Editing Centaurea diffusa (section)

===Control===
Effective control of diffuse knapweed requires a fusion of well-executed land management, biological control, physical control, chemical control and reestablishment of the native species. Any method of control must ensure that the root is removed or the plant will grow back. Additionally, native plant growth in areas where diffuse knapweed has been removed should be encouraged to prevent reestablishment.

====Biological control====
[[Biological control]] involves the introduction of organisms, usually natural competitors of the invasive species, into the invaded environment in order to control the invasive species. Since 1970, 12 insects have been released to control diffuse knapweed. Of these 12, 10 have become established, and 4 are widely established (''[[Urophora affinis]]'' and ''[[Urophora quadrifasciata]]'', the root boring beetle, ''[[Sphenoptera jugoslavica]]'', and the weevil ''[[Larinus minutus]]'').<ref name="Myers">{{cite web |url = http://culter.colorado.edu:1030/~tims/Myers09.pdf |title = Successful biological control of diffuse knapweed, ''Centaurea diffusa'', in British Columbia, Canada |author = Judith H. Myers |publisher = Biological Control |year = 2009 |access-date = 2009-12-18 |archive-url = https://web.archive.org/web/20100611075416/http://culter.colorado.edu:1030/~tims/Myers09.pdf# |archive-date = 2010-06-11 |url-status = dead }}</ref> 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.<ref>Myers, J.H., Risley, C., 2000. Why reduced seed production is not necessarily translated into successful biological weed control. In: Spencer, N. (Ed.), Proceedings X. International Symposium Biological Control of Weeds. Montana State University, Bozeman, MO, pp. 569–581.</ref>

Some of the more commonly utilized biocontrol agents are the [[Lesser knapweed flower weevil]] and the [[Knapweed root weevil]]. Individuals of these species lay their eggs on the seed heads of both diffuse and [[spotted knapweed]]. When the larvae emerge from the [[Egg (biology)|egg]]s, they feed upon the seeds of their host plant. As the females of this species can create from 28 to 130 eggs and each larva can consume an entire seed head, an adequate population of ''Larinus minutus'' can devastate entire stands of knapweed. The adult weevils feed upon the stems, branches, leaves and undeveloped flower buds. It is native to Greece and is now found in Montana, Washington, Idaho and Oregon.<ref>Groppe, K. 1990. ''Larinus minutus'' Gyll. (Coleoptera: Curculionidae), a suitable candidate for the biological control of diffuse and spotted knapweed in North America. In: Final Report C.A.B International Institute of Biological Control. Delemont, Switzerland, p. 30.</ref> Insects are also used for biocontrol, such as the [[Agapeta zoegana|Yellow-winged knapweed root moth]] (''[[Agapeta zoegana]]''), and several species of Tephritid flies, mostly ''[[Urophora affinis]]'' and ''[[Urophora quadrifasciata]]''.<ref name="Myers" /> 
====Physical control====
Physical control of diffuse knapweed primarily comprises cutting, digging or burning to remove the plants. 

'''Cutting'''  

While cutting the aboveground portion of diffuse knapweed will greatly decrease the spread of seeds, it does not remove the root. With only its root still intact, diffuse knapweed can survive and continue to grow. For a program of cutting to be effective, it must be long-term so that the effect of reduced seed spreading can be realized. 

'''Digging'''  

this removes both the portion above ground and the root of diffuse knapweed and has shown to be very effective; if the plant is properly disposed of, it can neither regrow nor spread its seeds. The largest problem with digging knapweed is that it is extremely labor-intensive. Additionally, the recently vacated soil should be planted with a native species to avoid knapweed reintroducing itself in the disturbed soil. 

'''Burning''' 

setting fire to a crowd of knapweed, if the fire is sufficiently severe, can successfully destroy the above ground and belowground sections of diffuse knapweed. However, precautions must be taken to first ensure that the fire is properly contained and that a new plant community is established to prevent the reintroduction of diffuse knapweed. 
====Chemical control====
Chemical control involves the use of [[herbicide]]s to control diffuse knapweed. The herbicide Tordon (picloram) is recognized{{By whom|date=September 2016}} as the most effective, but it is common to use multiple herbicides in order to reduce strain on local grasses. The herbicides 2,4-D, [[dicamba]], and [[glyphosate]] are also effective for control. In order to be most effective, it must be applied before the knapweed plants have released their seeds, regardless of which herbicide is used. 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.{{Citation needed|date=September 2016}}