Evaluation of Handgun and Broadcast Systems for Spray Deposition in Greenhouse Poinsettia Canopies

Authors: Derksen, Richard; Ranger, Christopher; CANAS, L - The Ohio State University; Locke, James; Zhu, Heping; Krause, Charles

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2010
Publication Date: 1/10/2010
Citation: Derksen, R.C., Ranger, C.M., Canas, L.A., Locke, J.C., Zhu, H., Krause, C.R. 2010. Evaluation of Handgun and Broadcast Systems for Spray Deposition in Greenhouse Poinsettia Canopies. Transactions of the ASABE. 53(1): 5-12.

Interpretive Summary: In the 2007 reporting year, consumers purchased potted flowering plants for indoor or patio use with a value of $661 million, 6 percent more value than in 2006. Poinsettia sales alone accounted for nearly 50 million pots. Producers make pesticide application decisions in part based on consumer demand for high quality and blemish free crops. Greenhouse structures pose unique pest management challenges that limit application equipment choices. Interior support structures as well as small walkways and alleys limit the size of equipment and maneuverability. The objective of this research was to determine differences in performance between different sprayers used to treat mature poinsettias and differences in the fate of the spray within the canopy with the aim to determine which techniques produced highest spray retention on the abaxial surface of leaves. A bench-top trial was conducted using a mature poinsettia canopy in a greenhouse. Spray retention was characterized by measuring spray deposits on nylon screen targets that were placed on the abaxial surface of leaves in the upper and lower part of the canopy. Treatments included a handgun used to apply different spray volumes at different pressures, a boom with twin-fan nozzles, and an air-assisted nozzle delivery system. Despite the relatively short distance between the upper and lower canopy sampling sites on the poinsettia plants in this study, significant differences in underleaf spray deposits were noted by elevation for most treatments. Statistically, there were no significant differences between treatments at either canopy elevation. Greater variability in mean spray deposits were noted at the upper canopy elevation compared to the lower canopy elevation. Overall, spray volume, as changed by application speed of the handgun treatment, did not significantly affect spray deposit at either canopy location. Increasing operating pressure by a factor of four did significantly change the atomization characteristics and droplet velocity of the handgun spray stream resulted in higher mean deposits in the upper canopy, they were not significantly greater than the mean deposits of the lower pressure handgun treatments. Higher operating pressure also did not improve canopy penetration and abaxial leaf surface spray deposits. While air-assisted delivery increased mean deposits over a non-air-assist boom treatment, the results were not significantly different. Overall, variability of results within some of the treatments was quite high. The high pressure handgun treatment produced the greatest variability across target plants. Broadcast applications with the TwinJet Boom nozzles and the Air-assist treatment produced lower variability in spray deposits. Variability could be important in terms of ensuring uniform results, especially if contact materials are being applied or if plant injury to sensitive ornamental plants could result from over application. Ultimately, distribution of spray by a handgun is going to be influenced by the skill of the operator and should take measures to ensure adequate application training. Producers will benefit from means to make more uniform applications and applying more predictable amounts of treatments in the target area.

Technical Abstract: Accurate placement of these pesticides in controlled environment greenhouse settings is critical for optimizing efficacy as well as for minimizing plant injury and off-target movement. However, there are few recommendations on how to make efficient applications of pesticides which provide the desired efficacy with the minimum amount of pesticide. Frequently handgun applications are made from one side of a treatment area but have been shown to result in significant differences in deposits between the side of the plant facing the spray stream and the opposite side. Broadcast spraying over the top of the canopy may improve spray distribution across the canopy. The objectives of this research were to determine how handgun spray volume and pressure influence underleaf spray deposits and how broadcast applications with twin-fan nozzles and flat-fan nozzle using air-assisted delivery affect underleaf spray deposits. A bench-top trial was conducted using a mature poinsettia canopy in a greenhouse. Sprayer treatments were used to a apply tank mix of BSF fluorescent tracer. Artificial targets were fixed to the abaxial surface of leaves in the upper and lower part of the canopy. Trials revealed significant differences between the amount of spray found on upper and lower canopy target areas. Handgun nozzle pressure was a more significant factor in depositing material on the abaxial surface of leaves than changing application rate. A boom system using dual-orifice twin-fan nozzles did not treat abaxial surface of leaves differently from the handgun applications. The flat-fan treatment with air-assisted delivery produced the highest mean deposits on the abaxial surface of leaves in the lower canopy area but overall there were no statistical differences in lower canopy deposits between treatments. The large amount of variability observed in these trials between test plants demonstrates the difficulty ornamental producers have targeting pesticide placement in the canopy like the abaxial leaf surfaces lower in the canopy. Variability in deposits could significantly impact efficacy and pest management strategies as well as pesticide choice.