Relative efficiencies of experimental and conventional foliar sprayers and assessment of optimal LWA spray volumes in trellised wine grapes

Background: Leaf wall area (LWA) has been proposed as an appropriate dose expression for field testing of plant protection products (PPPs) applied via foliar spray in trellised grapes. However, its efficiency could change depending on the characteristics of the crop or the pesticide application equipment (PAE). Herein, three spray technologies were evaluated. A traditional air-assisted tractor-mounted sprayer was compared with two portable knapsack sprayers: a backpack mistblower and a backpack hydraulic sprayer. Trials were conducted in trellised wine grapes at three selected crop stages (BBCH 55, 65, 75) covering the main period of canopy development. In each canopy stage, leaf deposition and coverage were sampled for each technology. The tractor-mounted sprayer was working at 200 L ha^-1 of LWA spray volume for the earliest stage and 370 L ha^-1 for the other two. Three higher volume rates were used for backpack sprayers up to 800 and 1250 L ha^-1 for the mistblower and the hydraulic system, respectively.

Results: Optimal LWA spray volumes differed among application devices in terms of efficiency and uniformity of deposition on the canopy. The efficiency of each spray application also was conditioned by the spray volume.

Conclusion: LWA is useful for defining optimal spray volumes in trellised grapes. However, both canopy density and spray technology should be considered to assist this process. Field testing of PPPs and subsequent label recommendations should consider the relative efficiencies of corresponding experimental and conventional spray technologies. © 2021 Society of Chemical Industry.