2003 Annual Report 4.What were the most significant accomplishments this past year? D. Progress Report: This report documents research conducted under a specific cooperative agreement between ARS and Ohio State University. Additional details of the research are in the report for the parent research project 3607-21620-006-00D, Biological, Microclimate, and Transport Processes Affecting Pest-Control Application Technology. In agricultural crop protection, to improve application efficiency and efficacy, fluorescent tracers are normally used to quickly and accurately determine amount of spray deposits and off-target losses. In cooperation with Erdal Ozkan, of the Ohio State University, five different fluorescent tracers have been investigated to determine influence of spray solutions with various pH values on the accuracy of fluorescent intensities to evaluate spray performances. The spray solutions with different pH values significantly influence fluorescent intensity for some tracers normally used in agricultural spray applications. Selection of spray solutions with in consistent pH values will result in inaccurate evaluation of spray performance and provide misinterpretive information on spray deposits and off-target sprays.