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United States Department of Agriculture

Agricultural Research Service

Research Project: Pesticide Application Technologies for Spray-drift Management, Maximizing In-field Deposition, and Targeted Spraying

Location: Crop Production Systems Research Unit

Title: Environmental and spray mixture effects on droplet size represented by water sensitive paper used in spray studies

Authors
item Thomson, Steven
item Lyn, Margaret -

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 21, 2011
Publication Date: June 24, 2011
Citation: Thomson, S.J., Lyn, M.E. 2011. Environmental and spray mixture effects on droplet size represented by water sensitive paper used in spray studies. Transactions of the ASABE. 54(3):803-807.

Interpretive Summary: Aerial application of chemical can produce droplets of a wide range in size. Smaller droplets are much more prone drift off-target, creating a potential environmental concern. Water sensitive paper (WSP) cards are frequently used in the field to provide visual representation of droplet size for spray drift and deposition studies. Droplets collected on WSP spread out on the surface of the paper, and standard “spread factor” equations are used to compensate for spread. To date, no data have been presented to consider the effects of environmental conditions and formulation on droplet size represented by WSP. Experiments were conducted in a controlled environment chamber to determine these effects, and preliminary results showed that droplet size represented on WSP can vary as much as 40% depending on whether water or a surfactant mixture is used. Size of the droplet stain was only slightly influenced by changes in relative humidity.

Technical Abstract: Water sensitive paper (WSP) cards are frequently used to provide visual representation of droplet size and density for spray drift and deposition studies. Droplets collected on WSP spread out on the surface of the paper, and standard “spread factor” equations are used to compensate for spread to characterize actual droplet size. To date, no data have been presented to consider the effects of ambient conditions and formulation on droplet size represented by WSP. These data would be useful for creation of more accurate spread factor equations, and significant effects on droplet size could be modeled into new equations to account for these variables. A study was conducted using a newly constructed enclosed chamber that allows independent control of temperature (T) and relative humidity (RH) to determine the effects of T, RH, formulation, and droplet volume on droplet diameter as represented by WSP. Droplets of a known diameter were placed on several WSP cards using five mixtures of Domark® fungicide, Syl-Tac® surfactant, and water while RH, T, and droplet volume were varied at three levels each. The WSP were optically scanned to obtain droplet size. Statistical procedures were used to determine the effect of T, RH, droplet volume, and spray mixture on stain area, and a model was developed over the droplet size range applied. A useful relationship of the influence of ambient conditions was derived, which indicated a linear 0.24%/ 1% 'RH influence on stain diameter. The effect of mixture on stain size was significant at the 1% level, and use of a surfactant was seen to increase the average stain diameter on WSP by as much as 40% over the application of water alone.

Last Modified: 12/19/2014
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