Centaurea diffusa1.jpg

Centaurea diffusa – Wikibooks, open books for an open world

Centaurea diffusa

White Knapweed
Centaurea diffusa1.jpg
Binomial: Centaurea diffusa
Kind: Annual or biennial
Circumstances: Gentle, dry, porous soils
Seed Dispersal: Wind

Diffuse knapweed (Centaurea diffusa), also referred to as white knapweed, is a member of the Genus Centaurea within the Household Asteraceae. It’s native to Asia Minor (Turkey, Syria), the Balkans, (Bulgaria, Greece, Romania), Ukraine, and southern Russia.


Diffuse knapweed is an annual or biennial plant, usually rising to between 10 and 60 cm in top. It has a extremely branched stem and a big taproot, in addition to a basal rosette of leaves with smaller leaves alternating on the upright stems. Flowers are often white or pink and develop out of urn-shaped heads carried on the suggestions of the various branches. Diffuse knapweed typically assumes a brief rosette type for one 12 months, reaching most measurement, then quickly rising and flowering throughout the second 12 months. A single plant can produce roughly 18,000 seeds.


Diffuse knapweed is taken into account an invasive species all through North America, having established itself in lots of areas of the continent. C. diffusa was first recognized from North America in 1907 when it was present in an alfalfa subject in Washington state. The seeds had presumably been transported in an impure alfalfa seed cargo coming from someplace within the species native vary. Now current in at the very least 19 states in the USA, it has invaded all contiguous states west of the Rockies and moreover in Connecticut, Massachusetts, and New Jersey. Parts of western Canada have additionally been infested by this plant.

The plant may be very proof against drought, spreads rapidly, and possesses different aggressive benefits which have allowed it to ascertain and flourish in its launched vary. Areas during which diffuse knapweed has been established usually are plains rangelands or forest benchlands. Land that has been lately disturbed—by human or pure processes—is favored for the institution of diffuse knapweed. It has the potential to prosper in semi-arid and arid environments and appears to favor gentle, dry, porous soils. Areas with massive quantities of shade or excessive ranges of water discourage diffuse knapweed progress.

Dispersion happens within the following methods:

  • Agriculture – alfalfa contaminated with diffuse knapweed seed can promote the unfold of diffuse knapweed;
  • Wildlife – wild animals consuming the seeds or transporting the seeds on fur;
  • Wind – seeds blown out of their capsules held on the plant are distributed over a brief vary, however when the plant dries out it might roll for nice distances like tumbleweed, releasing seeds alongside the best way;
  • Water – waterways carry seeds of their move for lengthy distances earlier than depositing them onto a shore the place they germinate.

Wind is the first means by which diffuse knapweed seeds are unfold.


Efficient management of diffuse knapweed requires a fusion of well-executed land administration, organic management, bodily management, chemical management and reestablishment of the native species. Any technique of management should make sure that the basis is eliminated or the plant will develop again. Moreover, native plant progress in areas the place diffuse knapweed has been eliminated needs to be inspired to stop reestablishment.

  • Cultivation: Diffuse knapweed is understood to ascertain extra simply and successfully in lately disturbed environments. Disturbed environments usually current low environmental stress as a result of extra sources can be found than are getting used. These out there sources typically permit the institution of an invasion in an ecological group. The focus of diffuse knapweed in such an space is usually linked to the extent of soil disturbance. Human disturbances typically result in much less species variety in a group. In flip, much less species variety can result in unused sources, which permit invasive species to extra readily set up. Areas akin to fallow land, ditches, rangelands, residential and industrial districts and roadsides are all disturbed habitats the place diffuse knapweed often establishes. Moreover, the elimination of foliage and different floor cowl will increase the chance that seeds will are available in contact with the soil and germinate.
  • Coppicing: Whereas chopping the aboveground portion of diffuse knapweed will drastically lower the unfold of seeds, it doesn’t take away the basis. With solely its root nonetheless intact, diffuse knapweed can survive and proceed to develop. For a program of chopping to be efficient, it have to be long-term in order that the impact of decreased seed spreading will be realized.
  • Pulling: This removes each the aboveground portion and the basis of diffuse knapweed and has proven to be very efficient; if the plant is correctly disposed of, it may possibly neither regrow nor unfold its seeds. The most important drawback with digging up knapweed is that this can be very labor intensive. Moreover, the lately vacated soil needs to be planted with a local species to keep away from knapweed reintroducing itself within the disturbed soil.
  • Flame: Setting hearth to a crowd of knapweed, if the fireplace is sufficiently extreme, can efficiently destroy the above floor and belowground sections of diffuse knapweed. Nevertheless, precautions have to be taken to first make sure that the fireplace is correctly contained and {that a} new plant group is established to stop the reintroduction of diffuse knapweed.
  • Contact herbicides (artificial): The herbicide Tordon (picloram) is acknowledged as the simplest, however it’s common to make use of a number of herbicides with a purpose to cut back pressure on native grasses. The herbicides 2,4-Dichlorophenoxyacetic acid, Dicamba, and Glyphosate are additionally efficient for management. As a way to be best, it have to be utilized earlier than the knapweed vegetation have launched their seeds, no matter which herbicide is used.
  • Biocontrols (microorganisms): The organic management of diffuse knapweed has been primarily approached by the usage of bugs. Biocontrol is best when a number of species of biocontrol organisms are used.
A few of the extra generally utilized biocontrol brokers are:

  • Lesser knapweed flower weevil (Larinus minutus). People of this species lay their eggs on the seed heads of each diffuse and noticed knapweed species. When the larvae emerge from the eggs, they feed upon the seeds of their host plant. Because the females of this species can create from 28 to 130 eggs and every larva can devour a complete seed head, an ample inhabitants of Larinus minutus can devastate total stands of knapweed. The grownup weevils feed upon the stems, branches, leaves and undeveloped flower buds. It’s native to Greece and is now present in Montana, Washington, Idaho and Oregon.
  • Knapweed root weevil (Cyphocleonus achates). Knapweed root weevils lay roughly 50 to 70 eggs on both diffuse or noticed knapweed. Because the title suggests, the larvae produced burrow into the basis the place they metamorphose into grownup type. At this level, they may tunnel by the basis to the floor the place they may feed on the leaves of knapweed vegetation. It’s native to Austria, Greece, Hungary and Romania and has been launched to Idaho, Montana, Washington and Oregon.


The most important influence of people on diffuse knapweed is definitely resulting from our efforts in controlling and eradicating its invasive populations. The a number of strategies outlined within the management part characterize a small pattern of actually a whole lot of approaches being tried with various ranges of effectiveness. Moreover lowering the unfold of diffuse knapweed, we’re additionally offering selective strain towards the people that can’t stand up to a sure technique of management. Selective strain, given adequate time, could cause the difference or evolution of invasive species akin to diffuse knapweed. If a person diffuse knapweed plant survives management efforts due to a trait it possesses, its progeny will make up a larger portion of the inhabitants than the vegetation that succumbed to the management.

The success of diffuse knapweed have to be attributed to a mixture of a number of mechanisms. Its invasiveness is because of a mixture of allelopathy, ERH and superior useful resource competitors. Nevertheless, probably the most significance have to be attributed to the ERH as a result of diffuse knapweed, whereas a really efficient invasive species in its novel atmosphere, is non-invasive and doesn’t set up monocultures in its native vary. It’s the variations, biotic and abiotic, between its novel and native environment that trigger it to be invasive.

To reveal that the ERH applies to diffuse knapweed, it’s important to indicate that the absence of pure enemies has a major optimistic impact on its success. One approach to present that is to look at the impact of introducing a few of diffuse knapweed’s pure enemies into its novel atmosphere. If diffuse knapweed, which usually thrives in its invaded atmosphere, is considerably inhibited by the introduction of pure enemies, it may be concluded that diffuse knapweed is extra aggressive within the absence of its pure enemies. A current effort at biocontrol of diffuse knapweed in Camas County, Idaho successfully decreased 8,000 ha (20,000 acres) of knapweed to minimal ranges by the discharge of the lesser knapweed flower weevil and the knapweed root weevil. Since each of the bugs launched are pure opponents of diffuse knapweed, and since this and different related efforts at biocontrol have been profitable, there’s vital proof that diffuse knapweed advantages from the absence of its pure enemies.

One other side of diffuse knapweed’s success depends on the impact of its allelopathic chemical substances in its novel atmosphere. Though there’s nonetheless debate in regards to the effectiveness of allelopathic chemical substances within the subject, the proof of allelopathic results demonstrated in a laboratory setting and its propensity to ascertain monocultures assist the significance of allelopathy to diffuse knapweed’s success.

Curiously, diffuse knapweed’s allelopathic chemical substances have been proven to have a deleterious impact on the North American opponents however have been helpful to its native opponents. Whereas diffuse knapweed’s native opponents are capable of compete extra successfully within the presence of allelopathic chemical substances, the novel competitor’s health is decreased. This example gives an instance of the effectiveness of the allelopathy mechanism benefiting from the ERH. The elevated effectiveness of allelopathic chemical substances trigger diffuse knapweed to expertise much less aggressive strain. In consequence, diffuse knapweed is ready to set up extra predominantly on this new space.

One other connection between allelopathy and the ERH is the truth that concentrations of allelopathic chemical substances have been discovered to extend when diffuse knapweed was planted in North American soil versus Eurasian soil. This impact might be because of the absence of unfavorable soil circumstances or soil microorganisms that exist in its native atmosphere. In consequence, the allelopathic chemical substances will be capable of attain greater concentrations, unfold farther and due to this fact be more practical. By effecting extra neighboring vegetation, the favorable adjustments in soil situation contribute to the success of diffuse knapweed.

Moreover the benefits that diffuse knapweed positive factors from the ERH and allelopathy, it additionally possesses a number of characteristically invasive traits. One issue resulting in the superior useful resource competitors of diffuse knapweed is its capacity to exist in drought circumstances. This benefit permits diffuse knapweed to commit its sources to competitors whereas its neighbors are conserving sources to outlive. The excessive variety of seeds produced by diffuse knapweed can be a standard trait of invasive vegetation. A better density of knapweed is not going to solely improve the focus of allelopathic chemical substances within the soil however may also prohibit the vitamins out there to native vegetation. Sadly, little or no analysis has been carried out to find out the relative aggressive capacity between diffuse knapweed and its novel opponents. Nevertheless, checks carried out on the impact of diffuse knapweed on North American grasses within the absence on allelopathic chemical substances demonstrated that the health of those grasses declined within the presence of diffuse knapweed. Regrettably, we can not resolve if diffuse knapweed is, for basic functions, a greater competitor from this knowledge alone. Comparisons of the deleterious results between these and different pairs of opponents to reach at a conclusion.

Diffuse knapweed is profitable in its novel vary primarily as a result of the organisms and circumstances that forestall it from changing into invasive in its native atmosphere are absent. It follows that the introduction of species from its native habitat can be an efficient technique of management. Nevertheless, the introduction of a non-native organism has the potential to end in one other invasive species outbreak. Due to this fact, any technique of organic management have to be preceded by evaluation of doable results.


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