Centaurea spp. is a large genus of over 400 species, most originating in the Mediterranean region. Many of the knapweeds have been introduced within the last 100 years and now represent a threat to pastures and rangelands. Knapweeds include annuals, biennials, short-lived perennials and perennials. Knapweeds are a highly competitive plant, threatening many desirable forage species. Knapweeds of concern in South Dakota included diffuse knapweed, spotted knapweed and Russian knapweed.
Since 1989 the South Dakota Department of Agriculture has been working with the United States Department of Agriculture on the release and evaluation of several knapweed biocontrol organisms. These agents include seed head flies (Urophora spp.) and (Terellia virens); root borers (Sphenoptera jugoslavica), (Agapeta zoegana) and (Cyphocleonus achates); and seed head weevils (Larinus minutus) and (Bangasternus fausti). The establishment and efficacy of these biological control agents are being monitored. Bioagent numbers on several species are reaching levels adequate for collection and redistribution.