Acroptilon repens (L.) DC.
Acroptilon repens (L.) DC.Centaurea repens (L.), Russian Knapweed
Threat Level | Category |
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Emerging | Forb/Herb |
Similar Species May be confused with the following native and/or non-native species. Landscape Alternatives lists native horticultural substitutes |
Centaurea spp. Landscape Alternatives |
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Description
Height
Russian Knapweed is a perennial herbaceous plant that grows 18-36 inches (45-90 cm) in height.Stems
Stems are erect with many branches.Leaves
Leaf characteristics are variable for this plant. Basal leaves form a rosette and are 2-4 inches (5-10 cm) long, 0.4-1 inch (1-2.5 cm) broad. They are oblanceolate and vary between irregularly pinnately lobed or entire. Lower stalk leaves range from oblong to linear-lanceolate and are deeply lobed. Upper stalk leaves are oblong, toothed, and progressively smaller near the apex of the stalk.Flowers
Each stem tip has a solitary, urn-shaped flower head with numerous pink or purple tubular flowers in late May through mid-June (in the United States). The individual florets are 0.6-0.7 inch (15-17 mm) in height. The flower heads are 0.25-0.50 inch in diameter with smooth papery bracts. Flowers turn straw-color at maturity.Fruit
Gray to ivory colored seeds are produced in late June and are small and oval in shape (0.8-1.2 inches [2-3 mm] long) with a small, lengthwise ridge. Individual plants can produce up to 1,200 seeds per year and remain viable two to three years in the soil.Images
Photo: Steve Dewey, Utah State University, Bugwood.orgMore images of Acroptilon repens
Life History
Russian Knapweed is a perennial herbaceous plant in the Aster (Asteraceae) family. It reproduces primarily vegetatively through an extensive horizontal rooting system. Seed reproduction is secondary. The original taproot can sustain horizontal rooting over extensive areas rapidly, estimated up to 23 feet (7 m). Buds from the horizontal roots can form adventitious flowering shoots, and some stands of Russian Knapweed are found in densities of 10-30 shoots per square foot. It is believed to be allelopathic and is toxic to horses.Habitat
In its introduced range, Russian Knapweed is found at lower elevations in semi-arid, open habitats and does well in clay soils. It is commonly found in highly disturbed areas such as roadsides, riverbanks, irrigation ditches, pastures, clearcuts, and croplands but can also be found in less-disturbed open grasslands, shrublands, and riparian forests.Origin & Distribution
Russian Knapweed is thought to be native to southwestern Asia including Mongolia, western Turkestan, Iran, and Turkish Armenia. It is now widely distributed and found on every continent except for Antarctica. Russian Knapweed was accidentally introduced to North American at least twice via contaminated Turkestan alfalfa seed. Seeds reached Canada around 1900 did not become a serious problem until 1928 when it was widely distributed in hay feed. Likewise, seeds were accidentally brought to California around 1910 and moved quickly into the intermountain west.Russian Knapweed is now found across much of western North America, including 5 Canadian provinces and 27 U.S. states. It is listed as a noxious weed in 18 of those states. States with the worst infestations are California, Idaho, Montana, Oregon, and Washington, though populations are reported as far east as Ohio, Kentucky, and Texas.
Sources
Carpenter, A. T. and T. A. Murray. Element Stewardship Abstract for Acroptilonrepens (L.) De Candolle. The Nature Conservancy, Arlington, VA. http://www.imapinvasives.org/GIST/ESA/index.html
USDA PLANTS Database Profile: Acroptilon repens (L.) DC.
http://plants.usda.gov/java/nameSearch?keywordquery=Acroptilon+repens&mode=sciname&submit.x=0&submit.y=0
Management Recommendations
he Nature Conservancy’s Element Stewardship Abstract reports “there is no single ‘silver bullet’ control method†for this species, suggesting integration of many techniques that focuses control on existing infestations and promotes use of native species. Management sites need continued monitoring and follow-up control to prevent reinfestation. Interested readers should consult this document for a more detailed account of control measures for this species.Mechanical Control
Cutting, Mowing, Discing, and Pulling: These methods will remove above-ground biomass of the plant, and if used repeatedly over the course of the growing season, will stress plants. If cut while flowering, this will also eliminate new seed production. However, Russian Knapweed’s extensive root system allows the plant to store energy and allow for regrowth after many repeated control events.Chemical Control
Foliar Spray Method
There are two herbicides that are reported as effective for controlling Russian Knapweed. To achieve maximum control, herbicides should be applied using a backpack sprayer or wick to prevent damage to non-target plants. Spraying during late fall, during the budding stage of the species will achieve best control. Readers should follow labels on specific herbicides and consult state guidelines for herbicide application.Picloram -- Picloram, trade names TordonTM and GrazonTM, contains a synthetic hormone, auxin, that causes continued cell growth to eventually kill dicot plants. It is reported to not effect grasses or monocots but may inhibit germination of perennial grasses.
Clopyralid -- Clopyralid, trade names TranslineTM, CurtailTM, and StingerTM, also contains a synthetic hormone, auxin, which causes continued cell growth to eventually kill dicot plants. However, it is more selective than picloram, only affecting certain families of broadleaved plants including composites (Asteraceae), legumes (Fabaceae) and smartweeds (Polygonaceae). It is reported to not effect grasses or monocots but may inhibit germination of perennial grasses.
Glyphosate -- Glyphosate, trade names Roundup®, Roundup® Ultra, Rodeo®, and Accord are amino-acid inhibitors that are less selective than clopyralid or picloram and will kill broadleaved plants and grasses. However, glyphosate adheres strongly to soil particles, biodegrades in the soil (half-life of 60 days) and will not leach into groundwater or inhibit germination of seeds applied to soils.