It has a highly branched stem and a large taproot, as well as a basal rosette of leaves with smaller leaves alternating on the upright stems. Biology and biological control of knapweeds pdf 45. In europe, it is generally is found on dry, light, porous soils. At one of these sites, white lake, plant density was also monitored in 1999 and 2001 table 1. Diffuse knapweed most flowers white, but may be light purple 20% to 50% of plants break from root crown and become tumbleweeds, spreading seeds may hybridize with spotted knapweed native to eastern europe and western asia always read herbicide labels and follow instructions for use and ppe. Diffuse knapweed national invasive species information. King county best management practices for diffuse 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. 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. Larinus curtus pdf the asotin county noxious weed control board distributes, free ofcharge, biological controls for diffuse knapweed, dalmatian toadflax, and poison hemlock. Diffuse knapweed establishes a rosette in its first season of growth and it commonly bolts the second year. The conservation services division provides technical and financial support, leadership and statewide coordination, and regulatory oversight to publicprivate landowners and agricultural businesses statewide on an array of natural resource management challenges. Russian knapweed and yellow starthistle contain toxins that are poisonous to livestock, especially horses, and diffuse knapweed forms a tumbleweed, causing problems on downwind structures.
Diffuse knapweed resources national invasive species. Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on youtube. It can quickly take over both disturbed and managed areas, outcompeting native species and reducing plant diversity and wildlife habit. These insects overwinter as adults, and emerge in the spring when they begin to feed on knapweed foliage. Diffuse knapweed prefers open sunny habitats and dry conditions and competes well on excessively drained soils.
Information on diffuse knapweed s fire adaptations and response to fire is lacking in the literature. Idaho association of weed superintendents university of idaho extension office. Within 2 years of burning, most diffuse knapweed rosettes were eliminated. Spotted knapweed is a shortlived, noncreeping perennial that reproduces from seed and forms a new shoot each year from a tap\ root. Invasive forest weeds resources extension forestry. Diffuse knapweed can spread as quickly as spotted knapweed, but russian knapweed spreads much slower. Factsheet spotted knapweed washington state noxious. Diffuse knapweed plants are also spread by the wind, as mature plant blow. While plants may regenerate from the crown, diffuse knapweed reproduces primarily by seed. Meadow knapweed is most common in washington and oregon.
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. Fact sheets for more information about individual invasive species, including those listed as prohibited noxious and noxious under the alberta weed control act. While although pollinators do use spotted knapweed, it displaces native vegetation that are typically higherquality food sources. Recent research completed by colorado state university shows that cattle grazing diffuse knapweed twice in spring decreased seed set by 50 percent. Diffuse knapweed factsheet invasive species of idaho. It is usually found on plains, rangelands, and forested benchlands, particularly on rugged or.
Diffuse knapweed typically grows 6 to 24 inches 1561 cm tall and consists of a single main stem divided. Diffuse knapweed containment click here to download pdf diffuse knapweed biological control of an explosive weed dale k. Purchase only certified weedseed free seed and hay. Spotted knapweed is an aggressive biennial, growing up to 5 feet tall. See separate pages on these invasive plants on this website. Meadow knapweed prefers moister and cooler habitats such as forest openings or along rivers and streams. It is widespread and increasing in the state, particularly along the front range. Spotted knapweed rosette leaves may be nearly entire. The all land types analysis revealed a site by land type interaction indicating that cover of diffuse knapweed was dependent upon site and land type at a site. Successful biological control of diffuse knapweed, centaurea. Diffuse knapweed containment click here to download pdf diffuse knapweed density and biological control agents were monitored at four longterm sites in british columbia from the mid to late 1970s to 1994, and from 2003 to 2008. Diffuse knapweed grows in disturbed, dry areas such as sandy areas, grasslands, pastures, woodland clearings, open forests, roadsides, rightofways and clearcuts. Dense infestations of spotted and diffuse knapweed can reduce productivity of grazing lands and.
Distinguishing the knapweed species by rosette alone is difficult. How many and what kind of agents for the biological control. Diffuse knapweed centaurea diffusa is a taprooted annual, biennial or shortlived perennial forb that reproduces by seed. Washington state university douglas county extension plant description. Therefore, the key to managing this plant is to prevent seed production.
Produces many seed heads, bracts covered with small spines and one larger spine at the tip. Diffuse knapweed flowers are mostly white or purple and are located on each branch tip. Animals grazing on knapweed should be held for at least 5 days before moving to weedfree areas. Diffuse knapweed seedlings first form low rosettes and may remain in this form. In the united states, diffuse knapweed is generally found on light, dry, porous soils. Diffuse knapweed is an annual or biennial plant, generally growing to between 10 and 60 cm in height. Diffuse knapweed can be confused with nonnative spotted and russian knapweeds, both of which need to be eradicated. Bee keepers value the flowers of spotted knapweed because of the flavorful honey produced from its nectar. Diffuse knapweed can be controlled by various integrated weed management techniques. Effects of postfire conditions on germination and seedling success of diffuse knapweed in northern arizona. Once established, diffuse knapweed can form monotypic stands on some sites. Please consult the plants web site and your state department of natural. Diffuse knapweed can be found in pastures, riparian areas, roadside, and waste areas in colorado. The bracts surrounding each flower bear 4 to 5 pairs of lateral spines and one, long terminal spine.
Diffuse knapweed is a bushy herbaceous taprooted biennial or shortlived perennial that grows to about 3 ft tall. Diffuse knapweed is a taprooted biennial, occasionally annual or shortlived perennial forb that reproduces by seed. How and when can i get knapweed biological control agents. You can call the colorado department of agricultures insecta ry at 9704647916 or toll free at. Hand dig or pull the rosette during their first year of growth. Diffuse and spotted knapweed colorado state university extension. The manual of montana vascular plants lesica et al. Distribution, biology, and management of diffuse knapweed centaurea diffusa and spotted knapweed centaurea maculosa volume 12 issue 2.
Diffuse knapweed comes from the eastern mediterranean and was brought over as a contaminant in crop seeds. Seeding desirable perennial grasses is essential to prevent weed reinvasion beck 1997. Diffuse knapweed survives in a wide range of soil and environmental conditions, and produces large numbers of viable seeds that are widely dispersed. Diffuse knapweed national invasive species information center. Diffuse knapweed can sometimes resemble spotted knapweed with the black tipped bracts. Diffuse knapweed centaurea diffusa also grows a single, branched stem from a. Division of agriculture alaska plant materials center.
Gloves should be worn because of the possibility of skin irritation. Any potential sightings should be reported to the minnesota department of agriculture. Diffuse knapweed has a deep taproot and may sprout following topkill from fire if the root crown survives and sufficient moisture is available. Diffuse knapweed is a strong competitor for water and nutrients, and the plants dense, spiny overstory reduces availability of more desirable forage species to grazing animals by as much as 90%. 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. Spotted knapweed prefers more moist areas than diffuse knapweed 20 to 200 cm of rain per year. Diffuse knapweed floral bracts have yellow spines with teeth appearing as a comb and a distrinct terminal spinte. Diffuse knapweed centaurea diffusa is a shortlived perennial, a biennial, or occasionally an annual. All three species have limited distribution in minnesota and are considered early detection species in the state. Brown, diffuse, and meadow knapweeds early detection. Distribution, biology, and management of diffuse knapweed. It is one of the only knapweeds that spread by tumbling by the wind like russian thistle. Biological control of diffuse knapweed centaurea diffusa and spotted knapweed c. Diffuse knapweed identification and management diffuse knapweed.
Seed adhering to surfaces and undercarriages of vehicles especially road maintenance. Diffuse knapweed will not tolerate flooding and shade. 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. The top photo 1a shows a dense population of spotted knapweed in full bloom in nebraska.
Diffuse knapweed centaurea diffusa is native to disturbed areas and seashores from southern europe to northcentral ukraine. Spotted knapweed bracts are, well, spotted, diffuse knapweed bracts have rigid sharp spines, and russian knapweed has opaque bracts. Diffuse knapweed identification and management diffuse. The data show that diffuse knapweed was evenly distributed at the kelsall property but not at the north boulder property table 1.
Invasive species plants terrestrial diffuse knapweed factsheet. Diffuse knapweed can grow 1 to 3 feet tall, and is diffusely branched above ground. There are eight bio bugs that feed on knapweed, cyphocleonus achates a root boring weevil whose larva, pupa, and adult cyphos feed on the roots of diffuse knapweed, injuring the plant and limiting its growth. Spotted knapweed, centaurea stoebe, is perhaps the most widespread species, followed in abundance by diffuse knapweed, c. Diffuse knapweed is of eurasian origin and was introduced to north america in the early 1900s, and has since spread to over a million hectares of rangeland in western canada and the united states story et al.
Diffuse and spotted knapweed are readily controlled with herbicides. The native diffuse knapweed has spinetipped bracts, not comblike tips on its bracts. It is a tough competitor on dry sites and rapidly invades and dominates disturbed areas. Plants overwinter as a rosette that resembles spotted knapweed. Piper, wsu diffuse knapweed, centaurea diffusa, a member of the plant family asteraceae, is believed to have been accidentally introduced into washington state during the early 1900s as a contaminant of alfalfa seed imported from eurasia. Diffuse knapweed is a shortlived perennial plant with. Diffuse knapweed centaurea diffusa distribution 2018 no known infestations present but extent unknown eradicated no data or insufficient data no warranty is made by wsda as to the accuracy, reliability, or completeness of this data for individual or aggregate use with other data.
This species is common throughout western north america but is not actually native to the north american continent, but to the eastern mediterranean. Diffuse knapweed is widespread in the western united states. A close relative of spotted knapweed in the asteraceae taxonomic family. Biology, ecology and management of montana knapweeds. Biological control of diffuse and spotted knapweed invasive. Squarrose knapweed should be severed at least 8 inches below soil surface. Diffuse knapweed jan 2014 pdf 650 kb alberta invasive species council canada. Field guide for managing diffuse, meadow, spotted, and. Spotted knapweed grows 8 to 40 inches tall with branched stems. This gives the plant a ballshaped appearance and tumbleweed mobility when broken off. Po box 315, twin bridges, mt 59754 406 6845590 888 6644153 fax. Brown knapweed centaurea jacea, diffuse knapweed centaurea diffusa, and meadow knapweed centaurea x moncktonii are all early detection species in minnesota as they are of high concern and are not known to be widely distributed in the state. Sunflower or aster family asteraceae reasons for concern.
Diffuse is a member of a large genus of over 400 species, most originating in the mediterranean region. Burning has been shown to give effective control of diffuse knapweed while stimulating grass regrowth. These knapweeds are herbaceous plants that can form dense. Diffuse knapweed is a biennial or, occasionally, an annual or shortlived perennial that reproduces and spreads solely from seed. University of nebraskalincoln extension ec173 revised. Spotted knapweed is listed as noxious, prohibited, banned or otherwise regulated in 16 states. However, when stressed by drought, grazing, or mowing, it may show shortterm perennial characteristics. Diffuse knapweed identification and control king county noxious weed information diffuse knapweed wa state noxious weed control board information page meadow knapweed pdf whatcom county noxious weed fact sheet. Diffuse knapweed has many spreading branches that give it a ballshaped, tumbleweed appearance a, whereas spotted knapweed appears more christmastree like, especially in dense stands b. Alaska plant materials center division of agriculture. King county best management practices diffuse knapweed. The leaves are alternate and variously covered with short to medium interwovengrayish hairs. 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 rosette photo by richard old, xid services, and bract, inset photo by steve dewey.
Weed research and information center, university of california. Location diffuse knapweed is wide ranging, although it prefers shrubsteppe and dry forest zones. The decline of diffuse knapweed in british columbia. Diffuse knapweed will not tolerate flooding or shade and thrives in the semiarid west generally in 9. Seed can also be spread in hay that is not certified to be weed free. Single upright stem with many branches, growing up to 40 tall.
Manual and mechanical small infestations of spotted knapweed can be controlled by persistent handpulling done prior to seed set. Establishment, impacts, and current range of spotted knapweed. Diffuse knapweed is a serious rangeland pest because it displaces forage grasses and has attained very high densities in dry rangelands in many areas of western north america. Refer to eddmaps distribution maps for current distribution of brown knapweed, diffuse knapweed, and meadow knapweed. Single upright stem with many branches, growing up. Spotted knapweed occurs in disturbed sites such as roadsides and overgrazed fields. Since 2003 the weed board has been introducing new weevils for the control of puncturevine, a moth for rush skeletonweed as well as a beetle for diffuse knapweed. Forest service forest health technology enterprise team. Skip to main content accessibility help we use cookies to distinguish you from other users and to provide you with a better experience on our websites. Disturb the soil as little as possible, to reduce germination of new seedlings. Because spotted knapweed can regrow from the base, care must be taken to remove the entire crown and taproot.
Defusing diffuse knapweed biological control of an explosive weed dale k. Flowers are usually white or pink and grow out of urnshaped heads carried at the tips of the many branches. Ecology and management of diffuse knapweed centaurea diffusa. Spotted knapweed often forms dense stands in natural communities decreasing diversity of native vegetation, and degrading the forage quality for wildlife habitats. Small infestations of spotted knapweed can be controlled by persistent handpulling done prior to seed set.
A lowseverity fire will not kill the belowground reproductive structures of diffuse knapweed, but a severe fire can kill some of the plant crowns. Figure 1 spotted knapweed may be attractive to the uninitiated but is a. Diffuse knapweed containment zone eradication zone jeffco open space county boundary. Livestock sheep, goats, cattle will eat diffuse knapweed. Executive office montana weed control association, inc. Females produce between 28 and eggs which they lay in clusters in open flowers.
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