Effects of Spray Release Height and Nozzle/Atomizer Configuration on Penetration of Spray in a Soybean Canopy

Authors: Thomson, Steven; Young, Lawrence; Bright Jr, Jerry; Foster, Phelesia

Submitted to: National Agricultural Aviation Association Meeting
Publication Type: Proceedings
Publication Acceptance Date: 12/10/2007
Publication Date: 12/10/2007
Citation: Thomson, S.J., Young, L.D., Bright Jr, J.R., Foster, P.N., Poythress, D.D. 2007. Effects of Spray Release Height and Nozzle/Atomizer Configuration on Penetration of Spray in a Soybean Canopy. Preliminary Results. National Agricultural Aviation Association Meeting, Washington, DC. AA07-008

Interpretive Summary: The deleterious effects of fungus on soybean health and yield have been well documented. Soybean rust is a serious problem that is beginning to show its effects in the United States. In order to combat this problem with aerial application, the best nozzle atomizer setups need to be evaluated for their effectiveness for within-canopy spray coverage of fungicide. This can also include evaluation of spray mixes and spray application heights. A preliminary study was conducted to evaluate three different nozzle/atomizer configurations on agricultural aircraft for canopy coverage and penetration. Deposition was evaluated by collecting spray droplets on water sensitive cards positioned above the soybean canopy. Spray was applied at three different altitudes, and the highest coverage within the soybean was noted for the Accuflo low drift nozzle in this preliminary study, across all altitudes. This trend was noted by imaging spray droplets on cards using a lab-mounted camera and image analysis. The Micronair atomizer operates by propeller to distribute spray, and smaller droplets were observed on spray cards than expected. Smaller droplets would be prone to drift and evaporation, and this may have caused percent coverage to be somewhat less from the Micronair atomizers. For subsequent tests, propeller blade angle for the Micronair will be increased by 10 to 15 degrees to promote larger droplets. Deflectors also may be used for the Micronairs, as this is a recommended adjunct for improving spray penetration. Different spray formulations and spray rates will also be evaluated, along with altitude and nozzle type.

Technical Abstract: Preliminary experiments were conducted using three nozzle/atomizer configurations to determine spray characteristics and relative penetration in a soybean canopy. Water was applied at three different spray release heights in a random sequence using an Air Tractor 402-B agricultural aircraft. Sampler stands were placed at twenty-four locations in the field with water sensitive paper (WSP) cards clipped onto stands just above the canopy and one foot off the ground on stands within the canopy. Weather data were recorded using two different stations on-site and wind was predominantly from the west and parallel to the direction of spray runs. Spray nozzles and atomizers compared were the Micronair AU5000, Accuflo (64 needle 0.020 opening), and CP-07. The three nozzles/atomizers were configured for a spray rate of 2 gallons/acre. A total of 54 runs were made over three days, and 18 of those runs (two complete replications; east to west runs) were analyzed for this preliminary study. Spray cards were scanned and analyzed using an image analysis system and programmed analysis macros written for SigmaScan software. Results indicated Volume Mean Diameter (VMD) within the expected ranges from published data for the CP nozzles. Statistical analysis was then performed. Altitude and Nozzle time Altitude interaction were significant effects on coverage at the 0.01 and 0.07 significance levels, respectively for the top cards. Nozzle type was not a significant effect for the top cards, but was significant at the 0.01 level for the bottom cards. Altitude alone had no obvious effect on coverage for the bottom cards, although it had an effect for the top cards. The highest percentage area of coverage was observed from the Accuflo nozzles, especially for the bottom cards. Average spray coverage from the Accuflo nozzles was 1.5 times higher than coverage from the CP nozzles or Micronair atomizers for the bottom cards within the canopy. The Micronair atomizer showed a smaller average VMD than expected (181 microns), and some of the finer droplets could have drifted or evaporated before reaching the cards. For subsequent tests, propeller blade angle for the Micronair atomizers will be increased by 10 to 15 degrees to promote larger droplets. Deflectors also may be used for the Micronair atomizers, as this is a recommended adjunct for improving spray penetration. Different spray formulations commonly used for control of soybean rust and spray rates will be evaluated.