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.

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.

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.

FIRST REPORT OF THE DISPERSAL INTO MONTANA OF UROPHORA QUADRIFASCIATA (DIPTERA: TEPHRITIDAE), A FLY RELEASED IN CANADA FOR BIOLOGICAL CONTROL OF SPOTTED AND DIFFUSE KNAPWEED

1985 ◽  
Vol 117 (8) ◽  
pp. 1061-1062 ◽  
Author(s):  
Jim M. Story
Keyword(s):  
Biological Control ◽  
British Columbia ◽  
The United States ◽  
Flower Head ◽  
The Other ◽  
Centaurea Maculosa ◽  
Spotted Knapweed ◽  
European Origin ◽  
Mature Flower ◽  
Diffuse Knapweed

Two tephritid flies of European origin have been introduced into North America for biological control of spotted knapweed, Centaurea maculosa Lam., and diffuse knapweed, C. diffusa Lam. One, Urophora affinis Frauenfeld, was released in British Columbia in 1970 and in 5 states, including Montana, in 1973 (Hanis 1980a; Maddox 1979; Story and Anderson 1978). The other, Urophora quadrifasciata (Meigen), was introduced at Ned's Creek, British Columbia but was not released in the United States. The larvae of both flies induce galls (1 larva/gall) in immature knapweed flower heads and thus reduce seed production. Galls of Urophora affinis occur in the flower-head receptacle whereas galls of U. quadrifasciata are in the ovary wall. In contrast with U. affinis, which has only a partial second generation, U. quadrifasciata normally has 2 complete generations per year, induces thinner galls, and attacks more-mature flower heads than does U. affinis (Harris 1980a).

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.

Successful biological control of diffuse knapweed, Centaurea diffusa, in British Columbia, Canada

2009 ◽  
Vol 50 (1) ◽  
pp. 66-72 ◽  
Author(s):  
Judith H. Myers ◽  
Caroline Jackson ◽  
Hillary Quinn ◽  
Shannon R. White ◽  
Jenny S. Cory
Keyword(s):  
Biological Control ◽  
British Columbia ◽  
Centaurea Diffusa ◽  
Diffuse Knapweed

DIFFUSE KNAPWEED INVASION INTO RANGELAND IN THE DRY INTERIOR OF BRITISH COLUMBIA

1983 ◽  
Vol 63 (4) ◽  
pp. 981-987 ◽  
Author(s):  
JUDITH H. MYERS ◽  
DENIS E. BERUBE
Keyword(s):  
British Columbia ◽  
Density Gradient ◽  
Flowering Plants ◽  
Flowering Plant ◽  
Seedling Density ◽  
Weed Invasion ◽  
Centaurea Diffusa ◽  
Diffuse Knapweed ◽  
Summer Growth ◽  
Grazed Grassland

Diffuse knapweed (Centaurea diffusa) was observed to invade a lightly grazed grassland in the interior Douglas-fir zone southeast of Kamloops, B.C. The presence of knapweed at densities of approximately 15 flowering plants/m2 reduced the growth of grass during the summer by about 2/3 and grass biomass by approximately 1/2. Knapweed seedling density dropped sharply over a distance of 10–20 m, but neither the ratios of seedling-to-rosette nor rosette-to-flowering plant changed significantly over this density gradient. Fertilization did not alter the grass or knapweed summer growth or biomass, but selective grazing by cattle might have obliterated any difference. The front of diffuse knapweed distribution advanced approximately 120 m during 3 yr, and scattered patches of plants occurred even further into the grassland. We conclude that overgrazing is not a necessary prerequisite to the invasion of diffuse knapweed into grassland.Key words: Knapweed, weed invasion, introduced weed, rangeland weed

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.

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.

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