2004 Annual Report 4.What were the most significant accomplishments this past year? D. Progress Report: This report serves to document research that was conducted under a Specific Cooperative Agreement between ARS and H. Erdal Ozkan of The Ohio State University/Ohio Agricultural Research and Development Center. 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. 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. 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. A single droplet generator has been under development. Preliminary results indicated that the droplet generator has capability to produce a single droplet from 100 µm to 1000 µm diameter or larger with wide range of liquid viscosity. The completion of development of the droplet generator will provide research tools to determine the optimal droplet size and chemical dosage to effectively control insects, diseases and weeds.