CROP PROTECTION AND PRODUCTION STRATEGIES FOR HORTICULTURAL CROPS
Location: Application Technology Research Unit
Title: Greenhouse Evaluation of Air-Assist Delivery Parameters for Mature Poinsettias
Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 18, 2010
Publication Date: December 1, 2010
Citation: Derksen, R.C., Ranger, C.M., Canas, L.A., Zhu, H., Krause, C.R. 2010. Greenhouse evaluation of air-assist delivery parameters for mature poinsettias. Applied Engineering in Agriculture. 26(6):947-953.
Interpretive Summary: In 2008, poinsettia sales alone accounted for nearly $154 million in wholesale sales making them the top selling potted flower. The threat to crop quality from insect pests such as aphids and whiteflies feeding on the undersides of leaves is crucial to the ornamental industry. A study was design to look at a range of air-assist application parameters that could affect spray deposition on the underside of leaves in a mature poinsettia canopy. All treatments applied tank mix of water and a fluorescent tracer. Artificial targets consisting of nylon screen with 50% opening were affixed to the underside of leaves in the upper and lower elevation of mature poinsettias. A five-port, air-assist nozzle with flat fan spray tip inserts was used as the delivery device. There was considerable variability in the results. Average spray deposit on the underside of leaves in the lower elevation of the poinsettia canopy were not statistically different between the 18 different application treatments. However, there was a significant three-way interaction in the upper elevation canopy between Air Outlet Speed, Travel Speed, and Nozzle Flow Rate. Pairwise comparisons showed that the highest Nozzle Flow Rate (1.17 L m-1) and slowest Travel Speed (3.2 km h-1) tended to produce the highest spray deposits in the upper elevation. The lowest Nozzle Flow Rate (0.39 L m-1) and the highest Travel Speed (6.4 km h-1) tended to produce the lowest underside leaf spray deposits. Higher deposits at the slower Travel Speed were likely due to the increased air velocity and turbulence in the canopy. There were indications that spray deposits on the undersides of leaves increased with increasing Air Outlet Speed which also likely increased turbulence in the canopy. However, Air Outlet Speed appeared to be a more significant factor in the upper elevation than the lower elevation. The dense nature of the mature poinsettia canopy and relatively large leaves likely dissipated the energy of the air and significantly reduced the amount of turbulence deeper in the canopy. Across all Air Outlet Speeds, for the range of application rates evaluated, spray deposits tended to increase with increasing application rate. However, droplet size was not evaluated as an independent factor and could also play a role in deposition. Producers and manufacturers can use these results to aid in design and selection of spray delivery equipment to maximize pesticide deposits on the underside of leaves to ensure efficacious application.
Understanding the performance characteristics of application equipment is important for helping make the most efficacious applications. While handguns making high volume applications are common in greenhouse production, it is difficult to achieve uniform distribution of product in a timely manner. Broadcast applications made using air-assistance can help aid canopy penetration and the volume of carrier required to make applications. The objectives of this research were to determine how air-assist sprayer application parameters influence spray deposits on the undersides of leaves in a mature poinsettia canopy. Bench-top trials were conducted using a motorized boom inside a greenhouse to treat a mature and dense poinsettia canopy. Sprayer treatments applied a tank mix of water and fluorescent tracer. Nylon screen targets were secured to the underside surfaces of leaves in the upper and lower elevation of target plants. A five-port, air-assist nozzle with flat fan nozzle tips was used to make the applications. Three Air Outlet Speeds, two Travel Speeds, and Three Nozzle Flow Rates were evaluated. Each treatment was replicated three times. Spray deposits were highly variable. Upper elevation spray deposits were significantly greater than lower elevation deposits. Higher Air Outlet Speed (36.0 m s-1), slower Travel Speed (3.2 km h-1), and Higher Nozzle Flow Rate (1.17 L m-1) tended to produce higher sprayer deposits on the underside surfaces of leaves. The combination of Travel Speed and Nozzle Flow Rate that produced the highest application rate (900 L ha-1) produced the highest deposits. However, the main effects produced no significant differences in spray deposits in the lower canopy area. Further improvements in directing sprays or providing canopy turbulence are necessary to improve deposition and management of insect pests feeding on the underside of poinsettia leaves.