A lowseverity fire will not kill the belowground reproductive structures of diffuse knapweed, but a severe fire can kill some of the plant crowns. Please consult the plants web site and your state department of natural. Diffuse knapweed department of agriculture conservation. A weed report from the book weed control in natural areas in the western united states diffuse knapweed. On the other hand, spotted knapweed can be the first species to recover from a burn. Within 2 years of burning, most diffuse knapweed rosettes were eliminated. Diffuse knapweed was found in one north dakota county in 1996 and infested approximately 20 acres. Spotted knapweed tolerates a wide range of temperature and moisture conditions, and is well adapted to openforest, pastures, and crp land in wisconsin. Burning has been shown to give effective control of diffuse knapweed while stimulating grass regrowth. Spotted k napweed has purple flowers very rarely white. Forest service forest health technology enterprise team.
It is usually found on plains, rangelands, and forested benchlands, particularly on rugged or. During the first year of growth, diffuse knapweed appears as a rosette in spring or fall. A weed report from the book weed control in natural areas in the western united states spotted knapweed. The plant has a white flower, grows to a height of 24 inches, and has a short taproot. In the united states, diffuse knapweed is generally found on light, dry, porous soils. Also, if you burn certain areas with sagebrush, it is possible to start the spread of diffuse knapweed. Mowing diffuse knapweed in british columbia at the bud stage and again at flowering reduced the number of plants producing seed by 77 to 99% compared to unmowed plants. It is often found in open, disturbed areas where it grows in tufted clumps. Diffuse knapweed is a shortlived perennial or sometimes biennial plant reproducing solely by seed. It is a possibility that severe fire may kill it, but seeds that are buried survive fire and regrow. Diffuse knapweed was introduced from europe and is a biennial or shortlived perennial forb, which reproduces only by seed. United states department of agriculture natural resources. Knapweed note natural resource ecology and management.
It has been two and a half years since my last surgery and no. Minutus prefers diffuse knapweed while obtusus prefers spotted knapweed. Diffuse knapweed identification and management diffuse. Also, rosettes of diffuse knapweed have more finely divided leaves than those of spotted knapweed figure 2. Diffuse is a member of a large genus of over 400 species, most originating in the mediterranean region. Thirteen biological pest control agents have been used against this plant and its cogener, diffuse knapweed, including the moths agapeta zoegana and metzneria paucipunctella, the weevils bangasternus fausti, larinus obtusus, and larinus minutus and cyphocleonus achates, and the fruit flies chaetorellia acrolophi, urophora affinis and urophora. Diffuse knapweed centaurea diffusa is a shortlived perennial, a biennial, or occasionally an annual in the sunflower family asteraceae. The plant is efficient at robbing the soils of nutrients and water and because it spreads quickly it can dominate a site to where there is no forage for livestock and wildlife. Spotted knapweeds arrival in north america is estimated in the early 1890s. 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. Centaurea diffusa wikibooks, open books for an open world. Spotted knapweed, centaurea stoebe, is perhaps the most widespread species, followed in abundance by diffuse knapweed, c.
Spotted and diffuse knapweed were first introduced to. Cultivation is effective when repeated, but diffuse knapweed typically grows in areas not conducive to. Seed remains viable in the soil five years or more, so infestations may occur a number of years after vegetative plants have been eliminated. Figure 10 plants of diffuse knapweed, more branched than those of spotted knapweed, grow 12 feet tall. Their larvae mine the root of diffuse knap weed, reducing plant vitality and providing a port of entry for fungal infection. Plants form dense colonies and readily reproduce by seeds, which can travel long distances. Figure 11 the flower of the diffuse knapweed plant is generally white but can be lavender or purple.
Diffuse knapweed north dakota department of agriculture. Larval feeding in the seedhead destroys the knapweed seed before it matures. Effects of postfire conditions on germination and seedling success of diffuse knapweed in northern arizona. The beetle feeds on the seed heads but is also a foliage feeder as an adult. 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 national invasive species information. Compared to spotted knapweed, the leaves of diffuse knapweed are small, and the numerous flower heads are narrow with spiny bracts. United states biological control of spotted and diffuse knapweeds. The flowers are white or sometimes purple, with small, sharp, rigid spines on the bracts. Spotted centaurea biebersteinii and diffuse knapweed centaurea diffusa are biennial to shortlived perennials, and considered regionally noxious under the bc weed control act. This plant may be known by one or more common names in different places, and some are listed above. Diffuse knapweed is generally a shortlived perennial or biennial in north dakota and invades habitats similar to spotted knapweed. Diffuse knapweed survives most low burning and medium fires. Insects that eat spotted knapweed weedbusters biocontrol.
Invasion biology introduced species summary project. Diffuse knapweed is considered an invasive species throughout north america, having established itself in many areas of the continent. Diffuse knapweed prefers open sunny habitats and dry conditions and competes well on excessively drained soils. However, mowing at the late bud to early bloom stage will reduce seed production. Diffuse knapweed cannot tolerate cultivation or excessive moisture and. Not listed on any labels except for diffuse knapweed on the banvel label. 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. Timing of application is not critical for controlling spotted or diffuse knapweed, grazonnext hl may be applied any time during the growing season or fall ditomaso et al. 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 hybrid alfalfa seed from germany. The seed is commonly spread by vehicles or by the sale and movement of contaminated sand and gravel. This plant can be weedy or invasive according to the authoritative sources noted below. Diffuse knapweed is found on plains, rangelands, and forested benchlands. Diffuse knapweed tumble knapweed, bushy knapweed asteraceae compositae, the aster family background.
Diffuse knapweed is a member of the aster family, thistle tribe. Diffuse knapweed is an annual or biennial plant, generally growing to between 10 and 60 cm in height. Similar to diffuse and spotted knapweed, russian knapweed was first introduced into canada around 1900 as a contaminant of alfalfa seed. Diffuse knapweed infests roadsides, waste areas, dry rangelands and disturbed sites.
However both species of weevils feed readily on both species of knapweed. They typically invade disturbed sites along roads and subsequently spread into disturbed especially overgrazed rangelands and pastures. Click on an acronym to view each weed list, or click here for. Diffuse knapweed, a biennial or shortlived perennial, and spotted knapweed, a perennial, are taprooted eurasian weeds invading rangeland in the western united states and canada. The seeds can germinate from spring through early fall. Diffuse knapweed is a native of eurasia, coming to the u.
However, its growth develops a ballshaped appearance and a tumbleweed. Spotted knapweed is distinguished from the closely related species, diffuse knapweed c. One larva can consume 100% of the seed in a single seedhead. In colorado, diffuse knapweed cover declined from 8. Plants profile for centaurea diffusa diffuse knapweed. Reductions of 95% or greater in diffuse knapweed stand density have been. Diffuse knapweed centaurea diffusa shortlived perennial, annual, or monocarpic perennial knapweed with a long fibrous taproot and single upright stem covered in fine hairs. Currently distributed throughout southern bc, both spotted and diffuse knapweed are a major concern in the omineca, peace river, kootenay. Seeding desirable perennial grasses is essential to prevent weed reinvasion beck 1997. It spreads by seed, aided by the tumbling of windblown mature plants, and it grows under a wide range of conditions. Bee keepers value the flowers of spotted knapweed because of the flavorful honey produced from its nectar. It is one of the only knapweeds that spread by tumbling by the wind like russian thistle. A biennial is a plant that completes its life cycle within two years.
Figure agapeta zoegana, a bright yellow moth, originates from the mediterranean region of europe. 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. Spotted knapweed and diffuse knapweed are both shortlived perennials that sometimes behave like annuals. 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 was brought in from europe mediterranean region. If you then carefully split this there is a good chance that there will be a small grub inside. One plant can give rise to 1 to 20 slender, upright stems 24 feet in height with most branching occurring in the upper half. Pdf the decline of diffuse knapweed in british columbia. The following section summarizes results of herbicides labeled for spotted and diffuse knapweed control on grazing lands and wildlands. Diffuse knapweed has hairy, greyishgreen, split leaves on many branches growing from a single upright stem. To support our efforts please browse our store books with medicinal info, etc. It produces toxic chemicals that can inhibit the growth of desired plants and is a highly competitive plant. Top american libraries canadian libraries universal library community texts project gutenberg biodiversity heritage library childrens library. Knapweed removal information how to get rid of knapweed.
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. Biology and biological control of knapweeds pdf 45. When the plant is broken off at the base, it can be blown around like a tumbleweed and disperse its seed. King county best management practices for diffuse knapweed. 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. The most successful agent for use against diffuse knapweed is the seed head feeding weevil, larinus minutus. Growth habit perennial, spotted is biennial or short lived perennial. Diffuse knapweed reproduces primarily by seed but may also regenerate from the crown. This species is common throughout western north america but is not actually native to the north american continent, but to the eastern mediterranean. Yellow starthistle is another less robust annual type. Spotted knapweed is a biennial or shortlived perennial. Because diffuse knapweed is an obligate outcrosser, seed production can be greatly reduced when diffuse knapweed is mowed prior to flowering.
Diffuse knapweed floral bracts have yellow spines with teeth appearing as a comb and a distrinct terminal spinte. Spotted knapweed has hairy, deeplycut leaves and purple flowers occasionally white on one or more upright stems. When combined with the widespread knapweed seedhead flies. Search the history of over 424 billion web pages on the internet. Diffuse knapweed centaurea diffusa, also known as white knapweed, is a member of the genus centaurea in the family asteraceae. Diffuse knapweed has white flowers very rarely purple and has sharp tipped bracts bracts are the scales around the seed head. A single plant can produce approximately 18,000 seeds. Spotted knapweed grows 12 to 60 inches tall, is more erect and has more limited branching than diffuse knapweed. Dead spotted knapweed stems generally remain erect during the winter unless crushed by heavy snowpack.
Life cycle of spotted and diffuse knapweed knapweeds can establish in most soil types but are most productive in sandy, welldrained soils and thrive in dry environments. Diffuse knapweed had spread to four counties by 2017 and infested nearly 750 acres. Diffuse and spotted knapweed biocontrol department of. Diffuse knapweed centaurea diffusa also grows a single, branched stem from a similar looking rosette. Spotted knapweed is listed as noxious, prohibited, banned or otherwise regulated in 16 states. Flowerheads are usually white sometimes pink to purple and are solitary or in clusters. History s potted knapweed is native to central europe and eastern to central russia, caucasia, and western siberia. Spotted knapweed produces chemicals that inhibit nearby plant growth, forming own habitat highly competitive with native vegetation, reducing forage for livestock and large game an hybridize with diffuse knapweed native to eurasia always read herbicide labels and follow instructions for use and ppe. Centaurea maculosa, the spotted knapweed, is a species of centaurea native to eastern europe description and habitat.
The physical appearance of diffuse knapweed is similar to spotted knapweed, except diffuse knapweed is generally shorter and more highly branched. Nu merous centaurea species introduced into the united states have become invasive, most notably, yellow st arthistle c. Bracts are not sharp tipped and are fringed in black giving the seed head a spotted appearance. 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. The earliest collection of spotted knapweed is from victoria, british columbia in 1893. Largescale control against diffuse knapweed has been seen at a number of locations along the front range. This biennial or shortlived perennial plant usually has a stout taproot andor pubescent stems when young. These two species of insects are nearly indistinguishable.
University of nebraskalincoln extension ec173 revised. It is currently found in the largest concentrations in the keremeos area, and in smaller patches in the east kootenay region, okanagan, merritt. Biological control of spotted and diffuse knapweeds. It is native to asia minor turkey, syria, the balkans, bulgaria, greece, romania, ukraine, and southern russia. The combination of 2,4d with aminopyralid in grazonnext hl. Diffuse knapweed often assumes a short rosette form for one year, reaching maximum size, then rapidly growing and flowering during the second year. If you pinch off an old flower head in the autumn, pull off any loose seed heads, there is a very hard kernel. 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. Diffuse knapweed has been observed at elevations up to 8,500 feet k. Diffuse knapweed the enemy diffuse knapweed centaurea diffusa this annual and sometimes biennial noxious weed is a native of eurasia and spread into the u. The strategy diffuse knapweed spread into lightly disturbed areas, and in some cases can invade crops such as alfalfa and grains. The enemy diffuse knapweed centaurea diffusa this annual and sometimes biennial noxious weed is a native of eurasia and spread into the u. It is a highly competitive plant which threatens to exclude many desirable species from pastures and wildlands. Diffuse knapweed is a nonnative biennial forb that reproduces solely by seed.