diffuse knapweed
      Centaurea diffusa (Lam.)
      Weed ID Links.       Flower comparison to spotted knapweed Plant
      Photo from slide show: Biological Control of Noxious Weeds, by Reeves Petrof.Description:
      Roots: The roots of diffuse knapweed are called "elongated taproots," which means a long slender, single root that goes into the ground. (1,2)

      Stems/Leaves: The leaves are smaller at the top and bigger at the bottom.  The leaves are divided into parts called toothed parts. Which means that the leaves are very thin and finely divided. The color of the leaves are a light green and they are covered with short hairs. The height of this knapweed is 1.5-2.5 ft. There is one single stem that comes up from the rosette, (a bunch of leaves bunched together at the bottom of the plant). (1,2)

      Flowers: The flowering occurs during late June, July-September.  They are either singular or in clusters at the top of the stems on the weed. The most common colors of the flowers are rose, lavender, or white. (1,2)
      Fruits/Seeds:  The seeds are oblong, (rectangle, triangle shape, and long.) They are usually dark brown or gray seeds with brown to gray stripes down the sides. They are approx. 3 mm. long. (1,2)
      Methods of Reproduction/Spread:   The plant reproduces by the spread of the seed. They also re-grow from the root. This weed can produce a number of 400-900 seeds per plant per year. Seeds can be moved if the seed head is mature and broken off by the wind or by vehicles. There is a wide environmental range of where this weed can grow.  If the seed is below a certain depth (3 cm), it will not grow.  (1)  
      Life Style/habits/Life Duration:  Diffuse knapweed is biennial, (can survive for a period of two years).  (1)
      Montana Infestation/History:  This knapweed was introduced in the early 1900's. It is found mostly in dry, light, porous, and absorbent soils. It was introduced in a small area but spread quickly. (1)

      This is the spread of diffuse and spotted knapweed over the period of 1925-now. http://www.mtweed.org/Awareness/Spread/spread.html.

      Environments favorable to infestation:        This plant is favorable to dry but absorbent soils. The soil has to be a light soil, not thick like a clay or thick mud. (1)
      Impacts: The most basic impact that this knapweed has caused is the loss of quality forage for livestock and wildlife. This knapweed spreads very quickly. In 1979 it spread approx. 756,000 acres in Montana alone. In 1925 there was one county that was infested with this weed. Now it is in every county in Montana. (1)
      Comments: I think that this knapweed spread very quickly in the years of 1975-1999. Some other interesting things are its effects against fire. Diffuse knapweed survives most low burning and medium fires. It is a possibility that severe fire may kill it, but seeds that are buried survive fire and re-grow. Also, if you burn certain areas with sagebrush, it is possible to start the spread of diffuse knapweed. (4)
      Native Range/ Probable Entry into N. America: This knapweed is native to Eurasia. It grows in the Western part of Asia, in the Eastern Mediterranean, and in Southern parts of former USSR. It could have been brought to the U.S. as a contaminant in alfalfa seed. (1)
      Methods of Control:
      1. Chemical: There is an herbicide called 2,4-D applied at a rate of 1 kg/acre eliminates knapweed. (An herbicide means an chemical that kills certain weeds.) (2)

      2. Cultural: Grasses that will not be harmed by the herbicide can by re-seeded to compete against the knapweed.

      Irrigation is another way to try to stabilize the knapweed and over take it.

      Fires are also another way of control. You can burn them down. That does not mean it will kill them though.

      Grazing is also another way. Do not over graze, though. (2)

      3. Biological: There are two seed head fleas called: (1) Urophora affinis; (2) U. quadrifasciata. They reduce seed production. They were indicated to be able to move several hundred yards in one year. Here is a list of many over biological controls agents: Agapeta zoegana, Bangasternus fausti, Chaetorellia acrolophi, Cyphocleonus achates, Larinus minutus, Larinus obtusus, Metzneria paucipunctella, Pelochrista medullana, Pterolonche inspersa, Sphenoptera jugoslavica, Terellia virens, Urophora affinis, and Urophora quadrifasciata. (2)

      4. Mechanical: If you want to pull or cut down the plant it is best to remove the rosette and part of the roots. There is only a 4% chance of it surviving. If you leave the rosette, there is a 38% chance of it surviving. You do the math!! (2)

      Tilling: Plowing or tilling an infested area several times a year for several years to control the weed. <

      5. Other: Flooding or shading can also kill or destroy this knapweed. How to Prevent Spread: Some ways to stop spread are to stay out of it. Wash off your vehicle before driving off with the seeds stuck in your tires, or in the vehicle. Do not move soil infested with seeds. Basically use precautions when and if you are near or in it.
      Links
      http://www.nwcb.wa.gov/weed_info/Written_findings/Centaurea_diffusa.html
      http://www.idahoweedawareness.org/vfg/weedlist/dknapweed/dknapweed.html
      http://www.invasive.org/browse/subject.cfm?sub=447
      http://www.kingcounty.gov/environment/animalsAndPlants/noxious-weeds/weed-identification/diffuse-knapweed.aspx
      http://ndweeds.homestead.com/diffuseknapweed.html
      http://www.cnr.uidaho.edu/rx-grazing/Forbs/Diffuse_Knapweed.html
      http://www.coopext.colostate.edu/adams/weed/dknapweed_mgt.htm
      http://www.idahoweedawareness.org/vfg/weedlist/dknapweed/dknapweed.html
      http://www.cwma.org/nx_plants/diff.htm
      BIBLIOGRAPHY
      (1) Rees, Norman, et. al., Ed., Biological Control of Words in the West, Western Society of  Weed Science in cooperation with USDA ARS, MT Dept. of Ag., and MT State University, Color World printers, Bozeman, MT, Feb., 1996.

      (2) Colorado State University Coop. Extension. Weeds in Northwest Colorado, 1997-98. [On-line] http://yampa.com/Routt/CSU/DiffuseKnapweed.html (3) Centaurea diffusa: Fire Effects. Author and date unknown. [On-line] http://www.wildfire.org/feis/plants/forb/cendif/fire_effects.html

      (4) Knapweed-Infested Rangeland (April 30, 1993). BIOLOGICAL CONTROL REDUCES DAMAGE. Author unknown. [On-line]. http://ceris.purdue.edu/napis/pests/misc/fKnap.txt
      By: Pam McKinney Published by: Pam McKinney. - Updated by: Lizzie and Markie, 3/09.
      Back - mtwow.org HOME