Spray coverage in pecan trees - results of spray deposition tests

Authors: Bock, Clive

Submitted to: Southeastern Pecan Growers Meeting Proceedings
Publication Type: Other
Publication Acceptance Date: 2/22/2020
Publication Date: 2/22/2020
Citation: Bock, C.H. 2020. Spray coverage in pecan trees - results of spray deposition tests. Southeastern Pecan Growers Meeting Proceedings. 1-20.

Interpretive Summary: Scab (caused by Venturia effusa) is the major disease of pecan in the southeastern US. In epidemic seasons yield loss is substantial in susceptible cultivars. Fungicide coverage from air-blast sprayers declines with height in the canopy. How application volume (L/ha), speed (kph) and use of a volute influence deposition (% area) at different heights is unknown. We quantified deposition using kromekote cards and vision pink dye at different heights and speeds in tree canopies. A 3785 L air-blast sprayer was used at 468, 935 and 1871 L/ha at 2.4 and 3.2 kph. A volute was also tested at 468 and 935 L/ha at 2.4 and 3.2 kph. Speeds tested did not affect deposition. Higher volumes resulted in significantly greater deposition in the canopy, but most of that increase was at heights <12.5 m. Use of a volute resulted in more uniform deposition at all heights, but numerically or significantly more at heights >15 m. The study demonstrates that higher volumes result in more deposition, but the effect declines rapidly with height. Volutes may increase deposition at heights >15 m.

Technical Abstract: Scab (caused by Venturia effusa) is the major disease of pecan in the southeastern US. In epidemic seasons yield loss is substantial in susceptible cultivars. Fungicide coverage from air-blast sprayers declines with height in the canopy. How application volume (L/ha), speed (kph) and use of a volute influence deposition (% area) at different heights is unknown. Deposition was quantified using kromekote cards and vision pink dye at heights of 5, 7.5, 10, 12.5 and 15 m in tree canopies. A 3785 L air-blast sprayer was used at 468, 935 and 1871 L/ha at 2.4 and 3.2 kph. A volute was also tested at 468 and 935 L/ha at 2.4 and 3.2 kph. Nozzles were selected to provide proportionally similar volumes to the upper and lower canopy positions at set speeds. Speeds tested did not affect deposition. However, without a volute, higher volumes resulted in significantly greater deposition in the canopy, but most of that increase was at heights <12.5 m. Although significant differences existed at =12.5 m, they were numerically small. In this study use of a volute resulted in more uniform deposition at all heights, but numerically or significantly more at heights >15 m, but less at heights <15 m compared to other treatments. The study demonstrates that higher volumes result in more deposition, but the effect declines rapidly with height. Volutes may increase deposition at heights >15 m.