The variable output nozzles and adjustable louver, developed for this citrus sprayer as part of a specialty crop research project, should soon be available for tree fruit sprayers.

The variable output nozzles and adjustable louver, developed for this citrus sprayer as part of a specialty crop research project, should soon be available for tree fruit sprayers.

Using autonomous tractors to perform pesticide spraying is possible—and may one day be practical—but given the expense of equipment and liability concerns of driverless tractors handling hazardous material, they’re not likely to be adopted soon, says a Cornell University researcher. However, two spinoffs from the autonomous tractor research that can improve spray applications could be available soon. The massive, integrated automation research project, funded by the Specialty Crop Research Initiative for almost $4 million, combined the robotic expertise of Carnegie Mellon University and the tractor know-how of the John Deere Company with ­university scientists and the Florida citrus industry to evaluate precision agriculture applications.

While the broad goals of the integrated automation project were to use autonomous equipment for precision agriculture and mechanical harvesting, the researchers also looked at precision spraying, which is why Cornell University’s Dr. Andrew Landers, Cornell’s pesticide application specialist, became involved. Landers, with years of pesticide application research, has helped growers across the nation improve their spray applications through workshops and publications.

Canopy density

A component of the integrated automation research was to develop intelligent control systems that go beyond current spray technologies that can detect tree or weed presence to switch nozzles on or off and can measure tree width, but at low accuracy. “We wanted the sprayer to take notice of the density of the canopy and adjust spraying to match whether the tree was big or little,” Landers explained. “If you have a little tree, you may only need a teaspoon of spray, but for a bigger tree, you might want two bucketfuls.”

Researchers developed a laser scanner-controlled system that could gather tree and canopy density data on the go to deliver variable-rate spray outputs matching the canopy in real time. The laser scanner senses the tree size and foliage density, sends a signal to the sprayer to enable it to make intelligent spray decisions, adjusting spray rates for each tree.

Landers sees several applications for canopy-density sensors on sprayers. Differences in canopy density within an orchard could be due to replants, blocks with alternating varieties that have different tree structure, pollenizers within a row that may be unpruned or have different growth habits, and blocks with different training systems. The canopy-density sensors would allow automated adjustments, fine-tuning spray amounts and coverage.

Research spinoffs

Two spinoff technologies that came out of the integrated automation project were adjustable liquid flow rate nozzles and adjustable airflow louvers. Both the nozzle and louver devices, which allow the sprayer to quickly adjust to match individual tree size and density, are expected to be available commercially in the coming year.

The variable-rate nozzles are the pulse width modulation type, already on the market for use with field crop boom sprayers. But the boom sprayer nozzles operated under much lower pressure than needed for spraying trees, Landers said. The research team worked with Wilger Industries and Capstan Ag Systems to develop new nozzle tips and bodies that would work under 150 psi. The new nozzles can pulse every 0.1 second, allowing an adjustable flow rate to match the size of the tree.

“This is the first time such technology has been ­available on a tree fruit sprayer,” Landers said.

The second spray application, patented by Cornell, is an adjustable airflow louver on the sprayer. The actuator allows the louvers to move from closed to a three-inch air gap within 0.25 seconds. “So now, you can quickly adjust the air coming out of the side of the sprayer to match the tree. If you have a little tree, you only need a little puff of wind.”

Two major manufacturers of orchard and vineyard sprayers are in the process of incorporating the adjustable louvers into their spray equipment, Landers said.

Landers has received a grant from the U.S. Environmental Protection Agency to continue field-testing automatic airflow adjustments of sprayers and is conducting trials in three vineyards and three apple orchards in New York. The EPA is interested in the reduced-risk aspect and improvement in spray deposition, particularly in early season spraying.


Landers has also been field-testing off-the-shelf Global Positioning Satellite systems like EZ Steer—an inexpensive GPS device commonly used by Midwest farmers to steer tractors—for tree fruit orchards. He believes using GPS to steer tractors during spraying could allow drivers to multitask, such as mow orchard row middles while spraying.

A GPS-guided tractor could also reduce operator fatigue at the end of the day and allow older people the opportunity to work. “In the Midwest, I’m told the EZ Steer has allowed Grandpa to sit in the tractor and feel a part of the family farming unit,” Landers said, adding that the EZ Steer devices are accurate to within two or three inches.

When GPS is incorporated with the spray controller, every row sprayed could be documented, which might be useful for traceability programs and to ensure that the spray rig operator didn’t miss or double dose a row, he said.

Driverless liability

Will autonomous tractors performing spray operations ever become routine in crops like apples? Landers is doubtful, but notes that the system worked well in the middle of a 15,000-acre Florida citrus grove that was part of the research, and that the tractors stayed on course.

“But suppose a sprayer rolled into a ditch?” he asked. “This was a research project, but in the real world, no laws and regulations yet have been developed to cover autonomous equipment.” A lot more testing would be needed for liability purposes, he added.

“But the integrated automation project resulted in important research spin offs that have real value to ­specialty crops like tree fruit,” he said.