By John Fulton, Alan Leininger, Cori Lee
Spray drones have become a hot topic not only in Ohio, but globally. In 2022, the number of spray drone application services grew substantially across Ohio. The main focus has been on application of fungicides in wheat, corn, and soybeans along with the application of cover crops using the dry spreader box option in the fall. With labor shortages and other challenges, spray drones have become a tool to complement the existing ground and aerial application equipment. To date, there has been limited deposition testing of this new spray technology but there are researchers at U.S. institutions and agencies researching drift and efficacy.
At The Ohio State University, we initiated deposition testing in 2022 to address questions around this technology. A couple of projects were conducted at the field scale level with one occurring in central Ohio partnering with Integrated Ag Services and Syngenta to look at fungicide application in corn to understand coverage and droplet size from the two different modes of application.
This fungicide application project included three replicated treatments across a field with no fungicide, a ground applied treatment, and a drone applied treatment. Both the ground machine and drone applied fungicide product to corn above the canopy at the R1 growth stage in early August. The ground machine was a Hagie with 15-inch nozzle spacing across the boom using TeeJet 04 tips applying at a rate of 16 gallons per acre (GPA). The spray drone was a Hylio with a boom setup that was programmed to fly 10 feet above the corn canopy at 12 miles per hour applying a rate of 2 GPA. The drone was equipped with TeeJet TT11001 tips. Fungicide was applied around tassel in early August. It should be noted that the ground machine applied eight times the volume of the drone sprayer in this study, so it is expected that more product would be applied to the corn with the ground machine.
Prior to application, water sensitive cards were placed across the replicated areas. Cards were placed in four locations to understand deposition in the canopy. The locations included the top leaf, the ear leaf, two leaves above the ear leaf (Ear Leaf -2), and two leaves below the ear leaf (Ear Leaf +2). Once each application was completed, cards were collected with the location noted. These cards were then processed using a digitizing scanner to estimate coverage and droplet size then averaged by location on the corn stalk.
These results are not intended to evaluate which application method is better or more effective, but rather the spray volume and nozzle setup for each machine and the resulting coverage and median droplet size at four vertical positions within the corn canopy. In general, the percent coverage decreased for the ground machine from top to bottom with the canopy. The ground machine resulted in an average coverage of 9.4% with a median diameter of 89 µm at the ear leaf. Refer to the sample card for the ground machine as an illustration of the coverage and droplet size. The drone sprayer generated more consistent coverage from top to bottom with fairly consistent percent coverage vertically at the four card locations within the canopy. At the ear leaf, the drone sprayer, applying 2 GPA, averaged 0.8% coverage with a median diameter of 68 µm. While the drone had lower percent coverage at 2 GPA than the ground machine at 16 GPA, the drone provided more consistent coverage vertically within the corn canopy and had a much smaller droplet size. Foliar corn disease severity was very low in this trial. However, analysis indicated a significant yield difference with the treated treatments (ground and drone) having a 10.4 bushels per acre advantage over the zero fungicide treatments. This study represents one field comparison but also emphasized the need for more research to understand proper setups for drone sprayers for applying crop protection projects. Ohio State has plans for similar projects in 2023 including conducting nozzle testing for different drone sprayer setups.
We want to thank Evan Delk and Dave Scheiderer from Integrated Ag Services for partnering with us on this study. Keep up with the latest from the Ohio State Digital Ag team on their social media using @OhioStatePA on Facebook, Twitter, and Instagram or subscribe to our quarterly newsletter, the Digital Ag Download (go.osu.edu/DigitalAgDownload).
Dr. John Fulton is a Professor in the Food, Agriculture and Biological Engineering Department at Ohio State University and can be reached at firstname.lastname@example.org.
Cori Lee is a student research assistant in the Agriculture and Biological Engineering Department at Ohio State University.