Spray coverage from pecan air-blast sprayers, with a radial air-flow and a volute-generated focused air-flow, as affected by forward speed and application volume

Authors: Bock, Clive; Cottrell, Ted; HOTCHKISS, MICHAEL - Retired ARS Employee

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2023
Publication Date: 3/17/2023
Citation: Bock, C.H., Cottrell, T.E., Hotchkiss, M.W. 2023. Spray coverage from pecan air-blast sprayers, with a radial air-flow and a volute-generated focused air-flow, as affected by forward speed and application volume. Crop Protection. 168:106234. https://doi.org/10.1016/j.cropro.2023.106234.
DOI: https://doi.org/10.1016/j.cropro.2023.106234

Interpretive Summary: Pecan (Carya illinoinensis) is an important specialty crop in the U.S.A. Several diseases and pests limit production and require frequent pesticide application to ensure yield is not compromised. Scab (caused by Venturia effusa) and aphid-elicited leaf chlorosis (caused by Melanocallis caryaefolia) are examples. In mature-tree pecan orchards, large air-blast sprayers are commonly used to apply the pesticides to control diseases and pests. The spray coverage, deposition and profiles are poorly defined under the range of application scenarios, limiting the recommendations that can be provided to growers to maximize control while minimizing input costs. To explore effects on spray coverage we set up a system (a simple patternator) using a 19-m-tall pole with spray cards to characterize coverage. Spray was applied at 2.4 km/h and 470 L/ha, 2.4 km/h and 940 L/ha, 2.4 km/h and 1870 L/ha, 3.2 km/h and 470 L/ha, 3.2 km/h and 940 L/ha, and 3.2 km/h and 1870 L/ha without a volute, and at 2.4 km/h and 470 L/ha, 2.4 km/h and 940 L/ha, 3.2 km/h and 470 L/ha, and 3.2 km/h and 940 L/ha, with a volute. Without a volute, application volume affected coverage at heights =17.2 m (higher volumes resulting in more coverage). Speed had a relatively minor effect. Volute use resulted in more spray coverage at >17.2 m compared to non-voluted sprayers. Regression analysis indicated a negative relationship between spray coverage and height for sprayers without a volute, but a positive effect with height when a volute was used. Spray coverage profiles affirmed the rapid decline in coverage with height without a volute. The results may help guide decisions on volute use, spray volume, and spray partitioning to different parts of the canopy to improve spray profile characteristics for applying more uniform spray coverage to mature pecan tree canopies.

Technical Abstract: Pecan is an important crop in the U.S.A. Several diseases and pests limit production and require frequent pesticide application to ensure yield is not reduced. Scab, a fungal disease and aphids are examples. In mature-tree pecan orchards, large air-blast sprayers are commonly used to apply the pesticides to control diseases and pests, but spray coverage, deposition and profiles are poorly defined. We set up a system using a 19-m-tall pole with spray cards to characterize coverage with height. Spray was applied at 2.4 km/h and 470 L/ha, 2.4 km/h and 940 L/ha, 2.4 km/h and 1870 L/ha, 3.2 km/h and 470 L/ha, 3.2 km/h and 940 L/ha, and 3.2 km/h and 1870 L/ha without a volute, and at 2.4 km/h and 470 L/ha, 2.4 km/h and 940 L/ha, 3.2 km/h and 470 L/ha, and 3.2 km/h and 940 L/ha, with a volute. Without a volute, greater application volume increased coverage at heights =17.2 m. Volute use resulted in more spray coverage at >17.2 m compared to non-voluted sprayers. Speed had a relatively minor effect. Spray coverage profiles affirmed a rapid decline in coverage with height without a volute. The results will help guide decisions on volute use, spray volume, and spray partitioning to different parts of the canopy to improve spray profile characteristics for applying more uniform spray coverage to mature pecan tree canopies.