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Title: Spray characterization of thermal fogging equipment typically used in vector control

item Hoffmann, Wesley
item Fritz, Bradley - Brad
item Lan, Yubin
item Huang, Yanbo
item Quinn, Brian

Submitted to: Journal of the Mosquito Control Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/2/2008
Publication Date: 12/20/2008
Citation: Hoffmann, W.C., Walker, T.W., Fritz, B.K., Gwinn, T., Smith, V.L., Szumlas, D., Lan, Y., Huang, Y., Sykes, D., Quinn, B.P. 2008. Spray characterization of thermal fogging equipment typically used in vector control. Journal of the American Mosquito Control Association. 24:550-559.

Interpretive Summary: Thermal fogging sprayers are often used to apply products for the control of human disease vectors, such as mosquitoes and flies. The selection and setup of these machines significantly affects the level of control achieved during an application. The distribution of droplet sizes produced by eleven different machines was evaluated with five commonly-used insecticides. Most of the fogger sprayers produced droplets between 3 and 15 microns, which is the desired size range of a fogging spray; however, some of the sprayers generated droplets over 50 microns in size, which meant that not all of the sprayers would be classified as fogging sprayers. Results from this study allow users of these sprayers to confidently select the sprayer and operational parameters that best fit their application situation.

Technical Abstract: The generation of insecticide laden fogs provides an effective method for controlling flying insects. One of the critical factors affecting the effectiveness of a thermal fogging application is the generation of droplets that will remain aloft in the fogging cloud and moves into the area where the insects are located. Droplet size spectra from different sprayers were measured by a laser diffraction instrument and Teflon-coated slides and the results are reported. The information presented can be used by applicators to select the sprayer that produces the droplet size spectra needed for their particular application situation. The objectives of this work were to present not only information on spray system droplet size generated by different sprayers, but to compare methodologies by which other similar systems can be evaluated and give applicators sprayer system performance data. A total of 56 replicated spray tests, comprised of 11 sprayers and five pesticides were completed for this study. There was a wide range in the droplet size spectra produced by the different sprayers tested. The volume median diameter (DV0.5) measurements for the sprays diluted in diesel ranged from 2.6 µm to 75.5 µm depending on the sprayer and the %Vol<20µm ranged between 12.0-100%. The DV0.5 measurements for the sprays diluted in water ranged from 27.9 µm to 59.9 µm and the %Vol<20µm ranged between 8.5-30.7%. The cold fogging equipment tested generated spray clouds with DV0.5 around 100 µm and would not be considered desirable for vector control sprays. The droplet sizes measured by the swinging slide method did not consistently match the droplet sizes measured by the laser diffraction instrument. Based on these trials, the use of the slinging slide method for sampling thermal fog sprays is not recommended without additional study examining the relationship between laser diffraction based droplet size measurements and swinging slide.