Drones to the Rescue: Treating a Historic Tree for Spongy Moth

These unmanned aerial vehicles (UAVs) offer precise targeting, minimizing chemical drift and environmental impact. They show a shift in treatment approaches for individual specimens like the historic white oak tree in Lewisburg, Pennsylvania.

While evaluating the health of a historic white oak tree (Figure 2, left) in Lewisburg, Pennsylvania, in early May 2024, Penn State Extension urban forester, Vinnie Cotrone, noticed that spongy moth larvae had just hatched and were beginning to feed on the leaves. Without a quick intervention, the 255-year-old Witness Tree dating back to 1769 would soon be defoliated, causing the tree to decline and die. The Shade Tree Commission and municipal officials were immediately informed that morning, and a search for rapid treatment options was explored.

Figure 2. (Left) Historic white oak tree located in Lewisburg, Pennsylvania, at the edge of the Lewisburg Cemetery. Note the proximity of houses. (Right) The historical plaque describes the significance of the large white oak tree located in Lewisburg, Pennsylvania. Photos: Vinnie Cotrone, Penn State

Treatment for spongy moth (formerly gypsy moth) on such a large white oak tree could involve spraying the canopy with Bacillus thuringiensis (Bt), an organically registered bio-control from the ground or air.  Finding an arborist with a large enough sprayer would be a major challenge. Transitional aerial spraying for spongy moths, conducted by helicopter and fixed-wing aircraft, cannot spray a single tree. Ten acres is typically the smallest area that can be sprayed with aircraft. But that has changed since drones have become larger and their use in agriculture has grown.

Unmanned aerial vehicles (UAV) or 'drones' for pesticide application offer several advantages. Drones can provide precision targeting, ensuring accurate application directly onto affected areas. They are adaptable to small acreage and singular specimens, making them efficient for targeted treatments. Drones maneuver well in tight spaces, such as urban areas, reducing the risk of damage to nearby structures during application. Additionally, they contribute to reducing environmental impact by minimizing pesticide use and runoff. Finally, they are easy to transport from one treatment area to another.

Figure 3. Nozzles below rotary blades deliver insecticides for spongy moth treatment. Photo: Tom Butzler, Penn State

Figure 4. The drone's folding design facilitates its transportation to different sites. Photo: Vinnie Cotrone, Penn State

While calling ISA Certified Arborist in the area to locate a licensed applicator to treat the historic white oak, the Lewisburg Shade Tree Commission was given the name of CNY Drones and quickly discovered that they were working in the area and could treat the oak within a few days. The advantages of treating with a drone fit nicely into a management strategy for a spongy moth problem in Lewisburg. The 70-foot witness tree sits along a street just outside of the cemetery. The 255-year-old oak tree is the only surviving witness tree of a survey delineating borough property (Figure 2, right). Treating this tree from the ground, even with an organic biological control like Bt, would have caused lots of spray drift and residents' concerns along the streetside. Using a drone would allow a small amount of the bio-insecticide to be applied right in the canopy of the tree (Figure 1).

Rick Jordan, from CNY Drone Services in New York, brought his equipment to central Pennsylvania. He chose the Agras T30, a rotary sprayer with 16 spray nozzles, XR TeeJet Nozzles-11002 VS (Figure 3), and an 8-gallon spray tank. Its foldable design makes transport in the back of a truck easy (Figure 4). The battery lasts 8–10 minutes and can easily be switched out with a fully charged battery.

Jordan used Foray, with Bacillus thuringiensis subsp. kurstaki as the active ingredient and the surfactant Wind-Fall was added to reduce drift (Figure 5). The aerial application of about 1 gallon of the bio-insecticide was completed within about 2 minutes.

Figure 5. Worker mixing Bacillus thuringiensis subsp. kurstaki, which will be loaded into the drone’s spray tank. Note the Personal Protective Equipment (PPE) worn by the applicator. Photo: Vinnie Cotrone, Penn State

Figure 6. Utilizing drones for pesticide application via drones requires a touch more know-how than traditional ground-based methods. Photo: Vinnie Cotrone, Penn State

Video footage of drone pesticide application in Union Co, PA.

Applying pesticides with this equipment requires more expertise than ground-based methods (Figure 6). Certification is essential for applicators and the specific crops and use sites they'll treat. Category 06 certification was necessary in this instance, focusing on ornamental and shade trees. Additionally, obtaining an FAA Part 107 (Remote Pilot Certificate) license is crucial. This certification authorizes commercial drone flights in the United States, ensuring legal compliance. In addition, an FAA 137 Certificate is required. This governs the use of aircraft, including drones, to dispense or spray agricultural chemicals.