On a cold rainy day with apple scab threatening, wouldn’t it be nice to push a button labeled “Fungicide” and let the orchard spray itself?

Spraying is one of those things all orchardists have to do. Whether conventional or organic, they spend a lot of time filling sprayers, mixing chemicals, and driving up and down fruit tree rows, blasting away.

“Orchard spray technology has not kept up with the changes that have taken place in the horticultural side of tree fruit production,” says Dr. Matt Grieshop, a Michigan State University entomologist. There should be a better way.

He and fellow researchers are looking for one. Armed with a $2.5 million Specialty Crop Research Initiative grant (and $2.5 million more in matching funds), they are mounting a project to totally change the way crop protectants, nutrients, pheromones, and growth regulators are applied.

If it all works, you can say goodbye to your airblast and tower sprayers. Say hello to fixed, permanent spray application systems you build right into your high-density apple or cherry orchard when you install the trellis system. You might be able to retrofit existing orchards as well.

The researchers call it the Solid-Set Canopy Delivery system.

It’ll probably look like another irrigation line or two, not on the ground but higher up in the trees, strung along trellis wires, with micro-emitters in or over the trees.

The project, which was funded for two years, involves three directors: Greishop, Dr. Jay Brunner at Washington State University, and Dr. Art Agnello at Cornell University, Geneva, New York. The team of 28 scientists includes engineers, entomologists, horticulturists, pathologists, economists, social scientists, and extension educators.

Traditionally, growers have used airblast sprayers to apply pesticides to apple trees, creating a vast plume of spray, a variable proportion of which hits the target. The result is often poor distribution within the canopy leading to ineffective disease or insect control, off-target drift leading to environmental pollution, and economic ­inefficiency.

With smaller trees in fruiting walls grown in tall spindle and slender spindle designs, and canopies no more than a few feet thick, huge air volumes are no longer needed to get good coverage, Grieshop said.

In the new high-density systems, infrastructures like trellises are already being built that would support a fixed spray application system. And the economics and social dynamics are changing as well—in directions that favor such a system and don’t favor continued use of airblast technology.

In some preliminary work done starting in 1998 by Drs. Art Agnello and Andrew Landers at Cornell University in New York, a fixed-in-place system gave more uniform spray coverage than airblast sprayers, Grieshop said. In a paper published in 2006, they reported how they ­developed and tested a fixed spraying system to improve application timing, reduce drift, and improve deposition in a high-­density orchard at Fowler Farms in New York State. Preliminary results were promising.

Their paper identified how such a system might be laid out and addressed the main engineering challenges of pipe diameter, sizes, emitters, flow rates, pressure changes, and injection systems. Inexpensive emitters were fitted to small-bore irrigation pipes mounted on the top and middle trellis wires.

Better timing

The Solid-Set Canopy Delivery system could have ­several advantages, according to Grieshop.

Instead of taking hours of up-and-down-each-row tractor driving, with its costs in time, fuel, and equipment, turning on the fixed system could pump critical pesticides to fight insects and diseases through plastic lines to micro-emitters in every tree in minutes.

No more carving up the alleys in wet, sloppy conditions. No more spraying long hours into the night to take advantage of precious time and low-wind conditions.

Timing has other important aspects as well.

Dr. Larry Gut, an entomologist at MSU and a participant in the project, and Grieshop have studied the behavior of codling moth and found it flies four hours a night at most, starting just before sunset, but it doesn’t fly if the temperature is below 60 degrees or if it’s even moderately windy.  A fixed-in-place, all-at-one-time system could target spraying of codling moth only when it is active. Gut is working on the idea of applying expensive mating disruption pheromones only during those brief times when they are needed.

“Timing is also important with the use of reduced-risk insecticides,” Grieshop said. “They are quite target specific and often have a short residual period.”

Grieshop heads the organic pest management program at MSU, so he is also concerned about organic program chemicals that are often easily washed off, have short residual activity, or depend on thorough coverage for their effectiveness. This system addresses all these issues.

Targeted delivery

A sociologist is evaluating such issues as worker safety and the urban/agricultural interface, where people, noise, and spray drift are all growing concerns.

While enclosed tractor cabs and space-suit-like personal protection equipment are parts of modern spray application, exposure is still more likely than it would be if a worker was mixing chemicals and turning on equipment in a centralized spray facility away from the orchard.

If workers are not in the orchard during spray application, it also opens the possibility of using materials, like Guthion (azinphos-methyl), that are hazardous to workers but might be environmentally less damaging than reduced-risk materials.

One of Grieshop’s interests in the project is the impact such a system might have on orchard ecology. What might happen to soil compaction and vegetation management if tractors hauling sprayers were removed from the orchard? What might the impact be on natural enemies and pollinators? Could less mechanical damage to trees reduce fireblight or cankers?

While it might be more expensive initially to install a permanent, fixed-in-place spray application system, the costs of operation should be much less if the costs of equipment, fuel, and labor for sprayer, tractor, and sprayer operator are eliminated.

Grieshop requested funding for five years, but received two years of funding. He is hoping that if research funds continue to be available and the project shows merit, it might be refunded.