|WOODS, DALE - California Department Of Food And Agriculture|
|DITOMASO, JOSEPH - University Of California|
|GORDON, TOM - University Of California|
|O'BRIEN, JOHN - University Of California|
|PITCAIRN, MICHAEL - California Department Of Food And Agriculture|
|POPESCU, VIOLA - California Department Of Agriculture|
|VILLEGAS, BALDO - California Department Of Food And Agriculture|
|YRIBE, A - California Department Of Food And Agriculture|
Submitted to: Government Publication/Report
Publication Type: Government Publication
Publication Acceptance Date: 8/1/2010
Publication Date: 9/1/2010
Citation: Woods, D.M., Bruckart, W.L., Ditomaso, J., Fisher, A.J., Gordon, T., O'Brien, J., Pitcairn, M., Popescu, V., Smith, L., Villegas, B., Yribe, A. 2010. Yellow starthistle rust: summary of release, establishment and biology in California. In D.M. Woods (ed.), Biological Control 2009 Annual Summary. California Department of Food and Agriculture, Plant Heath and Pest Prevention Services, Sacramento, California, pp.43-40.
Interpretive Summary: Yellow starthistle is an alien weed that has invaded about 20 million acres in the western U.S. It is especially abundant in Pacific western states. The spiny plant interferes with grazing livestock and outdoors recreation, it is fatally poisonous to horses, and it outcompetes desirable vegetation. A rust pathogen from Turkey was released in California for classical biological control of yellow starthistle. Although the rust initially caused infection at most sites, it persisted for three years at only 5% of the release sites and caused repeatedly high levels of infection at only one site. Efficacy of this rust pathogen appears to be limited by climatic requirements, especially hot dry summer conditions, which are common in California's Central Valley. It is possible that a different accession of this rust pathogen from a location with more similar climate to central California may be more effective.
Technical Abstract: The rust pathogen, Puccinia jaceae var. solstitialis, was collected in Turkey for use as a classical biological control of yellow starthistle, which is an invasive alien weed. During pre-release evaluation of risk to 65 nontarget plant species, the rust infected only the target weed and bachelor's button, which is both an ornamental and a weed. The rust was released by California Department of Agriculture at 176 sites in 40 counties in California during 2004-2006. Subsequent monitoring showed that the rust spread at only one site, and it persisted for three years at only 5% of the release sites. It appears that hot dry summer conditions in most of California limit the rust, and that lack of production of teliospores prevents reappearance of the rust in subsequent years. In controlled experiments, infection by the rust reduced the size of yellow starthistle rosettes, but plants could compensate enough by the end of the season to produce the same number of seeds. It is possible that a different accession of this rust pathogen from a location with more similar climate to central California may be more effective.