Spray nozzle knowledge optimizes herbicide application

Photo Credit : Erdal Ozkan

Ineffective spray nozzle tips hamper the application of herbicides and result in subpar weed control. Since nozzle tips are the most economical component of a $15 to $40+ per acre crop protection application, it pays to learn and optimize each application across the entire boom.

There is no simple nozzle expiration date telling you when to swap out spray tips. Nozzle companies recommend replacement of a tip when its flow rate exceeds a 10% difference (plus or minus) compared with a new nozzle.

“Rather than putting hard numbers associated with wear characteristics of nozzles, it’s best to make a habit of calibrating your sprayer before and during the spray season,” said Erdal Ozkan, an ag engineer at Ohio State University.

Ozkan also cautions growers about relying on calibration within sprayer controllers. “At any Extension meeting or field day, the comment always arises about controllers handling all calibration now,” he said. “I tell them that knowing the average flow rate across a boom isn’t calibration. While the controller may indicate an application rate of 15 gallons per acre, you can still have individual nozzles applying 25 gallons or 5 gallons per acre.”

Nozzle material differences

The choice of nozzle tip material and respective costs will help determine longevity. Ozkan is thankful he doesn’t see brass tips in use anymore because they’re cheap and don’t last. In terms of resistance to wear, he rated ceramic tips as the longest wearing, followed by hardened stainless steel, stainless steel, and plastic (which significantly outlasts brass).

Wear varies greatly from farm to farm. The amount and type of liquid passing through the tip impacts wear. More gallons per acre at higher pressures will wear nozzles out faster, covering fewer acres. The same is true when spraying more abrasive products such as wettable powders and liquid nitrogen, compared with spraying liquid emulsions. Even the nozzle tip storage time can corrode if improperly cleaned and stored in sunlight.

In examining nozzle styles, Ozkan said there hasn’t been much change in recent years. Obviously, improved sprayer controllers, GPS-controlled guidance, pulse width modulation (PWM) technology, boom section or individual nozzle control, and AI/camera-based spot spraying have led to a giant leap in spraying efficiency.

“We’re still seeing some reluctance to adopt the technology to its fullest extent due to the higher investment cost and greater electronic reliance,” he said. “But I rarely hear complaints from growers who have adopted this technology.”

Nozzle sizing

When changing nozzles, start by reading herbicide labels to understand application recommendations, especially for dicamba and 2,4-D.

Ozkan said flat fan nozzles are well suited for the vast majority of row-crop spraying. While there are 10 to 15 different flat fan nozzles, it’s most important to choose the right size for the application rate, droplet size and spray pressure. Nozzle manufacturers and universities have developed mobile apps that provide the exact nozzle flow rates required for any application parameters.

Since one nozzle won’t fit all applications, it’s best to have several types and sizes on the boom. “I recommend a minimum of three nozzles on a turret, so if winds pick up during spraying, you can quickly change to increase droplet size and reduce spray drift,” he said.

For growers interested in or invested in pulse width modulation technology, nozzle selection is critical. Matching a duty cycle in the 60% to 80% range with approximate ground speed variance will help select appropriate nozzles. Check out this University of Georgia Field Report.

How to gauge tip wear

There are several ways to test nozzle tip output, spray pattern overlap and pressure. Sprayers with modern controllers handle rate adjustment automatically, but manual calibration remains a critical step to check nozzle condition.

Using a manual process of capturing water at each nozzle still works well. Set your sprayer at 40 psi, capture the output for a specified time and record nozzle amounts. Calculate output compared with the nozzle tip manufacturer’s guidelines (found on its website). Then replace the tips that vary by 10% (plus or minus).

To simplify this task, Ozkan recommended the SpotOn sprayer calibrator (model SC-2) because it automatically calculates and displays tip flow rate, application rate and nozzle tip wear, all completed in about 10 seconds per nozzle. “We tested this tool years ago and found it to be very accurate,” he said.

If the flow rate is low on a tip, check for corrosion or a plugged screen. Clean tips with a toothbrush, never a metal object like a pocketknife or screwdriver. If the average flow rate is high (according to manufacturer specs) across most nozzles, check the pressure gauge or flow meter first. If those are fine, it’s time to replace all tips.