RESUMO
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 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%, on the DVS was 0.19%, and on 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 trees height 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. Disease control was 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.
