Spotted knapweed

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Spotted knapweed
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Taxonomy

• Family Asteracea Aster family
• Genus Centaurea L. knapweed
• Species Centaurea biebersteinii DC.
• Synonyms
• Acosta maculosa auct. non Holub
• Centaurea maculosa auct. non Lam.
• Centaurea stoebe L. ssp. micranthos (Gugler)
  Hayek
• Common name
• Spotted knapweed

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Species description

• Biennial or short-lived perennial with deep tap
  root.
• Juvenile plants and over-wintering adults are in
  the rosette form.
• Small plants have one unbranched stem with one
  flower head, large plants have multiple stems and
  as many as 100 flower heads.
• Mature plants grow to height of between 15 122
  cm (6 4).

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Species description

• Flower heads are 5 to 10 mm long and can occur
  singly or in clusters at branch tips.
• Each head bears stiff, black tipped bracts giving
  the plant its spotted appearance.

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Species description

• Seeds are 2.5 mm long.
• Seeds are oval, black or brown, with pale
  vertical lines.
• Each seed has a short bristly pappus about half
  the length of the seed.

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Biology

• Pollinated primarily by flies and bees self
  compatible.
• Each plant usually produces between 400 and 900
  seeds seed production is highly dependant on
  annual precipitation.
• Plants in irrigated fields produced as many as
  25,263 seeds.
• Rarely produces rhizomes population growth
  dependent almost solely on seed.

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Biology

• Three seed-germination types produced by parent
  plant
• Non-dormant seed germinates regardless of light.
• Seed with dormancy set by far red light.
• Dormant seed that does not germinate until buried
  with soil.
• Dormant seeds readily accrue in seed bank seeds
  viable as long as 8 years.
• Germinate over a range of soil depths, water
  content, and temperature.

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Biology

• Seeds germinate between late March and June of
  each year. Earliest plants to germinate have the
  highest survival.
• Seedlings have tap root as long as 80 cm after
  two months of growth.
• Seedling mortality is highly variable from year
  to year (precipitation), but averages about 12.

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Biology

• Juvenile and mature plants spend winter as a
  rosette.
• Rosette mortality has been reported as high as
  48 and was attributed to root grazing by weevils
  and underground rodents.
• Adult spotted knapweed flower 1-3 years over
  lifetime.
• Plants as old as 12 years have been documented.

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Geographic Range Native

• Central Europe and east to central Russia,
  Caucasia, and western Siberia.
• Found in elevations ranging from 578 to 3,040 m.
• Found in precipitation zones from 20 to 200 cm
  annually.

Spotted knapweed in Romania
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Geographic Range North America

• Introduced as contaminants in alfalfa and soil
  used as ship ballast.
• First recorded in Victoria, British Columbia in
  1893.
• Since spread to virtually every Canadian province
  and nearly every state in the US.

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Geographic Range United States

• Limited to San Juan Islands, WA, until 1920.
• 1920-1960 spread to 20 counties in Pacific
  Northwest.
• 1960-1980 spread to 48 counties.
• 1980-present spread to nearly every state
  including every county in Washington, Idaho,
  Montana, and Wyoming.
• Nevada

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Preferred habitats everywhere!
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What makes it invasive?

• Vacant niche
• Allelopathy
• Atmospheric CO2 / global climate change
• Resource availability / Competition
• Microevolutionary change
• Escape from biotic constraints??
• Biodiversity
• Disturbance / land use
• Anthropogenic

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What makes it invasive?Allelopathy

• According to Weir et al. (2003), a study as early
  as 1832 hypothesized that allelopathy could be
  responsible for spotted knapweeds success.
• Fletcher and Renney (1963) were first to extract
  substances with allelopathic potential from
  leaves, stem, and roots.
• Since 1963 numerouse studies have isolated
  chemicals such as cnicin, () catechin, and
  numerous polyacetylenes (Stevens 1986, Kelsey and
  Locken 1987, Locken and Kelsey 1987, Bais et al.
  2002 and 2003, and others).

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What makes it invasive?Allelopathy

• Ridenour and Callaway (2001) showed that spotted
  knapweed has negative effects on biomass of roots
  and shoots of Festuca idahoensis which are
  ameliorated by activated charcoal.

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What makes it invasive?Allelopathy

• Bais et al. (2003) reported that a mixture of
  ()-catechin and (-)-catechin was present in root
  exudates of spotted knapweed.
• Further studies showed that (-)-catechin was
  solely responsible for phytotoxic activity,
  whereas ()-catechin provided antimicrobial
  properties.
• (-)catechin inhibits root growth and germination
  in field soils of two North American grasses
  (Festuca idahoensis and Koeleria micrantha), by
  triggering a wave of reactive oxygen species
  initiated at the root meristem, which leads to a
  Ca2 signaling cascade triggering genome-wide
  changes in gene expression and ultimately death
  of the root system.

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What makes it invasive?

• Vacant niche
• Allelopathy
• Resource availability / Competition
• Atmospheric CO2 / global climate change
• Microevolutionary change
• Escape from biotic constraints
• Biodiversity
• Disturbance / land use
• Anthropogenic

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What makes it invasive? Competition / Resource
availability

• Callaway et al. (2004) showed that the presence
  of arbuscular mycorrhizae can significantly alter
  the competitive balance between spotted knapweed
  and native grasses / forbs.

AMF helps () SK or hinders (-) SK
-
-
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What makes it invasive?Competition / Resource
availability

• Numerous studies have determined how spotted
  knapweed and various other native species respond
  to manipulations of limiting resources such as
  nitrogen, phosphorus, and water (Story et al.
  1989, Herron et al. 2001, Blicker et al. 2002,
  Olson et al. 2003, Blicker et al. 2003, Sperber
  et al. 2003, and Hook et al. 2004).

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What makes it invasive?Competition / Resource
availability

• In a glasshouse studies, Blicker et al. (2002,
  2003) studied water N use of spotted knapweed
  in comparison with three native grasses.
• Spotted knapweed did not have the greatest WUE.
• Spotted knapweed did not use the most water.
• Spotted knapweed did not have the greatest NUE.
• Spotted knapweed did not use the most nitrogen.

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What makes it invasive?Competition / Resource
availability

• Herron et al. (2001) hypothesized that removal of
  nitrogen and phosphorus from soil would shift
  competitive balance to native bluebunch
  wheatgrass.
• Without nutrient manipulation, spotted knapweed
  had higher N uptake and biomass.
• When N was removed from soil, the competitive
  balance shifted to bluebunch wheatgrass.
• Phosphorus removal had no effect.

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What makes it invasive?Competition / Resource
availability

• Spotted knapweed is probably a better competitor
  for nitrogen when N levels are high.
• Probably not a better competitor for phosphorus.
• Does not use water efficiently deep tap root
• Arbuscular mycorrhizae can have a positive or
  negative effect on competition between spotted
  knapweed and native species.
• Callaway and Ridenour (2004) hypothesized that
  there could be a connection between allelopathy
  and competition for resources.

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What makes it invasive?

• Vacant niche
• Allelopathy
• Resource availability / Competition
• Atmospheric CO2 / global climate change
• Microevolutionary change
• Escape from biotic constraints
• Biodiversity
• Disturbance / land use
• Anthropogenic

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What makes it invasive? Atmospheric CO2 /
global climate change

• Ziska (2003) showed that leaf area significantly
  increased with each step increase in CO2.
• Leaf, stem, and root weight, as well as overall
  biomass also increased significantly with each
  step increase in CO2.

Future
Current
Pre-industrial
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What makes it invasive?

• Vacant niche
• Allelopathy
• Resource availability / Competition
• Atmospheric CO2 / global climate change
• Microevolutionary change
• Escape from biotic constraints
• Biodiversity
• Disturbance / land use
• Anthropogenic

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What makes it invasive?Biodiversity

• Ortega and Pearson (2005) studied bluebunch
  wheatgrass grassland types with spotted knapweed
  present at high and low densities in western
  Montana.
• impacts of strong invaders, such as C. maculosa,
  on native diversity may be evident even at low
  levels of invasion biotic resistance may not be
  a significant force in the real world.

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What makes it invasive?

• Vacant niche
• Allelopathy
• Resource availability / Competition
• Atmospheric CO2 / global climate change
• Microevolutionary change
• Escape from biotic constraints
• Biodiversity
• Disturbance / land use
• Anthropogenic

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What makes it invasive?Disturbance / Land Use

• Spotted knapweed densities are highly correlated
  with the degree of soil disturbance.
• Because spotted knapweed reproduces entirely by
  seed, disturbed soil allows for rapid
  establishment and spread.

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What makes it invasive?

• Vacant niche
• Allelopathy
• Resource availability / Competition
• Atmospheric CO2 / global climate change
• Microevolutionary change
• Escape from biotic constraints
• Biodiversity
• Disturbance / land use
• Anthropogenic

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Impacts

• Ecological
• Spotted knapweed monocultures eliminate native
  species.
• Can severely reduce wildlife forage.
• Alters biogeochemical cycling by increasing
  surface water runoff and stream sediment yield.

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Impacts

• Economic
• Reduction in quality and yield of livestock
  forage.
• Does have some nutritional value early in the
  spring and is used by sheep, goats, and cattle.
• Bucher (1984) claimed a loss of 156 million per
  year due to a 63 decline in forage in Montana.
• Reduces desirability of recreational areas.

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Impacts

• Social
• Rural economy and lifestyle can be severely
  affected by large infestations.
• Recreation opportunities can be limited by large
  infestations.

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Management

• Inventory and mapping are critical to proper
  management.
• Remote sensing has been effective tool for
  mapping spotted knapweed.

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Management

• Prevention
• Prevention of spotted knapweed to adjacent
  rangelands is most cost effective method.
• Seed dispersal can be limited by driving on
  designated roads.
• Grazing livestock in newly establishing areas
  early in spring.
• Minimizing all soil disturbances spotted
  knapweed is usually first invader on disturbed
  sites.

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Control Biological Control

• Numerous natural enemies have been approved as
  biological control agents.

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Bio-control Agents
Cyphocleonus spp. (root boring/gall weevil)
Agapeta spp. (root boring moth)
Urophora spp. (seedhead fly)
Urophora spp. (seedhead fly)
Sphenoptera spp. (root beetle)
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Control Biological Control

• Numerous natural enemies have been approved as
  biological control agents.
• Marginal success at best for all agents.
• Seed production has been dramatically decreased
  in some cases, but not enough to significantly
  decrease infestation.

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Control

• Burning
• Single low intensity fire may elicit positive
  response of spotted knapweed.
• Repeated annual summer burns before seeds develop
  has reduced populations 5-90
• Grazing
• Spotted knapweed can tolerate severe defoliation
  related to grazing.
• Repeated annual grazing in the spring during the
  rosette stage can reduce populations.

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Control

• Herbicides
• Picloram, clopyralid, dicamba, and 2,4-D provide
  effective control on spotted knapweed. Timing
  for best control varies depending on herbicide.
• Picloram provided nearly 100 control of spotted
  knapweed over 8 year span.
• Mowing
• Long-term mowing effects not known.
• Longest study of three years concluded that it
  provided partial control if done at the flowering
  stage.

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Eradication

• Little hope of eradication throughout all of
  introduced range.
• Best course of action is for regional land
  managers to form a comprehensive management plan
  that includes mapping, prevention methods, and
  multiple control methods.

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Summary

• Key biological characteristics
• Allelopathic
• Usually out-competes natives for nitrogen
• Thrives in disturbed sites
• Control strategies
• Grazing/fire to reduce seed production
• Chemicals can work picloram had best results
• Manipulate soil N to low levels where natives
  out-compete