Also, if you burn certain areas with sagebrush, it is possible to start the spread of diffuse knapweed. King county best management practices diffuse knapweed. Diffuse knapweed is a class b noxious weed nonnative species designated for control by state law rcw 17. Executive office montana weed control association, inc. Diffuse knapweed had spread to four counties by 2017 and infested nearly 750 acres. 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. It produces toxic chemicals that can inhibit the growth of desired plants and is a highly competitive plant. Diffuse knapweed national invasive species information. See separate pages on these invasive plants on this website. Diffuse knapweed can be confused with nonnative spotted and russian knapweeds, both of which need to be eradicated. Diffuse knapweed is a shortlived perennial or sometimes biennial plant reproducing solely by seed. Figure 6 bushy specimens of spotted knapweed, diffuse, and squarrose knapweed.
Although meadow knapweed is not currently found in arizona or new mexico, it is included in. A weed report from the book weed control in natural areas in the western united states spotted knapweed. Diffuse knapweed thrives in semiarid and arid environments with light, porous soils such as gravelly loam, and loamy sands. Spotted k napweed has purple flowers very rarely white. Biology and biological control of knapweed invasive. Knapweed in north america occurs up to altitudes of 3,000 m, two times the elevation known for european sites groppe 1992. Plants profile for centaurea diffusa diffuse knapweed.
The combination of 2,4d with aminopyralid in grazonnext hl. Minutus prefers diffuse knapweed while obtusus prefers spotted knapweed. Knapweeds flower from july to october and bolt in early may. Diffuse knapweed floral bracts have yellow spines with teeth appearing as a comb and a distrinct terminal spinte. Spotted knapweed tolerates a wide range of temperature and moisture conditions, and is well adapted to openforest, pastures, and crp land in wisconsin. Diffuse knapweed can sometimes be confused with spotted knapweed, which sometimes has whitepink flowers, but diffuse plants are shorter, stiffer, prickly and more of a greygreen. It spreads by seed, aided by the tumbling of windblown mature plants, and it. The physical appearance of diffuse knapweed is similar to spotted knapweed, except diffuse knapweed is generally shorter and more highly branched. A lowseverity fire will not kill the belowground reproductive structures of diffuse knapweed, but a severe fire can kill some of the plant crowns. Diffuse knapweed is a native of eurasia, coming to the u. 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. Seed remains viable in the soil five years or more, so infestations may occur a number of years after vegetative plants have been eliminated. A prolific seed producer, diffuse knapweed can produce up to 18,000 seeds per plant.
This gives the plant a ballshaped appearance and tumbleweed mobility when broken off. Diffuse knapweed is a nonnative biennial forb that reproduces solely by seed. Diffuse knapweed was found in one north dakota county in 1996 and infested approximately 20 acres. Diffuse knapweed is generally a shortlived perennial or biennial in north dakota and invades habitats similar to spotted knapweed. A mature spotted knapweed plant can produce up to 25,000 seeds that are dispersed by infested hay, wind, water, vehicles and equipment, animals, or shoes. Bracts are not sharp tipped and are fringed in black giving the seed head a spotted appearance. Diffuse knapweed survives most low burning and medium fires. Field guide for managing diffuse, meadow, spotted, and.
Seeds are commonly spread by the wind, as mature plants blow around in a tumbleweed fashion. Bee keepers value the flowers of spotted knapweed because of the flavorful honey produced from its nectar. Seeding desirable perennial grasses is essential to prevent weed reinvasion beck 1997. Diffuse knapweed establishes a rosette in its first season of growth and it commonly bolts the second year. It is usually found on plains, rangelands, and forested benchlands, particularly on rugged or.
Diffuse and spotted knapweed biocontrol department of. Diffuse and spotted knapweeds are listed as noxious weeds in arizona and new mexico. Distribution, biology, and management of diffuse knapweed centaurea diffusa and spotted. Some of the material in this manual was adapted from the manuals for the biology. 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, meadow, spotted, and squarrose knapweeds are invasive weeds common to western states. Also, rosettes of diffuse knapweed have more finely divided leaves than those of spotted knapweed figure 2. It is a possibility that severe fire may kill it, but seeds that are buried survive fire and regrow. In the united states, diffuse knapweed is generally found on light, dry, porous soils. Distinguishing the knapweed species by rosette alone is difficult. This species is common throughout western north america but is not actually native to the north american continent, but to the eastern mediterranean. Spotted knapweed grows 12 to 60 inches tall, is more erect and has more limited branching than diffuse knapweed.
Currently distributed throughout southern bc, both spotted and diffuse knapweed are a major concern in the omineca, peace river, kootenay. Diffuse knapweed was brought in from europe mediterranean region. 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 beetle feeds on the seed heads but is also a foliage feeder as an adult. We would also like to thank richard reardon of the forest health. Pdf sustainable control of spotted knapweed centaurea stoebe. Insects that eat spotted knapweed weedbusters biocontrol.
Pdf managing spotted knapweed centaurea stoebe using. Effects of postfire conditions on germination and seedling success of diffuse knapweed in northern arizona. Compared to spotted knapweed, the leaves of diffuse knapweed are small, and the numerous flower heads are narrow with spiny bracts. One plant can give rise to 1 to 20 slender, upright stems 24 feet in height with most branching occurring in the upper half. United states department of agriculture natural resources. A lowseverity fire will not kill the belowground reproductive structures of diffuse knapweed, but a. However, when stressed by drought, grazing, or mowing, it may show shortterm perennial characteristics. King county best management practices for diffuse knapweed. Its basal leaves leaves at the stem base have short stalks and grow 7 to 8 inches long. However, mowing at the late bud to early bloom stage will reduce seed production. The seeds can germinate from spring through early fall. 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 widespread and increasing in the state, particularly along the front range.
University of nebraskalincoln extension ec173 revised. It is a tough competitor on dry sites and rapidly invades and dominates disturbed areas. Pdf spotted knapweed is native to eastern europe, with a locally scarce but widespread distribution from the mediterranean to the eastern. However both species of weevils feed readily on both species of knapweed. Flowerheads are usually white sometimes pink to purple and are solitary or in clusters. Diffuse knapweed, a biennial or shortlived perennial, and spotted knapweed. Diffuse knapweed is a bushy, taprooted bienniel or shortlived perennial. Diffuse knapweed survives in a wide range of soil and environmental. 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. Centaurea maculosa, the spotted knapweed, is a species of centaurea native to eastern europe description and habitat. White flowers develop in urnshaped heads, in clusters, at the ends of the branches. The seed is commonly spread by vehicles or by the sale and movement of contaminated sand and gravel.
Squarrose knapweed has been listed as a noxious weed in arizona. Spotted knapweed is a biennial or shortlived perennial. Diffuse knapweed can be found in pastures, riparian areas, roadside, and waste areas in colorado. 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. Combining the root herbivore cyphocleonus with the seed feeding weevil larinus reduced spotted knapweed biomass and seed production. Spotted knapweed is listed as noxious, prohibited, banned or otherwise regulated in 16 states. Within 2 years of burning, most diffuse knapweed rosettes were eliminated.
Spotted knapweed is capable of producing flower buds until frost, but normally starts to senesce when soil water is depleted. This tap rooted member of the aster family is native to southeastern europe. Larval feeding in the seedhead destroys the knapweed seed before it matures. Diffuse knapweed can grow 1 to 3 feet tall, and is diffusely branched above ground. Spotted centaurea biebersteinii and diffuse knapweed centaurea diffusa are biennial to shortlived perennials, and considered regionally noxious under the bc weed control act. Dead spotted knapweed stems generally remain erect during the winter unless crushed by heavy snowpack. Diffuse knapweed is a prolific seed producer, producing 900 seeds per plant, under dry land conditions, and 18,000 under irrigation. Diffuse knapweed identification and management diffuse. Figure 11 the flower of the diffuse knapweed plant is generally white but can be lavender or purple. Po box 315, twin bridges, mt 59754 406 6845590 888 6644153 fax. Diffuse knapweed is a biennial to shortlived perennial that reproduces by seed. It grows from 8 to 40 inches tall, with branching stems covered in short, dense hairs and a very long tap root. A biennial is a plant that completes its life cycle within two years.
The leaves become smaller and less divided as they move up the stem. Disturb the soil as little as possible, to reduce germination of new seedlings. Seastedt et al reduction in diffuse knapweed by insects x 237 weed science, 51. Centaurea diffusa, also known as diffuse knapweed, white knapweed or tumble knapweed, is a member of the genus centaurea in the family asteraceae. 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.
Burning has been shown to give effective control of diffuse knapweed while stimulating grass regrowth. Centaurea diffusa is a biennial, annual, or shortlived perennial that is 840 in. Diffuse knapweed infests roadsides, waste areas, dry rangelands and disturbed sites. It is often found in open, disturbed areas where it grows in tufted clumps. Please consult the plants web site and your state department of natural. 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. Figure 10 plants of diffuse knapweed, more branched than those of spotted knapweed, grow 12 feet tall. Best management practices diffuse knapweed centaurea diffusa asteraceae class b noxious weed legal status in king county. Vehicles, machinery, wildlife, domestic animals and movement of. Therefore, the key to managing this plant is to prevent seed production. The plant has a white flower, grows to a height of 24 inches, and has a short taproot.
Institute of arctic and alpine research, and department of environmental, population and organismic biology, university of. Diffuse and spotted knapweeds reproduce by seeds while russian knapweed spreads locally by its lateral roots. Pdf the decline of diffuse knapweed in british columbia. 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. 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. Knapweed removal information how to get rid of knapweed. This biennial or shortlived perennial plant usually has a stout taproot andor pubescent stems when young. A more shortterm approach is to fertilize or combine fertilization with.
Managing spotted knapweed centaurea stoebe using restoration methods. Yellow starthistle is another less robust annual type. Diffuse knapweed north dakota department of agriculture. Largescale control against diffuse knapweed has been seen at a number of locations along the front range. Plants form dense colonies and readily reproduce by seeds, which can travel long distances.
Reductions of 95% or greater in diffuse knapweed stand density have been. The most successful agent for use against diffuse knapweed is the seed head feeding weevil, larinus minutus. Spotted knapweed rosette leaves may be nearly entire. While plants may regenerate from the crown, diffuse knapweed reproduces primarily by seed. Diffuse knapweed prefers open sunny habitats and dry conditions and competes well on excessively drained soils. Diffuse knapweed has white flowers very rarely purple and has sharp tipped bracts bracts are the scales around the seed head.
During the first year of growth, diffuse knapweed appears as a rosette in spring or fall. Spotted knapweed and diffuse knapweed are both shortlived perennials that sometimes behave like annuals. These two species of insects are nearly indistinguishable. It is one of the only knapweeds that spread by tumbling by the wind like russian thistle. In colorado, diffuse knapweed cover declined from 8.1092 423 167 522 428 1360 1585 741 475 1400 880 1048 894 163 291 1313 806 145 1246 145 254 648 1235 690 1171 213 62 1021 359 273 1360 1002 1368 9 888 228 1106 897 314 464 476