Invasive Weeds & Endangered Species Interactions: Can

Herbicides Facilitate a Positive Outcome?

George Beck, Scott Nissen & Jim Sebastian

Dept Bioag Sciences & Pest MgmtColorado State University

Broadleaf Herbicides & Desirable Forbs

• Are buffer zones always biologically necessary around threatened or endangered species?

• Selectively controlling weedy forbs among desirable forbs– Difficult with many older herbicides

• 2,4-D, dicamba– Particularly high rates needed to control many invasive

perennial weeds

– Research has shown selectivity does not just occur between grasses and forbs• Also within forbs

Broadleaf Herbicides & Desirable Forbs

• Rice, P.M. J.C. Toney, D.J. Bedunah, & C.E. Carlson. 1997. Plant community diversity and growth form responses to herbicide applications for control of Centaurea maculosa. J. Applied Ecol. 34(6):1397-1412.– Treated spotted knapweed infested grassland and early seral

forest• Sprayed 1989; plots split and one-half retreated 1992• Picloram (280 g/ha), clopyralid (280 g/ha), clopyralid + 2,4-D

(213 + 1121 g/ha)• Early v. late season applications

Broadleaf Herbicides & Desirable Forbs

• Rice et al. 1997:– Cover, standing crop, species richness:

• Grasses increased 1 to 2 yr post treatment then leveled to same as untreated plots

• Forbs declined 1 to 2 yr post treatment then increased to same as untreated plots

• Early season spraying caused greater forb decrease and grass increase than late season spraying

Western fringedprairie orchid;Platanthera

praeclara

Leafy Spurge Control Nearthe

Western Prairie Fringed Orchid

• Western prairie fringed orchid – Platanthera praeclara– Federally listed threatened species

• Leafy spurge encroaching into WPFO habitat– Competition from leafy spurge threatens orchid

survival• Sieg, C.H. & A.J. Bjugstad. 1994. Proc. 13th N.American

Prairie Conf. p. 141-146• USFWS 1996. Platanthera praeclara recovery plan. • Wolken et al. 2001 J. Range Manage. 54:611-616.

Leafy Spurge Control Nearthe

Western Prairie Fringed Orchid

• Erickson et al. 2006:– Sprayed quinclorac (Paramount) or imazapic

(Plateau) directly onto western fringed prairie orchid September when senescing• Quniclorac 842 & 1121 g ai/ha• Imazapic 140 & 210 g ai/ha

– At 10 & 22 months after application measured• Survival & fecundity of orchids

– Whether remained vegetative or flowered;– Plant height– Number of flowers & seed production

Leafy Spurge Control Nearthe

Western Prairie Fringed Orchid

• Neither imazpic or quinclorac influenced orchid survival– imazapic caused stunting, decreased flower

& seed production

Herbicide Effects on Western Prairie Orchid Flowering 10 MAT

0

10

20

30

40

50

60

70

80

Imaz 140g

Imaz 210g

Quin 842g

Quin 1121g

UntreatedFlowering

2000Flowering

2001Vege2000

Vege2001

a aab

ab

b a

a

bb

b

Perc

ent

ns

ns

Herbicide Effects Western PrairieOrchid Flowering 22 MAT

• No differences among treatments 2nd

year after spraying– All effects on flowering by imazapic

disappeared 2 years after initial treatments applied

Herbicide Effects on Western Prairie Flower Height, Raceme

Length, and Flower Number

• Quniclorac had no effect WPFO height, raceme length & flower number 10 and 22 MAT

• Imazapic decreased WPFO height by ~43% at 140 & 210 g/ha 10 MAT– Effect disappeared 22 MAT

• Imazapic decreased WPFO raceme length ~78% 10 MAT; – 58% 22 MAT at 210 g/ha

• Imazapic decreased WPFO flower number by ~73% 10 MAT – 70% 22 MAT at 210 g/ha

Herbicide Effects on Western Prairie Orchid Seed Set 12 MAT

0

2000

4000

6000

8000

10000

12000

14000

16000

Imaz 140g

Imaz 210g

Quin 842g

Quin 1121g

Untreatedb

a a

b

Num

ber

seed

s pe

r ca

psul

e

3%

15% 7%

0%

0%

b

Herbicide Effects WPFO Conclusions

• Quinclorac safe to use if WPFO present when controlling leafy spurge

• Imazapic caused temporary stunting and decreased fecundity WPFO– Most symptoms disappeared 2nd year following

treatment

Russian Knapweed Control &Native Forb & Shrub Establishment

• Experiment established May, 2009– Strip-strip plot – four replications; P=0.05

• 4 herbicide treatments– Aminopyralid at 126 g ai ha-1

– Untreated control

• 16 native seeded species– 10 forbs

– 4 shrubs

– 2 cool season perennial grasses

– Herbicides applied May 14, 2009

– Native species seeded April 2010

Common yarrowAchillea millifolium Penstemon spp.

GayfeatherLiatris punctata

CommonyarrowAchillea

millifolium

GayfeatherLiatris punctata

One-sided Penstemon

Penstemonsecundiflorus

Russian Knapweed Control & Native Forb Establishment

0

5

10

15

20

25

30

35

40

45

Amino 126 g ai/ha

Untreateda

a b

a

Plan

ts/m

2

b

a

a

a

RK control: mean aminopyralid=71%; untreated=0%

Data fall 2010; compare

within species

Louisiana sage

Louisiana sageArtemisialudoviciana

Fourwing saltbush; Atriplex canescens

FourwingsaltbushAtriplex

canescens

Winterfat; Krascheninnikovia lanata

WinterfatKrascheninnikovia

lanata

Russian Knapweed Control & Native Shrub Establishment

0

1

2

3

4

5

6

7

8

9

10

Louisiana

sage

Winterfat Fourwing

saltbush

Mean

shrubs

Amino 126 g ai/ha

Untreated

a

a

a

aPlan

ts/m

2

a

a

a

a

RK control: mean aminopyralid=71%; untreated=0%

Data fall 2010; compare

within species

RK Control & Native Forb &Shrub Establishment Summary

• Species richness is the number of species in a given area (% species established in area): – untreated controls:

• Forbs 8%; shrubs 0%, grasses 50%

• Aminopyralid 126 g ha-1

– 71% Russian knapweed control

– Forbs 63%; shrubs 56%; grasses 100%

Aminopyralid Effects Established Native Forbs & Shrubs

• Two Experiments initiated summer 2009– Steamboat Springs, CO

– 3 Timings• July 10; Sep 4; Oct 16

– 3 rates aminopyralid• 53 g ha-1 + non-ionic surfactant (0.25% v/v)

• 126 g ha-1 + non-ionic surfactant (0.25% v/v)

• 126 g ha-1

Western indian paintbrushCastilleja occidentalis

WesternIndian

PaintbrushCastilleja

occidentalis

Five nerve sunflowerHelianthella quinquenerva

Five nervesunflower

Helianthellaquinquenerva

Aminopyralid EffectsTotal Species Richness

0

2

4

6

8

10

12

14

16

2009 2010 2011

53 g nis Jul

126 g nis Jul

126 g Jul

53 g nis Sep

126 g nis Sep

126 g Sep

53 g nis Oct

126 g nis Oct

126 g Oct

Untreated

# s

peci

es

per

plot ns

aa

Native Forb and Shrub Tolerance to

Aminopyralid (Milestone® Herbicide)

Applications for Invasive Weed Control

Mary B. Halstvedt* and Vanelle F. Peterson, Dow AgroSciences LLC., Billings, MT and Mulino, OR; Travis Almquist, Luke Samuel, Rodney G Lym, North Dakota State University, Fargo; K. George Beck, Colorado State University, Ft. Collins; Roger L. Becker, University of Minnesota,

St. Paul; Celestine A. Duncan, Weed Management Services, Helena, MT; Peter M. Rice, University of Montana, Missoula.

® Trademark of Dow AgroSciences LLC

Experiments Established at 10 Locations

2006

Rod Lym, North Dakota

State University

2007

2004

Roger Becker,

University of

Minnesota

Peter Rice,

University of

Montana

George Beck, Colorado

State University

Celestine Duncan, Weed

Management Services

Four Ranking Catagories

T=Tolerant: Minimal symptoms - may be slight

cupping but less than 15%

MT = Moderately tolerant: Symptoms include

cupping/yellowing and can inhibit flowering, with

recovery the first growing season after application –

15-50% stand reduction

S = Susceptible: Severe Injury the season of application

and stand reduction the year after greater than 75% - and

may kill established plants. However, certain plants may

reseed from the seed bank.

MS = Moderately Susceptible: Injury could be

significant the first year may reduce stand by 50-75%

Results of 68 Forbs Evaluated 2 YAT

Tolerant M Tol MS Suceptible Tolerant M Tol MS Suceptible

1 YAT 2 YAT

Significant

recovery

Mile

sto

ne

Tran

slin

e

Tord

on

22

k

Gar

lon

3a

Van

qu

ish

2,4

-D a

min

e

2,4

-D L

V4

Par

amo

un

t

Tela

rX

P

Esco

rt X

P

Pla

teau

Cu

rtai

l

Re

de

em

R&

P

Gra

zon

P&

D

Ove

rdri

ve

Cim

Max

Ch

eck

Robust Spurge

Woods Rose

Penstemon

Blue Flax

Gay feather

*Data subjected to analysis of variance and means separated by Tukey’s HSD (α=0.05)

*Different colors signify statistical differences between counts in control v treated plots.

*Green signifies an increase in the population, white no change and red a decrease.

Conclusion

Overall Conclusion

• Herbicides an important part of ecologically-based weed mgmt– Newer herbicides more selective than older ones &

effects are transient• Exercise care to choose compounds will control

target without permanent injury to desirable forb, shrubs, & grasses– Continue to evaluate against native forbs & shrubs

• Spray buffers may not be generally necessary– Evaluate case by case using sound applied science– Buffers continuous source of invasive weeds– Ultimately an invasive weed will displace T&E plant

species