Management Information
Physical: Small areas can be eradicated by digging. Plants must be cut off below the soil, leaving no leaves attached (Julian and Rife UNDATED, in WSWB, 2003). Mowing has limited effectiveness for controlling O. acanthium. It usually only prevents seed production if done either immediately prior to flowering or when plants are just starting to flower. When mowing is conducted too early, it may only delay flowering. However, when plants are cut too late in the flowering process, viable seed may still develop in the capitula following cutting. Because there can be a wide variety in the maturity of plants, a single mowing is unlikely to provide satisfactory control (Sindel 1991, in WSWB, 2003). O. acanthium invasions may be prevented by manipulating the cropping environment (cultural control methods). For example, establishing and maintaining dense, vigorous, competitive pasture can effectively prevent O. acanthium establishment. Healthy pasture is particularly important in the autumn, when most O. acanthium seeds germinate.
Chemical: For herbicide control, Picloram, dicamba, 2,4-D, dicamba + 2,4,-D, and metsulfuron are effective for controlling O. acanthium (Beck 1991, Cargill et al. 1998, in WSWB, 2003). Application rates vary depending on stand density and environmental conditions. Herbicides should be applied in the spring before O. acanthium bolts, or in the fall to rosettes (Beck 1991, in WSWB, 2003).
Biological: Thistle invasion in unlikely to occur in ungrazed pasture. Goats will graze O. acanthium, reducing plant numbers and preventing seed production (Sindel 1991, in WSWB, 2003). No biological controls are currently available in the United States. Australia has released several biocontrol insects. Four control agents have been used in the biocontrol of O. acanthium a seed-feeding weevil Larinus latus was first released on 200 sites during 1993. It was found that the agents had eaten through 83% of the seed on released sites. A second control agent Lixus cardui, slower to spread than the first one was released a year later, this affected the growth of the plant. There are plans to release four more agents; thistle rosette destroying weevil Trichosirocalus sp and moth Eublemma amoena , and two fliesBotanophila spinosa and Urophora terebrans which attack rosettes and seed respectivley (CRC Weeds Dispatch, winter 2001). These control agents however, have failed host specificity tests in the U.S. Additional insects are being evaluated for release in the U.S. (Joley et al. 1998, in WSWB, 2003).  
Management Resources/Links
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