Submitted to: Plant Disease
Publication Type: Research Notes
Publication Acceptance Date: 11/1/2002
Publication Date: 12/15/2002
Citation: WOODS, D., PITCAIRN, M., LUSTER, D.G., BRUCKART, W.L. FIRST REPORT OF MUSK THISTLE RUST (PUCCINIA CARDUORUM) IN CALIFORNIA AND NEVADA. PLANT DISEASE. 86:814. 2002.
Technical Abstract: Musk thistle, Carduus nutans L. is an introduced weed of pastures, rangelands, and natural areas, in much of North America. Puccinia carduorum Jacky, an autoecious rust fungus originally collected in Turkey, has been evaluated for biological control of musk thistle since 1978, including a three-year field study near Blacksburg, Virginia, starting in 1987. Following release of the fungus in Virginia, rusted musk thistle was found in eight Eastern states by 1992, in Missouri by 1994 (1) and in Oklahoma by 1997 (2). On September 22, 1998, a rust disease was discovered on musk thistle near Mt. Shasta, California, and again near Mogul, Nevada, on August 12, 1999. The fungus was identified as P. carduorum on the basis of urediniospore morphology and pathogenicity on musk thistle. The ribosomal RNA internal transcribed spacer DNA sequence (ITS1 and ITS2) was identical to that of the isolate in the original field release in Virginia, thus verifying that the CA isolate is P. carduorum. The initial infestation in California was limited to a few plants that were green late in the season. Subsequent infection levels have increased to nearly 100% of the plants infected in field monitoring transects. The occurrence of P. carduorum in California is apparently the result of natural, unaided spread of the fungus on musk thistle from the East Coast of the U.S.