Centaurea diffusa Lamarck, diffuse knapweed, and Centaurea stoebe subsp. micranthos (S.G. Gmel. ex Gugler) Hayek, spotted knapweed (Asteraceae).

2013 ◽  
pp. 302-307 ◽  
Author(s):  
R. S. Bourchier ◽  
B. H. van Hezewijk
Keyword(s):  
Spotted Knapweed ◽  
Centaurea Stoebe ◽  
Centaurea Diffusa ◽  
Diffuse Knapweed

Biological Control of Diffuse Knapweed (Centaurea diffusa) and Spotted Knapweed (C. maculosa)

Weed Science ◽  
1982 ◽  
Vol 30 (1) ◽  
pp. 76-82 ◽  
Author(s):  
Donald M. Maddox
Keyword(s):  
Biological Control ◽  
Biological Control Agent ◽  
Reproductive Potential ◽  
Control Agent ◽  
Flower Head ◽  
Spotted Knapweed ◽  
Centaurea Diffusa ◽  
Weedy Species ◽  
Diffuse Knapweed ◽  
Number Of Seeds

Diffuse knapweed (Centaurea diffusa Lam.) and spotted knapweed (C. maculosa Lam.) presently infest approximately 1.5 million ha of pasture and rangeland in Washington, Montana, Idaho, Oregon, and California. The serious losses caused on lands where returns from herbicidal control are marginal or less prompted the testing and introduction of two strains of a seed-head fly (Urophora affinis Frlfld.) as a biological-control agent in these states. Over 27 000 flies were released in about equal numbers on both weeds during the years 1974 to 1977 and in 1979 and 1980. The fly became established in all states where it was released. The adult was found to disperse over 76 m from release point from 1974 to 1976, and to reduce the number of seeds per flower head in sampled heads by 80% in northern Washington and over 64% at the Heppner, Oregon site. A newly released moth (Metzneria paucipunctella Zell.) and a root-boring beetle (Spbenoptera jugoslavica Obenb.) are expected to cause additional pressure on these plants. The reproductive potential of the knapweeds is such that more natural enemies will be needed to provide enough stress to reduce these weedy species to an acceptable level.

Induction of bolting by gibberellic acid in rosettes of diffuse (Centaurea diffusa) and spotted (C. maculosa) knapweed

1986 ◽  
Vol 64 (11) ◽  
pp. 2428-2432
Author(s):  
Mahesh K. Upadhyaya
Keyword(s):  
Gibberellic Acid ◽  
Stem Growth ◽  
Field Conditions ◽  
Spotted Knapweed ◽  
Centaurea Diffusa ◽  
Diffuse Knapweed

An attempt was made to induce synchronous bolting of knapweed (Centaurea spp.) rosettes with gibberellic acid (GA3) under greenhouse conditions. Single or double (2 weeks apart) sprays of GA3 (0, 0.3 × 10−4, and 1.5 × 10−4 M) were applied to 10- to 115-day-old diffuse knapweed (C. diffusa Lam.) rosettes. With the exception of 10- and 25-day-old rosettes, highly synchronous bolting was induced by double applications of 1.5 × 10−4 M GA3. Bolted plants flowered within 8 to 10 weeks of treatment but did not form seeds because of the absence of pollinators in the greenhouse. The size of bolted plants and the percentage of plants bearing flowers depended on rosette age at the time of GA3 application. With a single GA3 application or with two applications at lower concentration, uneven and (or) irregular bolting occurred. Occasionally, the initial rapid stem growth induced by GA3 was arrested, resulting in the formation of aerial rosettes. GA3 also induced bolting in spotted knapweed (C. maculosa Lam.). Induction of synchronous bolting may be useful in mechanical, biological, and (or) environmental (e.g., winter-killing) control of biennial weeds. Its feasibility under field conditions, however, remains to be demonstrated.

Knapweed and Its Control in British Columbia

1987 ◽  
Vol 1 (3) ◽  
pp. 267-268
Author(s):  
Peter D. Graham Dyck
Keyword(s):  
British Columbia ◽  
Animal Species ◽  
Spotted Knapweed ◽  
Wild Animals ◽  
Native Plant ◽  
Forest Land ◽  
Weed Species ◽  
Centaurea Diffusa ◽  
Diffuse Knapweed ◽  
Agricultural Loss

In the last two decades the weed species, diffuse knapweed (Centaurea diffusa) and spotted knapweed (C. maculosa) have gained prominence in the British Columbia interior. These aggressive species have invaded over 40,000 hectares (100,000 acres) of British Columbia range and forest land and are spreading at a rate of about 10% per year. Knapweed can reduce the native forage by as much as 80 to 90% and thus destroy the food supply for cattle and wild animals such as elk and deer. If the weeds spread to their ecological limit over 1 million hectares in British Columbia could be affected, causing an estimated agricultural loss of $13 million annually (Cranston, R. 1985, B.C. Min. of Agric. 85–1). The potential extinction of native plant and animal species is a cost too great to be measured.

BIOLOGY OF CYPHOCLEONVS ACHATES (COLEOPTERA: CURCULIONIDAE), PROPAGATED FOR THE BIOLOGICAL CONTROL OF KNAPWEEDS (ASTERACEAE)

1999 ◽  
Vol 131 (2) ◽  
pp. 243-250 ◽  
Author(s):  
Brian M. Wikeem ◽  
George W. Powell ◽  
Allen Sturko
Keyword(s):  
Biological Control ◽  
Adult Emergence ◽  
Larval Survival ◽  
Specific Information ◽  
Spotted Knapweed ◽  
Degree Days ◽  
Centaurea Diffusa ◽  
Larval Production ◽  
Competition For Food ◽  
Diffuse Knapweed

AbstractCyphocleonus achates (Fahraeus) is a weevil used for the biological control of diffuse knapweed, Centaurea diffusa Monnet Del La Marck, and spotted knapweed, Centaurea maculosa Monnet Del La Marck, in North America. This research provided specific information on the biology of this insect in British Columbia. Adult weevils were released at six densities (1, 2, 4, 8, 16, and 32 male–female pairs) in each of 2 years into plots containing spotted knapweed. Larvae per plant, larval mass, larval survival, adult emergence, and air temperature were measured. Larval production increased with the release density of weevils in both the 1992 cohort and the 1993 cohort. Larval mass did not differ between years. Larval mass also did not vary with the release density of adults or the number of larvae per root. Larval survival of the 1993 cohort ranged from 17 to 48%, whereas that of the 1994 cohort ranged from 0 to 91%. Adult emergence began after the accumulation of 726–1144 degree-days. For both cohorts the date of first emergence occurred earlier, as the average number of larvae per plant increased for both cohorts. Increasing competition for food or space in the roots can induce early emergence. Sex ratios did not vary with date of emergence or release density of adult weevils. Adult emergence increased with the release density in the 1992 cohort, suggesting the average larval densities did not exceed the carrying capacity of the roots. The peak emergence rate increased with the release density in the 1992 cohort, but not in the 1993 cohort because of lower larval survival.

THE BIOLOGY OF CANADIAN WEEDS.: 6. CENTAUREA DIFFUSA AND C. MACULOSA

1974 ◽  
Vol 54 (4) ◽  
pp. 687-701 ◽  
Author(s):  
A. K. WATSON ◽  
A. J. RENNEY
Keyword(s):  
British Columbia ◽  
Biological Information ◽  
Spotted Knapweed ◽  
Eastern Canada ◽  
Centaurea Diffusa ◽  
Diffuse Knapweed ◽  
Semiarid Rangeland

A summary of biological information on Centaurea diffusa Lam. (diffuse knapweed) and C. maculosa Lam. (spotted knapweed) is presented. The knapweeds are common on semiarid rangeland, highway and railroad right-of-ways and waste places in southern British Columbia. Spotted knapweed is also common in eastern Canada.

Distribution, Biology, and Management of Diffuse Knapweed (Centaurea diffusa) and Spotted Knapweed (Centaurea maculosa)

1998 ◽  
Vol 12 (2) ◽  
pp. 353-362 ◽  
Author(s):  
Roger L. Sheley ◽  
James S. Jacobs ◽  
Michael F. Carpinelli
Keyword(s):  
Weed Management ◽  
Seedling Recruitment ◽  
Cost Effective ◽  
Management Program ◽  
Integrated Weed Management ◽  
Competitive Balance ◽  
Spotted Knapweed ◽  
Centaurea Diffusa ◽  
Diffuse Knapweed ◽  
Associated Species

Diffuse knapweed, a biennial or short-lived perennial, and spotted knapweed, a perennial, are taprooted Eurasian weeds invading rangeland in the western United States and Canada. Knapweed (Centaureaspp.) invasion is associated with reductions in biodiversity, wildlife, and livestock forage, and increased erosion. Spotted knapweed grows to about 1 m and usually has purple flowers, whereas diffuse knapweed is slightly shorter, usually with white flowers. Persistent flower bracts on diffuse knapweed bear a rigid terminal spine about 8 mm long with four or five pairs of shorter lateral spines. Bracts on spotted knapweed have dark spotted tips. Knapweed management involves a combination of containing infestations and control efforts. Hand pulling in areas with small infestations can be effective for controlling spotted and diffuse knapweeds. Picloram applied at 0.28 kg ha−1provides control for about 3 yr. Effective long-term control of knapweeds requires periodic applications of picloram, which are only cost-effective on highly productive range sites with a residual grass understory. About 12 insect species have been released for knapweed biocontrol. Seed production has been reduced by 46% by insects feeding in the flower heads. Although insects have not reduced spotted knapweed densities, they may stress the weed and shift the competitive balance to associated species. Sheep grazing reduces the density of very young seedlings and may limit seedling recruitment into the population. In areas without a residual understory of desired plant species, revegetation of knapweed-infested rangeland is required. Components of any integrated weed management program are sustained effort, constant evaluation, and the adoption of improved strategies.

scholarly journals Biological control and precipitation effects on spotted knapweed (Centaurea stoebe): empirical and modeling results

Ecosphere ◽  
2013 ◽  
Vol 4 (7) ◽  
pp. art80 ◽  
Author(s):  
Anastasia Maines ◽  
David Knochel ◽  
Timothy Seastedt
Keyword(s):  
Biological Control ◽  
Spotted Knapweed ◽  
Centaurea Stoebe

Elaiosomes on Weed Seeds and the Potential for Myrmecochory in Naturalized Plants

Weed Science ◽  
1990 ◽  
Vol 38 (6) ◽  
pp. 615-619 ◽  
Author(s):  
Robert W. Pemberton ◽  
Delilah W. Irving
Keyword(s):  
United States ◽  
The United States ◽  
Leafy Spurge ◽  
Spotted Knapweed ◽  
Canada Thistle ◽  
Weed Seeds ◽  
Naturalized Plants ◽  
Bull Thistle ◽  
Diffuse Knapweed

Seeds of plants naturalized in the United States were examined for the presence of elaiosomes. Seeds of 47 species belonging to 13 families (Asteraceae, Boraginaceae, Dipsacaceae, Euphorbiaceae, Fabaceae, Fumariaceae, Lamiaceae, Liliaceae, Poaceae, Polygonaceae, Resedaceae, Rosaceae, and Solanaceae) were found to have elaiosomes, indicating that these species are probably mymecochorous, i.e., dispersed by ants. These include important rangeland weeds such as bull thistle, Canada thistle, musk thistle, diffuse knapweed, spotted knapweed, and leafy spurge. Myrmecochory in naturalized species may enhance their weediness in areas where they are established and assist their colonization of new and relatively closed communities.

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