Researchers at Michigan State University’s Clarksville Research Center, in collaboration with Cornell University, have answered many of the questions posed about the viability of solid-set canopy delivery systems.
The high cost and short residual effects of the current crop of pesticides are increasing demand for more precise chemical delivery, and SSCDS are intended to meet that demand.
Per-acre capital costs of prototype SSCDS are 60 percent higher than conventional air blast sprayers.
Yet researchers say the efficiency and safety gains offered by the new system, as well as its usefulness beyond pest control, provides growers with a number of options to earn returns on their investments.
Matthew Grieshop, a Michigan State University associate professor of organic pest management, is one of the researchers on the project. “New generation pest controls are more specific and more expensive, which is driving demand for applying pesticides more precisely.
“Organophosphates are disappearing from the marketplace,” Grieshop said, “And with the pollination concerns surrounding the neonicotinoids, the fruit industry is facing the loss of a lot of their go-to products.”
The system under review consists of a central pumping station that pushes spray material down tree rows through tubing running along tree canopies.
The spray material is then applied via micro-sprinkler nozzles attached to support wires above trees in trellis systems and fruiting walls.
For the Michigan trial, the Clarksville researchers attached two lines of micro sprayers — one at 4.5 feet and another at 8 feet — to the tubing.
They fixed single, horizontally oriented micro sprayers on the upper line and two vertically oriented micro sprayers on the lower line, attached with a T-bracket, and spaced both sprayer sets at 6-foot intervals.
The system has four operational stages. First, operators pump spray material through the main line at low pressure. To spray, they close the return line and increase air pressure to apply chemicals.
For recovery, operators open the return valve and turn on the air compressor to blow residual material back into the spray holding tank. To clean the system, they close the return valve and run the air compressor to clear the micro sprayers.
Three years ago, Good Fruit Grower reported on the first-year results of this research project, which was being conducted in three states: Michigan, Washington and New York.
A recent report released new results from Michigan, incorporating findings from New York, for the last three years of study from 2013 to 2015.
WSU hasn’t worked on the project since 2014.
Michigan State University researchers ran field trials to compare SSCDS performance against conventional air blast sprayers. They used three tests to compare coverage: water-sensitive cards, tartrazine dye deposition and an insect pest bioassay.
The team placed water-sensitive cards both face up and face down, at 3-foot, 5-foot and 8-foot levels within the canopy. Then, they sprayed plots using both systems at 80 gallons per acre to compare coverage.
Over the three-year duration of the trial, SSCDS systems provided better coverage on cards facing up compared to cards facing down and tended to provide more coverage higher in the tree rather than lower in the tree, according to the researchers.
In contrast, air blast sprayers tended to provide better coverage of the undersides of leaves and the lower portions of the trees.
They also tested for spray distribution within the canopy. Using a food-grade, tartrazine dye mixed into spray applications, results showed much higher spray deposition on SSCDS-treated leaves compared with air blast-treated leaves.
The MSU researchers also evaluated SSCDS’s performance in providing disease and pest control against that of an air blast sprayer.
For pest management, they gauged the presence of codling moth, Oriental fruit moth, plum curculio and obliquebanded leaf roller after treatment; for disease control, they monitored for signs of apple scab.
The SSCDS provided comparable apple scab control to that of the air blast treatment. Results were consistent with SSCDS plots providing insect control equivalent to air blast sprayers as well, the researchers said.
“We collected field data on all three of those pests and apple scab at MSU and saw no difference between SSCDS and air blast-treated plots,” Grieshop said. “Both delivery systems significantly reduced damage compared to the untreated control.”
Cornell University entomologist Art Agnello said he compared the fruit quality of apples treated by air blast sprayers and SSCDS harvested from a New York state experimental orchard block.
“The data I sent over to Michigan State University for the grant proposal showed the fruit quality was comparable for both systems,” he said.
Grieshop said one obvious advantage is that this system does not require the use of a tractor.
For apple growers whose orchards lie on heavy clay soils, it means not running heavy equipment through the mud during scab season.
“It also means reduced incidence of ‘iron blight,’ equipment-inflicted tree damage,” Grieshop said.
While the system still requires a single operator, that operator stands outside the orchard and well away from the application process. And because the system is not complex, it requires far fewer skills to operate than tractor-based systems.
Grieshop said the application process is very fast, approximately 12 seconds. “We think we have far fewer concerns about spray drift because we are just misting the foliage,” he said.
That’s also a benefit for those growers whose operations are located near housing developments or commercial areas: SSCDS run very quietly, he said.
Grieshop has just begun exploring using the rapid applications made possible by SSCDS to re-think the rate and frequency at which pesticides are applied.
The basic idea would be to apply a full rate of pesticide followed by frequent, subsequent, low-rate applications targeted at maintaining coverage.
“For example, if we consider a pesticide with a seven-day reapplication window at 100 percent rate that is typically applied twice, we could make the first application at 100 percent, followed by three reapplications at 25 percent over the next 14 days,” he said.
It would save about one-eighth of the active ingredient and maintain pesticide residuals at a lower, more consistent level on the fruit. “This also could result in reduced residue at harvest,” he said.
When the trials began, three universities — MSU, Cornell and Washington State University — shared the grant to evaluate the system.
Last year, the U.S. Department of Agriculture did not fund the project, although MSU found some state money to continue the work and Cornell University continued to collect data.
Grieshop has written another grant proposal for 2016 that includes both Michigan State and Washington State universities. •
– by Dave Weinstock