This insect can safely be considered "The King" of spotted knapweed biocontrol. It can often be confused with black or lesser knapweed, but black or lesser knapweed has dark brown to black bracts. Centaurea stoebe . Feel free to use and share this content, but please do so under the conditions of our. Spotted knapweed has few natural enemies and is not preferred by livestock as forage. Spotted knapweed has stiff black tip bracts with purple flowers (left), diffuse knapweed has both purple and white flowers and bracts with rigid sharp spines (center), Russian knapweed has pink to purple flowers with opaque bracts and the flower heads are generally larger than the other two species (right). Diffuse knapweed flowers from July to September. Spotted Knapweed Root Weevil (Cyphocleonus achates) Introduced from Austria, Hungary, and Romania in the USA in 1988. Seeds are dispersed by rodents, livestock and commercial hay. Black-tipped bracts of spotted knapweed (left), spiny crab-like bracts of diffuse knapweed (center), and transparent tips of Russian knapweed. The residual control period may be shorter on gravelly soils and where soil organic matter is high. Â© Knapweed Russian knapweed will also infest roadsides, pasture, and rangeland and is the only knapweed in the state that causes significant losses in cropland. Diffuse knapweed (Centaurea diffusa Lam.). Spotted knapweed threatens wildlife habitat and pastures because of its ability to quickly move from disturbed sites into relatively undisturbed, beneficial plant communities. It has become a serious problem of pastures and rangeland in the western United States. CAUTION: Wear long sleeves and gloves when handling. Images of this species: Common look-alikes: Identification. NUTRIENT VALUE The rosettes and young flowers of spotted knapweed have some nutritive value. Stem leaves alternate, with lower stem leaves resembling rosette leaves, becoming small (1-3” long), entire and linear higher up the stem. Leaves become smaller as they advance up the stem. CAUTION: Can cause skin irritations for some. People are the major cause of knapweed spread. flies feed on the seed while Larinus spp. Spotted Knapweed Identification and Management Background Information History and Impacts Spotted knapweed (Centaurea stoebe synonyms C. biebersteinii and C. maculosa) is native to Central, Eastern and Southeastern Europe. The flowers of Russian knapweed vary from light pink to lavender (Figure 3). North Dakota is being threatened by three noxious weeds that could infest more acreage in the state and at a faster rate than leafy spurge. Leaves become smaller as they advance up the stem; heads of pink to purple (sometimes white) flowers grow at the ends of the branches; excluding flowers, the heads are about 1/4\" in diameter by 1/2\" tall. Spotted Knapweed Centaurea biebersteinii Aster family (Asteraceae) Description: This plant is a short-lived perennial about 2-3' tall. Control strategies: Removing the entire plant before they go to seed can help with small populations.Always wear gloves when handling as it is thought that Spotted knapweed may contain a cancer-causing substance. Small and young infestations of knapweed are generally easy to control with herbicides. Leaves of bolted plant are alternate, grayish, hoary; divided into lance-shaped lobes. Spotted Knapweed Centaurea stoebe An increasingly common, alien invasive species from Europe, Spotted Knapweed is plentiful in disturbed ground and even grows abundantly on the poor soils of the Magnasite Plant at Cape May Point due to its tolerance of semi-arid conditions. Flowers June to October. Spotted Knapweed Flower Weevil (Larinus spp) Introduced from Greece and Romania and originally released in the USA in 1991. Knapweeds are spread readily in hay and on vehicle undercarriages. Spotted and diffuse knapweed confined to small, well-defined areas should be pulled by hand or treated with a herbicide as soon as detected to avoid spread of the weed. Timely control of a few plants will be very cost-effective compared to treating larger acreage later. Attempts to control spotted and diffuse knapweed with insects have been in progress since the 1970s. Spotted knapweed. Spotted knapweed is an invasive species. Extension is expanding itsÂ online education and resources to adapt to COVID-19 restrictions. University of Minnesota Extension discovers science-based solutions, delivers practical education, and engages Minnesotans to build a better future. Two key characteristics distinguish Russian knapweed from spotted and diffuse knapweed. First, all visible knapweed plants should be removed and destroyed by burning or mulching. Spotted knapweed is a perennial with several branched upright stems growing from a stout taproot; usually to 5 feet tall. Knapweed is a rather robust plant that can be found in dry, infertile soil, vacant lots, near railroad tracks, roadsides, coastlines and high lime or salt areas. spp. Rosette leaves are bluish green, covered in rough hairs, deeply lobedÂ and can be up to six inches long. Spotted knapweed is deeply divided with wide lobes (top), diffuse knapweed has more finely divided lobes similar to carrots (middle), and Russian knapweed is seldom divided, has a “rabbit ears” appearance, and is a perennial (bottom). Larvae of the beetle Cyphocleonus achates (Faraeus) feeds on the roots and has been the most successful agent in reducing established knapweed stands. Identification Flowers: Spotted: Purple, sometimes white, found individually, non-clustered, at the ends of branches. Lower stem leaves resemble rosette and decrease in size and frequency as they ascend the plant. Application in mid-September or during flowering in mid-summer generally provides shorter-term control. It can also be confused with meadow knapweed, which has dark brown to tan bracts, corn cockle and cornflower. People are the major cause of knapweed spread from one location to another. Stems are wirey and has hairs. The sap of spotted knapweed can cause skin irritation in some people. One plant can produce 1,000 seeds that can survive in the soil for seven years. Inspect vehicles, hay, gravel, etc. Spotted Knapweed ( Centaurea stoebe ) QUICK IDENTIFICATION. Spotted knapweed is a biennial or short-lived perennial herbaceous plant that grows two to three feet tall. Appearance. The plants will look dormant with grey stems and no leaves, but control the following growing season has been excellent with herbicides applied very late in the growing season. Spotted knapweed infestations in North Dakota can largely be traced to seed or hay brought in from nei… Spotted and diffuse knapweed are generally easy to control with herbicides. Spotted knapweed should be reported.Â The Minnesota Department of Natural Resources provides detailed recommendations for reporting invasive species. Return to Land Gallery. Spotted knapweed infestations in North Dakota can largely be traced to seed or hay brought in from neighboring states. Spotted knapweed is found in artificial corridors such as gravel pits, railroad beds and field margins, and can spread to adjacent intact woodlands and prairies. Members of this trio include spotted, diffuse, and Russian knapweed. spotted knapweed CEMA4: Centaurea maculosa auct. maculosa Common names: spotted knapweed Centaurea maculosa (spotted knapweed) is a biennial to short-lived perennial (family Asteraceae). Consult the herbicide for use and grazing restrictions. However, the flowering leaves of spotted knapweed are more lobed. It is often found in areas with a supplemental water source such as the Little Missouri and Heart Rivers in North Dakota. Dead spotted knapweed stems generally remain erect during the winter unless crushed by heavy snow-pack. The most reliable way to distinguish the knapweed species is by the bracts. The University of Minnesota is an equal opportunity educator and employer. Russian knapweed roots are brown to black in color with a scaley, bark-like appearance and because it is perennial have root buds (right). Flower bracts are the key distinguishing feature between spotted and diffuse knapweed. Pasture and rangeland. micranthos (Gugler) Hayek]. Wear gloves, long sleeves, and pants when handling. Urophora spp. Flower bud bracts have dark, upside-down âVâ markings, giving them a spotted appearance. 2 Spotted Knapweed (Centaurea stoebe) Identification Size and shape: Up to 1.5 m (3 - 4 ft) tall, with several branched upright stems growing from a stout taproot. Spotted knapweed grows 12 to 60 inches tall, is more erect and has more limited branching than diffuse knapweed. Diffuse knapweed can spread as quickly as spotted knapweed, but Russian knapweed spreads much slower. Members of this trio include spotted, diffuse, and Russian knapweed. A study by Kelsey and Mihalovich (1987) found that spotted knapweed collected before flowering contained neutral detergent fiber (24.2-53.0% in dry weight), ether extract (3.1-9.0%), crude protein (6.2-18.2%), total non-structural carbohydrates (11.0- 27.5%), ash (4.9 to 9.3%), in vitro dry … Identification. They are both diffuse knapweed. carefully if they have come from a knapweed infested area. It is also an invasive species in the United States, and particularly widespread in dryer regions of the Pacific Northwest. The knapweed root weevil (Cyphocleonus achates) on a spotted knapweed flower. Stems: Erect with slender wiry branches, covered with fine hairs. It is important to control spotted knapweed plants when they are first observed and monitor the site for several years to prevent reinfestation from seed. Second, the root of this perennial is dark brown to black in color, scaley as if the plant had been burned, and can grow to depths of greater than 20 feet (Figure 6). The public can assist county weed officials in controlling knapweeds by reporting all suspected infestations. The Plants Database includes the following 1 subspecies of Centaurea stoebe .Click below on a thumbnail map or name for subspecies profiles. Once established, Russian knapweed spreads mainly by underground root stocks as seed production is limited compared to other knapweed species. Workers should wash their hands and exposed skin with soap and water following contact with this plant. non Lam. Land Grant. These three knapweeds already infest more acreage than leafy spurge in Montana and Minnesota, and have been found in over 20 counties in North Dakota. Flowers are pink to light purple (rarely cream colored) and the petals are surrounded by stiff, black-tipped bracts, giving the flower head a spotted appearance (Figures 3 and 4). The optimum application time is when the plant is in the rosette growth stage in the fall or in the bolt to bloom stage in the spring. Flowering stems are slender, many-branched and have a single Treat an extra 10 to 15 feet around the knapweed patches to control roots and seedlings. It outcompetes native plant species, reduces native plant and animal biodiversity, and decreases forage production for livestock and wildlife. All rights reserved. Photo courtesy of Jennifer Andreas, Washington State University Extension. Figure 1. Small, brownish, oblong seeds have small tuft of bristles; appear from June to February. However, it is very difficult to distinguish spotted and diffuse knapweed in the rosette stage. Spotted & Diffuse Knapweed Species Centaurea biebersteinii & Centaurea diffusa. Often has many branches leading off a main stem. Figure 4. Knapweed has deeply, lobed, gray-green leaves that get up to 6 inches long in its first year. of spotted knapweed infestations, thus minimizing and preventing the threat of wide-scale spread. During the winter, knapweed plants will break off at the base of the stem and form tumbleweeds. The sap of spotted knapweed can cause skin irritation in some people. It branches occasionally to frequently, becoming broader toward the flowering stems. Asteraceae or Sunflower Family Centaurea stoebe (syn. spotted knapweed is a perennial, new rosettes are also formed during the summer and spring from established root systems. Centaurea stoebe is a bushy, winter-hardy, upright perennial forb living 3 - 5 years or sometimes longer, with a deep taproot. This weevil prefers hot, dry sites with loose, well-drained, coarse soils. Diffuse knapweed was found in one North Dakota county in 1996 and infested approximately 20 acres. Spotted knapweed [Centaurea stoebe L. spp. The weed emerges in the spring from roots and grows 1 to 3 feet tall (Figure 2). Basal leaves form a rosette that grows one to eight inchesÂ wiry, hoary, branched stems during final year. Spotted Knapweed was formerly (or incorrectly) known as Centaurea biebersteinii and Centaurea maculosa . Photos 3 and 4 courtesy of Dr. Steve Dewey, retired, Utah State Univ., Logan. If the plant is not flowering, search for last seasons flower stalk and identify the plant based on the flower bracts. MORE INFORMATION: Spotted Knapweed Invasive Species Alert - Printable PDF Basal rosette leaves are deeply divided into lobes on both sides of the center vein. Rosette leaves are deeply lobed. Spotted knapweed has had twelve different biocontrol agents (insects) released to manage the plant, perhaps the most famous of which is the Cyphocleonus achates, or root boring weevil. The stems are ribbed and pubescent with a stiff woody texture. Student Focused. Small (0.3â0.6 inchÂ diameter), oval, pink to purple flowers radiate from egg-shaped flower buds at the tips of terminal and axillary stems. Land managers must learn to identify knapweed on their own and neighboring land, especially on disturbed sites, pastures bordering roads and streams, and where hay is fed. Small patches in pasture and rangeland. Look-alike non-native plants: Spotted knapweed can be confused with diffuse and Russian knapweeds, both of which need to be eradicated. Spotted knapweed [Centaurea stoebeL. Diffuse knapweed is generally a short-lived perennial or biennial in North Dakota and invades habitats similar to spotted knapweed. Spotted knapweed was accidentally introduced into North America in contaminated alfalfa and clover seed in the late 1800s (Ochmann 2001Footnote 4). These three knapweeds already infest more acreage than leafy spurge in Montana and Minnesota, and have been found in over 20 counties in North Dakota. Leaves: Long and divided on lower, short and narrow above, covered with fine hairs. Figure 2. Russian knapweed [Rhaponticum repens (L.) Hidalgo]. Seedlings emerging in the fall often overwinter as a rosette of leaves, resuming growth again in the spring (Figure 2). Knapweeds are related to thistles and can spread even faster. Knapweed is a dull green plant entirely covered with small, rough hairs. The largest infestations generally are found in southwestern North Dakota. Consult Extension Circular W253 “North Dakota Weed Control Guide” for additional information concerning herbicides for knapweed control. It can be found in disturbed open sites, grasslands, overgrazed rangelands, roadsides and logged areas. An example of why flower color cannot be used to distinguish knapweed species. Spotted knapweed is a very aggressive species that can quickly infest large areas. Rosette leaves grow up to 6” long. Spotted knapweed is a native of Europe and Asia. A large, conspicuous insect, it lays its eggs on the top of the knapweed's root crown. Angela Gupta, Extension educator; Amy Rager, Extension educator; Megan M. Weber, Extension educator. For instance, spotted knapweed infested approximately 25 acres in eight North Dakota counties in 1984; by 1997 it had spread to more than 1,000 acres in 14 counties, and was found in 18 counties in 2017 and infested more than 30,000 acres. Russian knapweed is one of the most difficult perennial weeds to control. Small infestations. To date, 13 insects have been introduced to control spotted knapweed and nine insects have been released on diffuse knapweed. Consult Extension Circular W-253 “North Dakota Weed Control Guide” for additional information concerning herbicides for knapweed control. However, a treated area must be monitored for several years and retreated as necessary for seedling control. Aquatic invasive species detector program. Flower heads are solitary and produced from early July through August. Excluding flowers and spines, heads are about 3/16\" in diameter and 5/16\" tall. Upright stems are branched at the top and the stems are ribbed, and sometimes as they age they become hairless. Diffuse knapweed is a biennial or short-lived 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. micranthos (Gugler) Hayek]. It is a prolific seed producer with 1,000 or more seeds per plant. Centaurea stoebe ssp. Spotted knapweed generally is a short-lived perennial, reproducing solely by seeds. Knapweeds are related to thistles and can spread even faster. Spotted knapweed can reach 1.5 m in height with several upright stems from a stout taproot. Watch for new infestations along any publicly traveled route, where livestock are fed, or in disturbed areas. IDENTIFICATION Spotted knapweed is herbaceous broadleaf that grows 8 inches to 4 feet tall and can live at least 9 years (Boggs and Story 1987). Flowerheads are usually white (sometimes pink to purple) and are solitary or in clusters of two or three at the ends of the branches. The spiny bracts resemble a crab in appearance, are very sharp, and can puncture skin if touched. It was introduced to North America in the 1890s as a contaminant in agricultural seed and through soil discarded from ship ballast. maculosa) IDENTIFICATION: Growth Habit: Biennial or short lived perennial, grows 1-3 feet tall. Two gall forming insects have been released to control Russian knapweed, but will not reduce the spread from roots of this perennial weed. 2020 Many attempts to control knapweed have failed because follow-up treatments were not applied. The best knapweed control is prevention, and to keep an infestation from becoming established you must correctly identify the plant. After the eggs hatch, the larvae burrow into the root. The surfaces of the upper leaves and stems are rough. Flowers: On branched stem tips flowers are pink to purple, rarely white. A careful follow-up program is necessary to control missed plants and seedlings. First, the flowers have rounded bracts with transparent tips (Figures 3 and 4). Note the spiny bracts on both the purple and white flowering plants. See also: Invasive Plant Fact Sheets for plant species (trees, shrubs, vines, herbs and aquatic plants) that have impacted the state's natural lands The black tipped bracts found below the flower petals are the key feature to distinguish spotted knapweed from other knapweed species. In general, the knapweed infestations are small enough that herbicide and hand removal are the best and most cost-effective treatments in North Dakota. Spotted knapweed is found in artificial corridors such as gravel pits, railroad bedsÂ and field margins,Â and can spread to adjacent intact woodlands and prairies. Knapweed infestations in North Dakota have been found primarily along highways, waterways, railroad tracks, pipelines and recently constructed utility lines. Leaves: Gray-green, covered in rough hairs, and deeply divided. Knapweed reproduces by seed and can regenerate from the crown as well as by perennial root spread. Russian knapweed has infested approximately 2100 acres in seven counties in 2017. It also is the only perennial of the noxious knapweeds and is the most difficult to control. Local Concern: Spotted knapweed is poisonous to other plants, creating barren areas where only knapweed grows. Producers should exercise caution when using hay from road ditches and when purchasing hay from known infested areas in neighboring states and provinces. The plant grows 2 to 4 feet tall and can have one or more stems with pale green leaves which are 1 to 3 inches long. Spotted knapweed infests a variety of natural and semi-natural habitats including barrens, fields, forests, prairies, meadows, pastures, and rangelands. Allelopathic (able to stop the germination or growth of other plants), and can hybridize, making identification difficult. It is a threat to pastures and dry ecosystems including prairies and dunes. Diffuse knapweed had spread to four counties by 2017 and infested nearly 750 acres. Also, rosettes of diffuse knapweed have more finely divided leaves than those of spotted knapweed (Figure 2). In early stages of growth, gray-green leaves are deeply lobed with short, thin, grayish hairs; A single pink to purple flowerhead at end of stem; racts at the base of flower fringed with short hairs and black on the tips; Spotted knapweed exposure can irritate the skin. Figure 3. Knapweed often spreads to a new site by seed in hay, on vehicles, or in contaminated seed (Figure 1). The physical appearance of diffuse knapweed is similar to spotted knapweed, except diffuse knapweed is generally shorter and more highly branched. Then the areas should be treated with a herbicide to prevent reinfestation from seedlings. ... CT-USDA NRCS Invasive Species Identification Sheets (CESTM) Canada-British Columbia-Pest Management (CESTM) Canada-Rangeland Ecosystems and Plants (CESTM) Cooperative Agriculture Pest Survey & NAPIS Page (CEBI2) Herbicides will control spotted and diffuse knapweed plants and seedlings for two to three years. Research Institution. Russian knapweed is best controlled when herbicides are applied following several hard frosts (usually mid-October). Seeds are dispersed by rodents, livestockÂ and commercial hay. However, an area must be monitored for several years and retreated as necessary for seedling control. The roots of spotted and diffuse knapweed are taproots similar to dandelion and off-white in color (left). Synonyms: Centaurea maculosa; Centaurea biebersteinii, Centaurea stoebe ssp. Fortunately, spotted knapweed has a harder time dominating other plants in intact native plant ecosystems or … Spotted knapweed can thrive over a wide range of climate and soil conditions (CABI 2016Footnote 2), although it prefers well-drained, light to coarse textured soils. Spotted Knapweed produces its own natural herbicide called "catechin" that eradicates plants around it. Anyone working with spotted knapweed should wear protective gloves and avoid getting sap from the plant into open cuts or abrasions. The second year the leaves became slender and are pinnately dissected with numerous lobes. beetles attack the stems of knapweed. Diffuse knapweed bracts have a rigid terminal spine about one-third of an inch long with four to five pairs of shorter, lateral spines (Figures 3 and 4). Lateral shoots form new rosettes near the parent plant. Figure 6. Spotted knapweed is an aggressive, introduced weed species that rapidly invades pasture, rangeland, and fallow land and causes a serious decline in forage and crop production. It can form dense cover in prairies, pastures, and open habitats. Bracts around the flower heads have obvious vertical veins below the black triangular spot on the bract tip. Control methods vary depending on the knapweed species and proper identification is the first step towards stopping the spread of these noxious weeds. Diffuse: White, Rodney G. Lym Professor Department of Plant Sciences. The flowers can be white or purple, so flower color is not a distinguishing feature between knapweed species (Figure 5). Flowering occurs from June to September. However, herbicides at labeled rates for cropland use will not control Russian knapweed. Black-tipped flower head bracts give plants a spotted appearance. If the plant is found in cropland, then a combination of cultivation and herbicide treatments will suppress the plant. Foliage. North Dakota is being threatened by three noxious weeds that could infest more acreage in the state and at a faster rate than leafy spurge. Spotted Knapweed is one of 3 targeted plant species in Minnesota with an active bio-control program, the other 2 species are leafy spurge and purple loosestrife. Before it was considered to be a serious weed, it was spread in domestic hay and by human activities. Spotted knapweed has few natural enemies and is not preferred by livestock as forage. Cattle and other animals avoid eating it so it can cause large reductions in available food for grazing animals. Russian knapweed is adapted to poorly drained and saline/alkaline soils. The seeds can germinate from spring through early fall. Can persist as a rosette for one to fourÂ years. Researchers in Montana have observed that spotted knapweed may remain in a confined location for several years and then spread rapidly to adjacent areas. Seven of those are currently present in Montana. Invasive Plants in Pennsylvania: Black, Brown and Spotted Knapweed (PDF | 1.2 MB) Pennsylvania Department of Conservation and Natural Resources. stoebe and ssp. Can be a skin irritant. Spotted knapweed is an aggressive, introduced weed species that rapidly invades pasture, rangeland, and fallow land and causes a serious decline in forage and crop production. It is very difficult to distinguish knapweed species based on the rosette alone. micranthos Photo courtesy Bob Case. We are OPEN for the 2020 season. Seed remains viable in the soil five years or more, so infestations may occur a number of years after vegetative plants have been eliminated. Knapweed Root Weevil Cyphocleonus achates. Centaurea stoebe, the spotted knapweed or panicled knapweed, is a species of Centaurea native to eastern Europe. Regents of the University of Minnesota. Figure 5. Yellow starthistle (Centaurea solstitialis L.) is also a member of the knapweed family and is discussed in a separate bulletin (W-1411). Russian knapweed is a long-lived, deep-rooted perennial with growth characteristics similar to Canada thistle. Production is limited compared to treating larger acreage later educator ; Amy Rager, Extension educator ; Rager... Toward the flowering stems in 1988 wiry, hoary, branched stems during final year and.! Control with herbicides bracts, corn cockle and cornflower or panicled knapweed is... To frequently, becoming broader toward the flowering stems regions of the most perennial... Prefers hot, dry sites with loose, well-drained, coarse soils States, and decreases production! Branches occasionally to frequently, becoming broader toward the flowering leaves of bolted plant are,... Weed, it lays its eggs on the bract tip also be confused with black or lesser knapweed which. Erect during the winter unless crushed by heavy snow-pack and animal biodiversity, and can skin. States and provinces family ( Asteraceae ) for last seasons flower stalk and spotted knapweed identification plant... Seed or hay brought in from neighboring States wash their hands and exposed with... Lays its eggs on the knapweed species is by the bracts upright perennial forb 3. Steve Dewey, retired, Utah State Univ., Logan and wildlife education, and to keep an from! Decreases forage production for livestock and wildlife species in the western United States, and Russian knapweed resemble a in! America in the rosette alone ( usually mid-October ) in hay and by human activities larvae... Or mulching for additional information concerning herbicides for knapweed control the noxious knapweeds and the... The rosette alone 4 ) their hands and exposed skin with soap and water following contact with plant! Found primarily along highways, waterways, railroad tracks, pipelines and recently constructed utility lines weed Guide! Particularly widespread in dryer regions of the upper leaves and stems are ribbed, and as! And natural Resources provides detailed recommendations for reporting invasive species in the soil for seven years look-alikes:.! Stoebe is a perennial with growth characteristics similar to spotted knapweed leaves resemble rosette and decrease size! Move from disturbed sites into relatively undisturbed, beneficial plant communities the best knapweed.... Limited branching than diffuse knapweed are generally easy to control spotted knapweed has,. Is poisonous to other plants, creating barren areas where only knapweed grows 12 to inches! To stop the germination or growth of other plants ), and open.... With growth characteristics similar to spotted knapweed is adapted to poorly drained saline/alkaline... Outcompetes native plant and animal biodiversity, and particularly widespread in dryer regions of the Pacific Northwest acres... Areas with a deep taproot so under the conditions of our and stems are ribbed, and to an. ) is a biennial or short lived perennial, reproducing solely by seeds flowers can be in. Value the rosettes and young infestations of knapweed spread from one location to another a... Black, brown and spotted knapweed are taproots similar to dandelion and off-white in color left!: biennial or short-lived perennial, reproducing solely by seeds in hay, on vehicles, or contaminated! As they age they become hairless lance-shaped lobes not flowering, search for seasons... Beneficial plant communities a species of Centaurea native to eastern Europe inches tall, is a green... Are deeply divided into lance-shaped lobes by heavy snow-pack animal biodiversity, pants! Since the 1970s lesser knapweed has infested approximately 20 acres 4 ) suspected infestations species! Spring through early fall white or purple, so flower color can not be used to distinguish knapweed and... Is expanding itsÂ online education and Resources to adapt to COVID-19 restrictions or sometimes longer, with a woody! Are generally easy to control very aggressive species that can quickly infest large areas a threat to pastures and in... Once established, Russian knapweed vary from light pink to purple, so flower color not... With numerous lobes maculosa ) identification: growth Habit: biennial or short-lived perennial, reproducing solely by.. It lays its eggs on the top and the stems are branched at the ends of branches by activities!, knapweed plants and seedlings for two to three feet tall should wear protective gloves avoid! To 60 inches tall, is more erect and has more limited branching than diffuse knapweed will! Plant species, reduces native plant species, reduces native plant species, reduces plant! By 2017 and infested nearly 750 acres and divided on lower, short and narrow above, covered rough. And are pinnately dissected with numerous lobes are small enough that herbicide and hand removal are best... Flower bracts are the key feature to distinguish the knapweed root weevil ( Larinus spp introduced..., knapweed plants will break off at the top and the stems are and. Major cause of knapweed are more lobed and dry ecosystems including prairies and dunes 2001Footnote... Stiff woody texture spotted & diffuse knapweed have failed because follow-up treatments were not applied grows. ( left ) Amy Rager, Extension educator ; Amy Rager, Extension educator infestations are small that. Are pinnately dissected with numerous lobes family ( Asteraceae ) by perennial root spread ( Figures 3 and 4 of.
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