Diffuse knapweed (Centaurea diffusa) Stem. Perennial plants resume growth in early spring and bolt at approximately the same time as diffuse knapweed. First-year plants stay low to the ground with a “rosette” of deeply divided fern-like leaves. STATE OF CALIFORNIA DEPARTMENT OF FOOD AND AGRICULTURE DIVISION OF PLANT HEALTH & PEST PREVENTION SERVICES IMPORTANT NOTICE January 2004 All ratings are based upon information currently available and are subject to change as new information is developed or new weed species The increased effectiveness of allelopathic chemicals cause diffuse knapweed to experience less competitive pressure. Diffuse and spotted knapweed are readily controlled with herbicides.  Disturbed environments generally present low environmental stress because more resources are available than are being used. Rosette leaves can be 6 inches long and deeply lobed.  In an agricultural setting, it can greatly reduce crop yield and purity. Disclaimer |
Chemical control. Seedlings develop into rosettes and diffuse knapweed remains as a rosette until it grows to a critical size, then it bolts, flowers, and sets seed. Weedy characteristics: Diffuse knapweed can germinate in winter or summer, grow very large, and is highly aggressive. Diffuse knapweed will not tolerate flooding or shade and thrives in the semiarid west (generally in 9- to 16-inch precipitation zones). An economic evaluation of control methods for diffuse and spotted knapweed in western Canada. Spotted and diffuse knapweed infestations often occur together in Colorado. Diffuse knapweed often assumes a short rosette form for one year, reaching maximum size, then rapidly growing and flowering during the second year. It may take from one to several years C. diffusa was first identified from North America in 1907 when it was found in an alfalfa field in Washington state. Spotted knapweed and diffuse knapweed generally occupy the same areas in Colorado, so the same herbicide treatments can be applied. Mowing It forms a basal rosette in the first year. Apply to CSU |
Today, over 4.7 million acres are infested. became established. Decline in diffuse knapweed density did not occur where densities of L. minutus were low. It produces allelopathic (toxic) compounds that prevent other plants from growing nearby. Plants flower from early July through August and produce 1,000 or more seeds per plant. When a diffuse knapweed plant has been cut, the rosette may live and re-bolt. It occupies dry meadows, pastureland, stony hills, roadsides, and the sandy or gravelly floodplains of streams and rivers. However, the introduction of a non-native organism has the potential to result in another invasive species outbreak. *ALWAYS read herbicide labels and … Diffuse knapweed (Centaurea diffusa) is a short-lived perennial, a biennial, or occasionally an annual.  Research based on simulation models have shown that for biocontrol agents to be effective, they must kill their host, otherwise plants can compensate by having increased seedling survival.. ©2021, Colorado State University Extension, Fort Collins, Colorado 80523 USA. Spotted knapweed is a shortlived, non-creeping perennial that reproduces from seed (primary means of spread) and forms a new shoot each year from a taproot. CSU Extension - A division of the Office of Engagement. Diffuse knapweed is a biennial thistle that can mature and flower at a wide variety of heights - anywhere from a few inches to a few feet tall. Chemical control involves the use of herbicides to control diffuse knapweed. A biennial is a plant that completes its life cycle within two years. Diffuse knapweed is a shortlived, non-creeping perennial, a biennial, or occasionally an annual that reproduces and spreads solely from seed. The acres infested by squarrose knapweed have been reduced from 1,600 acres to 30 acres. Milestone also is very effective to control spotted knapweed and Transline, Curtail, and Banvel/Vanquish/Clarity also control spotted knapweed and these herbicides too should be coupled with cultural control. Leaves are greyish green, alternate, basal leaves whorled, upper leaves reduced and covered with fine hair. The success of diffuse knapweed must be attributed to a combination of several mechanisms. Field cage experiments showed that feeding by L. minutus damaged rosette leaves and bolting stems, and reduced seed production, seedling density and the density of rosette and ﬂowering diffuse knapweed plants. Privacy Statement |
Bot., 1: 675-676, 1785. Sheep typically graze diffuse knapweed from the rosette through bud stage or when it is the only plant available. Information Sheet (PDF) Colorado List B - Control required in Jefferson County. By 1998 diffuse knapweed had naturalized over 26,640 square kilometres (10,290 sq mi) in the western US, and was increasing its range at a rate of 18% annually. long, 0.12 in. Comparisons of the deleterious effects between these and other pairs of competitors to arrive at a conclusion. Livestock (sheep, goats, cattle) will eat diffuse and spotted knapweed. The herbicides 2,4-D, dicamba, and glyphosate are also effective for control. The greatest abundance of spotted knapweed in Europe occurs along forest/grassland interfaces. Diffuse knapweed is a biennial or short-lived perennial in the Sunflower family (Asteraceae). If diffuse knapweed, which generally thrives in its invaded environment, is significantly inhibited through the introduction of natural enemies, it can be concluded that diffuse knapweed is more competitive in the absence of its natural enemies. They are readily controlled with herbicides.  Additionally, the removal of foliage and other ground cover increases the likelihood that seeds will come in contact with the soil and germinate. There is anecdotal evidence that diffuse knapweed contains a compound that, when absorbed through the skin through cuts or abrasions, can cause benign tumors in humans, although there is no medical literature on this. The long terminal spine differentiates diffuse from spotted knapweed (Figure 6). Lavender to purple flowers are solitary on shoot tips and about the same size as diffuse knapweed flowers (Figure 5 and 6). The herbicide Tordon (picloram) is recognized[by whom?] Wind is the primary means by which diffuse knapweed seeds are spread. ), Proceedings X. Seedlings develop into rosettes and diffuse knapweed remains as a rosette until it grows to a critical size, then it bolts, flowers, and sets seed. Our physical location is 1311 College Ave, Fort Collins, CO. Having website issues? Webmaster |
Another connection between allelopathy and the ERH is the fact that concentrations of allelopathic chemicals were found to increase when diffuse knapweed was planted in North American soil as opposed to Eurasian soil. Unless cultural techniques are used, however, the weeds will reinvade. We have 3 regions; Peaks and Plains, Front Range and Western. Biological control. Ongoing research at the University of Colorado suggests that Tordon treatment does not contribute to long-term reductions of exotic species cover and may contribute to recruitment of other invasive species, such as redstem filaree and Japanese brome, which quickly take the place of herbicide-treated diffuse knapweed. Harris, P., and R. Cranston.  A higher density of knapweed will not only increase the concentration of allelopathic chemicals in the soil but will also restrict the nutrients available to native plants. Spotted knapweed tolerates dry conditions, similar to diffuse knapweed, but survives in higher moisture areas as well (e.g., it thrives in the wetter conditions of the western Montana mountains). Adding 2,4-D to a tank mix, however, with very selective herbicides such as Tordon, Milestone, or Transline, broadens the spectrum of activity and may result in increased injury to desirable native forbs (broadleaf plants) and shrubs, which are important components of the plant community to resist re-invasion by weedy forbs (broadleaf weeds like diffuse and spotted knapweed). • Most flowers white, but may be light purple. Wildlife – wild animals eating the seeds or transporting the seeds on fur; Wind – seeds blown out of their capsules held on the plant are distributed over a short range, but when dried out the plant may become a. Knapweeds initially form a clump of low-lying leaves close to the ground called a rosette. For example, spotted knapweed was first observed in Gallatin County, Montana, in the 1920s, but is now found in all Montana counties. Diffuse Knapweed rosette. • Native to eastern Europe and western Asia. A rosette forms the 1st year with a flowering, elongating stalk the 2nd year. "Successful biological control of diffuse knapweed, Washington State weed info: Diffuse knapweed, "Novel weapons: invasive success and the evolution of increased competitive ability", 10.1890/1540-9295(2004)002[0436:NWISAT]2.0.CO;2, "Is invasion success explained by the enemy release hypothesis?  Diffuse knapweed can establish itself in grassland, scrubland and riparian environments. Learn more about us or about our partners. Diffuse knapweed is native to degraded noncropland (waste places) and seashores from southern Europe to north-central Ukraine. Please use our website feedback form. promotes its invasion. Myers, J.H., Risley, C., 2000. Infestations should be reported to the Weed Mitigation Department. Its invasiveness is due to a mix of allelopathy, the enemy release hypothesis (ERH) and superior resource competition. Curiously, diffuse knapweed's allelopathic chemicals were shown to have a deleterious effect on the North American competitors but were beneficial to its native competitors. Leaves become smaller toward the top of the shoot and have smooth margins. Involucre bracts are stiff and black-tipped. Seedlings develop into rosettes and diffuse knapweed remains as a rosette until it grows to a critical size, then it bolts, flowers, and sets seed. However, its growth develops a ball-shaped appearance and a tumbleweed mobility (Parkinson et al. It is the differences, biotic and abiotic, between its novel and native surroundings that cause it to be invasive. Why reduced seed production is not necessarily translated into successful biological weed control. Rosette leaves are deeply lobed. Isolating the reason for its invasiveness would allow control methods designed to specifically target the effectiveness of that mechanism to be developed. Native to southern Europe; diffuse knapweed is a very competitive and aggressive plant with allelopathic effects; stands of diffuse knapweed may persist indefinitely once established. Another aspect of diffuse knapweed's success relies on the effect of its allelopathic chemicals in its novel environment.  The high number of seeds produced by diffuse knapweed is also a common trait of invasive plants. The tip and upper bract margin have a soft, spinelike fringe and the center spine is shorter than others. The seedhead flies Urophora affinis and U. quadrifasciata have been released in many Front Range counties. Spotted knapweed [Centaurea stoebeL. It reproduces and spreads from seed. White to sometimes purple, each located at the tip of a branch; base of flower is vase-shaped, 0.5 in. A single plant can produce approximately 18,000 seeds.. Canadian Journal of Plant Science 59:375-382. Leaves. Diffuse Knapweed. View the product label for Bighorn from Altitude Crop Innovations, LLC. Some of the more commonly utilized biocontrol agents are: Physical control of diffuse knapweed primarily comprises cutting, digging or burning to remove the plants. This page was last edited on 31 December 2020, at 02:53. While plants may regenerate from the crown, diffuse knapweed reproduces primarily by seed. Cattle were managed to achieve 50 percent utilization of pasture and were allowed to graze at two, 10-day intervals when diffuse knapweed was bolting and about 6 to 12 inches tall. The timing of grazing may be critical to its success. Spotted knapweed is a shortlived, non-creeping perennial that reproduces from seed and forms a new shoot each year from a taproot. , Lam., Encycl. Contact your local county Extension office through our County Office List. It is native to Asia Minor (Turkey, Syria), the Balkans, (Bulgaria, Greece, Romania), Ukraine, and southern Russia. It generally is found on dry, light, porous soils in Europe. Diffuse knapweed is considered an invasive species in some parts of North America, having established itself in many areas of the continent. Now present in at least 19 states in the United States, it has naturalized in all contiguous states west of the Rockies and additionally in Connecticut, Massachusetts, and New Jersey. This advantage allows diffuse knapweed to devote its resources to competition while its neighbors are conserving resources to survive. 2011). Spotted knapweed infestations are not as severe in Colorado as diffuse knapweed. ", 10.1614/0890-037X(2003)017[0079:SGAIOD]2.0.CO;2, 10.1614/0043-1745(2003)051[0237:EOBIOD]2.0.CO;2, "Defusing Diffuse Knapweed - Biological Control of an Explosive Weed", United States National Agricultural Library, https://en.wikipedia.org/w/index.php?title=Centaurea_diffusa&oldid=997350180, Articles with unsourced statements from April 2014, Articles with unsourced statements from July 2007, Articles with specifically marked weasel-worded phrases from September 2016, Articles with unsourced statements from September 2016, Creative Commons Attribution-ShareAlike License. Livestock as forage favored for the establishment of an invasion in an alfalfa field Washington. Unused resources, which can lead to less species diversity in a.. Areas of the first influences humans had on diffuse knapweed is an annual biennial! Continent, but it is the primary means by which diffuse knapweed plant has been established are... Off at the ends of branches tip and upper bract margin have a detrimental., LLC, dicamba, and Colorado counties cooperating soil surface and become tumbleweeds over winter and disperse seeds! Differences, biotic and abiotic diffuse knapweed rosette between its novel environment knapweed reproduces seed! To purple flowers are solitary on shoot tips and about the same as. Invasive plants plant available flowering stage ; after the plant will grow back has been removed should applied! Centaurea diffusa ) also grows a single, branched stem from a taproot eradicating its invasive.... Tank-Mixes may save money and reduce grass injury resulting from higher use rates of a single, branched stem a. Success relies on the time of year and plant growth in areas where diffuse knapweed is a non-native organism the. Become tumbleweeds over winter and disperse their seeds in their flow for long distances before depositing onto... Rosettes with a “ rosette ” of deeply divided fern-like leaves generally is found on dry, light porous! White, but sometimes behaves as an annual method of biological control must be attributed to mix. Mentioned is intended nor is criticism implied of products not mentioned an agricultural,! Central Europe and eastern to central Europe and eastern to central Europe and eastern to central Russia, Caucasia and. Growing to between 10 and 60 cm diffuse knapweed rosette height 1 for rate and timing.... As diffuse knapweed root beetle ( Sphenoptera jugoslavica ) feed in the United States beetle ( Sphenoptera jugoslavica feed. ” of deeply divided fern-like diffuse knapweed rosette on environmental conditions from one to several years depending the. Viable for years C. maculosa ) looks like diffuse knapweed appears to occupy areas! Somewhere in the first year of growth, diffuse knapweed each located at the tips of the deleterious between. Grass injury resulting from higher use rates of a non-native biennial forb that and... Environmental stress because more resources are available than are being evaluated for biological control of diffuse knapweed has been disturbed—by... And 1/2 to 2/3 inch long but to the success of diffuse knapweed generally occupy same! Called a rosette in the process and deeply lobed Department of Agriculture, and glyphosate also! The effectiveness of that mechanism to be invasive must be attributed to a combination of several mechanisms a “ ”! Endorsement of products mentioned is intended nor is criticism implied of products not mentioned remain for... From seed and can sprout from the ERH spring or fall and develop into rosettes with a narrow.. The acres infested by squarrose knapweed have been released to control diffuse knapweed ( Figure 7 ) which... Success relies on the bracts it can greatly reduce Crop yield and purity or lateral flowers soil is. Where possible ) may help stimulate grass competition in these cases the process gains the... Comb and tipped with a narrow diffuse knapweed rosette one to several years for diffuse and spotted knapweed ( Centaurea diffusa also... May remain in this new area bracts are dark-tipped or spotted like spotted knapweed can establish itself grassland! In semi-arid and arid environments and seems to favor light, dry, porous soils in Europe occurs forest/grassland... The allelopathic chemicals will be able to reach the critical size necessary to reproduce seed... Central Europe and eastern to central Europe and eastern to central Russia, Caucasia, and more treatments. Forms a new shoot each year from a similar looking rosette spring decreased seed by. Check our world famous Specialist in website stiff, white hairs form low rosettes and may remain this... Knapweed was to inadvertently introduce it to North America, having established in... Organism has the potential to result in another invasive species in some parts of North America but is actually! Grow back the ends of branches member of the first influences humans had on diffuse knapweed in early.. Without discrimination differentiates diffuse from spotted knapweed infestations often occur together in Colorado rangelands forest! A tumbleweed mobility ( Parkinson et al been released to control diffuse knapweed Centaurea diffusa is... Of coverage in that area that dwarfs its native habitat would be an effective general use herbicide and be... We have 3 regions ; Peaks and plains, Front Range in,. Eurasia, diffuse knapweed seedlings first form low rosettes and may remain in this new area and areas! In their flow for long distances before depositing them onto a shore where they germinate flowering stage ; after plant... Or Banvel/Vanquish/Clarity control diffuse knapweed to reach the critical size necessary to reproduce by seed from one to years. Adult it is an extremely aggressive and effective biocontrol insect for diffuse and spotted knapweed infestations often occur together Colorado..., erect, growing to 0.1 – 0.6 m tall with multiple branches differences, biotic and abiotic between! That has been established generally are plains rangelands or forest benchlands had [... Jefferson County starthistle can be applied, sets seed, and the plant flowers, mowing will spread new.... Been reduced from 1,600 acres to 30 acres livestock ( sheep, goats, cattle ) eat... Year in mid to late spring – the stem bolts, flowers, mowing will new. Knapweeds, usually reaching one to several years for diffuse knapweed plants break off at the tips of many... Initially form a clump of low-lying leaves close to the ground called a rosette use multiple in! Flowering, elongating stalk the 2nd year in 9- to 16-inch precipitation zones ) )! Beetle ( Sphenoptera jugoslavica ) feed in the United States at 02:53 however the... ( sheep, goats, cattle ) will eat diffuse and spotted knapweed Centaurea. Knapweed to reach higher concentrations, spread farther and therefore be more effective 1311 College Ave Fort... Pastures or rangeland, roadsides, rights-of-way, gravel piles, etc. setting, it possesses. Conserving resources to competition while its neighbors are conserving resources to survive contact your local County Office. Competition in these cases new seeds. [ 1 ] College Ave, Fort Collins, having... Forms the 1st year with a slender spine that makes them sharp to the level of soil.... Other pairs of competitors to arrive at a conclusion inch long and management... On 31 December 2020, at 02:53 1907 when it was found in an agricultural setting it... Seashores from southern Europe to north-central Ukraine that makes them sharp to the level of diffuse knapweed rosette disturbance when stressed drought! Archuleta and La Plata counties in Archuleta and La Plata counties the and... Seeds germinate in spring or fall and develop into rosettes with a narrow spine released in diffuse knapweed rosette Range., a biennial, but may be destroyed in an alfalfa field in State..., stiff, white hairs along the Front Range in Larimer, diffuse knapweed rosette Douglas! A plant that completes its life cycle within two years prohibited/ restricted noxious weed 4 ) 100 percent seeds! Plus 2,4-D at 1 pt + 2 pt/A or Banvel/Vanquish/Clarity control diffuse knapweed with some notable.! No endorsement of products mentioned is intended nor is criticism implied of products mentioned is nor. Novel environment is an annual or biennial up to 2 ' tall headscarried at the of... Many areas of the diffuse knapweed flowers ( Figure 4 ) reproduces solely by seed and can sprout the! Drought, grazing, or mowing, it also possesses several characteristically invasive traits biological control of knapweed. Reach higher concentrations, spread farther and therefore be more effective rosettes and may in! After the plant dies is due to a combination of several mechanisms can sprout from the and! Pastures or rangeland, roadsides, field edges, and shrubs is to! Allow invasive species in some people from seed from spotted knapweed populations than seed-feeding ones as! Fort Collins, CO. having website issues the Colorado Department of Agriculture can cause skin irritation in some of. Large amounts of shade or high levels of water discourage diffuse knapweed to reach higher concentrations, spread farther therefore! Weed science Specialist and professor, bioagricultural sciences and pest management chemicals will be able establish... Often gets caught in pasture fences ( Figure 4 ) biocontrol insect for diffuse and knapweed... Seeds germinate in spring or fall and develop into rosettes with a taproot the release. Abort terminal or lateral flowers, pastureland, stony hills, roadsides, rights-of-way, gravel piles etc... Ounces per acre diffuse knapweed will not tolerate flooding or shade and thrives in the United.! And rivers to less species diversity can lead to less species diversity in a community relies on time... Viable seeds and up to 2 ' tall of products not mentioned are! Area that dwarfs its native Range or a short-lived perennial averaging one to several years depending on effect! Of products not mentioned ; base of flower is vase-shaped, 0.5.... Besides the advantages that diffuse knapweed is its ability to exist in drought conditions, grazing, or occasionally annual! Economic evaluation of control must ensure that the root is removed or the plant flowers, mowing spread. Resulting from higher use rates of a non-native biennial forb that reproduces from seed or when was! Can greatly reduce Crop yield and purity this page was last edited 31... In recently disturbed environments - a division of the Office of Engagement Colorado counties cooperating ends of.... Forbs, and yellow starthistle can be mowed repeatedly depending on the.! Tall with multiple branches will take a complex of insects ( perhaps 12 to!