March / April, 2004

Video Clips

• Slow Motion Shot
• Tractor Cab View (10 seconds)
• Auto Trunk Spray (15 seconds)
• Auto Trunk Spray (18 seconds)
• Hand Tree Trunk (15 seconds)

Automated Trunk Sprayers

By Renee Stern
Copyright 2004, Reprinted with permission from The Grower Magazine

A prototype that mechanizes trunk sprays offers cherry growers the promise of a speedier, safer and more efficient way to apply borer controls.

Department of Agricultural Engineering research specialist, Richard Ledebuhr, along with other Michigan State University researchers have developed an automated trunk sprayer to replace the current labor-intensive practice of applying pesticides by hand against peach tree borers and American plum borers. Tests this year pinpointed areas to improve, but still drew rave reviews.

"For a prototype, we were extremely pleased with what we were seeing," says Bill Klein, farm manager at MSU's Northwest Michigan Horticultural Research Station.

Speed and efficiency were "phenomenal," Klein says. The machine required one person compared to two with hand-spraying, and covered test blocks in a quarter of the time.

Those are important factors during busy spring and early summer months when orchard chores swamp growers, he says.

For some, hand-spraying is one chore too many. "I never put a spray on at my own farm until I got this machine," says Gary Thornton, emeritus professor at MSU Extension. Before leaving
the university, Thornton helped Richard develop the automated sprayer.

Ignoring borers can be costly, Thornton says. "I've had trees that have died from it." Even a slight drop in yield can mean the difference between profit and loss.

Consistent coverage was the prototype's main problem. Ledebuhr is tinkering with the sensor "eyes" that pick up a signal bounced off tree trunks; the machine uses that reflected signal to determine where to aim each spray blast.

"It was 95 percent accurate, but it missed some," he says. Trees that grow at an angle don't bounce the signal straight back to the sensor. Slopes and other terrain features can also throw
off the reflected beam.

Operators can trip a manual override to catch any misses they notice, he says.

Large trees with low branches also pose an access problem with the current design, Thornton says. Along with sensor improvements, the next version will incorporate changes to extend the reach.

To test coverage patterns, the researchers included a fluorescing dye as a tracer. Viewing the sites at night with black lights revealed little difference between the automated and hand sprayers, he says.

Also important to coverage is creating a ground-soaking puddle of pesticide around the trunk to tackle soil-line problems, says Jim Bardenhagen, director of MSU's Leelanau County Extension. The machine "does a really good job" when it comes to puddling material, a particularly effective tactic against greater peach tree borers, he says.

Accuracy wasn't the only design aim. Ledebuhr and Thornton were shooting for around 2 miles per hour, and hit speeds up to three times that on flat ground. "So that's a big plus for
growers," Ledebuhr says. "Five miles per hour was a comfortable speed."

At one test site, the machine covered in half a day what took hand-spraying two days, he says. Tweaking the sensors may reduce that speed, however.

"We hit very close to our objectives in the original construction, but we want to fine-tune and develop it further," he says.

Thornton says the automated sprayer was just as effective and twice as fast as hand-spraying -- on level ground. For now, advantages vanish on slopes.

Worker safety concerns also spurred work on the automated sprayer. An operator in a pressurized cab is exposed to smaller amounts of pesticides without needing a cumbersome protective suit, Ledebuhr says.

Applying the pesticide by hand also tends to produce a continuous spray, creating more chances of exposing anyone in the vicinity, Bardenhagen says.

Thornton says his interest in the project stemmed from a hand-spraying accident, in which a broken hose drenched the worker's protective gear.

Despite all the positive feedback, Ledebuhr says the machine requires additional study in one area: "We've got to see how this application process affects biological control" of target pests. The automated sprayer's squirt gun approach may not match in some unforeseen way the pressure spray of hand applications.

"Over the next two years we're going to watch the insect populations and control," he says.

But Bardenhagen says the equipment could fit well into a pest control program that incorporates mating disruption, perhaps alternating pesticides with pheromones for resistance management.

However, small orchard blocks may not be suited for mating disruption, nor are pheromones available to deal with American plum borers. In those cases, automated trunk sprayers are ideal, he says.

Cost comparisons between the two methods are hard to quantify after only one testing season, but the machine's off-the-shelf components should keep it relatively inexpensive, Ledebuhr says. And with labor typically the biggest chunk of a grower's operating costs, the ability to do more work with fewer people makes automation attractive.

"It was simple to set up and to use," Klein says. "That's unusual in prototype equipment."

"If (spraying) is easier and cheaper, they'll be more likely to do it," Thornton says.

For more information contact:
Richard Ledebuhr
Research Specialist
Michigan State University
113 Farrall Hall
East Lansing, MI 48824
Phone: 517-353-4507
Fax: 517-432-2892
email: ledebuhr@egr.msu.edu

Growers Magazine

Agricultural Engineering
Michigan State University
A.W. Farrall Hall
East Lansing, MI 48824-1323
(517) 355-4720

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April 23, 2004