It spreads by seed, aided by the tumbling of windblown mature plants, and it. Diffuse knapweed centaurea diffusa quick identification. Diffuse knapweed survives most low burning and medium fires. These weeds are well adapted to a wide range of habitats including open forests, rangeland, roadsides, pastureland, riparian areas, and ditch banks. Knapweed removal information how to get rid of knapweed. Also known as white knapweed and tumble knapweed, was introduced here as a contaminant of alfalfa from the caspian sea region of turkistan. This book was published by fhtet as part of the technology transfer series.
Diffuse knapweed infests roadsides, waste areas, dry rangelands and disturbed sites. Spotted knapweed is distinguished from the closely related species, diffuse knapweed c. Diffuse knapweed centaurea diffusa shortlived perennial, annual, or monocarpic perennial knapweed with a long fibrous taproot and single upright stem covered in fine hairs. Presently infestations of spotted knapweed in alaska are mostly managed manually by digging or pulling individual plants. The enemy diffuse knapweed centaurea diffusa this annual and sometimes biennial noxious weed is a native of eurasia and spread into the u. When a diffuse knapweed plant has been cut, the rosette may live and rebolt. Two cytotypes of the plant exist which have been named as either different species or subspecies. Yellow starthistle is another less robust annual type. United states biological control of spotted and diffuse knapweeds. University of nebraskalincoln extension ec173 revised. Identification seedling rosette is low lying with fnely divided leaves. Spotted knapweed is found at elevations up to and over 10,000 feet and in precipitation zones receiving 8 to 80 inches of rain annually. Diffuse knapweed is a native of eurasia, coming to the u.
Diffuse knapweed reproduces primarily by seed, and it is a prolific seedproducer. United states biological control of spotted and diffuse. However, when stressed by drought, grazing, or mowing, it may show shortterm perennial characteristics. Diffuse knapweed, is a biennial or shortlived peren. Biological control of spotted and diffuse knapweeds computer. Diffuse knapweed national invasive species information.
Focus on large blocks of uninvaded areas and keep them free of invaders. Established plants or stands of diffuse knapweed can be pulled or spot treated with picloram. Figure 11 the flower of the diffuse knapweed plant is generally white but can be lavender or purple. Native to the mediterranean region, diffuse knapweed was first recorded. In colorado, diffuse knapweed cover declined from 8. This plant can be weedy or invasive according to the authoritative sources noted below. Seastedt et al reduction in diffuse knapweed by insects x 237 weed science, 51. Because diffuse knapweed is an obligate outcrosser, seed production can be greatly reduced when diffuse knapweed is mowed prior to flowering. Diffuse knapweed populations and soil seed reserves were shown to decline by an average of 74% and 78%, respectively, at five sites in british columbia from the 1990s to 2009. These two species of insects are nearly indistinguishable. The single, occasionally double stem produces several spreading branches. This knapweed is widespread throughout rangeland in the western u. Diffuse knapweed minnesota department of agriculture.
A lowseverity fire will not kill the belowground reproductive structures of diffuse knapweed, but a. Within 2 years of burning, most diffuse knapweed rosettes were eliminated. A lowseverity fire will not kill the belowground reproductive structures of diffuse knapweed, but a severe fire can kill some of the plant crowns. Spotted centaurea biebersteinii and diffuse knapweed centaurea diffusa are biennial to shortlived perennials, and considered regionally noxious under the bc weed control act. It also thrives in disturbed habitats such as gravel pits, roadsides, railroad tracks, vacant lots, airports, trails and heavily grazed pasture. The single upright stem grows 15 to 60 cm in height and has numerous branches mostly on the upper half.
Diffuse knapweed, a classb designate noxious weed in franklin county, washington, centaurea diffusa is of the asteraceae family. The physical appearance of diffuse knapweed is similar to spotted knapweed, except diffuse knapweed is generally shorter and more highly branched. 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. Seed can also be spread in hay that is not certified to be weed free. Seed remains viable in the soil five years or more, so infestations may occur a number of years after vegetative plants have been eliminated. This is one of seven noxious weeds for which nebraska law mandates control. Spotted knapweed and diffuse knapweed are both shortlived perennials that sometimes behave like annuals. It is often found in open, disturbed areas where it grows in tufted clumps. Spotted knapweed integrated pest and crop management. Upright stems are branched at the top and the stems are ribbed, and sometimes as they age they become hairless. Centaurea diffusa, also known as diffuse knapweed, white knapweed or tumble knapweed, is a member of the genus centaurea in the family asteraceae.
It is one of the only knapweeds that spread by tumbling by the wind like russian thistle. Knapweed seed is easily dispersed by wind and water. Buds are urnshaped at the ends of branches with black spots on the bracts, without the long, rigid spines of diffuse knapweed. Diffuse knapweed north dakota department of agriculture. Larval feeding in the seedhead destroys the knapweed seed before it matures.
Controlling the spread of spotted knapweed is crucial to protecting alaskas native plants. I think that this knapweed spread very quickly in the years of 19751999. Reductions of 95% or greater in diffuse knapweed stand density have been. Additionally, diffuse knapweed seeds can remain dormant for several years, requiring any cutting program to be repeated several times annually spring, summer, and fall to be effective. Flowerheads are usually white sometimes pink to purple and are solitary or in clusters. It is a possibility that severe fire may kill it, but seeds that are buried survive fire and regrow. Some other interesting things are its effects against fire. Currently distributed throughout southern bc, both spotted and diffuse knapweed are a. Noxious weeds of nebraska nebraska extension publications. It has been two and a half years since my last surgery and no. Alaska plant materials center division of agriculture. Spotted knapweed is a biennial or shortlived perennial.
Plants profile for centaurea diffusa diffuse knapweed. Biology and biological control of knapweed invasive. The seed is commonly spread by vehicles or by the sale and movement of contaminated sand and gravel. Diffuse knapweed is a nonnative biennial forb that reproduces solely by seed. Plants form dense colonies and readily reproduce by seeds, which can travel long distances.
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. Pdf the decline of diffuse knapweed in british columbia. Affordable and search from millions of royalty free images, photos and vectors. Pdf sustainable control of spotted knapweed centaurea stoebe. This tap rooted member of the aster family is native to southeastern europe. These weeds are well adapted to a wide range of habitats including open forests, rangeland, roadsides, pastureland, riparian. Spotted knapweed is listed as noxious, prohibited, banned or otherwise regulated in 16 states. Compared to spotted knapweed, the leaves of diffuse knapweed are small, and the numerous flower heads are narrow with spiny bracts. It is a highly competitive plant which threatens to exclude many desirable species from pastures and wildlands. 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. Clopyralid, dicamba, and aminopyralid are registered for use on diffuse knapweed.
However both species of weevils feed readily on both species of knapweed. Bee keepers value the flowers of spotted knapweed because of the flavorful honey produced from its nectar. Spotted knapweed and diffuse knapweed are closely related noxious weeds infesting over 7 million acres in 17 western states duncan and jachetta 2005. 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. 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. We would also like to thank richard reardon of the forest health. King county best management practices for diffuse knapweed.
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. Diffuse knapweed identification and management diffuse. Diffuse is a member of a large genus of over 400 species, most originating in the mediterranean region. Spotted knapweed prefers welldrained, lighttextured soils that receive summer rainfall, including open. Diffuse knapweed tumble knapweed, bushy knapweed asteraceae compositae, the aster family. A winterhardy biennial or short lived perennial with a taproot. Forest service forest health technology enterprise team. Diffuse knapweed is very abrasive and bare skin contact can cause irritation, so wear gloves and a longsleeved shirt. Knapweed note natural resource ecology and management. A biennial is a plant that completes its life cycle within two years. Diffuse knapweed cannot tolerate cultivation or excessive moisture and. Effects of postfire conditions on germination and seedling success of diffuse knapweed in northern arizona. Only certified weedfree seed, hay and topsoil should be. Diffuse knapweed is a shortlived perennial or sometimes biennial plant reproducing solely by seed.
Executive office montana weed control association, inc. Burning has been shown to give effective control of diffuse knapweed while stimulating grass regrowth. Knapweed is a dull green plant entirely covered with small, rough hairs. Diffuse knapweed centaurea diffusa is an annual to short lived perennial plant that grows up to 40 inches tall from a long, stout tap root. After flowering, the dried plants may break off at the base of the stem and blow about like a tumbleweed, dispersing seed over long distances.
Also, rosettes of diffuse knapweed have more finely divided leaves than those of spotted knapweed figure 2. Distribution, biology, and management of diffuse knapweed centaurea diffusa and spotted. The colorado department of agriculture has released a number of biocontrol agents against diffuse and spotted knapweed including a two root boring beetles, two seed head feeding flies, seed head feeding weevils and seed head feeding moths. The seeds can germinate from spring through early fall. Several of these are well established in colorado and are probably having an impact on the knapweeds. Pdf spotted knapweed is native to eastern europe, with a locally scarce but widespread distribution from the mediterranean to. Diffuse and spotted knapweed biocontrol department of. This publication is available online or printed copies are available free from local extension offices. The stems and leaves are covered with fine hairs, giving the plants a pale green, almost white appearance at times.
Effect of biocontrol insects on diffuse knapweed centaurea. Please consult the plants web site and your state department of natural. This species is common throughout western north america but is not actually native to the north american continent, but to the eastern mediterranean. Figure 10 plants of diffuse knapweed, more branched than those of spotted knapweed, grow 12 feet tall. Monitor site annually until it is knapweedfree for. Spotted and diffuse knapweed reduce productivity of grazing lands and wildlife habitat and increase. Diffuse knapweed centaurea diffusa best management practices including impacts, history, habitat, description, reproduction, manual control, mechanical control, biological control, chemical control and best management pracoa ax kom. Diffuse knapweed grows in a variety of habitats in washington including river shores, rangeland and pastures. Knapweed reproduces by seed and can regenerate from the crown as well as by perennial root spread. Spotted and diffuse knapweed reduce productivity of.
Diffuse knapweed cannot tolerate cultivation or excessive moisture and is therefore uncommon on cultivated land. On the other hand, spotted knapweed can be the first species to recover from a burn. Diffuse knapweed was found in one north dakota county in 1996 and infested approximately 20 acres. The common name spotted knapweed most often refers to centaurea maculosa. Diffuse knapweed had spread to four counties by 2017 and infested nearly 750 acres. Diffuse knapweed is a biennial to shortlived perennial that reproduces by seed.
Mowing or chopping is most effective when diffuse knapweed plants are at fullbloom. Institute of arctic and alpine research, and department of environmental, population and organismic biology, university of. Biology and biological control of knapweeds pdf 45. Areas that are adjacent to known patches of diffuse knapweed should be monitored two to three times a year spring, summer, and fall and any new rosettes should be destroyed. Minutus prefers diffuse knapweed while obtusus prefers spotted knapweed. While plants may regenerate from the crown, diffuse knapweed reproduces primarily by seed. Diffuse knapweed establishes a rosette in its first season of growth and it commonly bolts the second year. Diffuse knapweed identification and management diffuse knapweed. During the first year of growth, diffuse knapweed appears as a rosette in spring or fall. Biological control of spotted and diffuse knapweeds invasive. Here, they are free to establish monocultures and choke out desirable, native or other beneficial species. One plant can give rise to 1 to 20 slender, upright stems 24 feet in height with most branching occurring in the upper half. Figure 1spotted knapweed may be attractive to the uninitiated but is a.
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