Cirsiumarvense is a noxious perennial weed which has become an increasing problem in North European countries partly because of restriction in use of effective herbicides.Mechanical weedingislabour intensive and expensive and therefore there is a need for an additional method likebiological control. An isolate PKDK101 of the fungus Phomopsiscirsii, which is virulent to C. arvense causing stem canker and die back was chosen to test the specificity of the fungus. A series of infection trials were successively carried out on 127 plant species (incl. ssp. and var.) belonging to 16 families in greenhouses in order to encircle the host range of P. cirsii. Susceptible plant species were found only in the thistle group (Cardueae) which contained 34 species belonging to 12 genera. Susceptible species were found in thirteen of these genera. Highly susceptible species included Carduusacanthoides, Carduuspycnocephalus, Cirsiumeriophorum, Cnicusbenedictus, Galactitestomentosa, Notobasissyriaca, Silybummarianum and Tyrimnusleucographus, which showed symptoms from girdling of stem, heart rot in rosettes to death of entire plants. Mild and restricted symptoms were observed on Carduuscrispus, Carduusnutans, Cirsium echinus, Cirsiumvulgare and Cynaracardunculusvar.scolymus (artichoke) with symptoms such as restricted necrotic leaf spots and too early senescence or death of entire leaf. Eleven hosts for P. cirsii were recorded but despite the expanded range of hosts we expect that its host range will be within Cardueae.P.cirsii,poses multi-target potential against several annual and biennial weedy thistles from warmer climates. The pathogenicity of P. cirsii towards the artichoke, however, could limit its field of application especially in the Mediterranean area. The potential of P. cirsii as a control agent, in areas where artichokes are cultivated, would depend on the existence of P.cirsii resistant varieties or the existence of P.cirsiiisolates non-pathogenic to artichoke.