ARS | Publication request: Population Densities of Yellow Starthistle (Centaurea Solstitialis) in Turkey

Submitted to: Weed Science
Publication Acceptance Date: January 1, 2004
Publication Date: September 1, 2004
Citation: Uygur, S., Smith, L., Uygur, F.N., Cristofaro, M., Balciunas, J.K. 2004. Population Densities Of Yellow Starthistle (Centaurea Solstitialis) In Turkey. Weed Science. 52(5):746-753.

Interpretive Summary: Yellow starthistle is one of the most important alien invasive weeds in the western United States, infesting 20 million acres. It interferes with land use such as grazing and recreation, displaces native species, and is toxic to horses. It is an alien plant that probably originated from the eastern Mediterranean. This weed has been targeted for biological control because it is presumably controlled by natural enemies in its land of origin, but not in the United States. However, there is no quantitative information about the abundance of this plant in its land of origin. We collected data on the seasonal abundance of the plant and determined that it is much less abundant than in California and often has many fewer seed heads per plant than expected. This gives us clues as to what types of natural enemies may effectively control the plant in the United States.

Technical Abstract: The geographic center of diversity for yellow starthistle appears to be in Turkey. Although this region is being explored to discover potential biological control agents, there is no quantitative information regarding the density or population dynamics of the plant. This information could help indicate what natural enemies are helping to suppress the plant in its land of origin. Densities of yellow starthistle plants and seeds were sampled during two years at three locations in central Turkey. Densities of mature plants were about 4% those measured at sites in California. Densities of flower heads and seeds produced per square meter were about 60% and 65%, respectively, of those measured in California. The greatest difference between the two regions appears to be the densities of mature plants, which indicates the importance of focussing research on natural enemies that reduce plant survival. Although plants at densities of 1 to 3 plants per square meter could produce 50 to 120 seed heads, this fell to 2 to 13 in the subsequent year. Learning what limits plant survivorship and reproductive potential should help us discover ways to control the plant in the United States.