NAAA eNewsletter - 07/07/2022

A field study by Alan Corr from Agri-Spray Consulting, Ken Ferrie from Crop-Tech Consulting and Matt Gill from the University of Illinois at Urbana-Champaign examined deposition from aerial applications in a corn canopy. The flying was done by David Baurer with Palmer Flying Service in Manito, Illinois. The project was sponsored by Bayer Crop Science. The purpose of the study was to identify potential causes for some of the streaking seen in corn fungicide applications from the 2021 season.

Several treatments were examined with a single replication, including different nozzle setups and application heights. For each treatment, an AT-802 made two adjacent passes with a 90-foot swath width. Spray coverage was captured on white sampling cards located in the top, ear level and lower parts of the corn canopy. The corn was just entering the VT growth stage. Sampling began at the center of the first pass and went to the center of the second pass to see if canopy penetration and deposition were reduced in the zone of overlap between the two passes.

Data for all the treatments showed high variability across the 90-foot swath, which is to be expected for sampling at a 5-foot interval in a plant canopy where much of the spray is intercepted by plant tissue. The results do show that with flat fan nozzles and the aircraft operated with a boom height of around 12 to 15 feet above the canopy, there was no indication of a reduction in spray coverage and deposition in the zone of spray overlap between the two passes. This was true for all three sampling locations in the canopy: top, ear level and lower parts of the canopy.

Flying much lower, with the wheels almost in the canopy, appears to have caused a roughly 15-foot gap with reduced spray deposition in the zone of overlap between the two passes. This reduction was found at all three sampling heights in the canopy. This reinforces the fact that aerial applicators need to fly at an appropriate height for their aircraft. Flying too low prevents the spray pattern from developing to its full width. It can also greatly reduce uniformity within the pattern itself. If you have had your aircraft pattern-tested at an Operation S.A.F.E. fly-in, do not expect to fly it at a much lower height in the field and use the same swath width.

When switching to straight stream nozzles, there was a gap in deposition between the two passes. This gap is to be expected, however, as the same target swath width of 90 feet was used by the pilot. Based on the results of this study, a 75-foot swath width would have been more appropriate for these nozzles. Straight stream nozzles create a larger droplet size that typically results in an overall narrower spray pattern. This trend has also been seen at numerous Operation S.A.F.E. fly-ins. When switching nozzles from flat fans to straight streams, it is critical to understand that swath width will have to be reevaluated and likely reduced. Have your spray pattern analyzed at an Operation S.A.F.E. fly-in to determine its optimum swath width.