2005 Annual Report 4d.Progress report. This report serves to document research conducted under a Specific Cooperative Agreeement between ARS and The Ohio State University. Additional details of research can be found in the report for the parent CRIS 3607-21620-006-00D Biological, Microclimate, and Transport Processes Affecting Pest Control Application Technology. (1) Fluorescent tracers provide a means of tracking spray movement when either environmental conditions or analytical techniques prohibit the use of active ingredients. Spray targets are typically washed with water to recover water soluble dyes. Stable analysis of fluorescence is essential to ensure accurate evaluation of pesticide spray application efficiency. In cooperation with H. Erdal Ozkan of The Ohio State University/OARDC, the fluorescent intensity of fluorescent tracers commonly used for the quantitative assessment of spray deposition and off-target loss was investigated with wash solutions over various pH conditions. For the water soluble tracers evaluated in this study, fluorescent intensity of Pyranine, Fluorescein and Tinopal was significantly influenced by the solution pH conditions; however, the effect was not the same for all tracers evaluated. Wash solution pH should be adjusted to above 8.43 instead of using purified distilled water only to minimize analytical errors. (2) Although considerable research has been done on effectiveness of low-drift nozzles for many years, answers to some questions are still unclear to applicators when selecting effective techniques to reduce spray drift. In cooperation with The Ohio State University/OARDC, wind tunnel experiments were conducted to assess ground spray deposits and airborne deposits with various air velocities for “low-drift” nozzles with open and sealed air intake holes, and conventional flat fan nozzles. Droplet sizes and spray patterns from all nozzles and drift retardants were measured with a laser imaging system and a portable spray patternator, respectively. There was no significant difference in both ground and airborne deposits for the “low-drift” nozzles with open and sealed air intake holes and conventional flat fan nozzles when their discharge flow rates were equal. Therefore, conventional flat fan nozzles when operated at low pressure could achieve the equal effectiveness in drift reduction potential as the “low-drift” nozzles.