Evaluation of Puccinia crupinae, the causal agent of a rust disease on common crupina (Crupina vulgaris), for biological control is described. Susceptibility of accessions of common crupina that represent both varieties of the target from the five populations in the United States indicate that the disease has potential to control common crupina, but differences were noted between accessions on the basis of pustule count, yield (i.e., number and weight of achenes per plant), and shoot dry weight data after multiple inoculations. One accession from Modoc, CA, was not affected in greenhouse tests and would likely not be affected in the field if a permit to release P. crupinae were granted. None of the nontarget species of 26 taxa from the tribes Cardueae and Cichoriae were symptomatic, so the pathogen is likely safe to use in North America.
Nomenclature: Common crupina, Crupina vulgaris Pers. ex Cass. var. brachypappa P. Beauv.; C. vulgaris var. vulgaris Pers. ex Cass.
Management Implications: Common crupina is an invasive plant of ranges and pastures in the states of California, Idaho, Oregon, and Washington. Because there are no other effective or practical management strategies, focus has been on developing an obligate rust fungus from Greece for biological control. In the United States, there are five distinct populations, representing two varieties of common crupina, var. brachypappa and var. vulgaris, that differ in morphology and in biology. Evaluation of a rust disease, caused by Puccinia crupinae, was made on representatives of each population and both varieties from all infestations of common crupina in the United States. Disease from P. crupinae did not develop in tests of 26 nontarget relatives in the Asteraceae, Tribes Cardueae and Cichoriae. The strain of P. crupinae under evaluation is thus considered host-specific. Data on dew temperature suggest the pathogen will establish and cause disease on common crupina in the field, if permit for release is granted. Also, severe disease developed under greenhouse conditions on all but the accession from Modoc, CA, and measurable damage occurred to at least one accession from Lake Chelan, WA, in multiple inoculation studies. Implications from this suggest that the accession from Modoc, CA, would not be adversely affected in the field by the strain of P. crupinae in this study. The rust disease would likely infect and potentially damage common crupina in the majority of its range in the United States, if released. Results also suggest need for at least one additional strain of P. crupinae, or another candidate biological control agent, to bring pressure on all populations of common crupina in the United States.