Puccinia carduorum on Carduus tenuiflorus in California. A. K. Watson, Associate Professor, Macdonald College of McGill University, Ste-Anne-de-Bellevue, Quebec H9X 1C0. K. Brunetti, Pest Management Specialist, Department of Food and Agriculture, Sacramento, CA 95814. Plant Dis. 68:1003-1005. Accepted for publication 18 June 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-1003.

Rust fungi (Puccinia species) were not reported to occur on Carduus species in North America, but in May 1980, Puccinia carduorum was collected from Carduus tenuiflorus in Alameda and Santa Barbara counties of California. Examination of vascular plant herbaria records indicated that the rust has been present since 1951 and probably occurs throughout the distribution range of its host in California. The form of the rust may be specific to C. tenuiflorus because C. pycnocephalus growing in association with C. tenuiflorus remained free of the rust and no specimens of C. pycnocephalus with rust have been deposited in herbaria.