No more airblast spraying?

MSU horticulturist Ron Perry, left, worked with engineers to design and install the system. Here he works with two technicians.

PHOTO BY RICHARD LEHNERT

Think of all the materials you put on your orchard through your airblast sprayer: Insecticides, fungicides, antibiotics, chemical thinners, plant growth ­regulators, sunburn protectants, foliar nutrients, anticracking agents.

Now suppose that, instead of lugging them up and down the alleys in dozens of trips and thousands of gallons of water in all sorts of weather, there was a fixed-in-place spray application system that could do all those things—and others as well. How about dispensing pheromones using emitters instead of putting up twisty ties? How about cooling the orchard with mists of water, or applying water for irrigation or frost control?

And how about doing these things in seconds instead of hours—putting on all your fungicide at the exact proper time instead of dragging the process out as the apple scab and cherry leaf spot spores ripen and infect new tissue or the critical time for apple thinning passes by.

Developing such a system is the goal of a $4.5 million, two-year project funded last year by the Specialty Crops Research Initiative. The system is called the Solid Set Canopy Delivery System, using the image of a solid-set irrigation system suspended in an orchard canopy.

Dr. Matt Grieshop, Michigan State University entomologist, is lead investigator. Twenty-six scientists across the country are co-investigators, exploring the idea of installing a stationary spray application system in the tree canopy, supported by the trellis, that could apply spray materials in a fraction of the time it would take using a tractor and sprayer.

Modern orchard systems—with densely spaced trees supported by trellises—were designed primarily to improve production and make it easier for workers to access the trees and fruit. Scientists now hope to take advantage of modern tree architecture to deliver another benefit—the ability to apply pesticides to the orchard without needing to drive a sprayer through it.

Two-year project

Originally, Grieshop said, the grant proposal asked for $12 million and five years. Only two years were approved, with a proviso that, if the work looked promising, the ­scientists could apply for more funding.

The scientists jumped into the new project this year, hoping to generate the data that would extend the project, which they think could lead to a paradigm shift of huge proportion—but can’t be done in two years.

“Airblast spraying was designed for orchards with huge canopies,” Grieshop said, “not for fruiting walls. It is outmoded technology.”

In use for more than half a century, the airblast sprayer may go the way of the dodo bird, he suggests.

In field days in Washington and Michigan, the researchers showed just how much they were able to do in one year.

Horticulturists, entomologists, pathologists, engineers, and economists established replicated trials at Washington State University’s research orchards in Wenatchee (apples) and Prosser (cherries), at Cornell University and at Fowler Farms in New York, and at several sites in Michigan, including orchards at the Clarksville Horticultural Experiment Station, at the East Lansing research orchard, and at the Belding farm of Ed and Mike Wittenbach.

John Nye with Trickl-eez Irrigation in Michigan is involved in designing the systems and in testing them in the commercial orchards in Michigan and New York.

Dr. Jay Brunner, director of WSU’s Tree Fruit Research and Extension Center in Wenatchee, said trials were conducted in Washington this summer to compare codling moth and mildew control in blocks where the pesticide was delivered through the solid set system versus by an airblast sprayer. Trials in the eastern United States are looking at how the different spray application systems affect control of fireblight and scab. The systems vary in design and type and density of emitters.

During a summer field day at WSU’s Sunrise research orchard, Brunner explained that the tubing the emitters are attached to forms a big loop. Once the loop is filled with solution, the pressure is raised using an air compressor, and the emitters all come on at the same time, delivering 100 gallons per acre of solution in 13 seconds. After the spray is applied, the solution in the system is recaptured, and the system is cleaned out with air.

In Michigan, experiments were set up in apples and sweet cherries, with the sweet cherries being grown in high tunnels. A few years ago, MSU horticulturist Dr. Greg Lang began work with the fixed-in-place spray system for sweet cherries in tunnels.

Two years ago, MSU entomologist Dr. Larry Gut began looking at delivering pheromones for mating disruption through a similar system.

Dr. Jim Flore said that disasters like the one that struck Michigan’s fruit crops this year because of very warm weather in March followed by April freezes may be preventable in the future. Research has shown that bud development can be set back two to four weeks by using evaporative cooling when temperatures rise above 50°F, he said.

Ines Hanrahan, with the Washington Tree Fruit Research Commission, will compare standard overhead cooling systems with the solid-set system for sunburn control. Typically, an overhead cooling system applies water for a 15-minute period when the temperature reaches a threshold. The solid-set system would apply water for only 35 seconds at a time but more frequently so the total amount applied would be the same, Brunner said.

Flore also envisions using the system to apply calcium sprays to prevent sweet cherries from cracking and to apply growth regulators such as ethephon.

Dr. Mark Whalon notes that, when moisture is adequate in the soil, nematodes can be used to eliminate plum curculio larvae pupating in the soil. Could this system provide that moisture?

Phil Schwallier, who works with chemical thinning of fruit and use of Apogee to shorten apple terminal growth, said, “This system should be used for everything. It should totally replace the airblast sprayer.”

MSU horticulturist Dr. Ron Perry was called on to work with engineers to develop the system itself. He was in charge of the installations at Clarksville.

MSU entomologist Dr. John Wise is studying deposition patterns. He wants to see how the application system affects the amount of spray deposited on the orchard floor and on the upper and lower surfaces of the leaves and how different kinds and placements of emitters affects coverage.

In New York, reservoir systems are being studied. Instead of filling the lines with spray material, reservoirs above each emitter could be filled with the exact amount of spray material needed to fill its space. Less material would be needed to fill the lines—a serious consideration. Perry said it takes 150 gallons of material to fill the lines in the two-acre test orchard at Clarksville, and 12 to 20 seconds to apply about 70 gallons per acre.

There was long discussion at the field day at the Clarksville station about how different materials require different levels of coverage on foliage and how the system would have to be operated differently to apply them.

Brunner said there are other issues to explore in the long term. For example, if an acre of orchard can be treated in a couple of minutes, can pesticides be applied at lower rates but more frequently?

“We’re thinking we can move more and more towards a low-residue approach, but that’s yet to be determined,” he said. “That’s not the objective of the current project.”

Grieshop and Wise both noted that wind affects airblast sprayers and the fixed system differently. A slight wind might help move the spray through the canopy when it’s applied by a solid-set system, Grieshop said. Airblast sprayers overcome the effect of wind by supplying abundant wind of their own.

Economists are also part of the project. The cost of installing such a system could be high but offset by savings in equipment, labor, and time—and the loss of fruit quality that can come from lack of application timeliness.