The spotted knapweed (Centaurea stoebe subsp. micranthos) biological control program moves to Arkansas

Spotted knapweed (Centaurea stoebe subsp. micranthos) is native to Eurasia and was introduced into North America in the 1890s. It is now found in Canada and has been recorded in 46 of the 50 United States. It is currently listed as a noxious weed in 17 states. Spotted knapweed has begun to spread very rapidly over the past 14 years in Arkansas. Since 1973, 13 biological control agents have been introduced into North America in attempt to control spotted knapweed. Only one of these agents, Urophora quadrifasciata (the UV fly) currently occurs in Arkansas. Studies have shown that the UV fly does not provide adequate suppression of populations in Arkansas. Recently, biological control has provided adequate suppression of some populations of spotted knapweed in the Western United States and Canada. It is thought, that the agent responsible for the decline is Larinus minutus (the knapweed seed head weevil). L. minutus adults were collected from the areas in and around Colorado Springs, Colorado in the late spring and summer of 2008 and 2009. Several releases of L. minutus have been carried out in Northwestern Arkansas in the summers of 2008 and 2009. Baseline studies on spotted knapweed density are currently being conducted, while more L. minutus releases and efficacy studies are planned, including measurements of plant and stem densities and seed production.