Dr. Andrew Landers says conventional airblast sprayers were designed with much more air volume and speed than what's needed in today's modern orchards.
This LIPCO tunnel sprayer can reduce drift by 90 percent compared to conventional sprayers, according to Dr. Andrew Landers.
Sprayers set up improperly can create a host of problems for growers, from contaminating equipment and operators to reaching unintended targets. A Cornell University researcher has found that growers can do better at keeping pesticide applications in the trees by modifying airflow and speed, and changing nozzle angles.
Effective spraying involves more than just paying attention to the sprayer, said Dr. Andrew Landers, an agricultural engineer at Cornell who specializes in pesticide application. There are many aspects of spraying that must be considered, including management of the system, the operator, weather conditions during spraying and maintenance.
Problems from inefficient spraying can result in damage to susceptible off-target crops, contamination of sensitive waterways, and reduction in the rate of application to the target crop, Landers said. Drift is also a problem because of public perception. Photos that look like "bonfires in the distance" (but are actually orchards being sprayed) show up on Web pages of antipesticide lobbying groups, he said. Moreover, sprayers not set up properly can create problems for applicators and contaminate equipment.
In an application trial using kaolin clay material that visually shows where the material is deposited, Landers found that some tractors were covered in white within 15 minutes of spraying when the sprayer was not set up properly.
"It's the operator that has to work in these conditions," he added. "We need to be very aware of getting our sprays on trees and not the tractor."
He also monitored the pesticide levels inside the cabs, air filters, near the inside windows, and seats on a dozen different tractors to see if the carbon filters were doing their job. Landers found very low to almost no micrograms of pesticide near the windows and tractor cab inlet and outlet vents, indicating that the filters are keeping the air inside the cab clean. However, significant amounts were found on the cloth seats of the tractors.
Landers thinks that the protective suits worn by applicators during tank filling are likely contaminating the tractor seats. This could be a potential site for exposure when the tractor is used the next day for a different orchard task and protective gear is not worn.
"You certainly need to be aware of this pesticide that could be lurking about on the seats," he said, adding that using a towel to cover the seat during pesticide application would be an easy remedy.
Airblast sprayers are predominantly used in the tree fruit industry, he said during the Great Lakes Expo in Grand Rapids, Michigan. "Many airblast sprayers are too big for modern planting systems; the fan diameter is too large, and the volume of air created is too great for the target canopy," Landers stated.
Traditional airblast sprayers direct the air from a single axial-flow fan, mounted directly behind the sprayer, in an upward and outward direction, he reported, and they are designed to move large volumes of air at low pressures.
As the airblast sprayer fan rotates counterclockwise, the right side lifts air upward and outward, while the left side pumps air downward, unless it's a very well-made airblast sprayer and has adjustable deflector plates or pitch propellers, he explained.
The result of the upward, outward, and downward motion is an imbalance in air distribution that can result in non-uniform application, deposition and disease control, he said.
Additionally, the volumes of air that come from most sprayers are not designed for today's modern plantings with semidwarfing rootstock and spindle training systems. "Most of the airblast sprayers were designed for pecan or walnut trees that are 30 feet tall," he said, adding that they were designed with way too much air volume and speed. He has found air speeds of up to 190 miles per hour advertised on some airblast sprayer manufacturers' Web sites.
Landers has conducted various trials with different sprayers at Cornell University to study the impact of fan speed, airflow, volume, and direction.
He found a dramatic reduction in drift from an AgTec P300 airblast sprayer, by reducing fan speed or PTO (power take off) speed by 25 percent—from 2076 rpm to 1557 rpm or 540 to 405 rpm PTO.
Drift was monitored by attaching water-sensitive cards to 14-foot-tall poles placed 20 feet apart, starting at the application site. At the higher PTO speed, equivalent to 2076 rpm fan speed, drift was detected up to 80 feet away, where 10 percent of the card was covered. At the high speed, cards 20 feet from the target had 75 percent coverage. Reducing the fan speed by 25 percent significantly reduced drift, resulting in only 16 percent card coverage at 20 feet.
"By reducing the PTO by 25 percent, we were able to reduce drift by 75 percent," he said, adding that it resulted in better deposition in the trees. When higher air speeds are used, the air blows right through the trees, especially in the early season when canopies are undeveloped.
Landers also tested growers' equipment to evaluate spray patterns, using a MIBO vertical patternator to assess nozzle orientation. He found great variability in spray patterns due to nozzle orientation in the growers' equipment. Many spray patterns resulted in a large quantity of material being blown above the target row.
The best spray pattern for most conditions tested occurred when the right-hand side nozzles were pointing horizontally to counteract the upward movement of the air from the fan and when the left-hand side nozzles were pointing 45 degrees upwards to counteract the downward direction of the air from the fan, Landers said. However, each sprayer design is different due to fan size and air volume, so no blanket recommendation can be made.
"The sprayer is like a hairdryer," he said. "At high flow, it's blowing through the tree, and when the sprayer is coming down the next row, it disrupts the droplets that were already on the trees. But if you go too low, you won't get enough penetration into the canopy."