Reductions of 95% or greater in diffuse knapweed stand density have been. Diffuse knapweed may suppress other vegetation by allelopathy 16,26. Once it has been established at a disturbed site, it continues to spread into the surrounding habitat. The beetle feeds on the seed heads but is also a foliage feeder as an adult. History s potted knapweed is native to central europe and eastern to central russia, caucasia, and western siberia. It is currently found in the largest concentrations in the keremeos area, and in smaller patches in the east kootenay region, okanagan, merritt. When the plant is broken off at the base, it can be blown around like a tumbleweed and disperse its seed.
It is currently found from yukon in the north, throughout most of western canada, east to ontario. Thomas thanks for your detailed and helpful response about all the biocontrol species in our area. Diffuse knapweed is a shortlived perennial or sometimes biennial plant reproducing solely by seed. Diffuse knapweed survives most low burning and medium fires. Diffuse knapweed was brought in from europe mediterranean region.
Knapweed removal information how to get rid of knapweed. Diffuse knapweed north dakota department of agriculture. Diffuse knapweed was found in one north dakota county in 1996 and infested approximately 20 acres. Picloram tordon, clopyralid stinger, 2,4d and dicamba banvel will control spotted and diffuse knapweed on range land. Diffuse knapweed centaurea diffusa is a shortlived perennial, a biennial, or occasionally an annual in the sunflower family asteraceae. This biennial or shortlived perennial plant usually has a stout taproot andor pubescent stems when young. Dead spotted knapweed stems generally remain erect during the winter unless crushed by heavy snowpack. A weed report from the book weed control in natural areas in the western united states spotted knapweed.
However both species of weevils feed readily on both species of knapweed. Diffuse knapweed is a bushy, taprooted bienniel or shortlived perennial. The duration of knapweed control on any site is dependent on herbicide properties, number and type of biological control agents present, and environmental conditions such as soil type, rainfall, and presence of competitive desirable vegetation. Diffuse knapweed national invasive species information. This species is common throughout western north america but is not actually native to the north american continent, but to the eastern mediterranean. Compared to spotted knapweed, the leaves of diffuse knapweed are small, and the numerous flower heads are narrow with spiny bracts. Centaurea diffusa wikibooks, open books for an open world. Plants form dense colonies and readily reproduce by seeds, which can travel long distances. Diffuse knapweed tumble knapweed, bushy knapweed asteraceae compositae, the aster family. Knapweed is a pioneer species found in recently disturbed sites or openings. If you then carefully split this there is a good chance that there will be a small grub inside. Centaurea diffusa, also known as diffuse knapweed, white knapweed or tumble knapweed, is a member of the genus centaurea in the family asteraceae.
Diffuse knapweed infests roadsides, waste areas, dry rangelands and disturbed sites. This plant may be known by one or more common names in different places, and some are listed above. Figure 11 the flower of the diffuse knapweed plant is generally white but can be lavender or purple. Spotted knapweeds arrival in north america is estimated in the early 1890s. Not listed on any labels except for diffuse knapweed on the banvel label. Distribution, biology, and management of diffuse knapweed. Although russian knapweed is closely related to the spotted and diffuse knapweeds, there are some distinct differences too, enough differences that it is sometimes considered a different genus, acroptilon repens. During the first year of growth, diffuse knapweed appears as a rosette in spring or fall. Spotted centaurea biebersteinii and diffuse knapweed centaurea diffusa are biennial to shortlived perennials, and considered regionally noxious under the bc weed control act. These herbicides are selective for broadleaf weeds and generally do not harm grasses when applied at recommended rates. Click below on a thumbnail map or name for species profiles. If you pinch off an old flower head in the autumn, pull off any loose seed heads, there is a very hard kernel. Spotted k napweed has purple flowers very rarely white.
Figure 10 plants of diffuse knapweed, more branched than those of spotted knapweed, grow 12 feet tall. The enemy diffuse knapweed centaurea diffusa this annual and sometimes biennial noxious weed is a native of eurasia and spread into the u. The seed is commonly spread by vehicles or by the sale and movement of contaminated sand and gravel. This book was published by fhtet as part of the technology transfer. Diffuse knapweed is native to the eastern mediterranean region to western asia, and from the former republic of the soviet union to western germany. Diffuse knapweed centaurea diffusa shortlived perennial, annual, or monocarpic perennial knapweed with a long fibrous taproot and single upright stem covered in fine hairs. The seeds can germinate from spring through early fall. Click on an acronym to view each weed list, or click here for a composite list of weeds of the u. Growth habit perennial, spotted is biennial or short lived perennial. It is a highly competitive plant which threatens to exclude many desirable species from pastures and wildlands. Biology and biological control of knapweed invasive. Diffuse is a member of a large genus of over 400 species, most originating in the mediterranean region. A weed report from the book weed control in natural areas in the western united states diffuse knapweed.
Spotted knapweed uc weed research and information center. Knapweed note natural resource ecology and management. Prohibited noxious, class 1 in the canadian weed seeds order, 2016 under the seeds act. Diffuse knapweed is generally a shortlived perennial or biennial in north dakota and invades habitats similar to spotted knapweed. However, its growth develops a ballshaped appearance and a tumbleweed. Story jm, piper gl 2001 status of biological control efforts against spotted and diffuse knapweed. Larval feeding in the seedhead destroys the knapweed seed before it matures. It is native to asia minor turkey, syria, the balkans, bulgaria, greece, romania, ukraine, and southern russia. Largescale control against diffuse knapweed has been seen at a number of locations along the front range.
Spotted knapweed and diffuse knapweed are both shortlived perennials that sometimes behave like annuals. Spotted knapweed is driving out native plants and destroying rangeland. It is one of the only knapweeds that spread by tumbling by the wind like russian thistle. Centaurea maculosa, the spotted knapweed, is a species of centaurea native to eastern. Burning may be an effective means of controlling diffuse knapweed in areas where seasonal or occasional fires are part of the natural ecosystem zimmerman 1997. Diffuse knapweed survives in a wide range of soil and environmental conditions, and produces large numbers of viable. To support our efforts please browse our store books with medicinal info, etc. This plant can be weedy or invasive according to the authoritative sources noted below. Spotted knapweed tolerates a wide range of temperature and moisture conditions, and is well adapted to openforest, pastures, and crp land in wisconsin. One larva can consume 100% of the seed in a single seedhead.
United states department of agriculture natural resources. Bracts are not sharp tipped and are fringed in black giving the seed head a spotted appearance. Im trying to establish some biocontrol insects on more remote knapweed populations in the garnet mountains. Similar to diffuse and spotted knapweed, russian knapweed was first introduced into canada around 1900 as a contaminant of alfalfa seed. Centaurea maculosa, the spotted knapweed, is a species of centaurea native to eastern europe description and habitat. Its basal leaves leaves at the stem base have short stalks and grow 7 to 8 inches long. Centaurea biebersteinii, centaurea maculosa misapplied name, centaurea stoebe ssp.
Plants profile for centaurea diffusa diffuse knapweed. United states biological control of spotted and diffuse. The plant has a white flower, grows to a height of 24 inches, and has a short taproot. It is a possibility that severe fire may kill it, but seeds that are buried survive fire and regrow.
It grows from 8 to 40 inches tall, with branching stems covered in short, dense hairs and a very long tap root. Seed remains viable in the soil five years or more, so infestations may occur a number of years after vegetative plants have been eliminated. Diffuse knapweed was first introduced to the pacific northwest at the turn of the century as a contaminant in alfalfa seed imported from turkestan, turkmenistan or. Flowerheads are usually white sometimes pink to purple and are solitary or in clusters. Jim story, an entomologist at montana state university, has gone to central and. Wilson1 and carol bell randall2 1 department of plant, soil and entomological sciences, university of idaho, p. Diffuse knapweed centaurea diffusa also grows a single, branched stem from a similar looking rosette. Invasion biology introduced species summary project.
Ill walk a little more slowly on weedy bike paths this week, and see if i can find a good spot to get some cyphocleonus weevils, and even agapeta moths. It produces toxic chemicals that can inhibit the growth of desired plants and is a highly competitive plant. Diffuse knapweed has white flowers very rarely purple and has sharp tipped bracts bracts are the scales around the seed head. Diffuse knapweed is an annual or biennial plant, generally growing to between 10 and 60 cm in height. Impacts of the biological control agent cyphocleonus achates on spotted knapweed, centaurea. George beck, colorado state university cooperative extension adapted from the colorado state university extension natural resources fact sheet diffuse and spotted knapweed identification and life cycle. Currently distributed throughout southern bc, both spotted and diffuse knapweed are a major concern in the omineca, peace river, kootenay. Wicked weed of the west science smithsonian magazine.
Click on an acronym to view each weed list, or click here for. It has been two and a half years since my last surgery and no problems have occurred in my other fingers at this point. Biology and biological control of knapweed linda m. Background information impacts and history diffuse knapweed is native to asia minor, the balkans, and the ukraine and crimea. Spotted knapweed s arrival in north america is estimated in the early 1890s. Diffuse knapweed centaurea diffusa, also known as white knapweed, is a member of the genus centaurea in the family asteraceae.
Diffuse knapweed is a biennial or shortlived perennial with a deep taproot in the aster family that is similar to the more common spotted knapweed, but is generally shorter and its upper stems have numerous spreading branches giving the plant a ball shape. A biennial is a plant that completes its life cycle within two years. Diffuse and spotted knapweed biocontrol department of. The doctor at the u of w said that there is a compound in knapweed that is cancer causing, this compound was isolated in russian knapweed and probably occurs in spotted and diffuse knapweed also. Diffuse knapweed is a native of eurasia, coming to the u. The plants database includes the following 37 species of centaurea. Spotted and diffuse knapweed were first introduced to. This species outcompetes natives through at least three methods. A weed report from the book weed control in natural areas in the. Effects of postfire conditions on germination and seedling success of diffuse knapweed in northern arizona. It spreads by seed, aided by the tumbling of windblown mature plants, and it.
It spreads by seed, aided by the tumbling of windblown mature plants, and it grows under a wide range of conditions. Centaurea diffusa diffuse knapweed centaurea diluta north african knapweed centaurea eriophora. The earliest collection of spotted knapweed is from victoria, british columbia in 1893. It has been two and a half years since my last surgery and no. The main identification features of spotted knapweed in comparison to five species that may appear similar. The earliest record of diffuse knapweed in north america is from an alfalfa field in washington state in 1907 86. Diffuse knapweed had spread to four counties by 2017 and infested nearly 750. When combined with the widespread knapweed seedhead flies. King county best management practices for diffuse knapweed. The following section summarizes results of herbicides labeled for spotted and diffuse knapweed control on grazing lands and wildlands.
Diffuse knapweed reproduces primarily by seed but may also regenerate from the crown. Also, if you burn certain areas with sagebrush, it is possible to start the spread of diffuse knapweed. Diffuse knapweed contains varying concentrations of phytotoxic secondary compounds 64,91,106. Russian knapweed centaurea repens aster family thistle subfamilyby thomas j. The most successful agent for use against diffuse knapweed is the seed head feeding weevil, larinus minutus. Box 442339, moscow, id 838442339 2 forest health protection, usda forest service, 3815 schreiber way, coeur dalene, id 838158363 for additional copies of this publication, contact. Diffuse knapweed had spread to four counties by 2017 and infested nearly 750 acres. However, mowing at the late bud to early bloom stage will reduce seed production. All imported and domestic seed must be free of prohibited noxious weed seeds. Russian knapweed is the most difficult to handle, since this perennial knapweed digs in for the long haul it can set roots as deep as 20 feet below the surface of the soil. Diffuse knapweed is a nonnative biennial forb that reproduces solely by seed. In colorado, diffuse knapweed cover declined from 8. Centaurea diffusa, also known as diffuse knapweed, white knapweed or tumble knapweed, is a.
Seeding desirable perennial grasses is essential to prevent weed reinvasion beck 1997. Cultivation is effective when repeated, but diffuse knapweed typically grows in areas not conducive to. Spotted knapweed centaurea stoebe 5 lookalikes table 1. Yellow starthistle is another less robust annual type. Spotted knapweed grows 12 to 60 inches tall, is more erect and has more limited branching than diffuse knapweed. Minutus prefers diffuse knapweed while obtusus prefers spotted knapweed. Spotted knapweed is a bushy biennial to shortlived perennial, to 3 ft tall, with a long.