Characteristics of Spray Coverage from Large Pecan Orchard Air-blast Sprayers

Authors: Bock, Clive; Cottrell, Ted; Hotchkiss, Michael - Mike

Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/9/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Pecan is a tall orchard crop cultivated in the U.S. for its nuts. It is challenging to apply pesticides due to the height of the trees (15-25 m tall). Air-blast sprayers are typically used to apply sprays, and rely on fans to power the spray towards the upper canopy, but little is known regarding how effective the sprayers are at providing good coverage to protect the tree. We performed a series of tests to determine effects of spray volume, speed and use of a volute on spray coverage using spray cards positioned on a 20 m pole at heights of 5, 7, 9, 11, 13, 15, 17, and 19 m. Spray was applied without a volute at 2.4 or 3.2 km/h and 470 L/ha, 940 L/ha, and 1870 L/ha, and with a volute at 2.4 km/h or 3.2 km/h and 470 L/ha and 940 L/ha. Spray coverage on cards was measured using image analysis. Without a volute there was greater coverage at 5 m compared to 19 m. Benefits of high volume declined rapidly with height, and at 19 m the differences between volumes were small. Speed affected coverage, but less than volume. Higher speeds resulted in more coverage. When a volute was used coverage was greater at 19 m compared to 5 m. The results confirm previous studies on the effect of volume and speed on spray coverage in pecan tree canopies and further illustrate the limitations of orchard air-blast sprayers for spraying tall pecan trees.

Technical Abstract: Pecan (Carya iliinoinensis) is a particularly tall orchard crop. Achieving adequate coverage with sprays throughout the canopy profile is challenging. Air-blast sprayers are typically used to apply sprays from the ground. We performed a series of tests to ascertain the effects of spray volume, speed and use of a volute on characteristics of spray coverage in the absence of a tree canopy. Kromekote spray cards were positioned on a 20 m pole at heights of 5.0, 7.2, 9.4, 11.6, 13.8, 15.0, 17.2, and 19.0 m. Spray with Vision Pink dye for visualization was applied without a volute at 2.4 or 3.2 km/h and 470 L/ha, 940 L/ha, and 1870 L/ha, and with a volute at 2.4 km/h or 3.2 km/h and 470 L/ha and 940 L/ha. Spray coverage on cards was measured using image analysis. For those sprays applied without a volute there was greater coverage at 5 m compared to 19 m. But despite more coverage with higher volume, the effect was not constant with height as the difference in coverage between volumes applied declined with height, and at 19 m the differences among treatments were negligible and inconsistent. The effect of speed was relatively small compared to volume, and also not consistent at different heights. However, the volute-based treatments had greater coverage at 19 m compared to 5 m, although the effect was minimal with 470 L/ha. At 940 L/ha spray coverage was greater, particularly at heights greater than 13.8 m. Use of a volute at spray volumes less than 940 L/ha will be marginal. The results confirm previous studies on the effect of volume and speed on spray coverage in pecan tree canopies and further illustrate the limitations of orchard air-blast sprayers for spraying tall pecan trees.