Impact of trellising on spray coverage and spotted-wing drosophila infestation: comparing the rotating cross-arm trellis to the T-trellis

ISHS Acta Horticulturae 1388: XIII International Rubus and Ribes Symposium Impact of trellising on spray coverage and spotted-wing drosophila infestation: comparing the rotating cross-arm trellis to the T-trellis

Authors:	A.J. Cato, A. McWhirt, E. Henderson, R. Keiffer, L. Herrera
Keywords:	RCA, IPM, SWD, spray coverage, blackberry, Rubus subgenus Rubus
DOI:	10.17660/ActaHortic.2024.1388.35
Abstract: Cultural controls are often the cornerstone of effective and diversified pest management plans. The rotating cross-arm (RCA) trellis system in blackberry (Rubus subgenus Rubus) has exhibited the potential to impact pest management as the plant canopy is modified to consist of a flat plane of canes, possibly allowing for increased spray penetration, while also creating a less ideal environment for pests including spotted-wing drosophila (SWD) (Drosophila suzukii). The objective of this study was to evaluate the impact of trellis type (RCA vs. T-trellis) on spray coverage of leaves and berries, determine how varying spray volume affects spray coverage and ultimately determine the impact of spray volume on SWD infestation. ‘Ouachita’ blackberries following a split-plot design with the trellis type (RCA vs. T-trellis) as the split plot factors and spray volume as subplot factors were established in Arkansas, USA, at two different locations and treated with two different spray volume treatments in 2020 (280 or 560 L ha^‑1) with an air-blast sprayer and three different spray volumes (187, 375, and 560 L ha^‑1) in 2022 with a hand-held blower sprayer. Spray coverage was assessed using water sensitive spray cards for all treatment combinations in each year and were analyzed using SnapCard following a spray with water. Spray coverage was observed to be significantly higher in the RCA compared to the T-trellis in both years for berries. Additionally, a reduction in spray volume did not correspond to a significant decrease in spray coverage in the RCA trellis, while the T-trellis saw a large impact of decreased spray volume on leaf spray coverage. Fewer SWD larvae were observed in the RCA compared to the T-trellis, but it is unclear whether an increase in spray coverage was the only driving factor.
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