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,~„~ h,;'~~ ~, Spotted knapweed germinates in spring or fall. Perennial
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<br />~ Spotted knapweed is native to central Europe, where it is
<br /> found in light, porous, fertile, well-drained and often calcareous
<br />x'~ _;Y~F'e. soils in warm areas. It occupies dry meadows, pastureland, stony
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<br />~, ,s ~~ Q1'µ and rivers. Spotted knapweed tolerates dry conditions, similar to
<br />~x~- ~ diffuse knapweed, but survives in higher moisture areas as well
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<br />2d ~~~~~ mountains). Spotted and diffuse knapweed infestations often occur
<br /> together in Colorado.
<br /> Management
<br /> Diffuse and spotted knapweed can be managed similarly. They are
<br /> readily controlled with herbicides. However, the weeds will reinvade unless
<br />Spotted knapweed infestations are not cultural techniques are used.
<br />as severe in Colorado as diffuse Chemical control. Reseazch conducted a[ Colorado S[a[e University
<br />knapweed. However, this weed spreads indicates that Tordon 22K (picloram) at 1 to 2 pUA, Transtine (clopyralid) at
<br />rapitlly. For example, spotted knapweed 0.67 [0 1 pUA, Curtail (clopyralid + 2,4-D) at 4 to 6 pUA, or BanveU
<br />was first observed in Gallatin County, Vanquish/Clarity (dicamba) at 1 [0 2 pUA control diffuse knapweed. Tank
<br />Montana, in the 7920s, but is now
<br />found in all Montana counties. Today,
<br />mixes of BanvellVanquish/Clariry plus 2,4-D at 1 pt + 2 pUA or BanveU
<br />over 4.7 million acres are infested. Vanquish/Clarity plus Tordon 22K at ] to 2 pt + OS to 1 pdA or Tordon plus
<br /> 2,4-D at 0.75 p[ + 2 pUA al] control diffuse knapweed. These tank-mixes
<br /> may save money and reduce grass injury resulting from higher use rates of a
<br /> single herbicide.
<br /> Spotted knapweed and diffuse knapweed generally occupy the same
<br /> areas in Colorado, so the same herbicide treatments can be applied. Weed
<br /> scientists a[ Montana State University indicate [hat 1 pUA of Tordon (0.25 ]b)
<br />Livestock (sheep, goats, cattle) will eat controls spotted knapweed for two to three years, but [he weed will reinvade
<br />diffuse and spotted knapweed. Recent the area unless other management techniques are used.
<br />research completed by Colorado State Cultural control. If desirable grass competition is evident in diffuse
<br />University shows that cattle grazing or spotted knapweed stands, judicious herbicide application that does not
<br />diffuse knapweed twice in spring
<br />decreased seed set by 50 percent and
<br />injure grasses may allow them to compete effectively with [he weeds.
<br />tumbling of/-site over winter by 15 Irrigation (where possible) may help stimulate grass competition in these
<br />percent. Cattle were managed to cases. However, infested rangeland or pastures often are degraded, allowing
<br />achieve 5o percent utilization of pasture knapweed invasion, and herbicides alone will not restore the land to a
<br />and were allowed to graze at two 10. productive state. Seeding suitable perennial grasses is necessary [o prevent
<br />day intervals when tliffuse knapweetl weed reinvasion.
<br />was bolting and about 6 to 72 inches Biological control. Many insects are being evaluated for biological
<br />tall. control of diffuse and spotted knapweeds. Researchers at Montana State
<br /> University believe it will take a complex of insects (perhaps 12) to reduce
<br /> diffuse and spotted knapweed populations.
<br />coloradostateuniversirycooperetive Several insects are available in Colorado, from the Colorado
<br />Extension weed specialist and proressor, Department of Agriculture. The seedhead flies Urophora a~nis and U.
<br />plant pathology and weed science. uadri asciata have been released in man Front Ran a counties. These
<br />9 f Y g
<br />Issued in furtherance of Cooperative insects cause plants to produce fewer viable seeds and abort terminal or
<br />Extension work, Acts of May 8 and June 30,
<br />lateral flowers
<br />1914, in cooperation with the U.S.
<br />department of Agricuaure, Milan A. Rewerts, .
<br />Root-feeding insects may have a more detrimental effect on knapweed
<br />Directorot Cooperative Extension, Colorado populations than seed-feeding ones. Larvae of the diffuse knapweed root beetle
<br />state universiry, Fort Collins, Colorado. (Sphenoptera jugoslavica) feed in the roots of diffuse knapweed. Larvae of the
<br />Cooperetive Extension programs are
<br />available to ali without tliscrimination.No
<br />yellow-winged knapweed moth (Agapeta zoegana) feed and the knapweed
<br />endorsement of products mentioned is root weevil (Cyphocleonus achates) in the roots of both knapweed species.
<br />intended nor is criticism implied of products
<br />not mentioned
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