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Title: Spray Delivery by Air Curtain and Axial Fan Orchard Sprayers to Nursery Trees

item Derksen, Richard
item Krause, Charles
item Brazee, Ross

Submitted to: Journal of Environmental Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2004
Publication Date: 3/1/2004
Citation: Derksen, R.C., Krause, C.R., Fox, R.D., Brazee, R.D., Zondag, R. 2004. Spray Delivery by Air Curtain and Axial Fan Orchard Sprayers to Nursery Trees. Journal of Environmental Horticulture. 22(1):17-22.

Interpretive Summary: In 2001, the nursery industry generated an estimated $12 billion in farm gate sales. Consumer demand is requiring the nursery industry to increase production while maintaining tighter controls over production techniques, especially those related to environmental stewardship. The proximity of many nursery production sites to urban areas increases the need for producers to be aware of the fate of spray materials they apply. To better understand the performance of sprayers that could be used to treat tree crops, an experiment was designed to study the fate of spray on the target crop as well as on the ground near the target crop. A conventional, axial-flow fan sprayer (DW) and an experimental, cross-flow fan sprayer were used to apply tank mixes containing food coloring and a copper-based fungicide. The target crop consisted of four year old, multi-stem, red maple trees. There were no significant differences in the overall levels of canopy deposits produced by either air delivery technique. Both sprayers produced deposits that were approximately four times higher on the side of the treatment row nearer the sprayer than the opposite side of the treatment row. Despite no differences in mean spray deposits in the canopy, the air curtain sprayer produced ground deposits two times higher than the conventional axial fan sprayer between the first and second downwind rows of the primary treatment row. These results show nursery tree producers and other needing to spray trees that uniform treatment requires spray delivery from both sides of a row. This research also benefits tree producers by illustrating means to improve the uniformity of deposits vertically through a tall canopy. However, it also illustrates to equipment operators the need to match the air delivery system to the canopy being treated to minimize off-target deposits.

Technical Abstract: More efficacious applications and greater sensitivity to the fate of chemicals are forcing nursery farm managers to understand best management practices associated with pesticide delivery equipment. These experiments were designed to identify the fate of spray in the canopy and near the target tree row in a commercial nursery production area. An experimental air curtain (CF) fan sprayer and a conventional, axial fan sprayer (DW) were used to make a single-pass treatment of one row of four year old, multi-stem, red maple trees, Acer rubrum L. Food coloring and a copper-based fungicide were tank mixed and applied to the target row. Spray targets consisting of untreated leaves placed in the canopy and plastic tape were replaced after each treatment. Colorimetry was used to assess leaves of deposits on foliar and ground targets. Electron microscopy was used to assess spray deposit morphology on artificial targets. Results of the tests indicate that the air curtain sprayer produced more uniform deposits vertically but not higher mean deposits than the traditional orchard type sprayer. The air curtain sprayer also produced somewhat higher ground deposits downwind of the treatment area. There were no differences in spray coverage between sprayers despite differences in the droplet spectrum produced by each sprayer. Evidence from the coverage and ground target samples indicates that the fans on the air curtain sprayer may need to be slowed to reduce air speed to retain more spray within the tree canopy. As operated, neither of the sprayers can be expected to produce uniform spray deposits around the nursery stock if treatments are made from one side of the row only. Canopy and ground target deposits indicate that alternate row spraying may not produce uniform deposits across two tree rows.