concern in there and that may force them to take calibration a step further. The underlying key is to understand the application system and ensure that it is as efficient as possible so that it performs well in the field.”