United States Department of Agriculture Field Guide for Managing Yellow Starthistle in the Southwest Forest Southwestern Service Region TP-R3-16-07 September 2014 Cover Photos Top left: Steve Dewey, Utah State University, Bugwood.org Top right: Steve Dewey, Utah State University, Bugwood.org Left center: Steve Dewey, Utah State Univeristy, Bugwood.org Bottom left: Cindy Roche, Bugwood.org Bottom right: Forest Service The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or part of an individual’s income is derived from any public assistance program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720-2600 (voice and TTY). To file a complaint of discrimination, write to USDA, Director, Office of Civil Rights, 1400 Independence Avenue, SW, Washington, DC 20250-9410 or call (800) 795-3272 (voice) or (202) 720-6382 (TTY). USDA is an equal opportunity provider and employer. Printed on recycled paper Yellow starthistle (Centaurea solstitialis L.) Sunflower family (Asteraceae) Yellow starthistle is an invasive plant that has been listed • Buds with spiny bracts form in June or July; each as a noxious weed in Arizona and New Mexico. This field bract has a central spine up to 2 inches long with 2 to guide serves as the U.S. Forest Service’s recommendations 3 pairs of lateral spines. for management of yellow starthistle in forests, woodlands, • Flowers May to December; yellow flowers borne at rangelands, and deserts associated with its Southwestern tips or in axils of winged stems. Region. The Southwestern Region covers Arizona and New Mexico, which together have 11 national forests. • Reproduces solely via seed; two types of smooth The Region also includes four national grasslands located seed—one type is lighter in color with a pappus of in northeastern New Mexico, western Oklahoma, and the barbed bristles, the other is darker without a pappus. Texas panhandle. • Leaves and stem become straw colored as seeds form; flower head becomes straw colored when seeds are mature; seeds are viable for up to 10 years. Description Yellow starthistle (synonyms: golden starthistle, St. Ecology Barnaby’s thistle, yellow cockspur) is an early maturing Impacts/threats winter annual. Native to Eurasia, it was introduced into Yellow starthistle is highly competitive and often develops North America as a seed contaminant in the mid-1850s dense, impenetrable stands that lower the diversity of and has persistently spread across the western United desirable flora and fauna species. The presence of sharp long States. It is found in foothill regions of southwestern New spines on seed heads of yellow starthistle degrades livestock Mexico and elsewhere in deserts, uplands, rangelands, and grazing, wildlife habitat, and recreational opportunities. mountainous areas of the Southwest. Yellow starthistle is When forced to graze mature yellow starthistle, livestock similar in appearance to two closely related species: C. (especially horses) can be affected by an incurable melitensis (Malta starthistle) and C. sulphurea (Sicilian neurological disorder known as “chewing disease.” A starthistle). neurotoxic sesquiterpene lactone in starthistles called repin is believed to be the underlying cause of the disorder. Growth Characteristics However, animals in general typically avoid the weed • Grey-green to blue-green, herbaceous plant covered because of the sharp spines and hairs. in fine, white cottony hairs. Location • Winter annual and occasional biennial; germinates fall to spring. Yellow starthistle prefers well-drained soils, hot dry summers, and 10 to 60 inches of precipitation. It occurs • Stout, rapidly growing, vigorous taproot; may grow in open woodlands, desert scrub, chaparral, rangeland, deeper than 36 inches. pastures, waste areas, cropland, and roadsides that generally • Rosette in fall/winter; deeply lobed leaves appear lie below 7,500 feet in elevation. It is commonly found ruffled; fine, cottony hairs. around residential subdivisions, agricultural land, and • Bolts May to June; stiff, openly-branched stems; 6 to recreation areas throughout the Western States. 60 inches tall; large stem 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 easily attaches to fur, 1 hair, or clothing; and it can be transported over far distances Table 1 summarizes management options for controlling by adhering to tires and undercarriages of road vehicles and yellow starthistle under various situations. Choice of equipment. Yellow starthistle seed may also be introduced individual control method(s) for starthistle depends on many into new areas through transported hay that is not certified local factors including degree of infestation, current land to be weed free. use, and site conditions (terrain, accessibility for treatment, microclimate, nontarget flora and fauna present, etc.). Other Invasive Features important considerations include treatment effectiveness, Yellow starthistle is a prolific seed producer and within overall cost, and the number of years needed to achieve dense stands can produce 50 to 100 million seeds per acre. control. Typically, more than one control method may be It is highly adaptable to environmental variation and grows needed for a particular site. rapidly. This allows yellow starthistle to out-compete native plant species for sunlight, space, water, and nutrients. Other Physical Control features that facilitate invasiveness include a deep taproot Yellow starthistle reproduces solely by seed, so physical that accesses available soil moisture, winged stems that methods should focus on reducing seed production and dissipate heat, and formidable spines at maturity that deter preventing seed germination. These methods usually have to grazing by livestock or wildlife. be repeated and must be timed properly to be most effective. Manual Methods Management Hand pulling or hoeing are most effective in a maintenance In many cases, 3 or more years of intensive management program for an area where yellow starthistle is relatively may be necessary to significantly reduce a yellow starthistle sparse. Take care to remove as much of the taproot as population. Early detection and eradication soon after possible. Anticipate that hand removal will need to be discovery will increase the possibility for control of a repeated in about 2 weeks to remove missed plants or those starthistle population. A high priority should be treatment maturing at a later time. Care should be taken to minimize of small or sporadic infestations on otherwise healthy soil disturbance and to properly dispose of plant debris by sites, which can then be shifted to larger infestations. The bagging and/or burning. following actions should be considered when planning a Mechanical Methods management approach to control starthistle: In suitable terrain, tillage in early summer with a plow or • Maintain healthy plant communities to suppress or disc that is repeated at a later time (about 4 to 6 weeks) can limit the impact of a starthistle infestation. effectively bury yellow starthistle plant parts. A harrow, • Incorporate sound grazing management with any knife, or drag pulled behind a tractor can be used to cut and control strategy. separate shoots from roots of larger mature plants. These methods are most commonly used in agronomic or roadside • Map known infestations and keep annual records of settings and should only be used when the soil surface is dry reported infestations. since fragmented plant segments in moist soils will regrow • Combine mechanical, cultural, biological, and and possibly magnify the problem. chemical methods to control yellow starthistle populations whenever possible. Mowing is a commonly used control technique for yellow starthistle along roadsides and in recreational areas. • Include monitoring and a followup treatment plan for Although it can be a cost-effective method for starthistle missed plants and seedlings. control, mowing is not feasible in many locations due to 2 Table 1. Management Options* Site Physical Methods Cultural Methods Biological Methods Chemical Methods Roadsides Use repeated, shallow Educate road crews to identify and Consider using weevils or Use truck spraying cultivation and/or report infestations along roads; rust fungus as biological equipment to apply mowing throughout implement requirements for vehicle control agents (see table 2). herbicide during early germination and operations in infested areas. Effectiveness of agents may growth. Clean equipment growing periods. be limited due to possible to prevent spread. Gravel and other road materials disturbances in agent life cycles transported into uninfested areas from roadside operations. should be weed free. Rangelands Use repeated, shallow Use certified weed-free hay and Use prescribed grazing For extensive and dense cultivation and/or seed. during spring with an intense, infestations, use ground mowing throughout short-duration approach in or aerial broadcast After passing through infested areas