S18 - Session P4 - Characterizing spray deposition from variable- and constant-rate spray technologies: Implications for future optimization to target trunk and foliar pests

Authors: Lauren Fessler, Grace Pietsch, Wesley Wright, Heping Zhu, Xiaocun Sun, Amy Fulcher *

Nursery producers use multi-row blocks to increase their land area usage and efficiency; however, spray droplets reaching interior rows can be a challenge. An airblast sprayer (Storm 2000, Tifone) retrofitted with laser-guided, variable-rate technology was used to assess spray characteristics on multi-row blocks of 2.4m red maple trees using D6-DC25 and D10-DC46 hollow-cone nozzle tips. The sprayer was operated in variable-rate mode (VRM) (plant characteristics controlled each nozzle's output in real-time) and constant-rate mode (CRM) (all nozzles discharged the maximum output). Two 3-row blocks of trees were separated by an internal driveway and were sprayed either from external driveways only or external and internal driveways. Water sensitive paper (WSP) was wrapped at 3 heights around the trunk and water sensitive cards (WSCs) were placed in the canopy and on the ground in exterior and interior rows of each block. Another set of WSCs was placed at 3 heights beyond the block to assess drift. CRM applied 2,060 L⸱ha -1 and VRM applied 290 L⸱ha -1 ( P = 0.0047). For each card location, including ground and airborne drift, CRM coverage exceeded 30% and was greater than VRM ( P < 0.05). Coverage for canopy cards exceeded 40% when sprayed from both external and internal driveways and was greater than when sprayed from external driveways only ( P < 0.0001). For wraps, total coverage was greater in CRM (69.4%) than VRM (38.3%) ( P < 0.0001). For directional portions of WSPs, trees had greatest coverage on the side proximal to the sprayer (74.4%) and least coverage on the side distal to the sprayer (43.7%) ( P < 0.0001). If high coverage is needed around the entire trunk to control trunk-boring pests, spraying from the internal driveways may be necessary. For foliar applications, it may be possible to achieve adequate coverage and reduce volume by spraying from only external driveways or using VRM.