2004 Annual Report 4.What were the most significant accomplishments this past year? D. Progress Report: This report serves to document research conducted under a specific cooperative agreement between ARS and the State of California, Dept. Food & Agriculture. Additional details of research can be found in the report for the parent CRIS 1920-22000-030-00D, "Evaluation and Characterization of Plant Pathogens for Biological Control of Weeds". Yellow starthistle (YST, Centaurea solstitialis) infests more than 14 million acres in the state of California, and it is considered a weed of importance in several other western states. In FY 2004, USDA APHIS and the California Department of Food and Agriculture permitted expanded experimental releases of a fungal pathogen for biological control of YST in California. This pathogen attacks all aboveground plant parts and is expected to spread naturally through the YST population. In 2004, the rust fungus was released in 21 additional counties of California. Cooperators with the California Department of Food & Agriculture organized meetings with representatives of County Agricultural Commissioner offices. At each meeting, the problem (YST) and an anticipated solution (release of the rust fungus) were described. This was followed by distribution of a sample of the spores, a misting bottle, wetting agent, and a plastic tent. Participants then observed a demonstration of the protocol to inoculate plants in the field. CDFA cooperators verified reports of infection. In addition, CDFA cooperators used inoculum delivered from FDWSRU in 2003 to increase the inoculum based on protocols developed at FDWSRU, to ensure the availability of inoculum for field inoculations. Biological control using the pathogen will be a useful addition to the limited options available to land managers for management of this invasive weed.