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ARS Home » Southeast Area » Byron, Georgia » Fruit and Tree Nut Research » Research » Publications at this Location » Publication #409493
Research Project: Healthy, Sustainable Pecan Nut Production

Location: Fruit and Tree Nut Research

Title: A Comparison of a Standard Radial Airflow and a Double-Volute-Generated Focused Airflow Air-Blast Sprayer to Control Scab in Tall Pecan Trees

Author
item Bock, Clive
item PAULK, BUCK - Shiloh Pecan Farms, Inc
item Hotchkiss, Michael - Mike

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Pecan is a valuable crop in the southern United States. The disease scab caused by the fungal pathogen Venturia effusa causes severe yield loss in widely grown susceptible cultivars. Control requires 10 to 15 or more fungicide applications a season. Spray application relies on large air-blast sprayers (SS). Some SS have been adapted to include a volute on one side to project spray higher into the canopy due to a decline in coverage with height. Recently, a grower-designed double-volute system air-blast sprayer (DVS) was assessed for scab control and spray coverage compared to an SS. Over three seasons, on foliage and fruit scab control was either equal too, or superior using the DVS sprayer. There were no discernible gradients in scab severity with either sprayer in 2017, but in 2018 the difference was significant, with the DVS having a shallower gradient, and in 2019 the DVS slope was numerically less steep compared to the SS. Mature fruit weight was significantly greater on trees treated using the DVS compared to the SS in 2017 and 2018 but was not different in 2019. Spray coverage studies showed that the DVS sprayer had significantly more coverage at heights >13.8 m (up to 19.0 m) compared to coverage using the SS. The slope in decline of spray coverage with height was significantly shallower with the DVS sprayer, and spray profiles reflected these differences. Thus, disease control was most often improved overall when using the DVS, and the DVS provided greater spray coverage at heights >13.8 m when compared to the SS sprayer. The DVS design may offer economical, superior scab control in pecan orchards where trees are >13.8 m tall.

Technical Abstract: Pecan (Carya illinoinensis) is a valuable crop in the southern United States. Scab (caused by Venturia effusa) is a major biotic constraint to pecan production in the southeastern region and requires 10 to 15 or more fungicide applications for control. Spray application relies on large standard orchard radial airflow air-blast sprayers (SS). Some SS have been adapted to include a volute on one side to project spray higher into the canopy due to a decline in coverage with height. Recently, a grower-designed and engineered double-volute-generated focused airflow air-blast sprayer (DVS) was assessed for scab control and spray coverage compared to an SS. Over three seasons, on foliage and fruit scab control was either equal too, or superior using the DVS sprayer. On mature fruit, in 2017, scab severity on the control was 9.07, the DVS was 0.19, and the SS was 0.24%, respectively; in 2018 severity was 84.4, 18.4 and 29.1%, respectively; and in 2019 was 32.7, 7.0 and 11.6%, respectively. There were no discernable gradients in scab severity with either sprayer in 2017, but in 2018 the difference was significant, with the DVS having a shallower gradient, and in 2019 the DVS slope was numerically less steep compared to the SS. Mature fruit weight was significantly greater on trees treated using the DVS compared to the SS in 2017 and 2018 but was not different in 2019. Spray coverage studies showed that the DVS sprayer had significantly more coverage at heights >13.8 m (up to 19.0 m), ranging from 18.4 to 14.1%, compared to coverage using the SS, which ranged from 7.9 to 2.9%. The slope in decline of spray coverage with height was significantly shallower with the DVS sprayer, and spray profiles reflected these differences. Thus, disease control was most often numerically or statistically improved overall when using the DVS, and the DVS provided greater spray coverage at heights >13.8 m when compared to the SS sprayer. The DVS design may offer economical, superior scab control in pecan orchards where trees are >13.8 m tall.