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Assessing the Impacts of Biological
Control on Spotted Knapweed in
Minnesota
Natasha Northrop
Minnesota Department of Agriculture
Legislative Commission on Minnesota Resources
(LCMR)
Spotted Knapweed, Centaurea stoebe
L. ssp. micranthos (Gugler) Hayek
(syn.=C. biebersteinii DC.)
Spotted Knapweed
Spotted Knapweed Infestation
Spotted Knapweed Biological
Control Agents
Agapeta zoegana
Urophora quadrifasciata
Cyphocleonus achates
Larinus obtusus
LCMR* Research Project: Biological Control
of Spotted Knapweed in Minnesota
*Legislative Commission on Minnesota Resources, now called the
Legislative-Citizen Commission on MN Resources (LCCMR)
Goals of SK Biocontrol Research
- Increase MDA’s knowledge of spotted knapweed &
biological control of this weed in Minnesota status of most release sites was unknown.
- Define trends related to site characterizations that
might affect biocontrol; define trends related to
the invasiveness potentials of sites.
- Determine control impacts of bioagents.
- Develop protocols for future management
decisions & best management practices.
Research Methods:
1) Obtain USDA-APHIS-PPQ Release, Monitor, & Harvest
Biocontrol Records; combine with MDA Records (2004)
2) Characterize each biocontrol site (2004)
a) visit each site once during growing season
b) topography, soil type, ownership, land use, etc.
c) delineate knapweed infestation area = acreage
d) vegetation observations; % knapweed cover (est.)
e) bioagent presence (sweep netting)
3) Revisit 10 sites w/high bioagent recoveries/combos (2005)
a) sample each site three times over growing season,
more detailed vegetation sampling
b) use random transect sampling within delineated
infestation areas
Advanced Technology in the Field
2005 Transect Sampling
quadrate data= # knapweed
stems, ht. of 5 random
stems, # rosettes, #
flowers, # seed heads, %
knapweed bloom, % cover
(knapweed, other forbs,
grasses, bare ground, etc.)
1 transect =
1m2 quadrate drop
+ sweep set (25 sweeps)
+ 1m2 quadrate drop
Identified Biocontrol Release Sites
with GPS Data
Bioagent Species and Releases in Minnesota, 1991-2004
Biocontrol Agent
Order
Family
Method of Damage to SK
Released
Agapeta zoegana
Lepidoptera
Cochylidae
Root Borer (L)
1,717
Bangasternus fausti
Coleoptera
Curculionidae
Leaves/Rosettes (A), Seedhead (A/L)
2,975
Chaetorellia acrolophi
Diptera
Tephritidae
Seedhead (A/L)
1,340
Cyphocleonus achates
Coleoptera
Curculionidae
Leaves/Rosettes (A), Root Borer (L)
3,745
Larinus minutus
Coleoptera
Curculionidae
Leaves/Rosettes (A), Seedhead (A/L)
61,646
Larinus obtusus
Coleoptera
Curculionidae
Leaves/Rosettes (A), Seedhead (A/L)
3,519
Metzneria paucipunctella
Lepidoptera
Gelechiidae
Seedhead (A/L)
5,470
Sphenoptera jugoslavica
Coleoptera
Buprestidae
Leaves/Rosettes (A), Root Borer (L)
100
Terellia virens
Diptera
Tephritidae
Seedhead (A/L)
600
Urophora affinis
Diptera
Tephritidae
Seedhead (A/L)
108,550
Urophora quadrifasciata
Diptera
Tephritidae
Seedhead (A/L)
41,400
Urophora spp. mix*
Diptera
Tephritidae
Seedhead (A/L)
565,663
(A)=Adult Stage
(L)=Larval Stage
Total:
*Release consisting of mixtures of U. affinis and U. quadrifasciata.
796,725
Peak Emergence Chart of Recovered Spotted Knapweed
Bioagent Species at 10 Biocontrol Sites in MN, 2005
Obstacles to Drawing Solid
Conclusions About Trends & Impacts of
Biocontrol on Spotted Knapweed in MN


No Pre-release data
– no Knapweed density, stem counts, rosette counts, etc.
before biocontrol.
– no records of other vegetation present at beginning of
invasion or before biocontrol.
– In general, what was the site like before biocontrol?
– Now we at least have baseline data to compare new
data to in the future.
High variability between the many unique sites
– both in site characteristics and the agent combinations
and numbers released; few trends could be identified
across sites within any parameters.
– indicates sites have to be treated on a site-by-site basis.
Other Observations & Lessons Learned



Visible decrease in knapweed.
Urophora flies – they’ve established everywhere and can
distribute on their own. We no longer put efforts into
moving them.
Sites with a combination of root agents and seedhead
agents seemed to give better control.
Best Biocontrol Impacts Observed =
Larinus spp.
Urophora spp.
+
Cyphocleonus achates
Agapeta zoegana
Other Benefits:



Minnesota Cooperative Weed Biological Control
Project: MDA, USDA-APHIS, MN DNR, MN
DOT, MN Association of County Ag.
Inspectors, USFWS, University of Minnesota,
Private Landowners.
Renewing and gaining new interest in the
program, and regenerating communication and
implementation between spotted knapweed
biocontrol collaborators.
Collaborators were great source of impact
feedback.
-Based on observations, we can now
make biocontrol recommendations.
-Data coming in later may modify
these recommended practices.
-Also started a 7 yr. IPM project with
MN DOT using biocontrol and
herbicide in 2006 – we’ll see!
For More Information
Natasha Northrop, MDA Weed Biocontrol Program:
[email protected]
MDA Spotted Knapweed Biological Control
Video: Using Advanced Technology for Efficient Fieldwork
www.mda.state.mn.us/weedcontrol/knapweed.htm
MDA Integrated Pest Management Program:
www.mda.state.mn.us/weedcontrol
MDA Weed Mapping System & Viewer
www.mda.state.mn.us/weedcontrol/mapping.htm
Legislative-Citizen’s Commission on MN Resources
www.commissions.leg.state.mn.us/lcmr/lcmr.htm
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