Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

Common 

Control

Measures

 (Draft: March 2005)

Cirsium arvense

Canada thistle

For Invasive Plants of the 

Pacific Northwest Region

 Prepared by: Linda Mazzu

USDA Forest Service, Region 6

Invasive Plants EIS Team

Updated: March 31, 2005
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Table of Contents

Introduction................................................................................................................................. 5

Some Tips to Consider............................................................................................................ 7

Prioritizing Treatments ........................................................................................................... 7

Decision Matrix for Prioritization for Treatment........................................................................ 8

Comparison Table of Proposed Chemicals*............................................................................... 9

Brachypodium sylvaticum – False-brome ................................................................................ 12

Ecological Characteristics of Note........................................................................................ 12

Management.......................................................................................................................... 12

Centaurea biebersteinii (C. maculosa) – Spotted Knapweed.................................................... 14

Ecological Characteristics of Note........................................................................................ 14

Management.......................................................................................................................... 14

Centaurea diffusa – Diffuse Knapweed .................................................................................... 17

Ecological Characteristics of Note........................................................................................ 17

Management.......................................................................................................................... 17

Centaurea pratensis (C. jacea x nigra, C. debeauxii) – Meadow Knapweed............................ 19

Ecological Characteristics of Note........................................................................................ 19

Management.......................................................................................................................... 19

Centaurea solstitialis – Yellow Star-thistle............................................................................... 21

Ecological Characteristics of Note........................................................................................ 21

Management.......................................................................................................................... 21

Chondrilla juncea – Rush Skeletonweed .................................................................................. 24

Ecological Characteristics of Note........................................................................................ 24

Management [23].................................................................................................................. 24

Cirsium arvense – Canada Thistle ............................................................................................ 26

Ecological Characteristics of Note........................................................................................ 26

Management.......................................................................................................................... 26

Cynoglossum officinale – Hounds Tongue............................................................................... 29

Ecological Characteristics of Note........................................................................................ 29

Management.......................................................................................................................... 29

Cytisus scoparius – Scotch Broom ........................................................................................... 32

Ecological Characteristics of Note........................................................................................ 32

Management [17].................................................................................................................. 32

Euphorbia esula – Leafy Spurge ............................................................................................... 34

Ecological Characteristics of Note........................................................................................ 34

Management.......................................................................................................................... 34

Geranium robertianum – Herb Robert ...................................................................................... 36

Ecological Characteristics of Note........................................................................................ 36

Management.......................................................................................................................... 36

Hedera Helix – English Ivy....................................................................................................... 37

Ecological Characteristics of Note........................................................................................ 37

Management.......................................................................................................................... 37

Hieracium aurantiacum – Orange Hawkweed, Hieracium pretense......................................... 39

Ecological Characteristics of Note........................................................................................ 39

Management.......................................................................................................................... 39

Hypericum perforatum – St. Johnswort.................................................................................... 41
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

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Ecological Characteristics of Note........................................................................................ 41

Management [18,30]............................................................................................................. 41

Ilex aquifolium – English Holly ............................................................................................... 43

Ecological Characteristics of Note........................................................................................ 43

Management.......................................................................................................................... 43

Lathyrus latifolius – Everlasting Peavine ................................................................................. 44

Ecological Characteristics of Note........................................................................................ 44

Management.......................................................................................................................... 44

Lepidium latifolium – Perennial Pepperweed........................................................................... 45

Ecological Characteristics of Note........................................................................................ 45

Management.......................................................................................................................... 45

Linaria vulgaris – Yellow Toadflax, Linaria genistifolia ssp. dalmatica – Dalmation toadflax47

Ecological Characteristics of Note........................................................................................ 47

Management [17].................................................................................................................. 47

Lythrum salicaria – Purple Loosestrife..................................................................................... 49

Ecological Characteristics of Note........................................................................................ 49

Management.......................................................................................................................... 49

Phalaris arundinacea – Reed Canarygrass ................................................................................ 50

Ecological Characteristics of Note........................................................................................ 50

Management [17].................................................................................................................. 50

Polygonum cuspidatum – Japanese Knotweed ......................................................................... 52

Ecological Characteristics of Note........................................................................................ 52

Management [17, 39]............................................................................................................ 52

Potentilla recta – Sulfur Cinquefoil .......................................................................................... 54

Ecological Characteristics of Note........................................................................................ 54

Management.......................................................................................................................... 54

Rubus discolor – Himalayan Blackberry .................................................................................. 56

Ecological Characteristics of Note........................................................................................ 56

Management [17].................................................................................................................. 56

Senecio jacobaea – Tansy Ragwort .......................................................................................... 58

Ecological Characteristics of Note........................................................................................ 58

Management.......................................................................................................................... 58

Taeniatherum caput-medusae – Medusahead rye ..................................................................... 60

Ecological Characteristics of Note........................................................................................ 60

Management [17].................................................................................................................. 60

References................................................................................................................................. 61
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

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Introduction

This document summarizes commonly used control methods for some of the most pervasive 

invasive species in the Pacific Northwest. Please use it as a ‘starting point’ for developing 

treatment alternatives to meet your objectives. It is not intended as the only document to use in 

making your determinations; there are too many treatments options available to discuss them all 

in one place. Use the reference materials and Internet links included to keep up-to-date with ever 

changing practices in the treatment of invasive plants, as success stories are shared throughout 

the region and the west.

Invasive plant management requires the integration of prevention measures as well as early 

detection and rapid response strategies using the treatments found in this guide. One of the best 

ways to manage invasive plants is through prevention. While the focus of this guide is on 

invasive plant treatments, the reader can find more information on prevention in the USDA 

Forest Service Guide to Noxious Weed Prevention Practices (USDA 2001).

The information in this guide is organized by species. Discussions on manual, mechanical, 

biological, cultural, prescribed burning, and herbicide treatments were usually included in each 

species discussion. If no information was found, then it was noted as such. All sources and 

authorities on invasive plant management were sought including studies describing the biology 

of species, websites of weed control boards and county extension sites, websites from 

universities and entities such as The Nature Conservancy. All approaches found were 

summarized even if from outside this country.

The following describes the categories of treatments included. In many cases, using a 

combination of treatments was considered more effective than using a single method. Because 

of this, the development of weed management plans for projects makes sense.

Manual: With new, small infestations, hand pulling can be the easiest and quickest method. 

Even larger populations can be controlled with hand pulling if the workforce is available and 

continual maintenance occurs. The Bradley Method is one sensible approach to manual control 

of invasive plants. [17, 22] This method consists of hand weeding selected small areas of 

infestation in a specific sequence, starting with the best stands of native vegetation (those with 

the least extent of infestation) and working towards stands with the worst infestation. Initially, 

new satellite populations (sometimes referred to as ‘spotfires’) that occur singly or in small 

groups should be eliminated from the extreme edges of the infestation. The next area to work on 

are those with a ratio of at least two natives to every invasive. As the native plants stabilize in 

each cleared area, work can then continue deeper into the center of more dense patches.

Mechanical: Traditional methods of mowing and cutting were the most common methods found 

in the literature. Other options do exist, though. Steaming or foaming equipment, for example, 

are being used more often with success. Therefore, creative solutions for treatments should 

always consider newer technology.

See http://tncweeds.ucdavis.edu/index.html for more information.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

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Biological: The effectiveness of biological controls is briefly summarized for each species. 

Details for each species of biocontrol are not provided, but through the references given, ample 

information can be found. To introduce any of the biological control agents in your state, first 

coordinate with your state agency to determine if the state introduced ample biocontrols in your 

area already or if you should obtain a permit for a new introduction. To obtain a permit you 

must complete an application through your APHIS_PPQ State Plant Health Office. You can get 

information and applications on line at http://www.aphis.usda.gov/ppq/weeds.

Cultural: Livestock grazing and such agricultural methods as plowing and disking were 

summarized in the document when found in the literature. Appropriate areas for these 

techniques may be limited, but they could be important tools.

Prescribed Fire: Prescribed burning can be an effective tool in invasive plant control, especially 

in combination with other techniques. The Fire Effects Information System [2] has a wealth of 

information not only on fire ecology for some of the species, but also other management 

methods.

Chemical: Damage to non-target vegetation is a major concern with most control methods, but it 

is most often associated with herbicide use. It is important when selecting a herbicide to find the 

one that is most effective with the least unintentional impact to non-target species. Herbicide 

selection should be tailored to the species and the situation. Careful application will minimize 

effects to non-target species. 

The chemicals listed for each species were found in the literature. Confirmation of their 

effectiveness was made through a variety of phone calls to contacts from the Oregon Department 

of Agriculture, various county weed coordinators, and researchers. If a chemical was 

recommended by only one source, its citation was listed.

Restoration/Monitoring: Restoration through revegetation should be a major component of all 

treatment strategies, especially where control treatments of aggressive species have left newly 

disturbed bare ground. If any information unique to a species regarding monitoring or 

restoration was found, it was also included in the discussions. A regional revegetation policy 

does exist and regional revegetation guidelines are being developed that recommend species for 

use.

Local native species are always preferred, but use of other desirable species such as non-native 

species that do not persist could be used as an interim step. A combination of native and 

desirable non-natives could be an initial mix for revegetation. A fast growing desirable nonnative such as sterile wheatgrass can germinate quickly and start filling in bare ground until a 

slower to germinate native species can start competing effectively.

** This document is expected to be updated on a regular basis as new species sections and 

more information on treatments are added.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

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Some Tips to Consider

 Always follow an integrated pest management approach (IPM) when tackling an invasive 

plant problem. IPM does not merely focus on the eradication of an invader but instead 

attempts to understand what makes it spread and focuses on reducing that spread through 

a combination of prevention, early detection/rapid response, treatment and restoration 

options. The main goal is to find the most effective methods with the least risk.

 Integration and perseverance are key to successful vegetation management programs (See 

Techline Winter 2003/2004). It is very unlikely that one method will do the trick. A 

combination of methods is usually the most effective for most aggressive species.

 Don’t expect a single treatment to do the trick for any species. Return visits and 

continued management are part of the process.

 Never underestimate the power of a group to manually tackle difficult species. For 

example, English ivy control in Portland or knapweed pulling in Wenatchee area. Not all 

species can be successfully controlled with only manual treatment, but some can.

 Be creative. Try techniques not usually used. The use of steam, hot foam, and propane 

torching are becoming popular solutions under the right conditions.

 Always, always, follow the Label when using herbicides. If you plan to apply 

herbicides yourself, go through application certification training at the state or federal 

level. There is a lot to keep track of when applying herbicides such as determining 

application rate, amount applied, applicator calibration and proper times to apply. 

 Talk to your local authorities. County weed coordinators, state coordinators or local 

university folks may have spent the most recent time on the species that you are 

concerned with. And they may be more than happy to assist with control measures.

 Plan ahead for revegetation. First assess the need for revegetation. It may not always be 

necessary if a healthy native population is already in place. Not every inch of bare 

ground needs to be revegetated. If revegetation is needed, make sure you have materials 

available to seed or plant treated sites as soon after treatment as possible.

 The planting of competitive desirable species can sometimes be the most effective 

method of control available for an invasive species.

 Establish a method to monitor treatment progress and overall effectiveness.

Prioritizing Treatments

The following table suggests a decision process for prioritizing treatments. This is especially 

important when budgets and staff time are limited. Focusing efforts on the wrong species or the 

wrong portion of an infestation can be ineffective and frustrating. 

The first step in prioritizing treatments is to understand where infestations are located, where 

they are spreading from and where infestation spread may be heading. Up-to-date inventories 

will help with this step as well as a working knowledge of ground disturbing activities in the 

vicinity of populations. For example, knowing where a species is located throughout a 

watershed will help to alleviate treatments focused downstream or downslope of a spreading 

infestation or activity that may cause spread through ground disturbance or movement of seed. 

Also, finding out where new satellites or ‘spot fires’ will also focus treatment efforts. 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

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Decision Matrix for Prioritization for Treatment

Priority Description Treatment – choice based 

on site-specific conditions

Highest Priority for 

Treatment

* Eradication of new species (focus on 

aggressive species with potential for 

significant ecological impact including 

but not limited to State listed high 

priority noxious weeds). See 

www.natureserve.org for an invasive 

species assessment protocol.

* New infestations (e.g. populations in 

areas not yet infested; “spot fires”; any 

State or Forest priority species).

1. Manual/mechanical - isolated 

plants or small populations.

2. Herbicide treatment if 

manual/mechanical is known 

to be ineffective or 

population too large.

3. Remove seed heads. This is 

an interim measure if 

cost/staff is an issue.

Second Priority for 

Treatment

* Areas of high traffic and sources of 

infestation (e.g. parking lots, 

trailheads, horse camps, gravel pits)

* Areas of special concerns: (e.g. 

botanical areas, wilderness, research 

natural areas, adjacent 

boundaries/access with national parks)

1. Manual/mechanical - isolated 

plants or small populations.

2. Herbicide treatment if 

manual/mechanical is known 

to be ineffective or 

population too large.

3. Remove seed heads. This is 

an interim measure if 

cost/staff is an issue.

Third Priority of 

Treatment

* Containment of existing large 

infestations of State-listed highest 

priority species or Forest priority 

species – focus on boundaries of 

infestation.

* Roadsides – focus first on access points

leading to areas of concern.

1. Manual/mechanical - isolated 

plants or small populations 

in spread zones.

2. Herbicide treatment for larger 

populations along perimeter.

Fourth Priority of 

Treatment

* Control of existing large infestations of 

State-listed and Forest second priority 

species

1. Disperse biocontrol agents on 

large infestations

2. Livestock grazing

3. Mechanical

4. Herbicide application

Fifth Priority of 

Treatment

* Suppression of existing large 

infestations – when eradication/control 

or containment is not possible.

1. Biocontrol on large 

infestations

2. Livestock grazing

3. Mechanical

4. Herbicide application along 

perimeters

Eradication: Attempt to totally eliminate an invasive plant species from a Forest Service unit, recognizing that this may not actually be 

achieved in the short term since re-establishment/re-invasion may take place initially. Control: Reduce the infestation over time; some 

level of infestation may be acceptable. Contain: Prevent the spread of the weed beyond the perimeter of patches or infestation areas 

mapped from current inventories. Suppress: Prevent seed production throughout the target patch and reduce the area coverage. Prevent 

the invasive species from dominating the vegetation of the area; low levels may be acceptable.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

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The following table summarizes those herbicides and their properties that may be useful in 

treating invasive plants when using an integrated pest management approach.

Comparison Table of Proposed Chemicals*

Chemical/Brand 

Names/Action

Properties General Uses/Known 

to be Effective on:**

Comparisons/Issues

***

Chlorsulfuron/

(Telar,Glean,Corsair)/

Sulfonylurea-Interferes 

with enzyme 

acetolactate synthase w/ 

rapid cessation of cell 

division and plant 

growth in shoots and 

roots.

Glean -Selective preemergent or early postemergent 

Telar – Selective preand post-emergent.

Chlorsulfuron can be 

used for many annual, 

biennial and perennial 

broadleaf species.

Use at very low rates on 

annual, biennial and 

perennial species; 

especially Canadian 

thistle, dalmation 

toadflax, hounds tongue

and perennial 

pepperweed.

Safe for most grasses.

Some soil residual.

Potential for offsite 

movement through 

runoff or wind erosion 

is substantial in 

conditions that favor 

these actions.

Damage to some aquatic 

plants possible at peak 

concentration. 

Offsite drift may cause 

damage to sensitive 

species up to 900’.

Clopyralid/

(Transline)/

Synthetic auxin -Mimics 

natural plant hormones.

Similar to picloram.

Contains 

hexachlorobenzene.

A highly translocated, 

selective herbicide 

active primarily through 

foliage of broadleaf 

species. Little effect on 

grasses. 

Particularly effective on 

Asteraceae, Fabaceae, 

Polygonaceae, 

Solanaceae. Some 

species include 

knapweeds, yellow 

starthistle, Canada 

thistle, hawkweeds.

Not as persistent as 

picloram, but problems 

still exist. Can persist 

from one month to one 

year. More selective 

than picloram. 

Potentially mobile 

depending on site 

specific conditions.

Off site drift may cause 

damage to sensitive 

species up to 300’.

Glyphosate/

(RoundUp, Rodeo etc.)/

Inhibits three amino 

acids and protein 

synthesis.

A broad spectrum, nonselective translocated 

herbicide with no 

apparent soil activity.

Translocates to roots 

and rhizomes of 

perennials. 

Low volume 

applications are most 

effective. 

Control for purple 

loosestrife, herb Robert, 

English ivy, reed 

canarygrass and other 

weeds common in 

wetland and riparian 

habitats.

Aquatic formulations 

can be used near water.

Rain within 6 hours of 

application may reduce 

effectiveness.

Complete control may 

require re-treatment.

Off site drift damage to 

sensitive species up to 

100’ possible.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

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Comparison Table of Proposed Chemicals*

Chemical/Brand 

Names/Action

Properties General Uses/Known 

to be Effective on:**

Comparisons/Issues

***

Imazapic/

(Plateau)/Inhibits the 

plant enzyme 

acetolactate, which 

prevents protein 

synthesis.

Selective against some 

broadleaf plants and 

some annual grasses. 

Use at low rates can 

control leafy spurge, 

cheatgrass, medusa head 

rye, and hounds tongue. 

Useful in grassland 

prairie habitat 

restoration because it is 

selective against annual 

grasses.

Off site drift may 

damage sensitive 

species up to 50’ 

possible; over 100’ if 

aerially applied.

Even very tolerant nontargets could be 

damaged directly. 

Some damage to aquatic 

plants at peak 

concentrations.

Imazapyr/

(Arsenal, Chopper, 

Stalker, Habitat)/ 

Inhibits the plant 

enzyme acetolactate, 

which prevents protein 

synthesis.

Broad spectrum, nonselective pre- and postemergent for annual and 

perennial grasses and 

broadleaved species.

Most effective as a postemergent. Has been 

used on cheatgrass, 

white top, perennial 

pepperweed, tamarisk,

dyers woad, woody 

species, spartina.

High potential for 

leaching. Highly 

mobile and persistent. 

Residual toxicity up to 

several years. May be 

actively exuded from 

the roots of legumes, 

likely as a defense 

mechanism by these 

plants.

Metsulfuron methyl/

(Escort)/ Sulfonylurea -

Inhibits acetolactate 

synthesis, protein 

synthesis inhibitor, 

block formation of 

amino acids.

Selective against 

broadleaf and woody 

species. Most sensitive 

crop species in the Lily 

family.

Use at low rates to 

control such species as 

houndstongue, perennial 

pepperweed, sulfur 

cinquefoil. Safest 

sulfonylurea around 

non-target grasses.

Potentially mobile in 

water or through wind 

erosion. Damage to 

some aquatic plants 

possible at peak 

concentrations.

Off site drift may cause 

damage sensitive plants 

up to 500’.

Picloram (Tordon)

Restricted Use 

Herbicide

Contains 

hexachlorobenzene.

Selective, systemic for 

many annual and 

perennial broadleaf 

herbs and woody plants.

Use at low rates to 

control such species as 

knapweeds, Canada 

thistle, yellow 

starthistle, 

houndstongue, 

toadflaxs, St. Johnswort, 

sulfur cinquefoil and 

hawkweeds.

Off site drift may cause 

damage to sensitive 

plants up to 1000’. Also 

can leak out of roots to 

non-targets. One 

application may be 

effective for 2 or more 

years. Can move offsite 

through surface or 

subsurface water. Can 

be relocated through 

livestock urine.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

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Comparison Table of Proposed Chemicals*

Chemical/Brand 

Names/Action

Properties General Uses/Known 

to be Effective on:**

Comparisons/Issues

***

Sethoxydim/

(Poast)/ Inhibits acetyl 

co-enzyme, a key step 

for synthesis of fatty 

acids.

A selective, postemergent grass 

herbicide.

Will control many 

annual and perennial 

grasses.

Potentially mobile, but 

degrades rapidly.

Off site drift up to 50’ 

possible.

Sulfometuron methyl/

(Oust)/ Sulfonylurea -

Inhibits acetolactase 

synthase, a key step in 

branch chain amino 

acid synthesis.

Broad spectrum preand post-emergent 

herbicide for both 

broadleaf species and 

grasses.

Used at low rates as a 

pre-emergent along 

roadsides. Known to be 

effective on canary 

reedgrass (but not 

labeled for aquatic use), 

cheatgrass and 

medusahead.

Offsite drift may cause 

damage sensitive plants 

up to 900’. Highly 

mobile by water or by 

wind erosion. 

Substantial damage has 

occurred to croplands in 

arid and wet regions.

Damage to some aquatic 

plants possible at peak 

concentration

Triclopyr/

(Garlon, Pathfinder, 

Remedy)/ Synthetic 

auxin - Mimics natural 

plant hormones.

A growth regulating 

selective, systemic 

herbicide for control of 

woody and broadleaf 

perennial weeds.

Not for broadcast 

application under 

proposed action. Little 

or no impact on grasses. 

Effective for many 

woody species such as 

scotch broom. Also 

effective on English ivy, 

Japanese knotweed.

Garlon 4 (ester 

compound) is toxic to 

fish and aquatic 

invertebrates. Amine 

formulations may be 

used near or over water. 

Offsite movement by 

water possible.

Off site drift may 

damage sensitive plants 

up to 100’.

* This table is a brief summary of some of the attributes of these herbicides. More information is provided in the 

species write ups or more information can be found from the references given.

**Please note: The information on effectiveness by species (third column) contains examples of just some of the 

species the herbicides can treat.

*** Issues listed in this table and in following species-specific tables were identified in Forest Service Risk 

Assessments prepared by Syracuse Environmental Research Associates, Inc. Risk assessments are available on the 

Region 6 Invasive Plant EIS website: www.fs.fed.us/r6/invasiveplant-eis.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

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Brachypodium sylvaticum – False-brome

Ecological Characteristics of Note

False-brome is an invasive perennial bunch grass that can rapidly invade a variety of 

environments including open and understory habitats. Although it is not rhizomatous, it forms 

coalescent clumps and can resprout from stem or root fragments when cut. False-brome 

reproduces rapidly from seed. It has been suggested that B. sylvaticum does not maintain a 

persistent (longer than 1 year) seed bank in soils, but this is not yet confirmed in North America. 

[44, 46, 47]

Management

Manual: Hand removal may effectively control small infestation, but care must be taken to 

remove all root fragments to prevent resprouting. [45, 47]

Mechanical: The Institute for Applied Ecology and the Eugene District BLM have conducted 

trials that include spraying with super heated foam. Hot foam reduced the cover of false-brome 

from 44 percent to 7 percent in one year, although seedlings remained and Himalayan blackberry 

seemed to fill in behind. [46] Repeated mowing may benefit control efforts by exhausting the 

seed bank and forcing the plants to send up new shoots that are more likely to take up herbicide.

[47]

Cultural: In Europe, false-brome is absent from heavily grazed sites, so grazing may eventually 

eliminate it. Grazing before seed set may benefit control efforts by exhausting the seed bank and 

forcing the plants to send up new shoots that are more likely to take up herbicide. [47]

Prescribed Fire: Burning appears to be ineffective. False-brome is frequently found in recently 

burned sites and it reported to resprout within 2 weeks of a burn. [45, 47] burning before seed 

set may benefit control efforts by exhausting the seed bank and forcing the plants to send up new 

shoots that are more likely to take up herbicide. [47]
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

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Chemical: [48]

A pilot study to control this species at the Oregon State University Research Forests was 

conducted in fall of 2002 using the herbicides Plateau (imazapic), Accord (glyphosate), the 

combination of Accord and Plateau and the combination of Accord and Oust (sulfometuron 

methyl) along with other herbicides not included under the Invasive Plant Program – Pacific 

Northwest Region Draft EIS. [49] Treatments with Accord, Accord + Plateau, and Oust + 

Accord reduced false-brome >90 percent after one year of treatment. Treatment with Plateau 

alone was ineffective. The following table is based on this pilot project with only one posttreatment data collection completed.

Herbicide Selectivity Effects to 

Natives

When 

to 

Apply

Method to 

Use* Issues/Concerns

Glyphosate 

(Accord)

Broad 

spectrum, nonselective and 

systemic.

Offsite drift up to 

100’. Most likely 

to kill non-targets 

including grasses. 

Adheres to soil 

which lessens

leaching or 

uptake by nontargets.

Late 

fall.

Backpack 

sprayer 

with six 

nozzle 

spray 

boom.

Rain within 6 hours 

reduces effectiveness. 

Surfactants can be 

damaging to aquatic 

species.

Accord + 

Imazapic 

(Plateau) 

Imazapic is 

selective for 

broadleaf 

plants and 

some grasses. 

Glyphosate is 

non-selective.

Offsite drift up to 

50’. Over 100’ if 

applied aerially.

Reduced native 

plant cover.

Late 

fall.

Backpack 

sprayer 

with six 

nozzle 

spray 

boom.

With imazapic even 

very tolerant nontarget species are 

likely to be damaged. 

Damage to some 

aquatic plants possible 

at peak 

concentrations.

Sulfometuron 

methyl (Oust) + 

Accord 

Broad

spectrum preand postemergent 

herbicide for 

both broadleaf 

and grasses. 

Glyphosate is 

non-selective.

Offsite drift may 

damage sensitive 

plants up to 900’.

Reduced native 

plant cover.

Late 

fall.

Backpack 

sprayer 

with six 

nozzle 

spray 

boom.

Sulfometuron methyl 

is highly mobile by 

water or by wind 

erosion. Damage to 

some aquatic plants 

possible at peak 

concentrations.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.

Restoration: Experimental studies of reestablishment of native species after removal of false 

brome are currently being conducted. A study done by the Institute for Applied Ecology and 

Eugene BLM found that seeding with blue wildrye and mulching resulted in relatively high 

establishment of the native grass. Mulching with blue wildrye straw appears to be an effective 

way to establish the species, inhibit the establishment of false-brome and increase survivorship 

of blue wildrye seedlings. [46]
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

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Centaurea biebersteinii (C. maculosa) – Spotted Knapweed

Ecological Characteristics of Note

Spotted knapweed reproduces entirely by seed. This species generally lives up to nine years or 

longer. It can produce up to 4,000 seeds per square foot. The majority of seeds are viable and 

can remain viable for up to 8 years. Seeds may germinate over a wide range of soil depths, 

moisture content and temperature. Plants may stay in the rosette stage for multiple years before 

bolting. Typically, the species bolts for the first time in May during its second growing season 

and flowers in July/August. Seeds are shed immediately and can be dispersed up to 3 feet from 

the plant through dehydration and expelling through the bracts. Of course, seed can be dispersed 

much farther on vehicles and trains. Spotted knapweed seeds germinate in either spring or fall. 

[2, 3, 17]

Management

Manual: Hand pulling/digging before seed production may be effective for small populations. 

The entire root crown must be completely removed. However, the effects of soil disturbance on 

knapweed seed germination are not well documented. [17]

Mechanical: In stands with little other vegetation, this may be possible if mowing occurs just 

after most flowering has ended, but before seeds have matured. This would make regrowth 

unlikely since moisture levels late in the season are probably too low for continued growth, but 

would offer a possible advantage of reducing reserves for flowering the following year. [17] It is 

considered moderately effective. [8] Mowing combined with mulching may increase 

effectiveness. Mowing may cause low growing forms.

Biological: A variety of biological control agents have been established. None of these, alone or 

in combination effectively control populations. Studies suggest that given sufficient time certain

biological control agents could reduce the density and aggressiveness of spotted knapweed. 

However, on a shorter timeline, they do not effectively eradicate populations unless integrated 

with other control techniques. [10]

Cultural: Long term grazing by sheep and goats has been found to control spotted knapweed. 

Cultivation may be effective, but application may be limited in most treatment areas. Plowing 

soils under to 7 inches, allowing 4 to 6 weeks for re-germination and then repeating for one 

growing season has been successful. Herbicide application may make cultivation more effective 

for large infestations. [10]

Prescribed Fire: Prescribed burning alone is probably not effective for controlling spotted 

knapweed and may cause increases. Studies have shown that moderate increases occur after 

fire. Fire may be useful in conjunction with herbicides under the right conditions by reducing 

old stem densities. A fuel model has been developed for this species. The fire severity depends 

on the amount of dry knapweed stems and the amount of fine grass fuels. [2]
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

15

Chemical (for spotted knapweed):[3, 4, 7, 8, 17]

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use *

Issues/Concerns

Clopyralid

(Transline)

Contains 

hexachlorobenzene.

Selective, 

systemic for 

particularly: 

Asteraceae, 

Fabaceae, 

Polygonaceae, 

[7] Some 

effects on 

Apiaceae, 

Solanaceae, 

Violaceae [17]

Off site drift 

may cause 

damage to 

sensitive 

plants up to 

300’. Little 

effect on 

grasses.

Up to the 

bud stage.

Backpack or

wick to 

minimize 

drift.

Less persistent than 

picloram. More 

selective than 

picloram. 

Potentially mobile 

in water. 

Picloram (Tordon)

Restricted Use 

Herbicide

Contains 

hexachlorobenzene. 

Selective, 

systemic for 

many annual 

and perennial 

broadleaf herbs 

and woody 

plants.

Off site drift 

may cause 

damage to 

sensitive 

plants up to 

1000’. Also 

can leak out 

of roots to 

non-targets 

[4].

Late spring 

prior to 

flower stem 

elongation

Backpack or 

wick to 

minimize 

drift.

One application may 

be effective for 2 or

more years. Wait 6 

10 12 months to 

reseed since 

picloram is 

persistent in the soil.

More mobile than 

clopyralid. Can 

move offsite 

through surface or 

subsurface water.

Can be relocated 

through livestock 

urine

Glyphosate Broad 

spectrum, nonselective and 

systemic.

Off site drift 

up to 100’ 

possible. Most 

likely to kill 

non-targets 

including 

grasses. 

Adheres to 

soil which 

lessens

leaching or 

uptake by 

non-targets.

Actively 

growing in 

bud stage.

Backpack or 

wick to 

minimize 

drift.

Only provides 

control during year 

of application. 

Not mobile in the 

environment.

Will not kill seeds 

or inhibit 

germination. Can 

reseed more quickly 

than with more 

persistent chemicals.

Surfactants can be 

toxic to aquatic 

species.

Rain within 6 hours 

reduces 

effectiveness.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

16

Restoration Issues: The allelopathic chemical, -catechin,, may reduce recovery potential as its 

presence in the soil may hinder the resurgence of natives. Also dormant seeds may germinate 

and re-infest an area. Replanting is preferred over allowing natural recovery. A native or less 

persistent species such as sterile wheatgrass is preferred. [17]

An integrated approach would involve late-fall cultivation, followed by a dormant seeding of 

grasses. The next spring requires treatment by herbicide at the point of first emergence with 

another reduced herbicide treatment or mowing in mid-summer. [9]
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

17

Centaurea diffusa – Diffuse Knapweed

Ecological Characteristics of Note

Diffuse knapweed reproduces entirely by seed and is a prolific seed producer. A single plant can 

produce up to 18,000 seeds. Under favorable conditions (high soil moisture), it has a biennial 

life cycle, but additional years are required to attain flowering size in less favorable conditions. 

The plants must reach a critical size in order to flower. Under favorable conditions a plant will 

bolt in May of its second growing season and flowers in July/August. Seeds mature by mid- to 

late August. Seeds germinate in both early spring (primarily) and fall. In the fall, diffuse 

knapweed breaks off at ground level and disperses widely as a tumbleweed. [2, 17]

Management 

A successful management program should set a goal of <5 percent knapweed cover. This is the 

assumed density of the weed in its native range. [17] A cumulative stress approach is necessary 

(i.e. a combination of treatments).

Manual: For small infestations, hand pulling before seed set is effective if done three times in 

one year. [17]

 Dig rosettes in the spring.

 Pull mature and immature plants in early summer before seeds form.

 Pull and bag (to remove seed from area) remaining plants in mid to late summer.

 All of the infestation must be pulled. All of the taproot must be removed. Pulling 

only portions of a large infestation will not be effective.

Mechanical: Mowing could actually increase populations of diffuse knapweed.

Biological: At least nine biological control agents are established in parts of the U.S. None of 

these, alone or in combination, effectively control populations. They may prove useful as part of 

an integrated program to weaken plants therefore making them more susceptible to other 

treatments. [17]

Cultural: Deep plowing may be effective where feasible because knapweed seeds will not 

germinate below 3 cm. Shallow plowing could actually increase diffuse knapweed. Grazing is 

not an effective control method for diffuse knapweed. It is generally unpalatable and the spines 

can injure livestock. [17]

Prescribed Fire: Fire may be effective in controlling this species. Low-severity fire may only 

top-kill diffuse knapweed. Dry soil conditions associated with burns may discourage reinfestation as moisture is the limiting factor for seed germination. Re-seeding of desirable 

species may be necessary. A fuel model developed for spotted knapweed may be useful to 

managers planning to burn fields infested with diffuse knapweed. Using prescribed fire to 

reduce big sagebrush in semiarid grasslands may expose sites to invasion by diffuse knapweed. 

[2]
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

18

Chemical (for diffuse knapweed):[3, 4, 7, 8, 17, 52]

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method 

to Use *

Issues/Concerns

Clopyralid

(Transline)

Contains hexachlorobenzene.

Selective, 

systemic for 

particularly: 

Asteraceae, 

Fabaceae, 

Polygonaceae, [7] 

Some effects on 

Apiaceae, 

Solanaceae, 

Violaceae [17]

Off site drift 

may cause 

damage to 

sensitive 

plants up to 

300’. Little 

effect on 

grasses.

Up to the 

bud 

stage.

Backpack 

or wick 

to 

minimize 

drift.

Less persistent than 

picloram. More selective 

than picloram. Potentially 

mobile in water. 

Picloram 

(Tordon)

Restricted Use 

Herbicide

Contains hexachlorobenzene. 

Selective, 

systemic for many 

annual and 

perennial 

broadleaf herbs 

and woody plants.

Off site drift 

may cause 

damage to 

sensitive 

plants up to 

1000’. Also 

can leak out of 

roots to nontargets [4].

Late 

spring 

prior to 

flower 

stem 

elongation

Backpack 

or wick 

to 

minimize 

drift.

One application may be 

effective for 2 or more 

years. Wait 6 10 12 

months to reseed since 

picloram is persistent in 

the soil.

More mobile than 

clopyralid. Can move 

offsite through surface or 

subsurface water.

Can be relocated through 

livestock urine.

Glyphosate

(RoundUp, 

Rodeo)

Broad spectrum, 

non-selective and 

systemic.

Off site drift 

up to 100’ 

possible. Most 

likely to kill 

non-targets 

including 

grasses.

Adheres to soil 

which lessens

leaching or 

uptake by nontargets.

Actively 

growing 

in bud 

stage.

Backpack 

or wick 

to 

minimize 

drift.

Only provides control 

during year of application. 

Not mobile in the 

environment.

Will not kill seeds or 

inhibit germination. Can 

reseed more quickly than 

more persistent chemicals.

Surfactants can be toxic to 

aquatic species.

Rain within 6 hours 

reduces effectiveness.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.

Monitoring: Conduct monitoring 2 or 3 times per year (spring, summer and fall). [17]

Restoration Issues: The allelopathic chemical, cnicin, may reduce recovery potential as its 

presence in the soil may hinder the resurgence of natives. Also dormant seeds may germinate 

and re-infest an area. Replanting is preferred over allowing natural recovery. A native or less 

persistent species is preferred. [17]
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

19

Centaurea pratensis (C. jacea x nigra, C. debeauxii) – Meadow 

Knapweed

Ecological Characteristics of Note

Meadow knapweed is a fully fertile hybrid between brown and black knapweed. It is a perennial 

with a taproot when a seedling; mature plants develop a cluster of somewhat fleshy roots below a 

woody root crown. Flowering peaks in July/August, but occasional flowers can be found west of 

the Cascades into November/December, particularly on damaged plants. [19]

Management

Manual: Hand pulling is difficult due to the species’ tough perennial root crown. The plants 

usually will not come out easily and will require digging. [34]

Mechanical: Repeated mowing may suppress the species’ ability to produce seed, but in some 

cases will only lower the blooming height. [51] Such mowing must be done before any seeds are 

formed, to avoid spreading the seeds. The season of growth and flowering may also be 

prolonged. This may be to an advantage in herbicide programs. [35]

Cultural: Little information is available on palatability. Regrowth after mowing may also be an 

advantage when combined with grazing. [35] In pastures where treated with herbicide, fertilizer 

should be added to encourage grass vigor and competitiveness. Repeated cultivation as with 

spotted knapweed may be useful in some areas.

Prescribed Fire: No information could be found specific to this species, but burning 

effectiveness is most likely similar to spotted knapweed.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

20

Chemical (for meadow knapweed):[3, 4, 7, 8, 17]

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method 

to Use *

Issues/Concerns

Clopyralid

(Transline)

Contains hexachlorobenzene.

Selective, 

systemic for 

particularly: 

Asteraceae, 

Fabaceae, 

Polygonaceae, 

[7] Some 

effects on 

Apiaceae, 

Solanaceae, 

Violaceae [17]

Off site drift 

may cause 

damage to 

sensitive 

plants up to 

300’. Little 

effect on 

grasses.

Up to the bud 

stage.

Two 

applications 

per season; 

one in spring, 

one in fall is 

also proving 

effective.

Backpack 

or wick to 

minimize 

drift.

Less persistent than 

picloram. More selective 

than picloram. Potentially 

mobile in water. 

Worked very well for this 

species in elk habitat.

Picloram 

(Tordon)

Restricted Use 

Herbicide

Contains hexachlorobenzene

Selective, 

systemic for 

many annual 

and perennial 

broadleaf 

herbs and 

woody plants.

Off site drift 

may cause 

damage to 

sensitive 

plants up to 

1000’. Also 

can leak out 

of roots to 

non-targets 

[4].

Late spring 

prior to 

flower stem 

elongation

Backpack 

or wick to 

minimize 

drift.

One application may be 

effective for 2 or more 

years. Wait 6 10 12 

months to reseed since 

picloram is persistent in 

the soil.

More mobile than 

clopyralid. Can move 

offsite through surface or 

subsurface water.

Can be relocated through 

livestock urine

Glyphosate Broad 

spectrum, nonselective and 

systemic.

Off site drift 

up to 100’ 

possible. 

Most likely 

to kill nontargets 

including 

grasses. 

Adheres to 

soil which 

lessens

leaching or 

uptake by 

non-targets.

Actively 

growing in 

bud stage.

Backpack 

or wick to 

minimize 

drift.

Only provides control 

during year of application. 

Not mobile in the 

environment.

Will not kill seeds or 

inhibit germination. Can 

reseed more quickly than 

with more persistent 

chemicals.

Surfactants can be toxic to 

aquatic species.

Rain within 6 hours 

reduces effectiveness.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.

An integrated approach of herbicide treatment combined with mowing or pulling has potential 

for control. Various combinations of spraying herbicide first, then pulling or mowing are being 

tested by Washington State University. [37]
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

21

Centaurea solstitialis – Yellow Star-thistle

Ecological Characteristics of Note

Yellow star-thistle typically begins flowering in late May and continues through September, 

sometimes into December or later. The time period from flower initiation to the development of 

mature viable seed is only 8 days. Infestations can produce 50-100 million seeds per acre. Two 

types of seeds can form, pappus bearing and non-pappus bearing. In either case, wind dispersal 

is not effective. Over 90 percent of seed fall within two feet of a plant. Non-pappus bearing 

seed can be retained in the flower head for a considerable amount of time, even into the winter. 

Over 90 percent of seed are germinable one week after seed dispersal. Seeds may stay viable 

from six to twelve years. [17]

Management

Manual: Manual removal is most effective with small patches or in maintenance programs 

where plants are sporadically located. This usually occurs with a new infestation or in the third 

year or later in a long-term management program. It is important to detach all above ground 

stem material. Leaving even a two inch piece of stem can result in recovery if leaves and buds 

are still attached at the base of the plant. The best time for manual removal is after plants have 

bolted but before they produce viable seed (early flowering). [21]

The Bradley method [22] of manual control can work on a larger population. Start removing 

plants at the outward edge of the population and working towards the interior. The technique 

requires repeated visits, but ensures that no new seeds are produced and soil disturbance is 

minimized. This method can control relatively large populations of less than 40 acres. [21]

Mechanical: Early summer tillage will control yellow starthistle provided that roots are detached 

from the shoots. Repeated cultivation may be necessary in the same season when rainfall 

stimulates additional germination between tillage. Conduct tillage before seeds are produced. 

Appropriate use of this technique is probably limited in areas with many non-target species.

Mowing can be useful but timing is critical. Mowing early growth stages results in increased 

light penetration and rapid regrowth. If stem branches are below the mowing height, flowers

could still develop. Mowing could also reduce biocontrol efforts, injure late growing forb 

species and reduce fall/winter forage. If conducted before viable seed production it may still be 

considered effective.

Biological: Six insects have become established for yellow starthistle control in the western US. 

These include three species of weevils and three species of flies. Only two have had any 

significant effect on reproduction in California; the hairy weevil and the peacock fly. The 

combination of these two insects reduced seed production by 43 to 76 percent. Although this 

level of suppression would not ensure long term management, it will certainly help in 

combination with other treatments. A more successful biocontrol program will likely require the 

introduction of plant pathogens or other insects capable of damaging roots, stems and foliage. 

[17]
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

22

Cultural: Grazing could be effective if properly timed. Early grazing would favor light 

penetration and stimulate growth of yellow starthistle. Late season grazing would allow heavy 

seed production since cattle and sheep would avoid the spiny heads. Grazing in May or June 

may be effective depending on effects to native vegetation. Short duration, intensive grazing (for 

only 3 to 5 days) may be most effective. Goats are becoming more popular as the grazing tool of 

choice since they will eat the plant during its spiny phase. [17, 21]

Prescribed burning: The ideal burning time is similar to the ideal mowing time (early flowering 

before seedset). Unfortunately early to mid-summer burning may not be feasible in some places 

due to climatic or environmental conditions. It may be best used after herbicide treatment (such 

as with clopyralid) in the first year. This would suppress legumes and stimulate grasses making 

a second year fire more effective in promoting species diversity.

Chemical (for yellow starthistle):[3, 4, 7, 8, 17, 21]

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method 

to Use *

Issues/Concerns

Clopyralid

(Transline)

* considered most 

effective [17]

Contains 

hexachlorobenzene.

Selective, 

systemic for 

particularly: 

Asteraceae, 

Fabaceae, 

Polygonaceae, 

[7] Some 

effects on 

Apiaceae, 

Solanaceae, 

Violaceae 

[17]

Off site drift 

may cause 

damage to 

sensitive plants 

up to 300’. 

Little effect on 

grasses.

January 

through May. 

Most effective 

on seedlings 

and rosettes. 

Will work in 

bolt or bud but 

at higher 

concentrations.

Backpack 

or wick to 

minimize 

drift.

Less persistent 

than picloram. 

More selective 

than picloram. 

Potentially mobile 

in water. 

Picloram (Tordon)

* most widely used 

in the West [17]

Contains 

hexachlorobenzene.

Selective, 

systemic for 

many annual 

and perennial 

broadleaf 

herbs and 

woody plants.

Off site drift 

may cause 

damage to 

sensitive plants 

up to 1000’. 

Also can leak 

out of roots to 

non-targets [4].

Late winter to 

spring in 

rosette through 

bud stage.

Backpack 

or wick to 

minimize 

drift.

One application 

may be effective 

for 2 or more 

years. Wait 6 10 

12 months to 

reseed since 

picloram is 

persistent in the 

soil.

More mobile than 

clopyralid. Can 

move offsite 

through surface or 

subsurface water.

Can be relocated 

through livestock 

urine
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

23

Chemical (for yellow starthistle):[3, 4, 7, 8, 17, 21]

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method 

to Use *

Issues/Concerns

Glyphosate (Round 

Up varieties).

Broad 

spectrum, 

non-selective 

and systemic.

Off site drift up 

to 100’ 

possible. Most 

likely to kill 

non-targets 

including 

grasses. 

Adheres to soil 

which lessens

leaching or 

uptake by nontargets.

Works best on 

seedlings. 

Will not 

control plants 

germinating 

after 

application, so 

use on mature 

plants is better 

for long term 

management.

Backpack 

or wick to 

minimize 

drift.

Only provides 

control during 

year of 

application. 

Not mobile in the 

environment.

Will not kill seeds 

or inhibit 

germination. Can 

reseed more 

quickly than with 

more persistent 

chemicals.

Rain within 6 

hours reduces 

effectiveness.

Triclopyr 

(various Garlon 

formulations; 

consisting of salts 

and ester).

Selective, 

systemic for 

woody and 

broadleaf 

species. Will 

remain in 

plants until 

they die. 

Growth 

regulating.

Little or no 

impact on 

grasses. Off 

site drift up to 

100’ possible.

Could inhibit 

ectomychorrizal 

growth.

Works best on 

seedlings. 

Will not 

control plants 

germinating 

after 

application, so 

use on mature 

plants is better 

for long term 

management.

Backpack 

or wick to 

minimize 

drift. 

Only 

selective 

treatments 

allowed 

by 

standards.

Only provides 

control during 

year of 

application. 

Garlon 4 (ester 

formulation) is 

more toxic to fish 

and aquatic 

inverts.

Offsite movement 

by water possible.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.

Restoration: Revegetation with desirable and competitive plant species can be the best long-term 

sustainable method. Unfortunately, few studies have been conducted on the restoration of 

yellow starthistle using a wide diversity of species, particularly natives. Perennials such as big 

bluegrass and thickspike wheatgrass provide a native alternative to non-native persistent species 

such as crested wheatgrass.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

24

Chondrilla juncea – Rush Skeletonweed

Ecological Characteristics of Note

Rush skeletonweed can produce by either seed or vegetatively. It is a somewhat long lived 

perennial which can produce seed without fertilization. This self fertilization produces clones 

resulting in well-adapted biotypes that can dominate an area. Three biotypes are known in the 

Pacific Northwest, with varying flowering times. Mature plants can produce 1500 flower heads 

with the capability of producing 20,000 seeds. Seeds can be wind dispersed up to 20 miles. 

Vegetative spread is possible from shoot buds found along lateral roots, and from shoot buds 

found near the top of the main tap root. Vegetative spread is also possible when a root fragment, 

as deep as four feet down, is left in the ground. When the plant stem or root is mechanically 

injured, vegetative growth is initiated. [23]

Management [23]

Mechanical: Since any mechanical damage to plants stimulates new growth resulting in satellite 

plants, such methods are not recommended. Frequently mowing rush skeleton weed plants 

infested with gall mites may decrease the rate of spread for the species.

Biological: Several biological controls have been released in the west. Most are very specific to 

biotype and are therefore only effective in specific areas. The gall mite is most effective against 

all biotypes. Rush skeletonweed still remains the dominant species, though, even with this 

biological control. The plant pathogen, rust fungus, is well established and is effective on the 

early flowering biotype.

Cultural: Continual grazing may decrease populations when seed production is prevented, but 

rotational grazing can increase population densities.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

25

Chemical (for rush skeleton weed)[7, 23}: Rush skeletonweed is a deep rooted, rhizomatous 

perennial considered tolerant to herbicides. Therefore, an aggressive follow up program with 

repeated applications will be necessary. Difficult to apply because of small leaves.

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method 

to Use * Issues/Concerns

Clopyralid

(Transline)

Contains 

hexachlorobenzene.

Selective, 

systemic for 

particularly: 

Asteraceae, 

Fabaceae, 

Polygonaceae, 

[7] Some effects 

on Apiaceae, 

Solanaceae, 

Violaceae [17]

Off site drift 

may cause 

damage to 

sensitive 

plants up to 

300’. Little 

effect on 

grasses.

Apply to 

rosette in the 

late fall or up 

to early 

bolting in 

spring.

Backpack 

or wick to 

minimize 

drift.

Less persistent than 

picloram. More 

selective than 

picloram. Potentially 

mobile in water. 

Plants less than five 

years old respond 

better to herbicides.

Picloram (Tordon)

Restricted Use 

Herbicide

Contains 

hexachlorobenzene.

Selective, 

systemic for 

many annual and 

perennial 

broadleaf herbs 

and woody 

plants.

Off site drift 

may cause 

damage to 

sensitive 

plants up to 

1000’. Also 

can leak out of 

roots to nontargets [4].

Apply from 

late fall to 

early spring

Backpack 

or wick to 

minimize 

drift.

One application may 

be effective for 2 or 

more years. Wait 6 

10 12 months to 

reseed since 

picloram is persistent 

in the soil.

More mobile than 

clopyralid. Can 

move offsite through 

surface or subsurface 

water.

Can be relocated 

through livestock 

urine. 

Plants less than five 

years old respond 

better to herbicides.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

26

Cirsium arvense – Canada Thistle

Ecological Characteristics of Note

Canada thistle produces an abundance of seeds that are easily dispersed by the wind. Most seeds 

germinate within a year, but some remain viable in the soil for twenty year or more. Vegetative 

reproduction is aided by a fibrous taproot capable of sending out lateral roots as deep as 3 feet 

below ground, and from which shoots sprout up at frequent intervals. It also readily regenerates 

from root fragments les than an inch in length. The species is usually dioecious. [3]

Management

Canada thistle management programs should be designed to kill established clones since the 

species spreads primarily by vegetative expansion of the root system. Prevention of seed 

production is also an important part of a management program. [53] It takes at least two growing 

seasons to determine whether a particular control method is effective. Remove or treat 

populations before they flower and set seed. [17]

Manual: The only manual technique found was hand cutting of flower heads using the same leaf 

and stem criteria described below under mechanical. Although not a control method per se, this 

technique would suppress seed production. [3]

Mechanical: Mowing may only be effective in rare cases where it can be repeated at monthly 

intervals. This intensity is not recommended in natural areas, where it would likely damage 

native vegetation, but may be practical along roadsides. [53] Mowing just twice a year, in midJune and September may reduce or contain Canada thistle. When mowing, cut high enough to 

leave >9 leaves per stem, or > 20 centimeters of bare stem tissue, as mature Canada thistle leaves 

and stems independently inhibit development of shoots from rootbuds.

Smothering Canada thistle with boards, sheet metal or tar paper can kill plants.

Biological: Overall, this method provides little or no control on Canada thistle populations, 

although some agents weaken and kill individuals. Most biocontrols are not adequately 

synchronized with its life cycle in North America. Management that delays flowering, such as 

mowing or burning, may help to synchronize a more susceptible stage with the biocontrol 

agent’s life cycle. At least three agents may be needed for effective control. [17]

Cultural: Little information is available on the effectiveness of grazing. Although sheep and 

goats have been known to eat young plants, livestock grazing has not been proven and is most 

likely a contributor to thistle establishment in overgrazed situations.

Tilling also may be effective in unique cases. Deep tilling repeated through the season until 

early August will ensure new shoots do not produce flower stalks. Tilling in mid- to late July, 

applying herbicide in mid-August and tilling again after three weeks has been successful in 

Canada.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

27

Prescribed Fire: Above ground parts will be killed, but below ground parts will survive even 

severe fires. There is abundant evidence that post-fire establishment of Canada thistle is 

common where seed source is available. [2]

Results are mixed on the use of prescribed fire as a management tool. Prescribed burns may be 

effective at stimulating growth of native species and thereby discouraging the growth of this 

invasive. It may be best if timed to emulate the natural fire regime of a site. Late spring burns 

may discourage the species, yet early spring burns may encourage it. Dormant season burning 

may be preferred because it stimulates growth of native vegetation, but may not be as effective 

as late spring burning. [2] Annual burns for several years may be required.

Chemical (for Canadian thistle):[3, 4, 7, 8, 17]

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use *

Issues/Concerns

Clopyralid

(Transline)

Selective, systemic 

for particularly: 

Asteraceae, 

Fabaceae, 

Polygonaceae,

[7] Some effects 

on Apiaceae, 

Solanaceae, 

Violaceae [17]

Off site drift 

may cause 

damage to 

sensitive plants 

up to 300’. 

Little effect on 

grasses.

Apply at 

basal rosette 

stage after 

the most 

leaves have 

emerged. 

Fall 

applications 

will reduce 

spring 

regrowth.

Backpack 

or wick to 

minimize 

drift.

Less persistent than 

picloram. More 

selective than 

picloram. Potentially 

mobile in water. 

Contains 

hexachlorobenzene.

Picloram 

(Tordon)

Restricted Use 

Herbicide

Contains 

hexachlorobenzene.

Selective, systemic 

for many annual 

and perennial 

broadleaf herbs 

and woody plants.

Off site drift 

may cause 

damage to 

sensitive plants 

up to 1000’. 

Also can leak 

out of roots to 

non-targets [4].

Apply at 

basal rosette 

stage after 

the most 

leaves have 

emerged.

Fall 

applications 

will reduce 

spring 

regrowth.

Backpack 

or wick to 

minimize 

drift.

Wait 6 10 12 months 

to reseed since 

picloram is persistent 

in the soil.

More mobile than 

clopyralid. Can move 

offsite through 

surface or subsurface 

water. 

Can be relocated 

through livestock 

urine.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

28

Chemical (for Canadian thistle):[3, 4, 7, 8, 17]

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use *

Issues/Concerns

Glyphosate Broad spectrum, 

non-selective and 

systemic.

Off site drift up 

to 100’ possible. 

Most likely to 

kill non-targets 

including 

grasses.

Adheres to soil 

which lessens

leaching or 

uptake by nontargets.

As above. 

Fall is the 

best season 

since 

translocatio

n to root is 

highest 

then.

Backpack 

or wick to 

minimize 

drift.

Only provides control 

during year of 

application. 

Not mobile in the 

environment.

Will not kill seeds or 

inhibit germination. 

Can reseed more 

quickly than more 

persistent chemicals.

Surfactants can be 

toxic to aquatic 

species.

Rain within 6 hours 

reduces effectiveness.

Chlorsulfuron

(Telar, Glean)

Glean -Selective 

pre-emergent or 

early 

postemergent; 

controls many 

annual, biennial 

and perennial 

broadleaf species.

Telar – selective 

for broadleaf 

species both preand post –

emergent [7]

Off site drift up 

to 900’ possible. 

Safe for most 

grasses.

Could apply 

at budbloom stage 

or to fall 

rosettes.

Backpack 

or wick to 

minimize 

drift.

Aerial 

spraying 

not 

permitted 

under 

standards.

Primarily suppressed 

regrowth and

secondarily reduces 

the number of root 

buds.

Extremely potent.

Damage to non-target 

terrestrial and some 

aquatic plants (at 

peak concentrations) 

plants more possible 

than animals.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.

Some considerations for use of herbicide include [17]:

 Different ecotypes respond differently to the same herbicide, so what is effective in one 

locale, or on one clone, may not be effective in another.

 Vary herbicides used at a site to prevent clones tolerant to one herbicide from becoming 

dominant. Select alternative herbicides with a different mode of action to minimize 

chances for tolerance to build.

 In many habitats, Canada thistle goes dormant shortly after native species, so there is 

only a limited window to apply herbicides when native species will not be affected.

 Herbicide absorption is enhanced in late summer and fall, when plants are in the rosette 

stage as shoot-to-root translocation is greatest at this time.

Monitoring: The best time to annually monitor sites is just before or during the blooming period, 

which corresponds with periods with 14-18 hours of daylight. [17]
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

29

Cynoglossum officinale – Hounds Tongue

Ecological Characteristics of Note

Houndstongue is a biennial or short-lived perennial species, which forms rosettes in the first year 

and flowers in the second. It flowers between May and July. It has a thick branching taproot, 

extending to depths >40 inches. It often occurs in dense stands. Seedlings are usually clustered 

around parent plants in densities of up to 405 seedlings per square foot. Estimates of total seed 

number per plant range from 50 to more than 2,000. Its spiny husk and protruding barbs enable 

long distance dispersal to occur. Seed viability in the soil is relatively short compared to other 

invasive plants. Seed can remain viable above ground on plants for up to two years. 

Houndstongue is most abundant in areas with more than 10 percent bare ground. Germination 

starts in late winter and early spring [2]. A relationship between burrs on cattle and 

houndstongue density in paddocks was shown by De Clerck-Floate in 1997. [29]

Management

Manual: Surface cultivation, digging and hand pulling are considered ineffective means of 

control because plants are capable of regenerating from the root crown. Hand pulling can reduce 

the size of populations up to 85 percent, though, if roots are completely removed. [2]

Mechanical: Severing the root crown 1 to 2 inches below the soil surface with a spade and 

removing top growth can be effective in controlling small infestations when done before 

flowering. Mowing at ground level can reduce re-growth by 60 percent as well as seed 

production in some cases. [18] Plowing is said to control houndstongue, but may not be 

appropriate in most areas.

Biological: Biological controls are being screened for possible use. One is approved in Canada. 

A native bacteria is being tested at Montana State University as an effective biological control as 

well. Spraying the plant with this bacteria interferes with its production of chlorophyll, 

weakening it so it will not resprout the following year. [18]

Cultural: No references to grazing as a management method were found, most likely due to the 

poisonous nature of the plant. Proper livestock grazing that promotes full recovery of desirable 

grass species and litter accumulation was recommended. [2]

Prescribed Fire: In some ecosystems re-establishing historic fire regimes can be effective at 

controlling invasive species, but more research is needed regarding the potential of prescribed 

burning to control houndstongue. [2]
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

30

Chemical (for houndstongue):[2, 3, 4, 7, 8, 17, 18]

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use *

Issues/Concerns

Metsulfuron

(Escort)

Selective for 

broadleaf and 

woody species.

Safest of the 

sulfonylureas on 

grasses.

Off site drift 

may cause 

damage to 

sensitive 

plants up to 

500’. 

Extremely 

potent. 

Most 

sensitive 

species in 

the Lily 

family. 

Mid-June or 

during 

active 

growth. 

Reapplicatio

n may be 

needed the 

first year to 

prevent seed 

production. 

Backpack or 

wick to 

minimize 

drift.

Potentially mobile in water 

or through wind erosion.

Damage to non-target 

terrestrial and some 

aquatic plants (at peak 

concentrations) more 

possible than animals. 

Picloram 

(Tordon)

Restricted Use 

Herbicide

Contains 

hexachlorobenzene

Selective, 

systemic for many 

annual and 

perennial 

broadleaf and 

woody species. 

Systemic.

Off site drift 

may cause 

damage to 

sensitive 

plants up to 

1000’. Also 

can leak out 

of roots to 

non-targets 

[4].

Apply at 

basal rosette 

stage after 

the most 

leaves have 

emerged.

Fall 

applications 

will reduce 

spring 

regrowth.

Backpack or 

wick to 

minimize 

drift.

Wait 6 10 12 months to 

reseed since picloram is 

persistent in the soil.

Can move offsite through 

surface or subsurface 

water.

Can be relocated through 

livestock urine.

Chlorsulfuron

(Telar, 

Glean)[2]

Glean-Selective 

pre-emergent or 

early post 

emergent; controls 

many annual, 

biennial and 

perennial 

broadleaf species.

Telar – Selective 

for broadleaf 

species both preand post-emergent 

[7]

Off site drift 

up to 900’ 

possible. 

Safe for 

most 

grasses.

Apply to 

rosettes, or 

6 to 11 inch 

bolts to 

prevent seed 

production 

completely.

Backpack or 

wick to 

minimize 

drift.

Aerial 

spraying not 

permitted 

under 

standards.

Damage to non-target 

terrestrial and some 

aquatic plants (at peak 

concentrations) possible.

Imazapic

(Plateau)[20]

Selective for 

broadleaf plants 

and some grasses.

Off site drift 

up to 50’ 

possible. 

Over 100’ if 

applied 

aerially.

Apply 

before 

bloom stage.

Backpack or 

wick to 

minimize 

drift.

Even very tolerant nontarget species are likely to 

be damaged. Some 

damage to aquatic plants 

at peak concentrations 

could occur.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

31

Restoration: Houndstongue seedlings have a comparatively low growth rate and are not strongly 

competitive. Interspecific competition can severely reduce the dry weight of first and second 

year plants. Therefore, revegetation can effectively control houndstongue re-introduction, 

although more research is needed.

Prevention is extremely important with houndstongue. The cleaning of cattle and equipment or 

clothing used for treatments when moving from infested to non-infested areas is very effective in 

reducing introductions. [2]
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

32

Cytisus scoparius – Scotch Broom

Ecological Characteristics of Note

Scotch broom can reproduce vegetatively or by seed. Bushes can produce up to 60 seed pods per 

bush by their second year. Only about 45-50 percent of the seeds produced will actually 

germinate. Seed can remain viable up to 80 years if stored correctly and will germinate when 

shad is removed and ground disturbed [53]. Initial growth is rapid for the first 4 to 5 years. 

Broom plants can grow over a meter tall in the first year. Soil disturbance while treating will 

encourage sprouting [17].

Management [17]

Manual: Hand pulling may be used to destroy seedlings or plants up to 1.5 meters tall. It is most 

easily accomplished after a rain when the soil is loose when the root system can be removed in 

its entirety. This will also minimize soil disturbance which encourages germination. As with 

hand pulling, hand digging or hoeing can be effective, but care must be taken to remove all roots. 

Hoeing may be used to expose and desiccate roots and will minimize the damage to roots of 

desirable vegetation. Use of a weed wrench is effective on mid-size plants.

Mechanical: Cutting using various tools or mowers is most effective when done as plants are 

flowering, but before seed set. Clipping low to the ground is best. At this stage, the reserve food 

supply in the roots is nearly exhausted. Brooms will most likely still resprout with this method, 

so repeated treatments will be needed. Return visits in the fall and winter will be necessary.

Biological: Three biocontrols may be present on scotch broom; a twig mining moth, a seed 

weevil and a shoot tip leaf tying moth. One was accidentally released in the 1920s, one was 

purposely released in the 1970’s and one in the 1980’s. While some predation has been noted, 

none have been very effective. They may slow the spread, but do not reduce existing 

populations significantly.

Cultural: In some areas of California, the use of angora and Spanish goats has shown promise for 

effective control. In the Cleveland National Forest, goats were herded for firebreak management 

of brush species over 79,000 acres. Desirable vegetation in weed treatment areas would need to 

be fenced, especially woody vegetation to keep goats from eating it, though. Sheep ae more 

selective than goats, but proper management to avoid soil compaction and movement of seed is 

important. Cattle grazing may not be effective, since it may be considered unpalatable and is 

slightly toxic.

Prescribed fire/flaming: Flaming during the winter months using a propane torch has been shown 

to be effective for smaller plants. Tiger torches used for tar roofing projects have been used. 

Flaming would reduce soil disruption caused by other manual or mechanical removal techniques.

Broadcast burning has been used, but is only effective in combination with other techniques such 

as herbicides. Burning is best followed by herbicide treatment of stumps, subsequent burning to 

exhaust the seed bank and underground reserves and revegetation with other fast growing native 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

33

shrubs. Herbicides could also be used before burning to desiccate the plants so they would burn 

more readily.

Chemical (for scotch broom) [7, 8, 17]:

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use *

Issues/Concerns

Triclopyr

(various 

Garlon 

formulations; 

consisting of 

salts and 

ester)

Selective, 

systemic for 

woody and 

broadleaf 

species. Will 

remain in 

plants until 

they die. 

Growth 

regulating.

Little or no 

impact on 

grasses. Off site 

drift up to 100’ 

possible.

Could inhibit 

ectomychorrizal 

growth.

Late spring 

during active 

growth. If 

too early, 

spring sap 

flow may 

wash off 

chemical.

Paint cut 

stumps or 

incised stem 

within 5-20 

minutes of 

cutting. 

Broadcast 

spraying not 

permitted.

Garlon 4 (ester formulation) 

is more toxic to fish and 

aquatic inverts. 

Offsite movement by water 

possible.

Glyphosate Broad 

spectrum, 

non-selective 

and systemic.

Off site drift up 

to 100’ possible. 

Most likely to 

kill non-targets 

including 

grasses. 

Adheres to soil 

which lessens

leaching or 

uptake by nontargets.

Most 

effective 

when applied 

from 

flowering 

through first 

hard frost.

Backpack or 

wick to 

minimize 

drift.

Provides some control. 

Repeated applications 

necessary.

Rain within 6 hours reduces 

effectiveness.

Picloram 

(Tordon)

Restricted Use 

Herbicide

Contains 

hexachlorobenzene. 

Selective, 

systemic for 

many annual 

and perennial 

broadleaf and 

woody 

species. 

Systemic.

Off site drift may 

cause damage to 

sensitive plants 

up to 1000’. 

Also can leak out 

of roots to nontargets [4].

Apply to 

young plants 

during active 

spring 

growth. 

Moderately 

effective.

Backpack or 

wick to 

minimize 

drift.

Use on cut 

stumps 

caused 

‘flashback’ 

through roots 

between 

treated and 

non-target 

plants [17]

Wait 6 10 12 months to 

reseed since picloram is 

persistent in the soil.

Can move offsite through 

surface or subsurface water.

Can be relocated through 

livestock urine.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

34

Euphorbia esula – Leafy Spurge

Ecological Characteristics of Note

Leafy spurge emerges in early spring. Stem elongation is very rapid as daily temperatures 

increase from May through June. As the growing season progresses, seedlings may appear to 

die, but their underground parts persist and adventitious shoots develop. It is the adventitious 

shoot that matures into a flowering shoot. Flowering forms on the main axis from May through 

July with flowering and seed development again occurring for a short time in the fall, usually 

from auxiliary branches. Seeds may remain dormant for 5 to 8 years following maturity. Seed 

dispersal is by explosive dehiscence up to 4 meters from the plant. Seeds can also float and 

disperse along waterways. Vegetative reproduction occurs from both crown and root buds that 

can overwinter. Seedlings have a remarkable capacity for vegetative reproduction and can 

develop root buds with 7 to 10 days of emergence. Roots have been excavated to a depth of over 

4 meters. [17]

Management

Mechanical: Repeated mowing or hand cutting may be used as a control of seed production, but 

it must be used in conjunction with herbicides for adequate control of stand expansion. Repeated 

mowing or cutting is necessary in a single season. A single cutting will stimulate the 

development of lateral branches and flowering. Repeated mowing could reduce the competitive 

ability of desirable species, though. [17]

Biological: Research is being conducted on at least fifteen insects as possible biological control 

agents. Some success has been found with the flea beetle combined with fall herbicide 

treatments.

Cultural: Grazing by domestic goats or sheep may help control leafy spurge. However favorable 

results are directly related to the grazing regime. Season long grazing by goats is more effective 

than rotational grazing, for example. [2] Multi-species grazing has been advocated for control of 

leafy spurge. This method could only be used when long term grazing is a possibility. Usually, 

in the first two years, sheep are grazed on an area with dense spurge. Starting in year three, 

cattle can be moved in. At year five, monitoring and maintenance grazing can be established.

[40]

In any case an integrated approach is most likely to be successful when treating leafy spurge. A 

combination of mechanical and chemical may produce the most effective results.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

35

Chemical (for leafy spurge) [2,7,17]:

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use * Issues/Concerns

Glyphosate Broad 

spectrum, 

non-selective 

and systemic.

Off site drift up 

to 100’ possible. 

Most likely to 

kill non-targets 

including 

grasses. 

Adheres to soil 

which lessens

leaching/uptake 

by non-targets.

Most 

effective 

when applied 

in spring to 

prevent 

flowering 

and repeated 

in early fall.

Backpack or 

wick to 

minimize 

drift.

Provides some control. 

Repeated applications 

necessary.

Rain within 6 hours 

reduces effectiveness.

Picloram 

(Tordon)

Restricted Use 

Herbicide

Contains 

hexachlorobenzene. 

Selective, 

systemic for 

many annual 

and perennial 

broadleaf and 

woody 

species. 

Systemic.

Off site drift may 

cause damage to 

sensitive plants 

up to 1000’. 

Also can leak out 

of roots to nontargets [4].

Apply in late 

spring when 

flowers and 

seeds are 

developing If 

needed also 

in early fall 

after stems 

have 

developed.

Backpack or 

wick to 

minimize 

drift.

Does not inhibit the 

germination of leafy 

spurge seed.

Wait 6 10 12 months to 

reseed since picloram is 

persistent in the soil.

Can move offsite 

through surface or 

subsurface water.

Can be relocated 

through livestock urine.

Imazapic

(Plateau)[20]

Selective for 

broadleaf 

plants and 

some grasses.

Off site drift up 

to 50’ possible. 

Over 100’ if 

applied aerially.

Apply during 

the fall.

Backpack or 

wick to 

minimize 

drift.

Even very tolerant nontarget species are likely 

to be damaged. Some 

damage to aquatic plants 

at peak concentrations 

could occur.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.

No other methods for control were found in the literature.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

36

Geranium robertianum – Herb Robert

Ecological Characteristics of Note

Herb Robert is a shade tolerant, low growing geranium described as a winter or spring annual, a 

biennial and even as a perennial. It spreads entirely by seeds. The root structure is shallow. 

Each flower produces 5 seeds capable of being ejected 15-20 feet. With adequate moisture, 

seeds begin germinating soon after dispersal. New seedlings appear several times throughout the 

growing season, which is from early spring to late fall and even into early winter. It has the 

ability to overwinter as seeds or as a rosette. Disturbance is not a requirement for the 

establishment of this species and it can become dominant in the understory of a forest 

community. [23]

Management

Manual: Hand pulling is quick and easy, due to the shallow roots, but stems are brittle, so care 

must be take to get the entire plant. This method is probably the most effective, but care must be 

taken not to pull desirable vegetation since the plant will mingle with natives. [23]

Biological: Although one species of aphid is known from its native range to feed specifically on 

the species, biocontrol may not be a true option because of the economic value of other 

ornamental geraniums.

Chemical (for herb Robert) [23]:

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use *

Issues/Concerns

Glyphosate Broad 

spectrum, 

non-selective 

and systemic.

Off site drift up 

to 100’ possible. 

Most likely to 

kill non-targets 

including 

grasses. 

Adheres to soil 

which lessens

leaching or 

uptake by nontargets.

Treat at low 

rates early in 

the season.

Backpack or 

wick to 

minimize 

drift

Has been 

used with or 

without a 

surfactant 

effectively. 

Complete control may 

require re-treatment. 

Rain within 6 hours 

reduces effectiveness.

Careful application is 

imperative since this 

species mingles with 

natives and desirable 

vegetation.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.

No other methods for control were found in the literature.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

37

Hedera Helix – English Ivy

Ecological Characteristics of Note

English ivy reproduces vegetatively and by seed, which is dispersed primarily by birds. New 

plants grow easily from cuttings or from stems making contact with the soil. Compounds in 

English ivy are somewhat toxic and include glycosides that cause vomiting, diarrhea, nervous 

conditions and dermatitis in sensitive individuals.

Management

Manual: Effective for small areas or when a large volunteer workforce is available.

 Remove from trees first. Cut the vines at shoulder height and ankle height and 

strip away from tree. Next pull up roots as much and as deep as possible. Keep 

extending the pulled area around the base of the tree until at least six feet is 

cleared. [12]

 When pulling ground ivy get all the roots you can as well. Use a shovel to extract 

root mats. Do not leave pulled plants on the ground as they can continue to grow. 

[13]

 Use crews to roll ‘ivy logs’ pulling a line of ivy, rolling and pulling again. On 

slopes use the cookie cutter method, removing ivy for a three foot circle. Plant 

with a native tree species. [12]

 Return annually. The second year should require only about 10 percent of the 

first year’s effort. [12]

 At the very least, clip any branches with blossoms to prevent the spread of seed 

by birds. [53]

Mechanical: String trimming prior to herbicide application was recommended.

Biological: No biological controls are currently available.

Chemical (for English ivy) [3, 8, 11, 12, 13, 14]:

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use *

Issues/Concerns

Triclopyr

(various 

Garlon 

formulations; 

consisting of 

salts and 

ester)

Selective, 

systemic for 

woody and 

broadleaf 

species. Will 

remain in 

plants until 

they die. 

Growth 

regulating.

Little or no 

impact on 

grasses. Off site 

drift up to 100’ 

possible.

Could inhibit 

ectomychorrizal 

growth.

Any time 

as long as 

temps are 

above 55 

degrees. 

Fall and 

winter 

minimize 

impacts.

Paint cut 

vines. 

Backpack 

spray to 

minimize 

drift.

Application rates vary (15-

30%) of Garlon 4 [3]. 

Effectiveness varied. 

Possibility of absorption to 

the host tree depending on 

thickness of bark. Could 

be used on string trimmed 

ground growth depending 

on size of infestation. 

Garlon 4 (ester 

formulation) is more toxic 

to fish and aquatic inverts. 

Offsite movement by water 

possible.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

38

Chemical (for English ivy) [3, 8, 11, 12, 13, 14]:

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use *

Issues/Concerns

Glyphosate Broad 

spectrum, 

non-selective 

and systemic.

Off site drift up 

to 100’ possible. 

Most likely to 

kill non-targets 

including 

grasses. 

Adheres to soil 

which lessens

leaching or 

uptake by nontargets.

Any time 

as long as 

temps are 

above 55 

degrees. 

Fall and 

winter 

minimize 

impacts.

Broadcast 

at diluted 

rate or 

paint on cut 

vine at full 

strength.

Provides some control. 

More effective after string 

trimming. If spraying on 

leaves, the waxy cuticle on 

leaf must be broken at the 

leaf edge.

Rain within 6 hours 

reduces effectiveness.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.

No other methods of control were found in the literature.

Restoration: After treating English ivy. rake disturbed areas and seed or plant cleared areas with 

natives or sterile wheatgrass [15]. Or mulch cleared areas with 8” thick mulch.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

39

Hieracium aurantiacum – Orange Hawkweed, Hieracium pretense

– Meadow or Yellow Hawkweed, Hieracium vulgatum – Common 

Hawkweed

Ecological Characteristics of Note

These hawkweeds are perennials with shallow fibrous root systems and rhizomes. They can 

reproduce by seed or vegetatively. Orange and yellow hawkweeds also produce stolons that can 

produce new plants. Yellow or meadow hawkweed can also develop new plants from the root 

buds [18]. Although, most populations begin from seed, these species will then aggressively 

spread through rhizomes or stolons. In a new site, less than 2 percent of the plants come from 

seedlings. Once established, vigorous stolon growth quickly expands the colony, forming dense 

patches with as many as 3,200 plants per square yard. [24]

Management

Manual: It is possible to control small infestation by carefully digging out rosettes. Any 

breakage of the shallow roots and rhizomes must be avoided. Even a small piece left in the soil 

may develop into a new plant. Anything removed must be taken off site and either burned or put 

in a refuse pile. Some authorities do not recommend manual removal at all. [18]

Mechanical: Mowing is considered ineffective. Cultivating and rotating in an annual crop works 

in agricultural situations, but this method has little application on Forest Service lands. 

Mechanical control procedures are generally not successful since any disturbance to the plant can 

stimulate the growth of new plants from fragmented roots, stolons and rhizomes. Such 

disturbance can re-distribute the hawkweeds and increase the rate of spread. [18]

Biological: No biological controls are currently available for release on the hawkweeds. The 

magnitude and complexity of these species suggests that biological control may not be 

successful.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

40

Chemical (for hawkweeds):[7,18]

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use *

Issues/Concerns

Clopyralid

(Transline)

w/ soluble 

nitrogen 

fertilizer

Selective, systemic 

for particularly: 

Asteraceae, 

Fabaceae, 

Polygonaceae,

[7] Some effects on 

Apiaceae, 

Solanaceae, 

Violaceae [17]

Off site drift 

may cause 

damage to 

sensitive 

plants up to 

300’. Little 

effect on 

grasses.

Apply after 

most basal 

leaves emerge 

but before 

buds form. 

Fall treatments 

may also be 

helpful, but 

research is 

limited.

Backpack 

or wick to 

minimize 

drift.

Less persistent than 

picloram. More 

selective than 

picloram. 

Potentially mobile 

in water. Contains 

hexachlorobenzene.

Adding fertilizer 

enhances the 

competitive ability 

of desirable 

species.

Picloram 

(Tordon)

Restricted 

use pesticide

Contains 

hexachlorobenzene

Selective, systemic 

for many annual 

and perennial 

broadleaf herbs and 

woody plants.

Off site drift 

may cause 

damage to 

sensitive 

plants up to 

1000’. Also 

can leak out 

of roots to 

non-targets 

[4].

Apply after 

most basal 

leaves emerge 

but before 

buds form. 

Fall treatments 

may also be 

helpful, but 

research is 

limited.

Backpack 

or wick to 

minimize 

drift.

Wait 6 10 12 

months to reseed 

since picloram is 

persistent in the soil.

More mobile than 

clopyralid. Can 

move offsite 

through surface or 

subsurface water. 

Can be relocated 

through livestock 

urine.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.

No other methods of control were found in the literature.

Restoration: After herbicide treatment, applying soluble nitrogen fertilizer can be effective in 

increasing the competitive abilities of grass. Fertilizing, when applied within 1 to 2 weeks of 

herbicide treatment is an important tool for restoring bare ground more quickly after the 

hawkweeds die back. [18, 37]
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

41

Hypericum perforatum – St. Johnswort

Ecological Characteristics of Note

St. Johnswort is a taprooted perennial weed which reproduces by seeds and short runners. The 

taproot may reach depths of 4 to 5 feet. Lateral roots grow 2 to 3 inches beneath the soil surface 

but may reach depths of 3 feet. Flowering begins in May and continues through September. 

Developing capsules become very sticky and contain 400 to 500 seeds. Seeds may remain viable 

in soil for up to 10 years. [18]

Management [18,30]

Manual: Hand pulling or digging of young plants in small, isolated infestations may be 

effective. Repeated treatments will be necessary because lateral roots can give rise to new 

plants. Pulled or dug plants must be removed from the area and burned to prevent vegetative 

regrowth.

Mechanical, Prescribed Burning, Cultural: Mowing is ineffective, but may discourage the spread 

of the plant if done before seeds form. Burning may increase the density and vigor of this 

species. Livestock avoid this species which can make them sensitive to sunlight, so grazing 

would select for the increase of this species.

Biological: Four biocontrols are currently recommended in Montana. Several have been 

released in the Pacific Northwest since the late 1940’s. Effectiveness varies by climactic 

conditions. The insects are more effective in areas with a Mediterranean climate rather than cool 

and damp since the native range of the species has a similar climate. [25] The Klamath weed 

beetle (Chrysolina quadrigemina) has had good success and another beetle (C. hyperici) is better 

adapted to wetter sites. Agrilus hyperici, a root boring beetle has become established in eastern 

Washington and northern Idaho
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

42

Chemical (for St. Johnswort)[7,18,20, 50]:

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use *

Issues/Concerns

Metsulfuron

(Escort) [20}

Selective for 

broadleaf and 

woody species.

Safest of the 

sulfonylureas 

on grasses.

Off site drift 

may cause 

damage to 

sensitive plants 

up to 500’. 

Most sensitive 

species in the 

Lily family.

Apply after 

plants have 

fully 

emerged and 

are in active 

growth.

Backpack or 

wick to 

minimize 

drift.

Potentially mobile 

in water or through 

wind erosion. 

Damage to some 

aquatic plants 

possible at peak 

concentrations 

Picloram

(Tordon)

Restricted Use 

Herbicide

Contains hexachlorobenzene

Selective, 

systemic for 

many annual 

and perennial 

broadleaf herbs 

and woody 

plants.

Off site drift 

may cause 

damage to 

sensitive plants 

up to 1000’. 

Also can leak 

out of roots to 

non-targets [4].

Apply in 

early growth 

stage before 

bloom.

Backpack or 

wick to 

minimize 

drift.

One application 

may be effective 

for 2 or more 

years. Wait 6 to 

12 months to 

reseed since 

picloram is 

persistent in the 

soil.

More mobile than 

clopyralid. Can 

move offsite 

through surface or 

subsurface water.

Can be relocated 

through livestock 

urine

Glyphosate/

(RoundUp, Rodeo 

etc.)/ Inhibits 

three amino acids 

and protein 

synthesis.

A broad 

spectrum, nonselective 

translocated 

herbicide with 

no apparent 

soil activity.

Off site drift 

damage to 

sensitive species 

up to 100’ 

possible

Off site drift up 

to 100’ possible. 

Most likely to 

kill non-targets 

including 

grasses. 

Adheres to soil 

which lessens 

leaching or 

uptake by nontargets.

In 

spring/summ

er, when 

plants are 

growing 

rapidly. 

Backpack or 

wick to 

minimize 

drift.

Aquatic 

formulation can be 

used near water. 

Rain within 6 

hours of 

application may 

reduce 

effectiveness. 

Complete control 

may require retreatment.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

43

Ilex aquifolium – English Holly

Ecological Characteristics of Note

With this dioecious species, female trees must grow within the pollinator range of the male trees. 

Birds usually spread the seed of this species and it also vegetatively reproduces by suckering or 

layering, where branches root into the ground.

Management

Mechanical: It was very difficult to find removal techniques for English holly. The ones listed 

are from Australia and New Zealand. [32, 33] Mechanical removal of branches is required for 

safe access to the holly stems. It is recommended that lower unlayered branches be removed to 

above head height. After this is accomplished all layered branches (those with roots 

underground) should be removed from the stem and carefully pulled out of the ground. Having 

moist soils will make this easier to accomplish. Be sure to clear the leaf litter away from the 

base of the trees to ensure that no buried branches have been overlooked. All branches removed 

must not be left on the ground as they will re-root.

Mechanical removal is combined with chemical treatments in New Zealand and Australia.

Chemical (for English holly) [32,33]:

Herbicide Selectivity Effects to 

Natives When to Apply Method to Use *

Issues/Concerns

Glyphosate 

(RoundUp)

Broad 

spectrum, 

non-selective 

and systemic

Off site drift 

up to 100’ 

possible. 

Most likely 

to kill nontargets 

including 

grasses.

Adheres to 

soil which 

lessens 

leaching or 

uptake by 

non-targets.

In 

spring/summer, 

when plants are 

growing rapidly.

Paint along 

horizontal cut 

stump. 

Drilling and 

injecting into 

the stem is 

used in NZ 

and 

Australia; 

please check 

label!

Frilling of 

bark and 

painting.

Rain within 6 hours 

reduces 

effectiveness.

Some formulations 

can be used over 

water.

Complete control 

may require retreatment.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.

Tordon is used in NZ and Australia, but was not analyzed in the risk assessments, nor labeled for cut stump, 

injection or frilling.

Garlon may be useful for this species, but the species was not listed on the label.

No other methods of control were found in the literature.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

44

Lathyrus latifolius – Everlasting Peavine

Ecological Characteristics of Note

This pea has a sprawling and climbing nature. It has escaped from gardens and is probably still 

valued as a garden specimen by some.

Management

Manual/Mechanical: Grubbing can be done using a spade or shovel to loosen the soil and dig up 

the root system. Re-sprouting may occur if the entire root system is not removed. Rotary or 

string trimming can cut back flowering, but the plant will re-grow after trimming.

Chemical (for everlasting peavine) [36]:

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use *

Issues/Concerns

Glyphosate 

(RoundUp)

Broad 

spectrum, 

non-selective 

and systemic

Off site drift 

up to 100’ 

possible. 

Most likely 

to kill nontargets 

including 

grasses. 

Adheres to 

soil which 

lessens 

leaching or 

uptake by 

non-targets.

In 

spring/summer, 

when plants are 

growing rapidly.

Backpack or 

wick to 

minimize 

drift

Rain within 6 hours 

reduces effectiveness. 

Some formulations 

can be used over 

water.

Complete control may 

require re-treatment.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.

No other methods of control were found in the literature.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

45

Lepidium latifolium – Perennial Pepperweed

Ecological Characteristics of Note

Perennial pepperweed produces dense stands with stems reaching up to 3 feet in height, but even 

up to 8 feet in wet areas. Its dense cover blocks sunlight from reaching the soil, thus suppressing 

the growth of other plants. Roots are enlarged at the soil surface in a woody crown and can 

extend at times into the water table. Roots as deep as 3 meters have been observed. The species 

is a prolific seed producer, capable of producing more than six billion seeds per acre. Seeds lack 

a hard cover, though, therefore viability may be short. Shoots flower and fruit in late spring and 

continue throughout much of the summer. Seeds either fall from the pod or can remain in pods 

until the following season. In addition to seeds, the species can spread by rhizomes which may 

grow to a length of ten feet. [17, 18]

Management 

With the exception of continual flooding, no non-chemical treatments have been found to 

effectively control this species. 

Biological: No biological agent is approved for perennial pepperweed. The risk is too great of 

releasing a control that would attack a valuable crop.

Cultural: Grazing may be effective by cattle, sheep or goats. There is potential for poisoning, 

which is currently being evaluated. [17]

Chemical (for perennial pepperweed) [7,17,18]

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use * Issues/Concerns

Metsulfuron

(Escort) plus 

surfactant

Selective for broadleaf 

and woody species.

Safest of the 

sulfonylureas on 

grasses.

Off site drift 

may cause 

damage to 

sensitive plants 

up to 500’. 

Extremely 

potent. Most 

sensitive 

species in the 

Lily family.

Apply 

during 

bud to 

early 

bloom 

stage.

Backpack or 

wick to 

minimize 

drift.

Aerial 

spraying not 

permitted 

under 

standards.

Potentially mobile 

in water or through 

wind erosion.

Damage to nontarget terrestrial and 

some aquatic plants 

(at peak 

concentrations) 

more possible than 

animals.

Chlorsulfuro

n

(Telar, 

Glean) plus 

surfactant

Glean-Selective preemergent or early post 

emergent; controls 

many annual, biennial 

and perennial broadleaf 

species.

Telar – Selective for 

broadleaf species both 

pre- and post-emergent 

[7]

Off site drift up 

to 900’ 

possible. 

Safe for most 

grasses.

Apply 

during 

bud to 

early 

bloom 

stage.

Backpack or 

wick to 

minimize 

drift.

Aerial 

spraying not 

permitted 

under 

standards.

Some soil residual.

Damage to nontarget terrestrial and 

some aquatic plants 

(at peak 

concentrations) 

possible.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

46

Chemical (for perennial pepperweed) [7,17,18]

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use * Issues/Concerns

Imazapyr/

(Arsenal)

Broad spectrum, nonselective pre- and postemergent for annual 

and perennial grasses 

and broadleaved 

species.

Off site drift 

may cause 

damage to 

sensitive plant 

species up to 

500’. 

Apply 

during 

bud to 

early 

bloom 

stage.

Backpack or 

wick to 

minimize 

drift.

High potential for 

leaching. Highly 

mobile and 

persistent. Residual 

toxicity up to 

several years. Can 

leak from roots of 

targeted species to 

non-targeted 

species.

Glyphosate 

(Rodeo or 

Accord)

For sites 

near water.

Broad spectrum, nonselective and systemicOff site drift up 

to 100’ 

possible. Most 

likely to kill 

non-targets 

including 

grasses. 

Adheres to soil 

which lessens

leaching or 

uptake by nontargets.

Apply 

during 

bud to 

early 

bloom 

stage. 

Best if 

done 

after 

early 

season 

mowing.

Backpack 

with 

adjustable 

spray 

nozzle.

Rain within 6 hours 

reduces 

effectiveness. 

Some formulations 

can be used over 

water. 

Complete control 

may require retreatment.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.

An integrated method of early mowing and herbicide treatment can be effective. This strategy 

involves mowing stems at the flowerbud stage, followed by a herbicide application to 

resprouting stems when translocation patterns favor accumulation below ground. [17]

Restoration: To successfully manage perennial pepperweed, competitive vegetation must be 

established immediately after its control to prevent re-invasion. [18]
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

47

Linaria vulgaris – Yellow Toadflax, Linaria genistifolia ssp. dalmatica 

– Dalmation toadflax

Ecological Characteristics of Note 

A toadflax plant may have a taproot as deep as one meter. Horizontal roots may grow to several 

meters long and can develop adventitious buds that may form independent plants. Once 

established both species can suppress other vegetation mainly be intense competition for limited 

soil water. Mature plants are particularly competitive with winter annuals and shallow-rooted 

perennials. Seeds can remain dormant for up to ten years. Both are quick to colonize open sites 

and are capable of adapting growth to a wide variety of environmental conditions.

Management [17]

Manual: Hand pulling can be very effective if staff or volunteers are available for persistent 

treatment. Pulling teams in nature preserves can easily eliminate plants in early June or when 

flowers are first emerging. This makes locating the species easy. Plants can be removed in large 

infestations to avoid a mulching effect on desirable species, but they can also be left on the 

ground in smaller infestations. By the third year in one study, plants were noticeably smaller and 

lower in vigor. It can take up to ten years for total control.

Cutting toadflax stands in the spring or early summer is an effective way to eliminate plant 

reproduction. However, the long dormancy of toadflax seeds requires that the process be 

repeated annually for up to ten years.

Mechanical: Mowing can reduce reserves, but is only a temporary solution since it does not 

reduce rhizome growth.

Biological: Five insects have been approved by APHIS for release. One species, a shoot and 

flower feeding beetle is primarily found in Canada where it was accidentally released. It has 

reduced total seed production in some stands. Calophasia lunula, a defoliating moth was 

released in several western states including Washington and Oregon. It failed to establish in 

most sites, but is widely distributed in eastern Washington. Cold temperatures may effect this 

species. Two small root boring moths had little effect. Some seed weight reduction was noted, 

but root mining in the winter resulted in doubling of stem production. A seed eating weevil 

(Gymnaetron antirrhini) can also reduce seed production and is now established in both Oregon 

and Washington. None of these species are considered highly effective.

Cultural: Intensive cultivation can be successful if repeated every 7 to 10 days, but may not be 

applicable in most areas. Grazing does not control any toadflax species. 

Prescribed Burning: Prescribed burning is not effective since it does not impact root buds or 

buried seed.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

48

Chemical (for toadflaxes) [7, 17, 20]:

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use *

Issues/Concerns

Picloram 

(Tordon)

Restricted Use 

Herbicide

Contains 

hexachlorobenzene

Selective, 

systemic for 

many annual and 

perennial 

broadleaf and 

woody species. 

Systemic.

Off site drift 

may cause 

damage to 

sensitive 

plants up to 

1000’. Also 

can leak out 

of roots to 

non-targets 

[4].

Apply to 

actively 

growing 

toadflax in 

the spring 

before 

bloom or in 

late summer 

or fall 

during 

regrowth.

Backpack or 

wick to 

minimize 

drift.

(Fall 

applications 

at lower rates 

are especially 

effective 

when made 

shortly after 

the first 

killing frost.

Wait 6 10 12 months 

to reseed since 

picloram is persistent 

in the soil.

Can move offsite 

through surface or 

subsurface water.

Can be relocated 

through livestock 

urine.

Chlorsulfuron

(Telar, Glean)

Glean-Selective 

pre-emergent or 

early post 

emergent; 

controls many 

annual, biennial 

and perennial 

broadleaf 

species.

Telar – Selective 

for broadleaf 

species both preand postemergent [7]

Off site drift 

up to 900’ 

possible. 

Safe for 

most 

grasses.

Apply to 

actively 

growing 

toadflax in 

the spring or 

fall.

Backpack or 

wick to 

minimize 

drift.

Aerial 

spraying not 

permitted 

under 

standards.

Some soil residual. 

Damage to non-target 

terrestrial and some 

aquatic plants (at peak 

concentrations) 

possible.

Imazapic

(Plateau)[20]

Selective for 

broadleaf plants 

and some 

grasses.

Off site drift 

up to 50’ 

possible. 

Over 100’ if 

applied 

aerially.

Apply 

during the 

fall.

Backpack or 

wick to 

minimize 

drift.

Even very tolerant 

non-target species are 

likely to be damaged. 

Some damage to 

aquatic plants at peak 

concentrations could 

occur.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.

Restoration: The recovery potential of areas that have been cleared of toadflax is very high. 

Communities that are in good condition may recover without replanting of desirable species as 

long as follow up control visits are conducted annually. However, replanting can help accelerate 

recovery. [17]
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

49

Lythrum salicaria – Purple Loosestrife

Ecological Characteristics of Note

Purple loosestrife has an extended flowering season from June to September. A mature plant 

may have as many as thirty flowering stems capable of producing an estimated two to three 

million seed per year. It also readily reproduces vegetatively at a rate of about 1 foot per year. [3]

Management

Manual: Hand-removal is only recommended for small populations or isolated stems. Pull 

before seed is set. The entire rootstock must be pulled out. Remove uprooted plants and broken 

stems from the area since they can resprout. Winter pulling has been found by some to be most 

effective. [16]

Biological: Biological control is considered the most likely candidate for effective long term 

control of large infestations. As of 1997, three agents have been approved by APHIS. [3]

Chemical (for purple loosestrife) [7, 8, 16, 17]:

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use *

Issues/Concerns

Glyphosate 

(Rodeo or 

Accord)

Broad 

spectrum, 

nonselective 

and 

systemic

Off site drift up 

to 100’ possible. 

Most likely to 

kill non-targets 

including 

grasses. 

Adheres to soil 

which lessens

leaching or 

uptake by nontargets.

Apply to 

actively 

growing 

plants at full 

flowering 

stage.

Backpack 

with 

adjustable 

spray 

nozzle or 

cut and 

paint stems.

Spray may take several 

times per season. 

For cut and paint, cut 

stems high, below 

inflorescence, so that plant 

will keep growing and 

absorb more.

A PVC applicator can be 

designed to wipe stem and 

cut. Also, a glove 

technique using nitrile or 

latex gloves on both hands 

covered with a fleecy, 

cotton glove can be used to 

wick up the top 1/3 of a 

plant after flowerheads are 

removed.[16]

Rain with 6 hours reduces 

effectiveness. Surfactants 

can be damaging to aquatic 

species.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.

No other methods of control were found in the literature
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

50

Phalaris arundinacea – Reed Canarygrass

Ecological Characteristics of Note

Reed canarygrass is a robust, cool season, sod-forming perennial that produces culms through 

creeping rhizomes. The species is morphologically variable and more than ten infraspecific 

categories (varieties, subspecies, forms and races) have been described. It is very tolerant of 

freezing temperatures and begins to grow early in the spring, therefore it can outcompete many 

other species. Reed canary grass is rarely fully eradicated and requires yearly, if not monthly 

attention.

Some debate exists on whether this species is native or a descendent of non-native cultivars or 

the vigorous result of crosses between cultivated varieties and native strains. Early botanical 

collections from the inland Pacific Northwest predated settlement of the area by people of 

European descent. Cultivars have been widely introduced for forage and erosion control. [17]

Management [17]

Manual: Removal by hand pulling is practical only for small stands and requires a large time 

commitment. It can be effective if done over the entire population 2 to 3 times per year for five 

years. Covering populations with black plastic may work as long as shoots are not allowed to 

grow beyond the plastic. It may take over two years to be effective, though, and re-seeding will 

be necessary.

Mechanical: Mowing or cutting can be effective, but again must be done multiple times in one 

year. 

Biological: No biocontrol agents for reed canarygrass are currently known.

Cultural: Discing and plowing can be effective especially after herbicide treatment but may not 

be appropriate in most situations. Grazing may be effective but the palatability of the reed 

canarygrass is questionable.

Prescribed burning: Fire may be effective in highly productive wetlands where a healthy seed 

bank of fire adapted species will readily colonize after burning. Lower quality areas may still be 

burned, but a more frequent cycle (every two to three years) may be required. The timing of 

burns is important. Early spring burns only accelerate growth, while late spring burns can 

weaken stands. Late autumn burns can also be beneficial.

Biological: No biocontrols have been identified for this species.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

51

Chemical (for reed canarygrass) [8, 17]:

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use *

Issues/Concerns

Glyphosate 

(Rodeo or 

Accord)

Broad 

spectrum, 

non-selective 

and systemic

Off site drift 

up to 100’ 

possible. 

Most likely to 

kill nontargets 

including 

grasses. 

Adheres to 

soil which 

lessens

leaching or 

uptake by 

non-targets.

Apply in 

early spring 

when just 

sprouting and 

before other 

wetland 

species 

germinate.

Backpack 

with 

adjustable 

spray nozzle.

Application 

followed in 

two to three 

weeks by 

prescribed 

burning has 

been 

effective.

Rain within 6 hours 

reduces effectiveness. 

Some formulations 

can be used over 

water.

Complete control may 

require re-treatment.

Sulfometuron 

methyl (Oust)

Broad 

spectrum preand postemergent 

herbicide for 

both 

broadleaf 

species and 

grasses.

Offsite drift 

may damage 

sensitive 

plants up to 

900’. 

Apply to preemergent or 

early postemergent 

plants. 

Backpack 

with 

adjustable 

spray nozzle.

Highly mobile by 

water or by wind 

erosion. Substantial 

damage has occurred 

to croplands in both an 

arid and wet regions.

Damage to some 

aquatic plants possible 

at peak concentrations.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

52

Polygonum cuspidatum – Japanese Knotweed

Ecological Characteristics of Note

Seeds do not appear to be a significant method of reproduction for this species in the United 

States. The primary mode is through extensive rhizomes which can reach 15-20 meters in 

length. Dispersal can occur when rhizome fragments are washed downstream. Rhizomes can 

regenerate even if buried up to 1 meter deep and have been observed growing through two inches 

of asphalt. Shoots generally begin to emerge in April and growth rates exceeding 8 centimeters 

per day have been recorded. [17]

Note: Hybridization is occurring. The treatments suggested are specifically for Japanese 

knotweed only. More literature review is needed for hybrid management or giant knotweed 

management.

Management [17, 39]

Manual: Digging out the rhizomes of this species is effective for small infestations or in 

environmentally sensitive area where herbicides cannot be used. It is extremely labor intensive 

and tends to spread the rhizome fragments and promote disturbance so it is not highly 

recommended. All plant parts should be removed from the site.

Mechanical: Cutting may be effective if done repeatedly. Every 2-3 weeks from April through 

August will reduce rhizome reserves. It does not come highly recommended. Hand cutting or 

weedeater/mowing have been used.

Covering, particularly in conjunction with cutting, may be useful in smaller stands. Several 

layers of black plastic or shade cloth weighted down by blocks, mulch or stones may work. This 

should be done either after cutting or when plants are fully grown for the season since this 

species is capable of emerging up through asphalt. No reports of successful long term control 

using covering have been found.

Biological: Biocontrols are still being researched in this species native habitat in Japan.

Cultural: Goats are reported to eat knotweed and in some limited circumstances may be an 

option similar to intensive mowing. They will eat desirable vegetation, therefore exclosures will 

need to be installed.

No other methods of control were found in the literature.

Integrated approach: Cutting or pulling in combination with herbicide is most effective since the 

manual/mechanical treatments will encourage the plant to send up new shoots. The more shoots 

per linear foot of root, the more likely you will be able to physically pull them out, exhaust their 

reserves or kill them with herbicide (see next page).
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

53

Chemical (for Japanese knotweed) [7,8,17,27]:

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use *

Issues/Concerns

Glyphosate 

(Rodeo)

Broad 

spectrum, 

nonselective and 

systemic

Off site drift up 

to 100’ possible. 

Most likely to kill 

non-targets 

including grasses.

Adheres to soil 

which lessens

leaching or 

uptake by nontargets.

Cutting and 

injection:

Most effective 

in fall when 

leaves are 

translocating to 

rhizomes. 

Could follow a 

prior cut in late 

spring or early 

summer.

Foliar spray:

When plants 

are 1 -2 meters 

tall.

Best if 

following a 

prior cut in 

spring.

1. Cut and 

paint stems. 

Cut between 

first and 

second 

internode then 

deliver into 

‘well’ created.

2. Stem 

injection 

(check 

label)**

below first or 

second node 

[27].

3. Backpack 

with 

adjustable 

spray nozzle. 

On young 

plants; may 

take more 

applications 

than other 

methods.

Rain with 6 hours 

reduces effectiveness.

Surfactants can be 

damaging to aquatic 

species.

Use formulations 

approved for use over 

water.

Low concentrations 

(<5%) may be most 

effective since higher 

concentrations can 

topkill the plants too 

fast to get the 

herbicide down to the 

roots (check with Mt. 

Baker – Snoqualamie 

on this or Portland 

area Nature 

Conservancy).

Triclopyr

(various 

Garlon 

formulations; 

consisting of 

salts and 

ester)

Selective, 

systemic for 

woody and 

broadleaf 

species. 

Will remain 

in plants 

until they 

die. Growth 

regulating.

Little or no 

impact on 

grasses. Off site 

drift up to 100’ 

possible.

Could inhibit 

ectomychorrizal 

growth.

Most effective 

in fall when 

leaves are 

translocating to 

rhizomes. 

Could follow a 

prior cut in late 

spring or early 

summer [27]

Cut and paint 

stems. Cut 

between first 

and second 

internode then 

deliver into 

‘well’ created 

[27]

Garlon 4 (ester 

compound) is toxic to 

fish and aquatic 

invertebrates. Amine 

formulations may be 

used near or over 

water. Offsite 

movement by water 

possible.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.

** Stem injection is only approved by the EPA in the state of Oregon and only for the product, Aquamaster. Approval 

for Rodeo should be available soon.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

54

Potentilla recta – Sulfur Cinquefoil

Ecological Characteristics of Note

Sulfur cinquefoil is a long-lived, taprooted perennial herb that typically flowers from late May to 

mid July. It reproduces primarily through seed; a single plant can produce thousands of seeds 

annually and it can be spread by roots if they are moved by tillage or on soil-moving equipment 

[41]. Seeds are dispersed primarily by wind from late summer through fall. Seeds appear to 

remain viable in the soil for more than four years, though studies specifically addressing 

seedbank persistence are lacking. In western North America, sulfur cinquefoil invades native 

forest, shrub and grassland plant communities as well as disturbed habitats that typically harbor 

weeds [17]. It can dominate a site within 2 to 3 years. New shoots can develop annually from 

the outer portion of the main root allowing a plant to live for extended periods as long as 20 

years [2]. 

Management 

Manual: Hand-digging may effectively control small infestations if the root crowns are 

completely removed. [41, 17]

Mechanical: Mowing is not an effective control method. [41, 17]

Biological: There are no approved biological controls for P. recta. Due to the plant’s close 

genetic relationship to native Potentilla species and to cultivated strawberries, finding a host 

specific biocontrol agent for P. recta is difficult. [17]

Cultural: Grazing appears to be ineffective in controlling sulfur cinquefoil, as the plant can still 

flower and produce seeds even when heavily grazed. Improper cattle grazing of infested areas 

may accelerate sulfur cinquefoil dominance if grasses and forbs are selectively removed. 

Ingestion of seed heads or attachment of seeds to the bodies or hooves of animals during grazing 

of infested sites may lead to establishment of new colonies if seeds are deposited in uninfested 

areas with grazing migration .[17] Tilling followed by seeding with desired vegetation may be 

effective in agricultural settings but is not practical for most natural areas. [17]

Prescribed Fire: Prescribed fire used alone does not appear to be effective, and may in fact 

increase sulfur cinquefoil recruitment. The use of prescribed fire as part of an integrated 

approach has not yet been studied. [17]
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

55

Chemical: Sulfur cinquefoil will re-establish within three to four years of herbicide treatment, so 

repeated applications are needed for long-term control. [43]

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use* Issues/Concerns

Picloram 

(Tordon) 

*considered 

most effective 

[17]

Selective, 

systemic for 

many annual 

and perennial 

broadleaf and 

woody species. 

Systemic.

Off site drift 

may cause 

damage to 

sensitive plants 

up to 1000’. 

Also can leak 

out of roots to 

non-targets [4].

In fall or 

spring prior 

to late bud 

stage [20].

Backpack or 

wick to 

minimize drift. 

Broadcast 

spray may be 

necessary for 

large 

infestations.

On dry sites 

Picloram is 

preferred because 

its residual activity 

will inhibit new 

plants from 

establishing from 

the seed bank [17]

Escort 

(metsulfuron) 

[41]

Selective for 

broadleaf and 

woody species.

Safest of the 

sulfo-nylureas 

on grasses.

Off site drift 

may cause 

damage to 

sensitive plants 

up to 500’. 

Extremely 

potent. Most 

sensitive 

species in the 

Lily family.

Apply after 

plants have 

fully 

emerged 

and are in 

active 

growth 

[20].

Backpack or 

wick to 

minimize drift. 

Broadcast 

spray may be 

necessary for 

large 

infestations

May cause grass 

injury.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.

Restoration: If sulfur cinquefoil populations are reduced (i.e. by herbicide, hand-digging), native 

plants are usually able to rapidly recolonize sites if sufficient native seed is still viable in the soil. 

Seeding of native species under adequate environmental conditions, reducing grazing pressure, 

and continued spot herbicide re-treatments, will result in a more rapid and stable restored native 

plant community. [17]
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

56

Rubus discolor – Himalayan Blackberry

Ecological Characteristics of Note

Canes of Himalayan blackberry can grow to lengths of up to 7 meters in a single season. Once 

first year canes have arched over and hit ground, daughter plants can develop where cane apices 

have rooted. Canes produce berries in the second year and then die, senescence commencing 

near the middle or at the apices of canes without daughter plants. Canes can continue to grow in 

the center of thickets adding to their impenetrable mass. The root crown can be up to 20 

centimeters in diameter from which many lateral roots can grow. Depths of 90 centimeters and 

lengths up to 10 meters have been documented. [17]

Thickets can produce 7,000 to 13,000 seeds per square meter. Dispersed seed remains viable for 

several years with germination increasing after the first year. Seed germinate mainly in the 

spring. Plants growing in shade do not produce seed and germination is reduced, but still occurs,

where full sunlight is not available. [17]

Management [17]

Manual: Best if the massive root crown is fully dug out. This method works best where native 

vegetation is an issue and/or where a large workforce of volunteers is available. After digging 

out root crowns, return in a year and remove new plants. Typically about 1⁄4 of the original 

amount should remain. This method can be effective over several years, especially if desirable 

vegetation that provides shade is planted [28]. The Bradley method would also work with this 

species. [22] This method would be useful to destroy seedlings and young plants up to 1 meter 

tall. For plants up to 4 meters tall, a claw mattock is effective for removing root crowns.

Mechanical: Mowing may have limited use where ground is flat and free of obstacles. Mowing 

or cutting of canes may have advantages over herbicides since these techniques will not stimulate 

adventitious root growth. Mechanical removal is best used as a first step to reduce above ground 

biomass before root crown removal.

Biological: The USDA will not support the introduction of insects as controls due to the risk 

these species may pose to commercially important blackberry species.

Cultural: The use of goats has proven effective in some areas of California. Grazing of goats 

must be combined with fencing of native vegetation to avoid impacts on these species. Sheep 

and cattle grazing have shown to reduce the amount of daughter plants arising from new canes.

Prescribed Fire: Used alone this method will not prevent resprouting from root crowns. Burning 

is best followed by stump herbicide treatment, subsequent burning to exhaust the seedbank and 

underground reserves and revegetation with fast growing native species.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

57

Chemical (for Himalayan blackberry) [7, 17]:

Herbicide treatments, in general, should be applied in conjunction with other treatments such as 

mechanical or prescribed fire. All the following could be applied after an earlier season cutting. 

Chemicals would suppress or weaken materials for burning, but can also stimulate the development 

of adventitious roots. [17]

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use *

Issues/Concerns

Glyphosate 

(RoundUp,

Rodeo)

Broad 

spectrum, 

non-selective 

and systemic

Off site drift up 

to 100’ possible. 

Most likely to 

kill non-targets 

including 

grasses. 

Adheres to soil 

which lessens

leaching or 

uptake by nontargets.

Most effective 

in fall when 

canes are 

actively 

growing and 

after berries 

have formed. 

Backpack 

with 

adjustable 

spray nozzle.

Rain with 6 hours 

reduces 

effectiveness. 

Surfactants can be 

damaging to aquatic 

species.

Use formulations 

approved for use 

over water.

Triclopyr

(various 

Garlon 

formulations; 

consisting of 

salts and 

ester)

Selective, 

systemic for 

woody and 

broadleaf 

species. Will 

remain in 

plants until 

they die. 

Growth 

regulating.

Little or no 

impact on 

grasses. Off site 

drift up to 100’ 

possible.

Could inhibit 

ectomychorrizal 

growth.

Most effective 

in fall when 

canes are 

actively 

growing and 

after berries 

have formed.

Cut and paint 

stems or 

Backpack 

with 

adjustable 

spray nozzle 

where nontargets are 

not an issue.

Garlon 4 (ester 

compound) is toxic 

to fish and aquatic 

invertebrates. Amine 

formulations may be 

used near or over 

water. Offsite 

movement by water 

possible.

Picloram 

(Tordon) [7]

Restricted Use 

Herbicide

Contains 

hexachlorobenzene

Selective, 

systemic for 

many annual 

and perennial 

broadleaf and 

woody 

species. 

Systemic.

Off site drift 

may cause 

damage to 

sensitive plants 

up to 1000’. 

Also can leak 

out of roots to 

non-targets.

Apply in late 

spring after 

leaves are fully 

developed. 

Could 

stimulate 

development 

of adventitious 

roots.

Backpack or 

wick to 

minimize 

drift. 

Reapplication 

will be 

required as 

regrowth 

occurs [7].

Wait 6 10 12 months 

to reseed since 

picloram is persistent 

in the soil.

Can move offsite 

through surface or 

subsurface water.

Can be relocated 

through livestock 

urine.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.

Integrated techniques are the most probable for success. A scenario where mechanical removal 

of large biomass in the summer, followed by hand removal of canes and roots, then herbicide 

treatment of new growth in the fall/winter may be most effective and least impacting to nontarget species. The sowing of such fast growers as sterile wheatgrass will reduce erosion 

possibility in the winter. Mixing in native seed or planting woody species for shade development 

will help to develop competition with the species.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

58

Senecio jacobaea – Tansy Ragwort

Ecological Characteristics of Note

Tansy ragwort is considered a biennial species. Under extremely favorable conditions, though, 

this species may behave like an annual. If conditions are poor or the plant is damaged, it may be 

induced into a mono- or polycarpic perennial habit. Polycarpic perennial plants often have large, 

woody rootstocks and more than one flowering stalk. Dispersal of the seed though not usually 

long distance (up to around 9 meters), can vary depending on climatic conditions. Seeds can 

remain viable in the soil for several years and as deep as 25 centimeters. The species also 

regenerates vegetatively, usually, but not always due to damage. [17]

Management

Manual: Hand pulling is effective if done when soils are moist and the hole left behind is 

mulched. This method is usually used after a population has been brought under control. Plants 

must be mature enough to bloom, at which point stems are firm and not easily broken. Because 

the primary root grows toward one side, the technique that works best is to tug firmly from one 

side and if the plant does not come out, move to the opposite side. [53]

Mechanical: Mowing is the most commonly used technique. It is most effective if done prior to 

flowering when the plant has exhausted its reserves, but before seeds have started to develop. 

Mowing can prevent flowering, but may also increase rosette density. [17] Mowing may also 

force tansy ragwort to keep growing as a perennial. [23]

Biological: Although an effective part of a long-term management strategy, the biocontrols in 

place will decline as the ragwort declines. Because of the ability for seed to remain dormant, 

they could effectively ‘outwait’ the decline of the biocontrol. [17] The most effective biocontrol 

is when all three of the agents (cinnabar moth, ragwort flea beetle and seed fly) are used in 

combination [8]. Biological control is not recommended for infestations found in Idaho, eastern 

Washington or eastern Oregon because insects are ineffective in these areas. [31]

Grazing: Sheep appear to be unaffected by the toxicity of tansy ragwort. Sheep could be allowed 

to graze the plants before they bolt as a pretreatment to cattle grazing.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

59

Chemical** (for tansy ragwort)[7]:

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use *

Issues/Concerns

Metsulfuron

(Escort) plus 

surfactant

Selective for 

broadleaf and 

woody species.

Safest of the 

sulfonylureas on 

grasses.

Off site drift 

may cause 

damage to 

sensitive 

plants up to 

500’. 

Apply to 

actively 

growing 

plants. 

Backpack or 

wick to 

minimize 

drift.

Potentially mobile in 

water or through wind 

erosion.

Damage to non-target 

terrestrial and some 

aquatic plants (at peak 

concentrations) more 

possible than animals. 

Most sensitive species 

in the Lily

Picloram 

(Tordon)

Selective, 

systemic for 

many annual and 

perennial 

broadleaf and 

woody species. 

Systemic.

Off site drift 

may cause 

damage to 

sensitive 

plants up to 

1000’. Also 

can leak out 

of roots to 

non-targets 

[4].

Apply up 

through 

flowering 

stage. Fall 

application 

after rains 

have initiated 

seed 

germination 

have also 

proven 

effective.

Backpack or 

wick to 

minimize 

drift.

Wait 6 10 12 months to 

reseed since picloram is 

persistent in the soil.

Can move offsite 

through surface or 

subsurface water.

Contains 

hexachlorobenzene.

Can be relocated 

through livestock urine.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.

* *Most publications state that 2,4-D or dicamba are the most effective chemicals to use.
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

60

Taeniatherum caput-medusae – Medusahead rye

Ecological Characteristics of Note

Medusahead germinates in the fall. Roots begin to grow immediately and continue to grow 

through the winter. Germination may be delayed by dryness or cold temperatures, but this 

species still occurs sooner than cheatgrass or bluebunch wheatgrass. Germination increases with 

temperature. Flowering and seed formation occur in May and June. Seed reach maximum 

viability in July. Medusahead can effectively remove soil moisture which is also an advantage 

over other species. Plant density once established may range from 500 plants per square foot in 

scablands to 2000 plant per square foot in valley bottoms. Established populations form stem 

mats up to 12 centimeters thick which decompose slowly. The dense litter cover enhances 

medusahead germination and may exclude cheatgrass. It also contributes to high fire danger in 

the summer. [17]

Management [17]

Cultural: Heavy spring grazing by sheep during the green stage of medusahead has been 

reported to assist in control. 

Prescribed Burning: Controlled burning in early June successfully controlled infestations in 

northern California. Burning in late May and early June meant that medusahead seed was still 

immature while associated annuals had cured, thus promoting a light by intense fire to arrest seed 

development. Single burns resulted in nearly complete elimination of medusahead for the next 

several years.

Chemical (for medusahead) [26]:

Herbicide Selectivity Effects to 

Natives

When to 

Apply

Method to 

Use *

Issues/Concerns

Imazapic

(Plateau)[26]

specifically 

labeled for 

medusahead

Selective for 

broadleaf plants 

and some 

grasses.

Off site drift 

up to 50’ 

possible. 

Over 100’ if 

applied 

aerially.

Early 

season post 

emergence.

Backpack or 

wick to 

minimize 

drift.

Even very tolerant nontarget species are likely to 

be damaged. Some 

damage to aquatic plants 

at peak concentrations 

could occur.

Sethoxydim

(Poast) [26]

Selective for post 

emergent grasses

Off site drift 

up to 50’ 

possible.

Fall soon 

after 

growth 

begins.

Backpack or 

wick to 

minimize 

drift.

Potentially mobile, but 

degrades rapidly.

* Usually the most conservative method(s) of application is listed. Others may be acceptable.

No other methods of control were found in the literature

Restoration: The planting of the native, Elymus elymoides, successfully established in nonnative annual grasslands with or without prior treatment. Success is dependent upon the current 

mix of species. 
Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

61

References 

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Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

62

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Preventing and Managing Invasive Plants Final Environmental Impact Statement April 2005

64

[47] TNC weeds website – Action Alert, last updated March 2002. See 

http://tncweeds.ucdavis.edu/alert/alrtbrac.html.

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[53] Fries, Mary. 2004. personal communication. Conservation chair, South Sound chapter, 

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