Title, arial 30pt Bold, all caps - Midwest Invasive Plant Network

PLANT COMMUNITY RESPONSE WHEN
CONTROLLING INVASIVE WEEDS WITH
AMINOPYRALID IN PRAIRIE RESTORATIONS
Mary B. Halstvedt, Dow AgroSciences; Billings, MT
Roger Becker, University of Minnesota; St Paul, MN
Rodney Lym, North Dakota State University; Fargo, ND

Mary B. Halstvedt, Field Research Scientist
Billings, MT
mbhalstvedt@dow.com

Presentation Objectives
‣ Role of aminopyralid in prairie restoration programs
‣ Review plant community data from 2 research locations to
illustrate response to herbicide application to shift
communities away from invading plant species
North Dakota State University study – 4 year old restoration
University of Minnesota study – 2 year old restoration
‣ Using current information to develop a treatment plan in
prairie restorations

Ecologically Based Weed Management
‣ Recognize plant communities are dynamic
‣ Direct weed infested communities on trajectory to more
desirable community that fits management goals
(resistant to invasion, resilient after disturbance)
‣ Utilize management tools in appropriate sequence and
combination to expedite development of desired plant
community
Herbicides can be a catalyst for rapidly changing plant
community composition
|

Prairie Restorations or Reconstruction
High priority across the Northern Plains and Upper Midwest

Canada thistle and other invasive weeds
can be an issue at various stages of the
restoration

Prairie restoration is complicated-requires
significant vegetation management tools

Milestone ® (Aminopyralid) is Effective on Many
Invasive Weeds
Canada thistle
Teasel
Sweet clover
Spotted knapweed
Crown vetch
Biennial thistles
And many more – see label
® Trademark of The Dow Chemical Company ("Dow) or an affiliated company of Dow Always read and follow label directions

Milestone ® Herbicide (Aminopyralid) Attributes
Important for invasive weed management programs in
natural areas:
Low use rate of 3 to 7 fluid oz/acre (0.06 to 0.1 lb ae/acre)
Reviewed and registered under the Reduced Risk Pesticide
Initiative of the U.S. EPA
Very low toxicity (“practically non-toxic”) to birds, fish, mammals and
aquatic invertebrates
Surface water breakdown in 16 hours
Can be applied to seasonally dry wetlands
Spray up to the water’s edge
Grass selectivity
A single active ingredient to improve selectivity
® Trademark of The Dow Chemical Company ("Dow) or an affiliated company of Dow
Milestone is not registered for sale or use in all states. Contact your state pesticide regulatory agency to
determine if a product is registered for sale or use in your state. Always read and follow label directions.
|

Studies have shown that Milestone ® can be used to
control invasive species and restore plant communities
Most native forb species were
moderately tolerant to tolerant, or
quickly recovered following treatment
Excellent grass tolerance
and forage increase with
treatment
® Trademark of The Dow Chemical Company ("Dow) or an affiliated company of Dow
|

Techlinenews.com
References will
be made to this
effort throughout
the presentation

Presentation Outline
‣ Review plant community data from 2 research locations to illustrate
response to herbicide application to shift communities away from
invading plant species
North Dakota State University study – 4 year old restoration
University of Minnesota Study – 2 year old restoration
‣ Using current information to develop a treatment plan in prairie
restorations

What is the prairie restoration goal?
A successful restoration is a diverse plant
community that will include different levels of
canopy cover and structural diversity to serve a
wider array of birds, pollinator insects and other
wildlife (taken from JB Bright TechLine article)

North Dakota State University Research
Almquist, T.L. and R. G. Lym. 2010. Effect of Milestone ® on Canada
Thistle (Cirsium arvense L.) and the Native Plant Community in a
Restored Tallgrass Prairie. Invasive Plant Sci. Manage. April-June 2010.

Effect of Milestone on Canada Thistle (Cirsium arvense L.) and the
Native Plant Community in a Restored Tallgrass Prairie
‣ The Nature Conservancy’s Glacial
Ridge Preserve
‣ 4 - year old restoration on sandy
beach-ridges of Glacial Lake
Agassiz
‣ Seeded in drill-strips with a mixture
of native grasses and forbs
http://www.minnesota-map.org/minnesota-map.jpg

NDSU Study Design
9 m
‣Randomized complete block
60 plots: Canada thistle-infested plots
were paired with non-infested restored
native sites.
‣30 native
‣30 Canada thistle-infested
6 m
4.5 m
All plots sub-divided
‣One sub-plot randomly chosen for
treatment
6 m
Aminopyralid
Check
‣Milestone ® (aminopyralid) at 7 fl
oz/ac applied September 2006
® Trademark of The Dow Chemical Company ("Dow) or an affiliated company of Dow

Materials and Methods
‣ Plant community composition: Foliar cover in three
randomly place 1-m 2 frames.
Bareground, litter, and individual plant species cover were
estimated in mid-July prior to herbicide treatment (baseline) and 10
and 22 MAT
Plant species were separated into high and low seral floristic quality
categories*. High seral species are from stable plant communities
and low seral indicate low quality prairie.
‣ Canada thistle control was determined by counting stem
density in six 0.25 m 2 quadrats.
*Defined by the Northern Great Plains Floristic Quality Assessment Panel (2001)

Native vs Canada thistle sites – No Herbicide Treatment
% Foliar Cover by Category
120
100
80
60
40
20
0
What impact does Canada thistle have on the prairie?
Native
Baseline
Canada
thistle
infested
Data will be presented in this stack
graph format in the categories listed
below. BG=bareground, Low=low seral
BG litter Invasive Low forb Low grass High forb high grass

% Foliar Cover by Category
Native vs Canada thistle area – No Herbicide Treatment
120
100
80
60
40
20
0
The Canada thistle impacts the grass cover more than forb cover
Native
Baseline 10 MAT 22 MAT
Canada
thistle
Native
Canada
thistle
Native
BG liter Canada thistle Low forb
Low grass High forb High grass
Canada
thistle

Treated
Non-treated

Canada Thistle Control
Evaluation date
Treatment
Prior to
treatment 10 MAT 22 MAT
Stems/m 2
Non-treated 17 16 12
Milestone ® 7 fl
oz/ac
15 0.1 1.3
LSD (0.05) NS 1.3 1.2
® Trademark of The Dow Chemical Company ("Dow) or an affiliated company of Dow

Results from Canada thistle-infested prairie restoration
% Foliar Cover by Category
100
90
80
70
60
50
40
30
20
10
0
Baseline 10 MAT 22 MAT
Milestone Untreated Milestone Untreated Milestone Untreated
BG litter Canada thistle Low Forb
Low Grass High Forb High Grass
Milestone ® was applied once at 7 fl oz/ac in the fall
® Trademark of The Dow Chemical Company ("Dow) or an affiliated company of Dow Always read and follow label directions

Low Seral Broadleaves
Dominated by
common ragweed,
black medick,
perennial sowthistle,
and dandelion

What are the main
high-seral forbs?
Should expect
impact on the forbs
based on tolerance
chart (44% of the
forb cover are
species that are
susceptible)
Canada thistle infested
0 MAT
Scientific namea Common name Treated Control
High-seral forbs
Ranking
Aster laevis L. Smooth blue aster

What are the main native forbs (High seral)?
16
Baseline
10 MAT 22 MAT
% Foliar Cover by Species
14
12
10
8
6
4
2
0
Milestone Untreated Milestone Untreated Milestone Untreated
White Aster Purple PC Max Sun CA gold
Ppl Rue G Alex W Berg Other
Milestone ® was applied once at 7 fl oz/ac in the fall
® Trademark of The Dow Chemical Company ("Dow) or an affiliated company of Dow Always read and follow label directions

Other Category: What new native forbs moved in that
were not in pre-data?
% Foliar Cover by Species
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
22 MAT
Milestone
Untreated
Stiff Sunflower Fringed loosestrife Missouri goldenrod

Percent Foliar Cover of Canada Thistle and Grasses Before
Treatment (Baseline) and 10 and 22 Months after Treatment with a
fall application of Milestone ® at 7 fl oz/ac
50
Baseline 10 MAT 22 MAT
% Canopy Cover
40
30
20
10
0
Untreated Milestone Untreated Milestone Untreated Milestone
Canada thistle Big Bluestem Slender Wheatgrass Other Grasses
® Trademark of The Dow Chemical Company ("Dow) or an affiliated company of Dow
Always read and follow label directions

The benefits of Canada
thistle control, removal of
undesirable species, and
increase in native grass cover
should lead to an overall
improvement in long-term
stability and composition of
the prairie which likely will
outweigh the short term
impacts of herbicide
treatment

University of Minnesota Study (Dr. Roger Becker): Milestone ®
and Transline ® for Canada Thistle Control and Forb Tolerance
Cooperator: JB Bright, USFWS Morris Wetland Management
District, Morris, MN (Kufrin WPA Ortonville, MN)
Research Question:
Lots of thistle to start with!
‣Will the use of herbicides early
in the restoration program
improve overall establishment of
grasses and forbs?
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University of Minnesota: Materials and Methods
‣ Randomized complete block design with 4 replications
‣ Plot size: 20 by 30 feet
‣ Herbicides applied with CO2 backpack – 20 GPA
‣ Treatments: Milestone ® at 5 fl oz/ac, Transline ® at 2/3 pt/ac
‣ Treatments in second year (2009) after seeding (2007)
‣ Timing: June and September 2009
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Site Information
‣ 6/20/2007: Spray with glyphosate and 2,4-D at 1 quart per acre of
each
‣ 6/21/2007: Broadcast seeded (vicon and culti-packer) into bean
stubble with roughly 78% grass/22% forb mix, consisting of both
purchased seed and remnant prairie harvest. At least 44 species
seeded at a rate of approx. 38 seeds per square foot.
‣ 6/25/2008: Mowed
‣ 6/30/2009 and 8/12/2009 – mowed with exception of plots
‣ 6/23/2010: Mowed

What forbs were seeded?
23
species
Seeded
OZ/Acre Seeds/Sq
Common Name Latin Name % of Mix Seeded Ft (1 OZ)
Common ox-eye Heliopsis helianthoides 1.34% 0.8 0.14
Golden Alexander Zizia aurea 1.43% 0.4 0.3
Harebell Campenula rotundifolia 3.93% 0.016 20.6
Heart leaf golden Alexander Zizia aptera 0.31% 0.096 0.275
Hoary vervain Verbena stricta 1.22% 0.16 0.64
Large Flowered Beardstongue Penstomen grandiflorus 1.53% 0.4 0.32
Leadplant Amorpha canescens 0.76% 0.16 0.4
Maximillian sunflower Helianthus maximilliani 5.53% 1.6 0.29
N. leaf purple coneflower Echinacea angustifolia 1.53% 0.8 0.16
Prairie cinquefoil Potentilla arguta 6.07% 0.096 5.3
Prairie coneflower Ratibida columnifera 9.27% 0.81 0.96
Prairie coreopsis Coreopsis palmata 1.12% 0.41 0.23
Prairie onion Allium stellatum 1.22% 0.41 0.25
Purple prairie clover Dalea purpureum 11.35% 2.8 0.34
Prairie Sage Artemisia ludoviciana 3.26% 0.048 5.7
Rough blazing star Liatris aspera 1.07% 0.25 0.36
Showy goldenrod Solidago speciosa 10.26% 0.41 2.1
Showy tick trefoil Desmodium canadense 2.29% 1.6 0.12
Smooth aster Aster laevis 2.72% 0.19 1.2
Stiff goldenrod Solidago rigida-summer 9.18% 0.816 0.94
Solidago rigida - fall
White prairie clover Dalea candidum 9.54% 2 0.4
Wild bergamot Monarda fistulosa 7.63% 0.4 1.6
Yarrow Achillea millefolium 7.44% 0.16 3.9

Herbicide Application Dates
June 25, 2009:
Canada thistle emerged and up
to 30 inches, bud stage
September 23, 2009:
Canada thistle stage: New thistle shoots
vegetative and 6 to10 inches - some old shoots
that emerged last spring remain with 30-40 %
green tissue

Plant Community Response Data:
2010, 2011, and 2012
‣Total cover by category: July and September
Canada thistle, native forbs, exotic forbs, native grass,
and bareground
‣Plant density (forbs) by species per square yard

Plant Community - % Cover by Category – July 2010
Evaluation - 1 YAT
100
% Cover by Category
80
60
40
20
0
Milestone
Summer
Milestone
Fall
Transline
Summer
Transline
Fall
Untreated
Bare Grd Canada thistle Native Forbs Exotic Grasses
No statistical differences within the cover category (P=0.1)

Forb Density by Species – 1 YAT
Density per square Yard
40
35
30
25
20
15
10
5
0
*
Note: Canada goldenrod (S. canadensis) was not a planted species
*Statistical difference (P=0.1)
Milestone
Summer
Milestone
Fall
Transline
Summer
Transline
Fall
Untreated
CA gold Rigid gold PP Clover Gld Alex Wild Berg
Yarrow White sage White aster Heath aster other
Other includes smooth blue aster, long headed coneflower, oxeye sunflower,
white prairie clover, Maximillian sunflower, and hoary vervain

Plant Community - % Cover by Category – September
2010 Evaluation
100
% Cover by Category
80
60
40
20
0
Milestone
summer
Milestone
Fall
Transline
summer
Transline
Fall
Untreated
Mow
Bare Grd Canada thistle Native Forbs Exotic Grasses

“Results were very
enlightening because
native forbs were visually
more robust in herbicide
treated plots compared to
mowed plots. The
herbicide treatments
greatly reduced
competition from Canada
thistle and opened a niche
for native forb and seeded
grasses to thrive”. (J.B.
Bright, USFWS Kufrin WPA)

Kufrin WPA – 2 Years after treatment

Plant Community - % Cover by Category – July 2011
Evaluation - 2 YAT
% Cover by Category
100
80
60
40
20
0
b
ab
Milestone
Summer
Milestone
Fall
b a ab ab ab
b b b
Transline
Summer
Transline
Fall
a
Untreated
c
Mow
CT Native Forb Sweet clover Native Grass Bare Grd
Statistics across cover category (P=0.1)

Total Forb Density by Species – July 2011 (2 YAT)
Density per square Yard
40
35
30
25
20
15
10
5
0
No statistical differences (P=0.1)
Milestone
Summer
Milestone
Fall
Transline
Summer
Transline
Fall
Untreated
CA goldrod Rigid goldrod PP Clover GlAlex
Wild Berg yarrow White sage White aster
Heath aster
other
Other includes long headed coneflower, oxeye sunflower, white prairie clover,
Maxmillian sunflower, and hoary vervain
Note: Canada goldenrod (S. canadensis) was not a planted species

2012 Plant Community Evaluation – 3 years after herbicide
and mowing

Plant Community - % Cover by Category – July 2012
Evaluation - 3 YAT
100
% Cover by Category
80
60
40
20
0
ab
Milestone
summer
a a a a a a
a
Milestone
Fall
ab ab ab b
Transline
Summer
Transline
Fall
Untreated
Mow
Canada thistle Native Forbs Exotic Native Grasses Bare Grd
Statistics across cover category (P=0.1)

Total Forb Density by Species – July 2012 (3 YAT)
Statistics –total density top letter – wild bergamot in green (P=0.1)
a
Density per square Yard
100
80
60
40
20
0
ab
bc
Milestone
summer
ab
ab
Milestone
Fall
ab
ab
Transline
Summer
ab
ab
Transline
Fall
a
Untreated
c
b
Mow
CA gold Rigid gold PP Clover Gld Alex Wild Berg
yarrow White sage White aster Heath aster other
Other includes long headed coneflower, giant goldenrod, oxeye
sunflower, white prairie clover, Maximillian sunflower, and hoary vervain

Density per square Yard
60
40
20
0
Total Forb Count by Species – July 2012 (3 YAT)
a
Milestone
summer
Without wild bergamot
a
Milestone
Fall
Transline
Summer
Transline
Fall
Untreated
CA gold Rigid gold PP Clover Gld Alex yarrow
White sage White aster Heath aster other
a
Mow
Other includes long headed coneflower, giant goldenrod, oxeye sunflower, white prairie
clover, Maximillian sunflower, and hoary vervain
Statistics –total density (P=0.1)
a
a
a

Forb density per sq yd
100
90
80
70
60
50
40
30
20
10
0
Best Treatment option if Canada thistle is the target
Milestone
2010
Milestone
2011
Milestone
2012
Untreated
2010
Untreated
2011
Untreated
2012
Gold Alex Wild Bergamont CA Goldenrod
Rigid Goldenrod Prple Prairie Clover White Sage
Yarrow
Grass
Forb
Milestone ® at 5 fl
oz/ac in June of 2009
Other
More forb cover
but dominated
by one species
No statistical differences comparing by year (P=0.1)
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Summary and Conclusions – Minnesota Study
‣ Plant communities are dynamic! These data may be
different if Canada thistle did not decline in untreated.
‣ 3 years after herbicide treatments:
Forb cover was equal across herbicide treatments and
untreated and the mowing had the lowest forb cover.
Native grass cover was statistically the same for all herbicide
treatments, mowing, and untreated.
Wild bergamot became very dominant on the site and highest
in the untreated.
Forb density was equal across all inputs. Forb diversity was
equal across herbicide treatments but slightly higher in the
summer treatments and closer to the untreated.

Milestone Herbicide ® (aminopyralid) is an important
tool for invasive plants management in natural areas
to restore plant communities or facilitate recovery of
desirable grasses and forbs.
Selective weed control gives
desirable vegetation a
competitive advantage.
®
Trademark of The Dow Chemical Company ("Dow) or an affiliated company of Dow

Integrated Weed Management in Prairie
Restorations
‣Site survey – mapping invasive weeds – the big
picture
|

Dense
Scattered
Broadcast
treatments
versus large
patch spraying
High Priority – near road

Integrated Weed Management in Prairie
Restorations
‣ Site survey – mapping invasive weeds – the big picture
‣ Management history of site
‣ Desired plant community characteristics
‣ Develop plan for using management tools in the right sequence
and combination to expedite establishment of desired plant
community
Herbicides can be a catalyst for rapidly changing plant
community composition
|

Developing a Herbicide Control Strategy
‣ Focus on areas where invasive
species are having the most
impact on plant community
‣ Utilize current information to
understand the benefit and risk of
treatment
What are the main forbs and what
is the tolerance to herbicide?
What grasses are present to
respond to removal of invasive
weed?
‣ Choose appropriate herbicide rate
and application timing to create
mosaic of greater forb diversity

In new restorations that are likely to be prone to Canada
thistle invasion, consider planting forbs that are more
tolerant to Milestone ® ®
Trademark of The Dow Chemical Company ("Dow) or an affiliated company of Dow

Thank You to my co-authors and the technicians
and students that conducted these research
projects
Dr. Roger Becker, University of Minnesota; St Paul, MN
Dr. Rodney Lym, North Dakota State University; Fargo, ND
® Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow