Spray efficacy in orchards has been the subject of in-depth research on effective application approaches for many years, with the focus on improvements in spray coverage. Good coverage results in improved efficacy as well as reduced spray drift and less wasted material on the ground. Fine-tuning sprayers for the conditions of each application can therefore help improve spray coverage while also reducing off-site movement of pest control materials.
During last December's Almond Conference in Sacramento, almond growers heard about research regarding fine-tuning spray efficacy from industry leaders and specialists.
“Our studies are directed at controlling navel orangeworm and improving the performance of the products that we have,” said Brad Higbee, director of Entomology Research, Wonderful Orchards. “We don’t have a lot of options when it comes to controlling navel orangeworm; the diamides and insect growth regulators are the main groups we have, along with mating disruption.” Higbee noted, “What we need to keep in mind is that the place the residues need to be to have the most effect is on the hull — the nut itself,” adding that the problem in targeting residues on almond hulls and nuts is that canopy density and the dynamics of hull splitting make this difficult.
Testing Variables
Higbee’s presentation highlighted research on quantifying spray coverage at various elevations, as well as positioning of the spray, along with machinery comparisons to improve performance of residual insecticides in controlling navel orangeworm.
Higbee added that a typical ground sprayer covers the bottom half of the tree efficiently, while the top half receives relatively weak coverage. Tower sprayers can improve this uniformity of spraying trees, especially for the upper parts of the canopy, but don’t work as well for the lower parts of the tree canopy in terms of coverage.
“The standard ground application at 2 miles per hour, delivering about 200 gallons per acre with an Air-O-Fan [AOF], remains among the best in coverage; however, above 12 feet within the tree, there is a severe drop-off in coverage and residue deposition,” he said. “Power take-off–[PTO] based machines are as effective as engine drive sprayers, and we found the Progressive Ag tower to be a top performer with spraying depth.”
Second Spray
A qualitative leap was made with the addition of a second spraying, Higbee said, bringing vast improvements in coverage. “Residues sit for 30 days and when we analyzed these plots, they did not indicate much loss in activity. With a second spraying, we doubled the residue on the trees and saw a 55-60% reduction in damage,” Higbee said.
Joel Siegel of USDA Agricultural Research Service (ARS) has done extensive research on biological targets pertaining to spraying assessment, examining the kill of eggs over the height of trees, with both aerial and ground applications. “The challenge remains that ground application decreases as it reaches greater heights, and aerial application has the greatest coverage at the top of the tree, with decreasing coverage as you go down,” he told the Almond Conference audience.
Air as a Factor
Another key factor examined during the presentation was on the speed and quality of air associated with spraying. Matt Strmiska of Adaptiv shared the value of and components surrounding air with spraying.
“It is important to think about where the air is targeting and the rate it hits the tree, especially with controlled nozzle positioning,” he said, and suggested using flagging tape attached to nozzles to see the direction of air flow on sprayers.
In a joint trial evaluated by USDA ARS, using an engine-drive sprayer with 4.5 ounces per acre of Altacor, at 2 mph, resulted in a 75% kill rate in comparison to a PTO at 65%.
“If air cannot reach your target, know that both water and your insecticide will not either,” Strmiska said. “Adjusting RPMs can make a difference. These variables are important to investigate and test.”
With regard to fine-tuning spray coverage, consider the impact and potential results with slight variations in spray elevation, speed, target and locations of application. These adjustments can provide significant coverage improvements for better outcomes: more effective treatments and less waste of material.
For more detail and data, view the presentation “Pest Management: Fine Tuning Spray Efficacy” at Almonds.com/ConferencePresentations.
