Lym, Rodney G.

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Yellow starthistle is an extremely invasive, fast spreadingmember of the knapweed family and native of the Mediterra-nean region. Yellow starthistle was first collected in NorthDakota in Grand Forks County in 1964 and was added to thestate noxious weed list in 1999 after plants were observed inseveral newly seeded CRP fields. Yellow starthistle has thepotential to dramatically reduce crop and forage production,decrease native plant and wildlife habitat, poison horses, andcause severe economic loss in both crop and wildlands.How do I identify this plant? Yellow starthistle is anannual which often grows 3 feet or more tall (Figure 1) and isbranched with winged stems (Figure 2). Each stem terminatesin a bright yellow flower with needle-like, straw colored bractsthat are often up to 2 inches long (Figure 3). Lower leaves aredeeply lobed while upper leaves are entire. Both stems andleaves are covered with pubescent hairs that give the planta grayish appearance. Yellow starthistle reproduces (and thusspreads) only by seed (Figure 4). A single plant can produceas many as 150,000 seeds, of which 90 percent or more areviable and can remain dormant in the soil for a few years.Most yellow starthistle seeds are plumed and disperse whenmature. However, some seeds are plumeless and stay inthe flower head until winter storms disperse them in blowingsnow. Yellow starthistle has a long tap root similar to spottedknapweed or dandelion.What is yellow starthistle’s growth cycle?Yellow starthistle seeds can germinate either in the fallfollowing cool rains and overwinter as a rosette (Figure 5) orin the spring after snowmelt. Yellow starthistle begins to bolt inlate May to early June. Flowering starts in early to mid July,similar to Canada thistle. Yellow starthistle can often go unno-ticed until the plant begins to flower, but once the bright yellow,dandelion-like flowers bloom, the plant is easily detected.YellowStarthistle(Centaurea solstitialis)Identification and ControlRodney G. LymNDSU Department of Plant SciencesNorth Dakota State UniversityFargo, North Dakota 58105FEBRUARY 2002W-1222Figure 1. Yellow starthistle.Figure 1. Winged stems of yellow starthistle.STOP THE SPREADFlowering continues until mid to late August, then the plantdries to a straw color, the seeds mature, and the cycle repeats.Why is this plant a concern? Livestock and wildlifewill not graze where yellow starthistle grows because of thesharp spines around the flower. Yellow starthistle is adaptedto a wide variety of environments and will out compete mostnative plants for nutrients and moisture, reducing both nativewildlife and plant diversity. Yellow starthistle can cause “chew-ing disease” in horses, which is a lethal neurological disorder.However, to present symptoms, such as the inability to eat ordrink, stiff or trembling legs and a stiff swollen “frozen” face, ahorse must eat an amount nearly equivalent to its body weight.Where in the state is this plant found?Yellow starthistle is most likely to be found in recently seededpastures or CRP fields; along highways, railroad tracks andother transportation or communication lines, or anywherelivestock is brought into the state. Previous infestations in thestate can be traced to contaminated grass seed includingthose used in CRP, contaminated hay, and from movementof out-of-state livestock and vehicles into North Dakota.All known infestations in North Dakota have been treated andthe areas are being observed for reinfestation. Even thoughyellow starthistle only spreads by seed, it has infested over 15million acres in California alone. In addition, yellow starthistlepresently infests over 1 million acres in Idaho and has beenfound in the neighboring states of Montana, South Dakota,and Minnesota.How do I control this plant? Prevention is the bestmethod to keep yellow starthistle from invading North Dakotacropland, rangeland, and wildlands. Herbicides are the mosteffective yellow starthistle control method and the most com-monly used are Curtail, Redeem, and Tordon. Consult thelatest edition of NDSU Extension Service Circular W-253,the North Dakota Weed Control Guide, for recommended userates and locations. Biological control is in the research stageand is not recommended in North Dakota because of thelimited yellow starthistle acreage. Cultural control methodssuch as grazing, mowing, burning, cultivation, and maintainingcompetitive forages can be used in conjunction with herbicidesto keep yellow starthistle from establishing in North Dakota.NDSU Extension Service, North Dakota State University of Agriculture and Applied Science, and U.S. Department of Agriculture cooperating. SharonD. Anderson, Director, Fargo, North Dakota. Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. We offer our programsand facilities to all persons regardless of race, color, national origin, religion, sex, disability, age, Vietnam era veterans status, or sexual orientation;and are an equal opportunity employer. 3M-02-02This publication will be made available in alternative format upon request to people with disabilities (701) 231-7881.For more information on this and other topics, see: www.ag.ndsu.nodak.eduIf you find this weed, report itto your local weed officer.Figure 3. Yellow starthistle flowers.Figure 4. Yellow starthistle seeds.Figure 5. Yellow starthistle rosette. HELP STOP THE SPREAD

Yellow Starthistle (Centaurea solstitialis): Identification and Control

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