Biological Control of Canada Thistle using a Rust Fungus and Releasing APHIS-Approved Pathogens for Control of Russian Knapweed and Russian Thistle - Colorado Department of Agriculture

Goals / Objectives
1) Routinely establish epiphytotics of systemic rust disease, caused by the fungus Puccinia punctiformis, in disease-free Canada thistle patches in Colorado by inoculating newly emerged rosettes in the fall with ground telia-bearing leaves collected in the respective states; 2) Improve efficiencies of inoculation, through research, to optimize inoculation timing, reduce amount of inoculum, and mass produce teliospores of the fungus for inoculations; 3) Train producers and stakeholders in Colorado and surrounding states (Wyoming, Kansas, New Mexico, Utah and Arizona) in establishing successful epiphytotics; 4) Monitor Canada thistle densities in inoculated and non-inoculated sites to document success of this biological control approach and 5) Assist in releasing APHIS-approved pathogens for control of Russian knapweed and Russian thistle.

Project Methods
Disease-free Canada thistle field sites will be located at the start of the project. Spores of the rust fungus Puccinia punctiformis will have been collected from areas with diseased Canada thistle in Colorado the preceding spring and used to inoculate disease-free areas in farmers' and ranchers' fields in the fall. Systemically diseased Canada thistle shoots will emerge from root systems of inoculated plants the following spring and provide spores for subsequent inoculations. New epidemics will be established in disease-free sites every year of the project. Thistle population densities per unit area will be counted each year to document changes in population density. Thistle densities in non-inoculated sites will also be counted per unit area each year to use as a basis of comparison with the inoculated sites. Farmers and ranchers will be instructed on how to recognize diseased thistle plants, collect spores, and perform inoculations. Successful establishment of rust epidemics and Canada thistle control will be documented and published as scientific articles and technical bulletins for instruction on further implementation by farmers and ranchers. To improve efficiency of inoculations we will: 1) Determine age of rosettes and temperatures that most actively stimulate P. punctiformis teliospore germination to optimize inoculation timing; 2) Determine annual distance of movement of the fungus by aeciospores, wind-blown telia-bearing leaves, and roots to establish inoculation patterns that maximize disease spread and biological control and 3) develop a greenhouse procedure to mass produce teliospores of P. punctiformis that can be used for in-field inoculations to establish epiphytotics of systemic disease. This will be done by determining light and temperature treatments that maximize conversion of aecia to telia and result in maximum amount of teliospore production. Releases of biological control pathogens on Russian knapweed and Russian thistle will be accomplished by removing the pathogens from the USDA, ARS, Foreign Disease Weed Science Research quarantine facility according to APHIS-approved procedures and transferring the pathogens to the Colorado Department of Agriculture (CDOA) Insectary. At the insectary, the pathogens will be increased and released into the field under supervision of CDOA staff. After release, disease progress and damage to the target weed will be monitored.