Management Information
DiTomaso (2001) states that mechanical, cultural, biological, and chemical control options are available for management of C. solstitialis. Most often a single method is not effective in the sustainable control of C. solstitialis and other range weeds. A successful long-term management program should be designed to include combinations of mechanical, cultural, biological, and chemical control techniques.
Physical: Mowing can be used as a mechanical option for control provided it is well timed and used on plants with a high branching pattern. Cultural control options include grazing, prescribed burning, and re-vegetation with competitive species. Burning should be timed to coincide with the very early C. solstitialis flowering stage; at this time, it has yet to produce viable seed, whereas seeds of most desirable species have dispersed and grasses have dried to provide adequate fuel. Fire has little, if any, impact on seeds in the soil. In addition to controlling C. solstitialis, burning will reduce the thatch layer, expose the soil, and recycle nutrients held in the dried vegetation. Re-vegetation programs using perennial grasses or legumes can be effective for management of C. solstitialis, but establishment may be difficult in areas without summer rainfall.
Chemical: Clopyralid and picloram (not registered in California) are the most effective herbicides for full season control of the weed. Unlike most post-emergence herbicides, they provide both foliar and soil activity. The best timing for application is when C. solstitialis is in the early rosette stage. Clopyralid gives one season of control and is generally used at 110gm a.e./ha; 290gm product/ha. Picloram has longer soil residual activity than clopyralid (two to three years) and is applied at 0.28kg and 0.42kg a.e./ha. Glyphosate is a non-selective herbicide that is also effective on C. solstitialis. It will control bolted plants at 1.1kg a.e./ha; 9.4 liters product/ha or 1% solution and can be used as a late season spot treatment to small infestations or escaped plants.
Biological: Sheep, goats, or cattle are effective in reducing C. solstitialis seed production when grazed after plants have bolted but before spines form on the plant. Goats will eat the plant even in the spiny stage. Six biological control agents of C. solstitialis have been imported from Europe and are well established in the western United States. Of these, most effective are the hairy weevil (Eustenopus villosus) and the false peacock fly (Chaetorellia succinea). These insects attack the flower/seed head, and directly or indirectly reduce seed production by 43 to 76%. They do not, by themselves, provide sustainable management of C. solstitialis but can be an important component of an integrated approach. The most widely studied pathogen for C. solstitialis control is the Mediterranean rust fungus, Puccinia jaceae. It can attack the leaves and stem of C. solstitialis, causing enough stress to reduce flowerhead and seed production. The organism is currently under investigation and has not been released for use.  
Location Specific Management InformationCalifornia
DiTomaso (2001) reports that in California, burning is best performed at the end of the rainy season when flowers first appear. C. solstitialis should be green at this time and will require desiccated vegetation to burn. Most annual vegetation other than C. solstitialis, particularly grasses, should have dried and shed their seeds by this time. Burning can also increase the recovery and density of perennial grasses.
Management Resources/Links
4. Hierro, Jose´ L., Ozkan Eren, Liana Khetsuriani, Alecu Diaconu, Katalin Torok, Daniel Montesinos, Krikor Andonian, David Kikodze, Levan Janoian, Diego Villarreal, Maria E. Estanga-Mollica and Ragan M. Callaway., 2009. Germination responses of an invasive species in native and non-native ranges. Oikos 118: 529538, 2009 doi: 10.1111/j.1600-0706.2009.17283.x,
Summary: Abstract: Studying germination in the native and non-native range of a species can provide unique insights into processes of range expansion and adaptation; however, traits related to germination have rarely been compared between native and nonnative populations. In a series of common garden experiments, we explored whether differences in the seasonality of precipitation, specifically, summer drought vs summer rain, and the amount and variation of annual and seasonal
precipitation affect the germination responses of populations of an annual ruderal plant, Centaurea solstitialis, from its native range and from two non-native regions with different climates. We found that seeds from all native populations, irrespective of the precipitation seasonality of the region in which they occurred, and non-native populations from regions with dry summers displayed similarly high germination proportions and rates. In contrast, genotypes from the non-native region with predominantly summer rain exhibited much lower germination fractions and rates. Also, percent germination was strongly correlated with variation in precipitation in winter, the season that follows germination for C. solstitialis. Specifically, germination was lower for native and non-native populations experiencing greater variation in winter precipitation. This correlation, however, was greatly influenced by the non-native region with summer rain, which also exhibited the greatest variation in winter precipitation among studied regions. These results suggest that rather than
general climatic patterns, the degree of risk experienced at early developmental stages could exert an important control over the germination strategy of C. solstitialis populations in both native and non-native ranges. Also, these findings reveal a largely unique germination response in C. solstitialis genotypes. Results Page: 1
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