several crops where it causes economic Impacts Literature Cited Caution: Herbicides can be dangerous to Perennial sowthistle can form dense losses due to reduced crop yields, increased Alaska Exotic Plant Information Clearinghouse. the user and the environment unless used monospecific stands by the spread of its cultivation and herbicide expenses, and land 2005. Invasive Plants of Alaska. Alaska Association according to the label directions. Federal law rhizome-like roots. At high densities perennial depreciation. of Conservation Districts Publication. Anchorage, requires that the user read, understand, and sowthistle can drastically reduce water Alaska. follow all label directions. Consult with a UAF resources and likely decreases native plant Guidelines for Control Options Butterfield, C., J. Stubbendieck, & J. Stumpf. Cooperative Extension Service office near you diversity. It may also modify or retard the Manual Options: When hand-pulling, use (1996). Species abstracts of highly disruptive exotic for more information on use of herbicides. successional establishment of native species a shovel and take care to get as much of plants. Retrieved from Northern Prairie Wildlife Mention of a herbicide in this publication does not constitute a recommendation for use by Perennial (Butterfield et al. 1996). It is also a host to the root as possible. Mechanical Options: Research Center Web Site: http://www.npwrc. Mowing or cutting to reduce seed production usgs.gov/resource/othrdata/exoticab/exoticab.htm. the USDA, nor does it imply registration of a a number of plant pests and a problem in product under Federal Insecticide, Fungicide, and root reserves should be done a few times Rutledge, C.R., and T. McLendon. (1996) An Sowthistle and Rodenticide Act, as amended. Mention of per season for several years. Tillage that Assessment of Exotic Plant Species of Rocky a proprietary product does not constitute an Mountain National Park. Retrieved January 30, buries all root fragments more than 12 inches endorsement by the USDA. deep is reported to be effective; however, 2005 from Department of Rangeland Ecosystem tillage implemented incorrectly may increase Science, Colorado State University, Northern numbers by breaking up the rhizomes into Prairie Wildlife Research Center Home Page: separate pieces that can grow into new plants. http://www.npwrc.usgs.gov/resource/orthradata/ Herbicide Options: This weed is relatively Explant/explant.htm resistant to many, but not all, common Royer, F. & R. Dickinson. (1999). Weeds of the broadleaf herbicides (Butterfield et al. 1996, Northern U.S. and Canada. Edmonton, AB, Rutledge and McLendon 1996). The type Canada: The University of Alberta Press. of herbicide recommended depends on site Alaska Administrative Code, Title 11, Section factors and surrounding plant composition. 34.020. Prohibited and restricted noxious weeds. For more information on chemical treatment The U.S. Department of Agriculture (USDA) prohibits options, contact your local Cooperative Photo Credits discrimination in all its programs and activities on the Extension Service office. All photographs are by US Forest Service staff. basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, Annual sowthistle and spiny sowthistle may parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all be controlled through hand-pulling or cutting or part of an individual’s income is derived from any prior to flowering. Herbicide application is public assistance program. (Not all prohibited bases generally unnecessary for these two species apply to all programs.) Persons with disabilities who except for in cases with large infestations. require alternative means for communication of program information (Braille, large print, audiotape, etc.) should Figure 3. Perennial sowthistle appears above Notes: Sowthistle is a relative of chicory, and contact USDA’s TARGET Center at (202) 720-2600 with a brownish stem and yellow flowers. This its roots have been used to make a coffee-like (voice and TDD). photograph taken in the fall, shows the plants after beverage. Because of the high hydrocarbon To file a complaint of discrimination, write to USDA, many of the flowers have gone to seed. Perennial content of its milky sap, sowthistle has been Director, Office of Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410, or call sowthistle is capable of invading undisturbed areas investigated as a source of oil for manufacture United States Forest Service R10-PR-17 and has heavily infested this estuarine meadow (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA Department of Alaska Region October 2007 of plastics and pharmaceuticals. is an equal opportunity provider and employer. next to Hyder. Agriculture Scientific Name: Sonchus arvensis common in Alaska, known to grow in less bracts are of variable lengths and green with Perennial Sowthistle Family: Sunflower family (Asteraceae) than a dozen locations from Fairbanks to white margins. Seeds are dark brown and By Melinda Lamb and Tom Heutte, Biological Common Names: creeping sowthistle, field Ketchikan. prominently ridged and wrinkled with soft Technicians, US Forest Service, Alaska Region, sow-thistle, field sowthistle, moist sowthistle white bristly pappus. Of the two recognized State and Private Forestry. Perennial sowthistle (including both Description subspecies, ssp. uliginosus lacks glandular Additional information on this plant can be subspecies Sonchus arvensis ssp. arvensis Despite the common name, sowthistles hairs on the floral bracts and stalks; these obtained from your local UAF Cooperative and ssp. uliginosus) is an invasive plant that resemble dandelions more than they do the glandular hairs are generally present on ssp. Extension Service office, Alaska State Forestry is problematic throughout North America. true thistles such as Canada thistle. Perennial arvensis (figure 2). office, or from: It is listed as a noxious weed in Alaska and sowthistle usually grows 2–4 feet high and Similar Species: Spiny sowthistle (Sonchus US Forest Service therefore prohibited in the state by law has an extensive horizontal root system that asper) and annual sowthistle (Sonchus oleracus) State & Private Forestry (11 AAC 34.020). In southeast Alaska, it is grows up to 10 feet deep. All parts of the plant are annual herbs with short tap roots that Forest Health Protection invading remote areas such as riparian and exude a milky white juice when broken. Long distinguish them from perennial sowthistle, 3301 “C” Street, Suite 202 beach sites on Admiralty Island, Glacier Bay stems arise from a basal rosette of dandelion- which has long horizontal roots. The leaves Anchorage, Alaska 99503 National Park, and Portland Canal (AKEPIC like leaves. Stems are branched only at the of spiny sowthistle are shallowly lobed Phone: (907) 743-9455 2005). Sowthistle is a serious problem in top. Leaves are alternate, lance-shaped and with spiny margins and have distinctive, 2770 Sherwood Lane, Suite 2A agricultural areas because it has been found 2.5–16 inches long, with a clasping base and large rounded clasping flanges at the base Juneau, Alaska 99801-8545 to reduce crop yield greatly (Royer and prickly margins that vary from deeply toothed around the stem. Annual sowthistle can be Phone: (907) 586-8811, ext 283 to nearly entire (figure 1). Flower heads are Dickinson 1999), and it also reduces the distinguished from spiny sowthistle by the 3700 Airport Way 1–2 inches across and bright yellow. The floral growth of native plants in a variety of settings. acute pointed shape of the leaf base, which Fairbanks, Alaska 99709 In the lower 48 states and interior Alaska clasps the stem. Phone: (907) 451-2799 perennial sowthistle is primarily found along Or: roadsides or in agricultural areas. It has the Life History Figure 2. Glandular hairs are visible on the floral www.fs.fed.us/r10/spf/fhp potential to cause severe impacts to native bracts. Sowthistle is a perennial herb that reproduces http://akweeds.uaa.alaska.edu vegetation in tidal meadows and beach fringe from seed and spreading rhizome-like roots. www.dec.state.ak.us/eh/pest/index.htm sites, which provide important habitat, cover, A single plant can produce 4,000–13,000 below ground; with new buds arising from the and food for a variety of wildlife, including seeds that can remain dormant in the soil for rhizome-like roots in the spring, around the black bears, brown bears, deer, and migratory up to 6 years (Alaska Exotic Plant Information same time that sowthistle seeds germinate. waterfowl. Clearinghouse. 2005). Seeds are dispersed Two other species of sowthistles also occur by wind, by small hooks on the pappus that Habitat in Alaska; annual sowthistle (Sonchus oleracus readily attach to clothing and animal hair, and This plant can grow in a variety of habitat, but L.) and spiny sowthistle (Sonchus asper L. by birds that feed on the seeds. Spreading it prefers fine-textured soils, especially loams, [Hill]). Many of the occurrences of spiny rootstocks, however, are the primary means of and alkaline or neutral conditions. Perennial sowthistle are found along road corridors on invasion into new areas, as plants are capable sowthistle is highly tolerant of salty soils. It Prince of Wales Island. Of the three species of producing new plants from buds on the is commonly found in cultivated fields (both of sowthistle, annual sowthistle is the least roots up to 2 feet in depth. Early in the season grain and row crops), waste areas, meadows, the plants have a basal rosette that could be sloughs, woods, lawns, roadsides, beaches, Figure 1. Clasping leaf base on perennial sowthistle Cover Photo mistaken for dandelion. Plants over-winter ditches, and river and lakeshores (figure 3). . Perennial Sowthistle in flower.