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Home , Centaurea solstitialis

United States Department of Agriculture

Field Guide for Managing Yellow Starthistle in the Southwest

Forest Southwestern Service Region TP-R3-16-07 Revised June 2017 Cover Photos Top left: Steve Dewey, State University, Bugwood.org Top right: Steve Dewey, Utah State University, Bugwood.org Left center: Steve Dewey, Utah State University, Bugwood.org Bottom left: Cindy Roche, Bugwood.org Bottom right: USDA Forest Service

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Printed on recycled paper Yellow starthistle ( solstitialis L.) Sunflower family ()

Yellow starthistle is an invasive that has been listed • Reproduces solely via seed; two types of smooth as a noxious in Arizona and New Mexico. This field seed—one type is lighter in color with a pappus of guide serves as the U.S. Forest Service’s recommendations barbed bristles, the other is darker without a pappus. for management of yellow starthistle in forests, woodlands, • Leaves and stem become straw colored as seeds , and deserts associated with its Southwestern form; head becomes straw colored when seeds Region. The Southwestern Region covers Arizona and are mature; seeds are viable for up to 10 years. New Mexico, which together have 11 national forests. The Region also administers 4 national grasslands located in Ecology northeastern New Mexico, western Oklahoma, and the Impacts/Threats Texas panhandle. Yellow starthistle is highly competitive and often develops dense, impenetrable stands that lower the diversity of Description desirable flora and fauna species. The presence of sharp, Yellow starthistle (synonyms: golden starthistle, St. long spines on seed heads of yellow starthistle degrades Barnaby’s thistle, yellow cockspur) is an early maturing livestock grazing, wildlife , and recreational winter annual. Native to , it was introduced into opportunities. When forced to graze mature yellow as a seed contaminant in the mid-1850s and starthistle, livestock (especially horses) can be affected by has persistently spread across the western United States. an incurable neurological disorder known as “chewing Yellow starthistle is similar in appearance to two closely disease.” A neurotoxic sesquiterpene lactone in starthistle related species: C. melitensis (Malta starthistle) and C. species called repin is believed to be the underlying cause sulphurea (Sicilian starthistle). of the disorder. However, animals typically avoid the weed because of the sharp spines and hairs. Growth Characteristics Site/Distribution • Grey-green to blue-green herbaceous plant covered in fine, white cottony hairs; winter annual and Yellow starthistle prefers well-drained soils, hot dry occasional biennial. summers, and 10 to 60 inches of precipitation. It occurs in open areas in woodlands, desert scrub, chaparral, • Stout, rapidly growing, vigorous taproot; may grow , pastures, waste areas, cropland, and roadsides deeper than 36 inches. that generally lie below 7,500 feet in elevation. It is also • Germinates fall to spring; rosette in fall/winter, common around residential subdivisions, agricultural land, deeply lobed leaves with fine, cottony hairs appear and recreation areas. The species is found in foothill areas ruffled; bolts May to June with stiff, openly- of southwestern New Mexico and elsewhere in deserts, branched stems, 6 to 60-inches tall with large stem uplands, rangelands, and mountains of the Southwest. wings. Spread • Leaves alternate, linear to oblanceolate; margins When unassisted, yellow starthistle seed rarely moves far smooth, toothed, or wavy. from the parent plant. However, seed readily attaches to

• May to December, yellow flowers borne at fur, hair, or clothing. The seed can be transported afar by tips or in axils of winged stems; flower heads with adhering to tires and undercarriages of road vehicles and spiny bracts form in June or July; each bract has a equipment. The seed may also be introduced into new central spine up to 2 inches long with 2 to 3 pairs of areas through transported hay that is not certified to be lateral spines. weed free.

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Invasive Features years needed to achieve control. Typically, more than one Yellow starthistle is a prolific seed producer and in dense control method may be needed for a particular site. stands can produce 50 to 100 million seeds per acre. It Physical Control grows rapidly and is highly adaptable to environmental variation. This allows yellow starthistle to out-compete Yellow starthistle reproduces solely by seed, so physical native plant species for sunlight, space, water, and methods should focus on reducing seed production and nutrients. Other features that facilitate invasiveness include preventing seed germination. These methods usually have a deep taproot that accesses available soil moisture, to be repeated and must be properly timed to be effective. winged stems that dissipate heat, and formidable spines at Manual Methods maturity that deter grazing by livestock or wildlife. Hand pulling or hoeing are most effective in a maintenance program for an area where yellow starthistle is relatively Management sparse. Take care to remove as much of the taproot as Due to its abundant seed production, early detection and possible. Anticipate that hand removal will need to be eradication of yellow starthistle soon after discovery repeated in about 2 weeks to remove missed or increases the chances for successful control. A those maturing at a later time. Care should be taken to commitment to repeated management actions is a must, minimize soil disturbance and to properly dispose of plant and a combination of methods and repeated treatments will debris by bagging and/or burning. improve effectiveness. The following actions should be Mechanical Methods considered when planning a management approach to When using machinery to manage yellow starthistle, the control starthistle: equipment should be cleaned after use to prevent • Maintain healthy plant communities to suppress or movement of seed into un-infested areas. limit the impact of a starthistle infestation. Tillage – In suitable terrain, tillage in early summer with a • Incorporate sound grazing management with any plow or disc that is repeated at a later time (about 4 to 6 control strategy. weeks) can effectively bury yellow starthistle plant parts. A harrow or drag pulled behind a tractor can be used to cut • Combine mechanical, cultural, biological, and and separate shoots from roots of larger mature plants. chemical methods to control yellow starthistle These methods are most commonly used in agronomic or populations whenever possible. roadside settings and should only be used when the soil • Include monitoring and a follow-up treatment plan surface is dry since fragmented plant segments in moist for missed plants and seedlings. soils will regrow and possibly magnify the problem.

• Map large infestations and keep annual records of Mowing – Mowing is commonly used for yellow reported infestations. starthistle along roadsides and in recreational areas. Table 1 summarizes management options for controlling Although it can be a cost-effective method for starthistle yellow starthistle under various situations. Further details control, mowing is not feasible in many locations due to on these management options are explained below. Choice rocks or steep terrain. Some vegetation management of individual control method(s) for starthistle depends on experts do not recommend mowing since plants not cut many local factors including the extent of infestation, closely to the surface often produce side branches that can current land use, and site conditions (terrain, accessibility form additional flowers, even with repeated mowing and for treatment, microclimate, presence of non-target flora proper timing. and fauna, etc.). Other important considerations include Despite its limitations, mowing over a 3-year period has treatment effectiveness, overall cost, and the number of been reported to provide over 90 percent control when two

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Table 1. Management options* Site Physical Control Cultural Control Biological Control Chemical Control Roadsides Use repeated, shallow cultivation Use seed and mulch certified to Consider using flies, Use truck spraying and/or mowing throughout be weed-free. Gravel and other , or fungus as equipment to apply germination and growing periods. road materials transported into classical biocontrol agents during early un-infested areas should be weed (see table 2). Usefulness growth. Clean equipment free. of biocontrol agents may to prevent spread. be limited due to possible Educate road crews to identify disturbances in agent life and report infestations along cycles from roadside roads; implement requirements operations. for vehicle operations in infested areas. Rangeland Use repeated, shallow cultivation Use seed and forage hay certified Use prescribed grazing For extensive and dense and/or mowing throughout to be weed-free; use pellets for during spring with an infestations, use ground or germination and growing periods. horses in backcountry areas. intense, short-duration aerial broadcast spraying. approach in combination If feasible, combine prescribed After passing through infested For less dense with other control fire with herbicide spraying. areas, inspect and remove any infestations, consider methods. Closely manage seed from animals, clothing, and ATV or backpack grazing to prevent vehicles before entering treated spraying. Clean ground overuse. or un-infested areas. equipment to prevent Consider using flies, spread. weevils, or rust fungus as classical biocontrol agents (see table 2). Wilderness Hand methods can be used by Use seed and forage hay certified Same as above. Use backpack or hand- and other starting at the edges of an to be weed-free; use pellets for held sprayers. Broadcast natural infestation and working toward horses in backcountry areas. spraying by aerial or areas the center. Pull before plant ground methods may be After passing through infested reaches full bloom. used on thicker stands if areas, inspect and remove any allowed. Clean ground seed from animals, clothing, and equipment to prevent vehicles before entering treated spread. or un-infested areas. Post signs warning visitors to inspect for and remove seeds. * Choice of a particular management option must be in compliance with existing regulations for the land resource.

timely, repeated mowings are made per year. Since timing starthistle may also be burned in early to mid-summer (late is critical, best results occur when mowing is completed in intense, uniform fire required for starthistle control. Yellow the early flowering stage before viable seed production, May to early July) during the early flower stage. Despite i.e., when no more than 2 to 5 percent of the spiny heads its effectiveness in selected situations, risks associated with are in bloom. After mowing, no leaves should be left burning should be thoroughly assessed in a specific below the level of the cut. management plan for prescribed fire.

Prescribed Fire Cultural Control Burning from January to May can eliminate yellow Educational programs focused on the biology and starthistle in the seedling to early bolting stages. However, identification of nonnative weed species should be burning during this time is often limited since there sponsored for local land managers and others to help find, generally is insufficient fine, dry fuel available to carry the report, and monitor suspected infestations. Vehicles,

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humans, and livestock should be discouraged from Classical Biological Control traveling through infested areas. A program to check and Control with classical biocontrol agents (, remove seed from vehicles and livestock should be pathogens, etc.) is most suitable for sites where other implemented to help stop dispersal. Hay, straw mulch, control methods are impractical. Biocontrol agents should seeds for planting, and other similar materials should be be used only if infestations are large enough to sustain certified to be weed free before use in unaffected areas or agent populations. Needs of the biocontrol agent should be areas previously treated for starthistle. Gravel and other considered before implementing other weed treatments. road materials transported into un-infested areas should USDA-approved biocontrol agents listed in table 2 have also be weed free. been found to establish well in the western United States Biological Control and contribute significantly to reduce seed production. Several biocontrol agents have been released in Arizona Grazing and New Mexico for control of yellow starthistle, but In , properly timed spring grazing with cattle, experience with these agents is still limited. For further goats, or sheep has been shown to reduce yellow information on biocontrol of yellow starthistle, see Wilson starthistle’s growth, canopy cover, survivability, and et al. (2003) in the “References and Further Information” reproductive capacity. This approach is based on intensive section of this field guide. livestock grazing of yellow starthistle after stems on rosettes have begun to bolt but before spiny seed heads Organisms (insects, pathogens, etc.) used as biocontrol develop. Cattle and sheep avoid starthistle once the flower agents in southwestern States should be adaptable to arid heads produce spines, whereas goats continue to browse environments and local conditions. Public, tribal, and plants even during the flowering stage. For this reason, private land managers may obtain biocontrol agents for goats are popular for controlling yellow starthistle in release directly from local offices of the USDA Animal relatively small infestations. and Plant Health Inspection Service (APHIS) when these agents are available. Other sources for biocontrol agents Although grazing can reduce starthistle presence, owners include locally developed insectaries or private companies. of horses and other livestock should ensure that suitable alternative forage is available. Owners should also look for A permit must be obtained from APHIS before biocontrol signs of toxicity or so-called “chewing disease” in agents can be transported across State lines. Regulations starthistle stands that have flowering heads. Prescribed and permit applications (PPQ 526 permit forms) pertaining grazing with an intensive, short-duration approach can be to interstate shipment of biocontrol agents can be found at part of an effective control strategy to manage starthistle, https://www.aphis.usda.gov/aphis/ourfocus/planthealth/im especially when combined with other control methods (see port-information/permits/regulated-organism-and-soil- “Integrated Control Methods” at the end of this section for permits/sa_apply/ct_plantpest_howtoapply. Although more information). A system using short periods of intense biocontrol agents may be collected and released internally livestock grazing has been adopted in other countries for in a given State without an APHIS permit, the State’s starthistle control. In this system, infested pastures are department of agriculture or agricultural extension service intensively grazed for 3 to 5 days, often by using electric should be consulted for any regulations relating to fencing. After livestock have been moved to another part movement of these agents within the State. of the pasture, the grazed area is allowed to recover for at Chemical Control least a month before grazing is repeated. The system Yellow starthistle is best controlled with a selective, post- typically results in more uniform and complete forage emergent, broadleaf herbicide since these chemicals have utilization. In addition, desirable forage is not completely little or no effect on grass species. The primary entry point grazed and can rapidly recover. Ultimately, this increases for herbicide into the plant is through the leaves with only seasonal forage production and stocking capacity.

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Table 2. Classical biocontrol agents approved for yellow starthistle

Species Type of Site of Impact on Host Use/Considerations for Release Agent Attack Bangasternus Flower buds/ Larval feeding in the head can reduce the B. orientalis is a good flier and orientalis seed heads number of seeds by 40 to 60 percent. disperses well. It is difficult to establish at sites where E. villosus is already established. Chaetorellia fly seedheads Internal larval feeding reduces the number of Disperses very well, thus it is australis developing seeds in the bud by 80 to 100 widespread in most areas it was percent. established. Eustenopus weevil Young Adult feeding and oviposition can destroy It is now widely established in villosus flower buds young buds, which appear as brown, dry and California, , Washington and and tilted heads. Larval feeding in the head can and is abundantly available for seedheads reduce the number of seeds by 90 to 100 collection and redistribution. percent. weevil Pollen, Adult feeding on pollen and flowers does L. curtus is a strong flier and is flowers, little to damage the plant; larval feeding in expected to disperse well on its own. seedheads seed heads results in seed reduction of 75 to 100 percent. Urophora fly Seedheads Internal larval feeding reduces the number of The presence of high densities of U. sirunaseva developing seeds in the head by about 50 sirunaseva at a site does not appear to percent. Heads infested with this fly interfere with survival of other seed produce fewer seeds than heads infested head-infesting agents. with Chaetorellia flies. Puccina jaceae rust fungus leaves and Stress caused by agent reduces production of Released in 2004 in California, the var. solstialis stem flower heads and seed. rust has not demonstrated a strong record of persistence

minor entry through roots. annual, it should not be sprayed during or after flowering as these treatments will be ineffective. All shown in table 3 will effectively control Yellow starthistle establishment is closely tied to yellow starthistle when properly applied. Of the rainfall events, which can complicate herbicide compounds recommended, and are spraying. New plants can be produced throughout the the most commonly used since they provide some year, and propagation from year to year can be highly residual activity in the soil and will control seedling variable. Therefore, infested areas should be checked emergence for a few months after spraying. Aquatically closely for seedling abundance before deciding to spray. approved herbicide formulations and surfactants must be used in or near water. Each herbicide product has Herbicides may be applied by backpack or hand-held specific requirements and restrictions; therefore, it is sprayers, ATV or UTV sprayers, or conventional boom important to read the label carefully and follow all sprayers that are pulled or attached to a tractor or truck. instructions when mixing and spraying. Aerial application via fixed-wing airplane or helicopter may be warranted for large, monotypic infestations. Herbicide Application Any equipment used to spray herbicide should be The most effective time to spray yellow starthistle is calibrated. Because herbicides listed in table 3 may usually late autumn to early spring during the seedling impact desirable broadleaf and woody species, to rosette stage. Spraying is also effective later in spring precautionary measures should be taken if nontarget when plants have 4 to 6 inches of growth and good species need to be protected. growing conditions exist. Since yellow starthistle is an

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Table 3. Herbicide recommendations

Common Broadcast Product Spot Treatment Time of Chemical Name 1 Treatment 2 Remarks Example(s) (spray solution) Application (active ingredient) (rate per acre)

Clopyralid Reclaim 0.25–0.67 pints 1–3% Fall to early spring Selective broadleaf herbicide. Stinger during early rosette Most perennial grasses are Transline stage. tolerant; residual.

3 Clopyralid + 2,4-D Curtail 0.25–1 pint 1–3% After most rosettes Same as above. have emerged, but before flower heads form. Perspective 3–4.5 ounces Consult label for Lower rate for Selective herbicide used on non- + chlorsulfuron spot applications. rosette; higher rate crop sites; may cause temporary at bolting. Fall or injury to some grass species. spring. Aminocyclopyrachlor Streamline 4.75–9.5 ounces Same as above. Same as above. Same as above. + metsulfuron methyl Milestone 3–5 ounces 3–5% Rosette through Labeled for use in natural areas bolting stage. such as wildlife management areas. No grazing restrictions.

4 Picloram Tordon 22K 1–1.5 pints 1–3% Fall to early spring, Selective broadleaf herbicide; at early rosette may pose a risk to groundwater stage. in permeable soils or in areas where the water table is near the surface.

4 3 Picloram + 2,4-D Grazon P+D 2 quarts (1:4 1–3% Same as above. Same as above. mixture) Metsulfuron methyl Escort XP 1 ounce NA Same as above. Selective broadleaf herbicide. Most perennial grasses are tolerant; residual. Metsulfuron methyl + Cimarron Max Rate III (1 NA Same as above. Same as above. 3 2,4-D + ounce Part A + 4 pints Part B) Dicamba + Overdrive 4 ounces 1–3% Same as above. Selective broadleaf herbicide; diflufenzopyr not for use where surface water is present. Remedy 3 pints 1–1.5% Best on seedlings to Selective broadleaf herbicide; early rosette stage. little residual.

3 2,4-D several 1 quart 5–10% Rosette to early bud Non-persistent; growth manufacturers in the spring. regulator; may be less effective alone.

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Table 3. Herbicide recommendations (cont.)

Common Broadcast Product Spot Treatment Time of Chemical Name 1 Treatment 2 Remarks Example(s) (spray solution) Application (active ingredient) (rate per acre)

Imazapyr Arsenal 1 pint 1% All stages. Nonselective herbicide. In addition to spray drift, nontarget plants may also be killed or injured by imazapyr through runoff, residue movement in soil, or root exudates from treated plants. Use only in areas where total plant control is desired such as roadsides. Rodeo Rodeo: 4.5–7.5 Rodeo: 0.75–2% One week before Nonselective herbicide. Use only Round Up pints Round Up: 1–2% reseeding. for site preparation in a reseeding Round Up: 1.5– program. 4 quarts

1 Trade names for products are provided for example purposes only, and other products with the same active ingredient(s) may be available. Individual product labels should be examined for specific information and appropriate use with yellow starthistle. 2 Spray solution is the herbicide/water ratio in a spray mix that may be used for spot treatment with backpack or hand-held sprayers. The amount of product applied during an annual growing season must not exceed the maximum application rate per acre as specified by the product label – refer to the product label for the site type and application. 3 2,4-D is a restricted use pesticide in New Mexico only. A certified applicator’s license is required for purchase and use. 4 Restricted use pesticide - A certified applicator’s license is required for purchase and use.

Integrated Control Methods combination can benefit the range plant community Using a combination of control methods will improve by increasing species diversity and enhancing the treatment effectiveness for yellow starthistle. The quality and quantity of forage. Consider introducing following treatment combinations may be used to manage biocontrol agents after the last burn. infestations: • Herbicide–reseed–graze – While experience in New Mexico and Arizona is limited, a herbicide– • Herbicide–burn – As an initial treatment, use herbicide in a broadcast spray for seedlings and reseed–graze treatment sequence has been used in young plants in the rosette stage during fall or early California with some success. In this approach, a spring. The treatment will eliminate the majority of broadcast application of glyphosate is made to the the yellow starthistle population and allow grasses to infested site in late winter. The area is then reseeded become established. The herbicide treatment can one week later with a variety of appropriate then be followed the next year (or possibly in 2 perennial grasses by using a no-till drill. Two weeks years) with prescribed fire, which may require after seeding, a broadcast application of clopyralid authorization from local air quality authorities. is made to control pre-emergent and post-emergent Burning is best performed when non-target grasses yellow starthistle plants. Light fall grazing is have dried but before yellow starthistle produces recommended for several years after planting until seed which is likely to occur during late May or June perennial plants are well established. Treated areas in New Mexico and Arizona. This treatment should be closely monitored to determine if further herbicide application is necessary.

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Management Strategies DiTomaso, J.M. and E.A. Healy. 2007. of California and Other Western States. University of Strategies to contain, reduce, or eradicate yellow starthistle California Agriculture and Natural Resource require long-term planning, integrated management, and Publication 3488. Pp. 250–260. Available at follow-up monitoring. Due to yellow starthistle’s prolific http://books.google.com/books (accessed 17 June seed production, initial treatment should attempt to 2010). eliminate live plants and disrupt flower production as much as possible. A high priority should be treatment of Duncan, K., K. McDaniel, and M. Renz. 2005. Chemical small or sporadic infestations on otherwise healthy sites, Weed and Brush Control for New Mexico which can then be shifted to larger infestations. Rangelands. New Mexico State University Cooperative Extension Service. Las Cruces, NM. Regardless of the strategy employed, the key to successful pp. 12. Available at http://aces.nmsu.edu/pubs/ yellow starthistle control is persistent, long-term _circulars/CR_597.pdf (accessed 17 June 2010). management. In many cases, 3 or more years of intensive management may be necessary to reduce a starthistle Encycloweedia Datasheets by California Department of infestation significantly. Since it is ordinarily useless to Food and Agriculture. Available at treat an area only one time without retreatment, sufficient http://www.cdfa.ca.gov/phpps/IPC/weedinfo/ resources must be allocated for the area where control is centaurea2.htm (accessed 17 June 2010). attempted. After initial treatment, it is especially important Enloe, S.F., J.M. DiTomaso, S.B. Orloff, and D.J. Drake. that resources are also available to respray or retreat 2005. Perennial Grass Establishment Integrated treated areas as necessary. Treated areas should be with Clopyralid Treatment for Yellow Starthistle monitored, and secondary treatment made to control newly Management on Annual Range. Weed Technology emerged or missed plants. Always encourage growth of 19:94-101. perennial grasses and other desirable plant species that will Gerlach, J.D., Jr. and J.M. DiTomaso. 2000. Yellow compete with yellow starthistle for soil moisture, light, Starthistle (Centaurea solstitialis). In C. C. Bossard nutrients, and space. et al. (eds.) Invasive Plants of California’s Wildlands University of California Press. Berkley, References and Further CA. Available at http://www.cal-ipc.org/ip/ Information management/ipcw/online.php (accessed 17 June Davison, J.C., E. Smith, and L.M. Wilson. 2007. Livestock 2010). Grazing Guidelines for Controlling Noxious Weeds Great Basin and Invasive Weeds: Yellow Starthistle in the Western United States. Available at (Centaurea solstitialis) fact sheet. Available at http://www.cnr.uidaho.edu/rx-grazing/Livestock http://www.usu.edu/weeds/plant_species/ _Grazing_Guidelines%28Davison_et_al. weedspecies/ystarthis.html (accessed 17 June %202007%29.pdf (accessed June 2010). 2010).

DiTomaso, J.M. Undated. Yellow Starthistle. UC Weed Lym, R.G. 2002. Yellow Starthistle Identification and Research Information Center Web site. Available at Control (Stop the Spread Factsheet). North Dakota http://wric.ucdavis.edu/yst/yst.html (accessed 18 State Univ. Extension Service Publication W-1222. June 2010). Available at http://www.ag.ndsu.edu/pubs/plantsci/ DiTomaso, J.M. 2001. Element Stewardship Abstract for weeds/w1222w.htm (accessed 17 June 2010). Centaurea solstitialis L. Available at http://www. invasive.org/weedcd/pdfs/tncweeds/centsol.pdf (accessed 17 June 2010).

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Murphy, A. 2005. Least Wanted: Yellow Starthistle Fact Suggested Web Sites Sheet. Plant Conservation Alliance. Available at Invasive Plant Atlas of the United States. Available at: http://www.nps.gov/plants/alien/fact/ceso1.htm http://www.invasive.org/weedus/index.html. (accessed 17 June 2010) For information about calibrating spray equipment: NMSU Turner, J.L., K. Duncan, and J. LeFevre. 2011. Russian Cooperative Extension Service Guide A-613, knapweed and yellow starthistle poisoning of Sprayer Calibration. Available at horses. Guide B-170. Cooperative Extension Serv., http://aces.nmsu.edu/pubs/_a/A-613.pdf College of Agriculture, Consumer, and Environmental Sciences. New Mexico State Univ. Herbicide labels online: Las Cruces, NM. Available at http://aces.nmsu.edu/ http://www.cdms.net/ pubs/_b/b-710.pdf. USDA Plants Database. 2010. Available at: Whitson, T.D., et al. (ed.). 2000. Weeds of the West. http://plants.usda.gov/index.html. Western Society of Weed Science in cooperation with Cooperative Extension Services. University of Wyoming, Laramie. Available at http://plants.usda.gov/java/invasiveOne?pubID=W SWS (accessed 17 June 2010)

Wilson, L.M., C. Jette, J. Connett, and J.P. McCaffrey. 2003. Biology and Biological Control of Yellow Starthistle. 2nd ed. USDA Forest Service FHTET- 1998-17. Available at http://www.cnr.uidaho.edu/ crissp/CRISSP%20pdf/StarthistleBook.pdf (accessed 17 June 2010).

Zouhar, Kris. 2002. Centaurea solstitialis. In Fire Effects Information System. USDA, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available at http://www.fs.fed.us/database/feis/plants/forb/ censol/all.html (accessed 17 June 2010).

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For more information or other field guides, contact: USDA Forest Service Southwestern Region Forest Health 333 Broadway Blvd., SE Albuquerque, NM 87102 Or visit the Southwestern Region’s website for : http://www.fs.usda.gov/goto/r3/invasivespecies

The use of trade or firm names in this publication is for reader information only and does not imply endorsement of any product or service by the U.S. Department of Agriculture. Recommendations made here for pesticide use are not obligatory, nor do they imply that discussed uses have been registered. All uses of pesticides must be registered by appropriate State and/or Federal agencies before they can be applied.

CAUTION: Pesticides can be injurious to humans, domestic animals, desirable plants, and fish or other wildlife—if they are not handled or applied properly. Use all pesticides carefully and lawfully. Follow recommended practices for the disposal of surplus pesticides and pesticide containers.