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Ups & downs of spraying wheat fungicide

Updated: 02/04/2013 @ 9:49am

Wheat growers have enough on their minds during the hectic spring season on top of deciding between fungicides and which fields to treat. When time is of the essence, farmers have yet another ball in the air when combating a fungal outbreak: Spray with a ground rig or an aerial applicator? Both accomplish the task effectively, agronomists and applicators say, but they come with subtle differences.

Wet weather is one factor to consider when treating wheat late in the season, says Joel Ransom, extension agronomist at North Dakota State University.

“When you’ve got a high disease pressure and need to apply for scab control, it’s not a great time to be out in the field with a ground rig,” Ransom says, adding that scab, or fusarium head blight, is a threat normally occurring in wet conditions. “It’s muddy enough that it might be difficult to get the ground rig into the field.”

Custom application costs also have to be considered. Nationwide, custom ground rig application is typically $1-2 cheaper per acre than aerial application, says Scott Bretthauer, agricultural engineering researcher at the University of Illinois.

Additional costs for a ground rig, such as yield loss from the rig’s tire tracks, also have to be factored in.

“The issue with ground rigs is you’re going to drive over the crop,” says Bretthauer. “The amount of damage in terms of yield reduction is based on the boom width. Obviously, the wider the boom, the fewer passes you have to make so there’s less damage.”  

Tom Miller, custom applicator in Ingalls, Kansas, says figuring loss from compaction is simple: Take the total width of your tires, then divide that figure by your boom width. With two tracks each at 15” with a 90-foot spray boom, damage comes to 2.7%, he says.

“You’re running anywhere from 2% to 4% that you take out of that field, depending on tire size, boom width and if it’s a two or three wheel rig,” says Miller. “Then, take that times your gross revenue per acre, and that tells you how much was lost to tire tracks.”

To reduce compaction loss, Terry Faurot, farmer and custom applicator in Scott City, Kansas, sprays with a 120-foot boom.

“I’ve had a lot of people call me because they know I’ve got a 120-foot boom,” says Faurot. “If I had a 100-foot boom, they’d be looking for somebody else because I’d have extra tracks in the field.”   

Timeliness is also a key factor when weighing air versus ground treatment. Airplanes have the distinct advantage of traveling at faster speeds across the field, but they can spend just as much time turning as they do spraying, says Vern Hofman, professor emeritus of agricultural engineering at North Dakota State University. And, trips back to the airport to refill water and chemical may lengthen application time, he notes.

If the farmer is in a serious time crunch, adds Faurot, ground rigs can spray at night and are likely to be more available when demand for custom applicators peaks.

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