Spray coverage profiles 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

Pecan (Carya illinoinensis) is an important specialty crop in the U.S.A., but yield is limited by several diseases and pests. In mature-tree pecan orchards, large air-blast sprayers are commonly used to apply the pesticides to control these 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 of sprayer setting parameters such as travel speed and spray volume rate on spray coverage on tall targets we set up a system (a simple vertical patternator) using a 19-m-tall pole with cards attached at eight height levels from 5 to 19 m above ground, allowing to determine the vertical distribution pattern of two air-blast sprayers with different air discharge systems. Spray was applied with a standard radial-flow air-blast sprayer during six treatments being combinations of two travel speeds: 2.4 and 3.2 km/h, and three spray volume rates: 470, 940 and 1970 L/ha, as well as with a focused air-flow system (a volute) sprayer during four treatments being combinations of two travel speeds: 2.4 and 3.2 km/h, and two spray volume rates: 470 and 940 L/ha. Results show that using a standard radial air-flow sprayer, application volume affected coverage at heights <= 17 m (higher volumes resulting in more coverage). Higher speed using a standard radial air-flow sprayer resulted in greater spray coverage, but was inconsistent with the focused air-flow system. Using a focused air-flow system more spray coverage occurred at >17 m compared to a standard radial air-flow sprayer. Spray coverage profiles affirmed the rapid decline in coverage with height using a standard radial air-flow sprayer. 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.