Tordon

Weed Management

Reference Guide

Larimer County, Colorado

Information compiled and edited by Chad Clark

and the Land Stewardship Team

Larimer County Department of Natural Resources

5th edition

Don Hijar • David Moore • Glenn Ledall • Dave Rady

605 25th Street, Greeley, CO

970-356-7002

1-800-782-5947

www.PawneeButtesSeed.com info@PawneeButtesSeed.com

The Right Seed Every Time

Pawnee Buttes Seed, Inc. provides more than 400 varieties of

native and introduced grass, forb, and shrub seed for

reclamation, pasture, turf, and wetlands.

Our emphasis is on educating our customers on proper

management techniques to ensure grass stand longevity

and conservation of our natural resources.

Colorado Owned Since 1998

Conservation District

‘To educate, promote, and provide information on the wise

and proper management of our natural resources’.

The printing and distribution of this reference guide is supported

by the Ft. Collins Conservation District. They promote

conservation of natural resources on private land by identifying

and addressing issues related to water quality and quantity, noxious

weeds, range & pasture management, soil erosion, and wildlife

habitat enhancements. The District is actively involved in

organizing educational workshops on water usage, innovative farm

practices, and pasture management for small acreage landowners.

They have purchased a Dew Drop Drill that is available for hire

through the Weed District office to help landowners with

revegetation projects. Northern Colorado Conservation Districts

website is: www.nococd.org

Ft. Collins Manager

Jeanene Hess

(970) 221-0611

ftcollinsconsvdist@qwestoffice.net

If you would like to contribute to future editions of this guide

please contact the Weed District office at 970-498-5768.

About This Book

The pur pose of t his guide i s t o pr ovide i nformation he lpful t o

livestock producers, land managers, small acreage landowners and

others i nterested i n r angeland & p asture weed m anagement. T he

information pr ovided i s c oncise but ha rdly c omplete. For m ore

detailed information check the references section on page 81.

Behind-the-scenes efforts that make this guide possible go largely

unnoticed. We want to thank everyone who helped us out. A very

special thanks goes out to Jim Sebastian for his research, photos

and expertise that helped make all of this possible.

Table of Contents

Contacts……………………………………………………………5

Weed District Functions…………………………………………..6

Weed District Services………………………………….…………7

Weed Law……………………………………...………………..8-9

Larimer County Weed Management Plan Summary……..………8-9

Enforcement Procedures………………………...……………….10

Management Methods……………………..…………………11-13

Restoration/Re-vegetation………………….…………...……14-15

Plant Identification Index………………………………………...16

Plant Identification Management Guide……..……………….16-56

List A Species in Alphabetical order…………...…………….18-23

Larimer County Weed List in Alphabetical Order………..….24-36

Troublesome Weeds in Alphabetical Order……………...…..37-45

Poisonous Plants…………………………………...…………46-56

Poisonous Plants Quick Reference……………………………….49

Plant Photos (unnumbered)…………………………after page 56

Herbicide Reference Guide……………………..……………57-78

Herbicide Index……………………………………...……….60-61

Alphabetical Listing of Herbicides………………….………..62-78

Calibration Guide…………………………………………….79-80

References……………………………………………….………81

Glossary………………………………………………………82-83

Index………………………………………………………….84-87

Blank Notes Page…………………………………….…………..88

Did you know?

We have added these boxes throughout the book

to add anecdotal information to each section. For

instance, this book was written, edited, compiled

and designed by Chad Clark, Tim D’Amato (author

of the original document), Maxine Guill, Bobby

Goeman, Casey Cisneros and Steve Priest. This

book would not be possible without all their effort

and hard work.

Larimer County Weed District

For questions, concerns, sprayer loans or retail sales:

970-498-5768 (phone)

970-498-5776 (fax)

Or visit our website at:

www.larimer.org/weeds

Office address (Please call ahead for appointment):

2649 East Mulberry #6, Fort Collins, CO 80524

Shop yard address (Please call ahead for appointment):

614 East Vine Drive, Ft. Collins, CO 80524

The Land Stewardship Team:

Tim D'Amato

Land Stewardship Manager

970-498-5769

tdamato@larimer.org

Maxine Guill

970-498-5779

[email protected]er.co.us

Bobby Goeman

970-498-5766

[email protected]er.co.us

Casey Cisneros

Parks & Open Lands

970-679-4571

ccisneros@larimer.org

Chad Clark

970-498-5768

cclark@larimer.org

Weed District Functions

1. Assist landowners with noxious weed problems through plant

identification, weed control recommendations, and

development of vegetation management plans.

2. Promote noxious weed education and awareness by way of

community presentations, site visits, and tours of collaborative

field research plots demonstrating best management practices.

3. Manage noxious weeds on county property and roadside

rights-of-way.

4. Enforce the Colorado Noxious Weed Act on non-compliant

property owners.

Cost-Share Programs - For residents within the Weed District

boundary, our cost share program offers partial reimbursement for

herbicides and/or mowing. Call 970-498-5768 for a pre-approval

site visit or more information.

Herbicide Sales - All Larimer County residents may now

purchase herbicide through the Larimer County Weed District.

Please call for products and prices.

Sprayers for Loan - There are 25 gallon, 65 gallon, and 100

gallon sprayers available for residents of Larimer County. Please

call 970-498-5768 to reserve a sprayer. Sprayers are picked up

and dropped off at the shop yard at 614 East Vine Drive.

Free Site Visits - A weed specialist will identify weeds, give

management recommendations, approve cost share and offer

estimates for spraying, seeding, hydro-mulching and/or mowing.

Do Not Spray Requests - A request that the Larimer County

Weed District refrain from spraying the roadside adjacent to your

property with pesticides. Property owners requesting NO

SPRAY are responsible for noxious weed management within

that zone. Requests need to be submitted annually.

Weed Law

Colorado Noxious Weed Act (C.R.S. 35-5.5): In enacting this

article the general assembly finds and declares that there is a need

to ensure that all the lands of the state of Colorado, whether in

private or public ownership, are protected by and subject to the

jurisdiction of a local government empowered to manage

undesirable plants as designated by the state of Colorado and the

local governing body. In making such determination the general

assembly hereby finds and declares that certain undesirable plants

Did you know?

The Larimer County Weed District was originally

created in 1960 to address Canada thistle on irrigated

farmland and only encompasses about 1/6 of the

eastern portion of Larimer County (see map on page 6.)

In order for the weed district to provide site visits,

management recommendations, and compliance with the

State Noxious Weed Act, personnel must charge time

against an 'enterprise fund', money raised through

contract work. The necessity of raising funds to be

active outside the district is burdensome on the weed

program and would be unnecessary if all constituents

paid a mill levy to support the district. The district

hopes to introduce a ballot initiative sometime in the

future, proposing expansion of the district to include all

of Larimer County.

constitute a present threat to the continued economic and

environmental value of the lands of the state and if present in any

area of the state must be managed. It is the intent of the general

assembly that the advisory commissions appointed by counties

and municipalities under this article, in developing undesirable

plant management plans, consider the elements of integrated

management as defined in this article, as well as all appropriate

and available control and management methods, seeking those

methods which are least environmentally damaging and which are

practical and economically reasonable.

Larimer County Weed Management Plan Summary

The Larimer County Weed Management Plan follows the

guidelines of the Colorado State Noxious Weed Act which went

into effect in 1992. The Act prioritizes 71 noxious weed species

into 3 lists: A, B, and C.

• List A species are not well established in Colorado, are

potentially a large problem to this state, and require

mandatory eradication by local governing agencies.

Prescribed techniques for management of List A species

are hand pulling, digging, or herbicide application.

Mowing, grazing, and insect bio-control are not acceptable

forms of management for these species.

• List B species are common enough in parts of the state

that eradication is not feasible, though the species are still

recommended for eradication, suppression, or containment

depending on distribution and densities around the state.

Prevention of seed dispersal may be accomplished by

mowing, hand pulling, tillage, grazing, or herbicide

application.

• List C species are widespread and well established.

Control of List B and C species is recommended but not

required by the state. However, local governing bodies,

such as Larimer County, may require management.

All local governing agencies (cities and counties) are required to

have a weed management plan, and that plan must contain, at a

minimum, the List A species. Agencies can then choose weed

species of local concern to add to management plans.

• The Larimer County Weed Management Plan requires

eradication of all List A species, as mandated by the state,

and containment or suppression measures for 16 species

identified as significantly troublesome in Larimer County.

County outreach programs emphasize identification and

management of 16 species. The County reserves the

right to enforce on any state-listed noxious weed if the

infestation size and density deems it necessary.

• The Larimer County Weed Management Plan cannot be

enforced on private or public property without first

applying the same measures to any land or rights-of-way

owned or administered by the County that are adjacent to

such properties.

• The Larimer County Weed Management Plan can be

accessed at: www.larimer.org/weeds

Enforcement Procedures

The Colorado Noxious Weed Act mandates that every local

governing agency manage noxious weeds within their jurisdiction.

It is the obligation of the Larimer County Weed District to

conduct enforcement procedures to ensure the detrimental effects

of noxious weeds are not imposed on the environment and/or

economy of the county. The weed district will make every effort

to assist landowners in compliance prior to carrying out

enforcement action. The weeds that will be enforced upon are on

the Larimer County Noxious Weed List and Weeds Mandated for

Eradication by the State of Colorado. Enforcement procedures

are:

• When a noxious weed problem is brought to the attention

of the weed district and confirmed by a weed specialist, a

notice to enforce will be sent by certified mail.

• A courtesy notice is sent prior to the enforcement notice,

at the discretion of the district office, if time allows for

subsequent effective management.

• County weed management personnel will be available for

site visits and management recommendations free of

charge.

• Upon receiving the enforcement notice, the land owner

has ten days to:

o Manage the weed in the prescribed manner.

o Present a weed management plan.

o Option for waiver.

• After 10 days via legal Right of Entry, Larimer County

can enter upon the property of non-compliant landowners

and conduct appropriate management action (mowing,

spraying, etc).

• The land owner is responsible for all costs of management

action.

Management Methods

This guide contains a short summarization of the most

troublesome weed species in the Larimer County area and

management options. Weed management decisions vary

according to plant life cycles, infestation size, environmental

conditions and management objectives. For more detailed

information, consult the Larimer County Weed District website at

www.larimer.org/weeds.

General Information

• Early control of new weed infestations through proper

identification and eradication, early detection and rapid

response (EDRR) saves substantial time and expense.

• An established stand of a perennial weed such as leafy

spurge or Canada thistle cannot be completely controlled

in one season, persistence is necessary.

• Understanding plant life cycles and growth stages is

necessary to effectively manage weeds.

• The best management practice is using an integrated

method of two or more of the following controls.

Biological Control

• Insects are available through Colorado Dept of

Agriculture, Toll Free 866-324-2963.

• Insect bio-control is best used on large weed infestations

or in areas of rugged terrain where other management

options are not practical.

• Eradication of a weed species will not be attained strictly

through insect bio-control.

• Expect 3-5 years following release for establishment and

impact on a target weed.

• Livestock grazing can provide suppression of some weed

species, but results are no greater than what mowing

would accomplish.

• Repeated and intense grazing constitutes a disturbance

itself, which is often the initial cause of weed infestations.

Chemical Control (see more detailed information – pg 57)

• Herbicide application can provide the most effective and

time-efficient method of managing weeds.

• Most recommendations in this guide are for ‘selective’

herbicides, or products that can be broadcast applied and

not injure most grass species.

• Spot-spray applications of non-selective herbicides

(Roundup and others) should generally be effective for

controlling any of the weeds listed in this guide, however,

it is important to note that because it is non-selective it

may injure or kill adjacent desirable vegetation.

• Always consult the product label for specific rates and

uses (pasture, non-cropland, riparian, etc.)

• Proper surfactant choice is critical for effective use of

many herbicides (see label).

• Herbicide rates are given in amounts of product per acre.

Spray equipment calibration is necessary for accurate

measuring and mixing of an herbicide prior to application.

Refer to instructions on page 79-80 of this guide for

simple calibration steps.

• The herbicide ‘Tordon’ is frequently cited as a product

that provides effective control for many noxious weed

species. Tordon is a “Restricted Use Pesticide,” a

classification that restricts the purchase and use to a

certified pesticide applicator or to usage by anyone under

the direct supervision of a certified applicator (see page 59

for instructions on how to become certified).

Cultural Control (see more detailed information – pg 14)

• Cultural control, the establishment of desirable and

competitive vegetation, prevents or slows down invasion

by non-native species and is essential for effective weed

management.

• Establishment of desirable vegetation can often be attained

by controlling weed populations and shifting dominance to

desirable existing vegetation.

• Without desirable existing vegetation, re-seeding becomes

necessary.

• Moisture levels or areas prone to erosion may warrant the

use of a hydro-mulch to help seed germination and soil

stability.

Mechanical Control

• Mowing a weed infestation may prevent seed dispersal

and provide suppression, but plants typically re-grow and

often set seed from a reduced height.

• When digging or hand pulling any biennial species always

sever the root at least 2-4 inches below soil surface or re-

growth may occur.

Restoration/Re-vegetation of Range or Pasture

The first thing one should know and realize is that a

restoration/re-vegetation project is a process and can take several

years for the desired results. A project intending to restore the

land to desired vegetation requires diligence and persistence. It is

never a simple solution. The purpose of this section is to establish

a base or checklist of factors to help the landowner determine if

restoration/re-vegetation are viable options and to emphasize the

Grass Grazing

Long ago, successful cattlemen coined the phrase, “Take

half and leave half.” A grazing study by Crider tested

the effects of leaf removal on root development. Taking

50% of the leaves and the roots continue to grow

normally. Harvest another 10% and half the root growth

stops, and at 80% root growth stops completely for 12

days. A large actively growing root system is vital to

supply the leaves with moisture and minerals needed for

pasture production. With Larimer County being a semi

arid climate re-growth may take from three weeks to

four months during dry periods. Not given the time for

growth, weeds will take hold and the pasture will become

less productive.

time, scope and costs involved. Range or pasture disturbed by

excessive grazing, drought, weed invasion and other factors,

should first be evaluated for recovery potential before making a

decision to re-seed. Often times a change in grazing schedule or

duration, or control of weeds allows existing, though suppressed,

desirable grasses to recover without re-seeding.

If a site is so highly disturbed that recovery is not possible

through management, then re-vegetation becomes necessary.

Successful re-vegetation requires several years and proper soil

preparation, seed placement and timing. Often, after seeding a

good way to lock in moisture is by hydro-mulching the seeded

area. Many other factors need to be considered prior to seeding:

• Existing Vegetation - One of the greatest barriers to

successful re-vegetation is weed competition. It is

essential to minimize weeds prior to planting grasses.

• Cost - Are you prepared to absorb the costs associated

with this type of project? Not only are there several steps

that are costly just to prepare the land but the time

required may be the most costly endeavor of the project.

• Soil composition - Different soils require different seed

mixes and fertilization. If you are unsure of your soil

type, be sure to consult the NRCS or a soil scientist to get

an idea about what type of vegetation the soils on your

property can support.

• Soil compaction - This can impede moisture penetration

and grass root establishment. If severe enough,

mechanical tillage such as deep chiseling or ripping

becomes necessary prior to seeding.

• Cover crop - The establishment of residual plant stalks

helps to protect grass seedlings from wind and capture

snow for increased soil moisture. This is accomplished by

planting sterile hybrid forage sorghum or sudangrass in the

spring prior to planting grass seed the following winter.

The cover crop has completed its life cycle by fall, but the

decaying stalks and leaves serve as seedling protection,

ground cover and contribute organic matter to the soil.

• Species selection - Based on landowner objectives of

grazing, haying, wildlife habitat, etc., a landowner must

decide on native or non-native grasses, and which species

and varieties are best suited to a particular soil type and

moisture availability.

• Grass seeding - Referred to as ‘drilling,’ requires the right

planting equipment, proper depth of seed placement (0.25

– 0.5 inches) and correct seeding rate.

• Timing - The Natural Resource Conservation Service

(NRCS) recommends various optimum times for grass

seeding based on elevation and availability of water.

• Unforeseen factors - Drought, flood, excessive heat,

excessive cold, new plant invasions, wildlife movement,

drainage, fire, natural disaster, or any other event that is

not planned for can cause a project to be unsuccessful. It

is always important to have an alternative plan or to be

ready to change direction with a project if any event

affects it course.

Site visits and recommendations on species selection and planting

techniques are provided by the Larimer County Weed District and

the Ft. Collins NRCS office – 970-295-5655. Several seed

companies serve the Larimer County area and can blend seed

mixes according to local needs and refer landowners to

commercial seeders. For a brief list of companies please refer to

our website at www.larimer.org/weeds.

Plant Identification & Management Guide

Proper identification of the plant(s) on your property is essential

for creating a management scheme and for a successful project.

Please call the weed district for a free site visit.

The plants in this guide are split into the following groupings:

List A species found in Larimer County (Pages 18 to 23)

Common name (Genus species) Pages

Cypress spurge (Euphorbia cyparissias) 20

Mediterranean sage (Salvia aethiopis) 18-19

Myrtle spurge (Euphorbia myrsinites) 20

Orange hawkweed (Hieracium aurantiacum) 21

Purple loosestrife (Lythrum salicaria) 22

Yellow starthistle (Centaurea solstitialis) 23

Larimer County Weed List (Pages 24 to 36)

Common name (Genus species) Pages

Bull thistle (Cirsium vulgare) 24-25

Canada thistle (Cirsium arvense) 26-27

Common teasel (Dipsacus fullonum) 27

Dalmatian toadflax (Linaria dalmatica, Linaria genistifolia) 35-36

Diffuse knapweed (Centaurea diffusa) 30

Hoary alyssum (Berteroa incana) 28

Hoary cress (Cardaria draba) 29

Houndstongue (Cynoglossum officinale) 29

Leafy spurge (Euphorbia esula) 32

Musk thistle (Carduus nutans) 24-25

Perennial pepperweed (Lepidium latifolium) 33

Russian knapweed (Acroptilon repens) 31

Scotch thistle (Onopordum acanthium) 24-25

Spotted knapweed (Centaurea maculosa) 30

Tamarisk or saltcedar (Tamarix ramosissima) 34-35

Yellow toadflax (Linaria vulgaris) 35-36

Troublesome Weeds are asked about quite often, though they are

not currently on the County Weed List (Pages 37 to 45)

Poisonous Plant species in Larimer County (Pages 46 to 56)

Following are written descriptions organized with the following

bullet points designating what information are relayed in them:

• Lifecycle, history, plant characteristics, and location

 Toxic properties

 Pasture management tip

à Biological control recommendation

1 Mechanical control recommendation

d Chemical control recommendation

 Recommended Control - Highlighted text is the

recommended control for the species determined from

research conducted by the Weed District, Colorado State

University and others. Herbicide recommendations are

generally given as the original brand name, although other

brand names may exist, see index on page 60-61 or the

individual herbicide page for a listing of all names. The

exception, 2,4-D and dicamba, are referred by chemical

names because the brand names are too numerous to list.

Pictures of plants can be found after page 56 with Figure

numbers that correspond to the Figure numbers in the text.

st A Species – Found in Larimer County

Mediterranean sage (Salvia aethiopis) (Figure 3)

• A biennial member of the mint family that reproduces only by

seed. Mediterranean sage germinates in the spring, summer or

fall. The plant initially appears as a rosette with large velvety

leaves that are very similar in appearance to common mullein.

The distinguishing feature between the two plants is the foul

Did you know?

Beginning in January of 2012, a permit called

the National Pollutant Discharge Elimination

System (NPDES) has been set up as per the

Clean Water Act. The permit is available

through the Colorado Department of Public

Health and Environment (CDPHE)

and is specific

to applications in or near water. Check with

the CDPHE or the Weed District before making

any applications in or near water to insure

compliance.

aroma of Mediterranean sage, easily detected from pinching a

leaf. The plants bolt (send up a flowering shoot) in May,

flower and set seed in June-July. A square stem, common to

most plants in the mint family, is another useful identification

characteristic of Mediterranean sage. The flowers are white,

arranged on a globe-shaped inflorescence that comes to a

point. Soon after setting seed, the plants dry, break off at the

base and tumble with the wind, spreading seed.

• Mediterranean sage is a prolific seed producer that can spread

rapidly if not controlled. The plant is a problem in rangeland

and pasture areas of Idaho, Washington and Oregon. Small

populations occur in Boulder, Garfield, Larimer and

Montezuma Counties in Colorado. It is believed that the

spread of seed in Colorado has come from contaminated hay.

In Larimer County, the Mediterranean sage population is

located near Berthoud, Campion and in the Blue Mountain

area both just north of the Boulder County line. Intense

eradication efforts are being conducted in Larimer County

with hopes of eliminating Mediterranean sage from the county

in the next few years. Report any suspected sightings in

Larimer County immediately to the Weed District office!

 The plant is not palatable to livestock or wildlife.

à An insect bio-control agent that feeds on Mediterranean sage

has been tested on sites in Colorado but has not been effective.

1 Mowing Mediterranean sage is not an effective means of

control, as the plants readily re-grow. Digging or hand pulling

is effective if enough of the root (3-4 inches) is removed to

prevent re-growth. If flowering plants are manually removed,

bagging and disposal is necessary to prevent seed dispersal.

d Dicamba, 2,4-D, Escort, Telar, Milestone and Tordon provide

effective control of Mediterranean sage. Good coverage of

the leaf surface area as well as a non-ionic surfactant in the

spray mix is critical to ensure adequate uptake of the herbicide

through the wooly leaves of Mediterranean sage.

 The most common recommendation for control of

scattered plants in small areas is hand pulling or digging.

Flowering plants must be bagged. When manual removal

is not feasible on larger areas, an herbicide application of

Escort + 2,4-D + non-ionic surfactant in a tank mix is most

effective at rosette stage.

Myrtle spurge (Euphorbia myrsinites) (Figure 6),

Cypress spurge (Euphorbia cyparissias) (Figure 4)

• These two spurge species have simple perennial life cycles

and reproduce only by seed. Both were formerly sold as

ornamental plants until placed on the prohibited sales list by

Colorado Department of Agriculture in 2003. These drought-

Invasive Plant Species in Larimer County

Invasive plants are a threat to the economy and

environment of Larimer County. These invaders,

better known as noxious weeds, originated in other

parts of the world and when introduced into this

country, have flourished. Infestations of noxious

weeds threaten our native plant communities, reduce

species diversity and in doing so, reduce wildlife

habitat. Noxious weeds on rangeland and farmland

are extremely costly to agricultural producers,

either reducing yields or imposing a management

expense.

The Larimer County Weed District is working to

minimize existing weed problems in the County, and

eliminate new invaders before they take hold. The

District assists residents with site visits, plant

identification, management recommendations,

provides educational information on invasive species,

and works with residents to be compliant with the

Colorado State Noxious Weed Act.

hardy ornamental plants have escaped into natural areas and

become an invasive species problem in the foothills and Estes

Park.

• Myrtle spurge tends to have a decumbent (flattened) growth

structure, with very waxy, succulent leaves. Flowering occurs

in April and May. A very caustic latex sap is present

throughout the leaves and stems that may cause a rash on skin,

or permanent damage if in contact with the eye. Seed

longevity is estimated to be 8 years in the soil.

• Cypress spurge grows 4-30 inches tall and produces yellow-

green flowers in the spring that continue into autumn. The

plant has numerous leaves that are very narrow. Like myrtle

spurge, the stems and leaves of cypress spurge contain caustic

latex that is irritating to skin and eyes.

 Myrtle spurge produces diarrhea in cattle although they tend

to avoid eating it. People who get the milky sap on their skin

can develop dermatitis.

à There are no insect bio-control agents available for either of

these spurge species.

1 Mowing is not practical because of the plants’ decumbent

growth structure. The most common recommendation for

control of myrtle spurge and cypress spurge is hand

pulling or digging, with proper caution to prevent skin or

eye contact with the caustic latex present throughout the

plant.

d Excellent control can also be attained from application of

2,4-D, with adequate surfactant to penetrate the waxy leaf

surface.

Orange hawkweed (Hieracium aurantiacum) (Figure 1)

• A perennial forb of the sunflower family that reproduces by

seed, underground rhizomes or above ground stolons (runners

similar to those on strawberries). Orange hawkweed grows to

12 inches tall and produces showy flowers from mid-June

through August. The flowers are arranged in clumps at the

end of the stems. Leaves are at the base of the plant in a dense

mat, with occasional 1-2 leaves on the stem. The stems are

bristly or hairy, and when broke apart produce a milky juice.

As the plants mature, seed heads are formed that are very

similar to dandelion seed heads, readily blowing in the wind.

• Orange hawkweed thrives in moist meadow sites and is a

widespread problem in wildland areas of the Pacific

Northwest. Infestations are more limited in Colorado with

sites reported in mountain counties. In Larimer County, very

small patches have been found and recently eradicated (or

nearly so) in Rocky Mountain National Park, in the Waltonia

neighborhood and on adjacent US Forest Service lands.

Report any sightings or suspected sightings in Larimer

County immediately to the Weed District office!

à Grazing and insect bio-control are not viable management

options for this List A species.

1 Hand pulling or digging can reduce seed production and stress

plants, but this perennial will readily grow back.

d Milestone, Transline, Tordon, and 2,4-D provide excellent

control of orange hawkweed.

 The most common recommendation is an application of

Milestone prior to seed production.

Purple loosestrife (Lythrum salicaria) (Figure 2)

• Purple loosestrife was formerly sold as an ornamental garden

plant, and is now listed as a noxious weed due to invasive

tendencies in riparian areas. Purple loosestrife is a

rhizomatous perennial that reproduces by rootstalks and seed.

Showy purple/lavender flowers appear mid-summer, arranged

along a spike at the tops of the plants. Stalks are distinctively

square shaped and leaves are lance shaped with smooth edges.

Plants grow 6-8 feet tall and can produce 2.5 million seeds

that can remain viable for 20 years.

• Infestations in Colorado are often found inter-mixed with

cattails along streams, ponds, and sloughs. Purple loosestrife

is most problematic in New England states and the upper

Midwestern U.S. where solid stands occur over hundreds of

acres, displacing native wetland plants and diminishing

wildlife habitat. Few infestations are known to exist in

Larimer County, and hopefully those found will be eradicated

before becoming large scale problems similar to those found

in other states. Report any sightings or suspected sightings

in Larimer County immediately to the Weed District

office!

à Insect bio-control agents are available for use on purple

loosestrife but are not a feasible management choice in

Colorado where eradication is possible.

1 Hand pulling or digging is only effective if all the rootstalk is

removed. Purple loosestrife infestations are difficult to spot

before flowering occurs in July.

d Most infestations occur in standing water, and herbicide use is

limited to those that have an aquatic label. Rodeo, Garlon 3A,

Habitat, Clearcast and several formulations of 2,4-D

effectively control purple loosestrife and are registered for use

in and around water.

 A common management practice is to wait till the

flowering stage when plants are most visible, then cut and

bag seed heads and spot-spray the remaining portion of

the plant with an herbicide.

Yellow starthistle (Centaurea solstitialis) (Figure 11)

• A member of the knapweed genus, this annual forb is

extremely invasive and could become Colorado’s worst weed

problem if infestations are left uncontrolled. Yellow

starthistle germinates in spring, summer or fall, depending on

rainfall. Plants first emerge as a bluish-green rosette with

deeply lobed leaves. Plants grow 2-4 feet tall with stems that

are distinctively winged. Bright yellow flowers, similar in

color to dandelion flowers, occur singly on the ends of

branches. Below the flowers are sharp laterally extending

thorns, ½ - 1 inch long.

• Yellow starthistle infests 15-20 million acres in California and

millions more in other western states with climate and

elevation similar to Colorado. Several small infestations have

been discovered in Colorado, including one in Larimer

County west of Berthoud. Seed introduction occurs when

construction equipment, livestock feed, bedding straw, and

other carriers are brought in from other states. Aggressive

action is being taken to eradicate yellow starthistle by the

Colorado Department of Agriculture and Larimer County

Weed District. Report any sightings or suspected sightings

in Larimer County immediately to the Weed District

office!

 Yellow starthistle, like Russian knapweed, if eaten over a

period of months by horses will cause an incurable disease

called “Chewing Disease”. Affected horses are unable to bite-

off and chew their food and will subsequently starve to death.

à Insect bio-control agents are available but not recommended

for management on Colorado’s limited infestations.

1 Grazing and mowing are ineffective for managing this very

resilient noxious weed. Hand-pulling or digging any annual

plant is effective. If in the seed stage, or even late flower

stage, plants must be bagged and properly disposed.

d Herbicide applications need to occur prior to seed

production. Milestone, Transline, and Tordon all provide

excellent control of yellow starthistle.

Species on the Larimer County Weed List

Biennial Thistles

Bull thistle (Circium vulgare) (Figure 17)

Musk thistle (Carduus nutans) (Figure 15)

Scotch thistle (Onopordum acanthium) (Figure 16)

• These three thistle species are found in Larimer County from

the plains to 9,000 feet. The plants are tap-rooted biennials

that reproduce only by seed. Germination occurs in early

spring, late summer or early fall. Newly emerged plants over-

winter in a rosette stage, bolt, then flower in the spring or

early summer of the following season. From mid-summer

into fall, these thistles begin producing seed which is attached

to a white cotton-like material, referred to as pappus, which

carries seed in the wind. Seed longevity is variable but can

last up to 10 years.

o Bull thistle grows 2-5 feet tall and has a more branched

growth form than musk or Scotch thistle. The leaves are

deeply lobed and tipped with a yellow-tan colored thorn.

Flowers are deep purple and with very spiny bracts below.

o Musk thistle grows to 8 feet tall. Leaves are somewhat

lobed with wavy margins and a prominent, light green mid-

vein. Flowers appear singly, on the end of stalks, are rose

colored and with by broad, pinecone-like bracts below

which is a good identification characteristic.

o Scotch thistle can grow to 12 feet tall. Leaves, particularly

at the rosette stage, are covered with white hair giving them

a gray-blue color. Flowers are purple with spiny bracts

below, much like those of bull thistle.

• Musk thistle is the most common of these three species, and

found throughout Larimer County. Bull thistle and Scotch

thistle are less common and should be aggressively controlled

where found to prevent further spread in this area.

• Management of these species, or any biennial weed species, is

a matter of depleting the seed bank in the soil. Effective

control measures must be applied for several consecutive

years without further seed production.

à An insect agent, Rhinocyllus conicus, was released in 1969 for

suppression of musk thistle. The seedhead-feeding weevil had

unintended impacts on native thistle species and is no longer

released but is present throughout the western United States.

This insect appears to provide suppression of musk thistle

populations cyclically but does not provide long term control.

1 Mowing and grazing can provide suppression but plants often

re-grow and set seed from a reduced height. Manual removal

by pulling or digging is effective if carried out prior to

seed production. With matured plants, it is important to

properly bag and dispose of them to prevent seed spread.

d Herbicides must be applied prior to the late flowering

stage or seed may still be produced. A number of products

provide excellent control: Milestone, Perspective,

Transline, Telar, and Tordon.

Colorado Thistles

Fifteen native and five non-native thistle

species are found in Colorado. Four of the

five non-

native thistles are listed in this book,

(only plumeless thistle is not found in Larimer

County). Native thistles are an important

part of many ecosystems ranging from 3,500

feet in elevation to the tundra. Native

thistles are valuable to pollinators, browsing

animals and contribute to the beauty and

diversity of native plant communities. It is

important that land managers discriminate

between native and non-native species when

managing weeds.

For more information, check

out the Thistles of Colorado gu

ide available at

the Larimer County Weed District office.

Canada thistle (Breea arvense) (Figure 18)

• A deep-rooted perennial plant that reproduces by seed or

extensive underground rootstalks. Seeds can remain viable in

soil for up to 20 years. Canada thistle plants first appear in

early spring in a rosette growth stage, soon producing stalks

that grow to 4 feet tall. Leaves have shallow lobes with wavy

margins. Pink or purple flowers (sometimes white) appear

from June – August. Seed is produced in late summer

attached to pappus, a cotton-like material, and dispersed by

wind.

• Canada thistle is the most common noxious weed problem in

Colorado. This aggressive invader is costly to agricultural

producers as well as managers of roadsides and natural areas.

 Canada thistle may accumulate high levels of sulfates

which can result in blindness and death.

 Canada thistle can accumulate nitrates which cause respiratory

difficulty, brownish discoloration of mucous membranes,

drowsiness, weakness, tremors, and staggering gait. High

doses of nitrate will cause sudden death.

• Controlling Canada thistle, as with any deep-rooted perennial

plant, requires several years of management and monitoring.

à Insect agents are available but have not been effective in

Larimer County.

1 Livestock grazing and mowing effectively suppress Canada

thistle through the summer and can prevent or slow down seed

production and dispersal, but plants will quickly re-grow with

no further management action. Hand pulling a deep-rooted

perennial is futile. Shallow tillage such as disking or

sweeping has shown to be counter-productive. Re-growth is

quick and the spread of root stalk results in more dense and

uniform stands of Canada thistle than before.

d Herbicides are effective and should be applied in spring prior

to seed set or in the fall before a hard frost. Milestone,

Perspective, Transline and Tordon all provide excellent

control of Canada thistle. Dicamba, Telar, 2,4-D and

combinations of these products provide suppression but not

long term control.

 Best management of Canada thistle is mowing in the

summer followed by an application of Milestone in the fall.

Spot treating escaped plants in subsequent years is critical

if eradication is desired.

Common teasel (Dipsacus fullonum) (Figure 10)

• A tap-rooted biennial plant that reproduces only by seed.

Plants germinate in late summer or early fall, over-winter in a

rosette stage, bolt and flower in the spring or early summer.

The rosette leaves are dark green with a wrinkled surface.

Stem leaves are narrow, up to ten inches long, and cup-shaped

at the base to catch rainfall. Plants grow to six feet tall

producing purple flowers on dense, prickly heads. Below the

flower heads are spiny bracts which grow longer than the

head.

• Common teasel thrives on moist sites and is widespread along

ditch banks, streams, river bottoms and ponds in Boulder and

Jefferson Counties. Though not yet common in Larimer

County, this escaped ornamental plant potentially threatens

our wetland plant communities.

à There are no insect bio-control agents available for teasel

control.

1 Effective management requires prevention of seed production,

which can be accomplished by hand pulling or digging where

feasible. Mowing can reduce seed production but plants will

re-grow and set seed from a reduced height.

d A number of herbicides selectively control common teasel:

Milestone, Transline, 2,4-D, dicamba, Escort, Telar, and

Plateau. Proximity to water needs to be considered when

selecting an herbicide. Be sure to read labels carefully.

 The most effective treatment for infestations at water’s

edge is Milestone. If plants are in standing water apply

Rodeo (glyphosate approved for aquatic infestations).

Hoary alyssum (Berteroa incana) (Figure 21)

• Hoary alyssum is an annual, biennial or short-lived perennial

plant found along roadsides and disturbed areas of range and

pasture. Plants grow 1-3 feet tall, with rosette leaves, 2-3

inches long and lance shaped, appearing at the base of the

plant. Smaller upwardly pointing leaves, alternately arranged,

are present along the stalks. Plants produce small white 4-

petaled flowers, notched at the center, and arranged in tight

clusters. Flowering occurs spring through summer.

• This non-native invasive plant was added to the Larimer

County weed list in 2011 and is becoming increasingly

common in some areas of Larimer County, particularly in the

Estes Valley and Red Feather Lakes area. It has also been

confirmed near Pinewood Springs and Loveland.

• While hoary alyssum is not currently on the State of

Colorado’s weed list, it has been added to the Larimer County

Noxious Weed list.

 Hoary alyssum is toxic to horses, causing laminitis, limb

edema, diarrhea, dehydration, intravascular haemolysis, and

hypovolemic shock, and abortion in pregnant mares.

Mortality in horses has been observed when horses consumed

a diet of hay containing 30-70 percent hoary alyssum. When

mixed with alfalfa hay, hoary alyssum can remain toxic for up

to nine months.

à No insect bio-control agents are available.

1 Hand pulling or digging is effective but persistence is

necessary.

 Escort, Plateau/Panoramic, and Telar provide excellent

control of this mustard species.

Hoary cress (Cardaria draba) (Figure 19)

• Also known as white top, hoary cress is a perennial plant that

grows from a rosette stage to flowering plant in the very early

spring. Plants grow to 2 feet tall with white flowers. Leaves

are lance-shaped and blue-green in color. Plants thrive along

roadsides and in alkaline soils.

• Hoary cress is a List B species on the state weed list and was

added to the Larimer County weed list in 2011.

à No insect bio-control agents are available for this species.

1 Mowing and grazing can provide suppression but plants often

re-grow and set seed from a reduced height.

 Escort, Plateau/Panoramic, (Clearcast inside ditches-see

label) and Telar provide excellent control of hoary cress.

Applications should be made in the spring at the flowering

stage.

Houndstongue (Cynoglossum officinale) (Figure 9)

• Houndstongue is a tap-rooted biennial plant that reproduces

by seed only. Plants germinate in summer/fall, and over-

winter as rosettes. Leaves are light green, 4-12 inches long

with smooth edges. Houndstongue bolts in the spring,

growing 1-4 feet tall and produces red-purple flowers in mid-

summer and seed by fall. Seeds are Velcro-like, attaching to

clothing and animals. There is no data available on seed

longevity in the soil.

• Scattered infestations of houndstongue can be found

throughout Larimer County. The plants appear to do best in

areas of high moisture. The seeds are a nuisance to people

and animals.

 Houndstongue contains alkaloids that can lead to permanent

liver disease and photosensitization when consumed in hay.

à No insect bio-control agents are currently available but may

be in the near future.

1 Digging or hand pulling scattered plants is effective.

 The most effective herbicides for controlling houndstongue

are dicamba, Escort, Telar, 2,4-D, Plateau, and Tordon.

Knapweeds

Diffuse knapweed (Centaurea diffusa) (Figure 13)

Spotted knapweed (Centaurea maculosa) (Figure 14)

These two species are similar in appearance and frequently

found together, along with hybrids of the two.

• Diffuse knapweed is primarily a biennial that germinates in

summer/fall and over-winters as a rosette. The plants grow 1-

2 feet tall with finely divided leaves and produce mostly

white, sometimes lavender flowers in spring/summer. Below

the flowers are spiny bracts. By late summer seed is

produced, plants begin to dry, and by winter break off at the

base and become tumbleweeds.

• Spotted knapweed is a short-lived perennial that grows to 3

feet tall. Unlike diffuse knapweed, spotted knapweed does

not become tumbleweed. Rosette leaves appear at the base of

the previous year’s growth in fall or spring. Spotted

knapweed produces pink-purple flowers from June through

October. The bracts beneath the flowers appear as black

spots, which distinguish spotted from diffuse knapweed.

• Diffuse and spotted knapweeds are prolific seed producers

that can spread very rapidly and remain viable in the soil for

15 years. Infestations are found from Estes Park to Pinewood

Springs, along Hwy 287 from Livermore to Wyoming, and in

the Red Feather Lakes area.

à Numerous insects have shown fair to good results for both

knapweed species. Most effective have been a seed head

weevil Larinus minutus and root weevils Cyphocleonus

achates and Sphenoptera jugoslavica.

1 Mowing can reduce seed production and prevent plants from

blowing and dispersing seed, but serves only to suppress

infestations. Hand pulling either of these tap-rooted plants

is effective as long as plants that have produced seed are

bagged.

d Herbicide applications of Transline and Tordon provide

best control when applied prior to the late flower stage to

prevent seed production.

Russian knapweed (Acroptilon repens) (Figure 12)

• A perennial weed that reproduces from seed and vegetative

root buds. Seeds remain viable for 2-3 years. Russian

knapweed emerges in the spring, bolts in early summer, and

flowers by mid-summer. The plants grow to 3 feet tall with

blue-green leaves. Russian knapweed has black roots, evident

upon pulling a plant, and is a useful identification

characteristic. The flowers are pink-purple with papery bracts

beneath. This weed is allelopathic, meaning it exudes a

chemical that inhibits the growth of other plants, often

resulting in solid stands of Russian knapweed.

• Russian knapweed is a widespread problem in Colorado, and

becoming more common in Larimer County.

 If it is eaten over a period of months by horses it can cause an

incurable disease called “Chewing Disease”. Affected horses

are unable to bite-off and chew their food and will

subsequently starve to death.

à There are currently no insect bio-control agents available for

Russian knapweed though some may become available for

releases in the near future.

1 Mowing reduces seed production and stresses the plant, but is

not an effective management tool.

d Milestone, Perspective, Telar, Tordon, Transline, and Plateau

all provide excellent control of Russian knapweed.

 The most effective recommendation is an application

of 7 oz/acre Milestone + 1 oz/acre Telar; or 4-5 oz

Perspective (in areas with no livestock grazing – see label).

Leafy spurge (Euphorbia esula) (Figure 5)

• Leafy spurge is a deep-rooted perennial that reproduces by

rootstalks and seed. Seed can remain viable for 8 years.

Plants emerge in early spring, grow 2-3 feet tall and produce

yellow-green flowers in April - May. The leaves are narrow,

1-2 inches long. The entire plant contains milky latex, which

is an identification characteristic for leafy spurge. The latex

can easily be seen after tearing a leaf or breaking a stem.

• Leafy spurge infests millions of acres in Montana, North

Dakota, and Wyoming. It is the worst noxious weed problem

in Ft. Collins and much of Larimer County. This perennial

invader has taken over many acres along the Poudre River

from the middle section of the Poudre Canyon to the Weld

County line, along the North Fork of the Poudre from

Livermore to Seaman Reservoir, Bellvue, Rist Canyon,

LaPorte, and north of Ft. Collins, however, small infestations

found throughout the County and can easily be managed.

 Leafy spurge can produce salivation and diarrhea in cattle

although they avoid eating it. The latex is also irritating and

damaging to skin and eyes of humans.

à Several species of flea beetle (Apthona spp.) have been

effective in significantly reducing stands of leafy spurge.

Effectiveness is site-dependant and varies from year to year.

à Mowing, grazing, and herbicide application can be compatible

with insect bio-control, but these management efforts should

occur in late summer or fall.

1 Sheep and goats can be trained to browse leafy spurge.

Mowing and grazing are effective in depleting root reserves.

Hand pulling or digging can reduce seed production and stress

plants, but this perennial will readily grow back.

d 2,4-D and dicamba provide suppression of leafy spurge, but

not long term control. Tordon and Plateau are fairly effective

but can injure cool season grasses such as smooth brome.

 Paramount and Perspective tankmixes with Overdrive

provide best control with little or no grass injury (rate

dependant). Management efforts require several years for

effective control.

Perennial pepperweed (Lepidium latifolium) (Figure 20)

• Perennial pepperweed, or tall whitetop, is a perennial forb

with rhizomes, that grows to 5 feet tall. Flowering occurs

early in the spring or summer with white flowers arranged in

dense clusters at branch tips. This plant is tolerant of saline

soils and typically found in wetland areas.

• Perennial pepperweed is a List B species on the state weed list

and was added to the Larimer County weed list in 2011.

à No insect bio-control agents are available for this species.

1 Mowing and grazing can provide suppression but plants often

re-grow and set seed from a reduced height.

 Escort, Plateau/Panoramic, (Clearcast inside ditches-see

label) and Telar provide excellent control. Applications

should be made in the spring at the flowering stage.

Did you know?

Many weed management recommendations in this

guide are a result of collaborative field

research studies conducted by Larimer County

Weed District and the Colorado State

University Weed Science program, composed of

Jim Sebastian, Dr. Phil Westra, Dr.Scott

Nissen, Dr. George Beck,

Dr. Andrew Norton, as

well as Dr. Rich Hansen

(APHIS) and all of their

graduate students. Field

tours can be arranged by

contacting the Weed District office.

Tamarisk/saltcedar (Tamarix ramosissima) (Figure 31)

• A deciduous shrub or small tree introduced into this country

for erosion control, windbreaks and as an ornamental.

Tamarisk is often referred to as saltcedar, due to the presence

of cedar-like leaves that exude salt creating saline soils that

exclude other vegetation. These plants thrive on wet soils,

growing to 30 feet tall and often forming solid stands.

Tamarisk flowers are pink and bloom from April until

September, resulting in as many as 600,000 seeds produced

from a single tree. Fortunately the seeds are short-lived,

remaining viable for just a few months following dispersal.

Tamarisk seedlings grow very rapidly, as much as 6 feet

within a season, and are capable of flowering within a year of

germination.

• This highly invasive plant infests an estimated 1.5 million

acres along waterways in the western United States. The

Arkansas and Colorado River corridors are heavily infested

and demonstrate what can result if tamarisk is not managed.

In Larimer County tamarisk can be found around ponds, lakes,

reservoirs and gravel pits. Residents here are in the enviable

position of eliminating tamarisk at an early stage of

infestation, as opposed to facing extensive stands such as

those along the Arkansas or Colorado River.

à A defoliating insect that feeds on tamarisk, Diorhabda

elongata, was released in western Colorado in 2005 and has

had promising results. In Larimer County, sparse stands of

tamarisk are not extensive enough to justify insect releases

when other management methods can result in eradication.

1 Mechanical treatments, such as cutting, bulldozing and fire are

temporarily effective, though an herbicide application is

necessary to prevent subsequent sprouting. Smaller trees are

pulled out of the ground with a weed wrench.

d The most common method of controlling tamarisk, referred to

as a cut-stump treatment, consists of cutting a tree at the base

and applying an herbicide to the stump to prevent re-

sprouting. The application must be immediate or the sap can

dry and prevent herbicide movement to the roots.

 The most effective herbicides are Habitat and Garlon,

which must be applied with a crop oil concentrate.

Smaller trees can be controlled by a foliar application of

these products.

Toadflaxes

Dalmatian toadflax (Linaria genistifolia) (Figure 7)

Yellow toadflax (Linaria vulgaris) (Figure 8)

• These two closely related plants are perennials that reproduce

from seed or rootstalks. The plants are members of the snap

dragon family, and were introduced into this country as

ornamental garden flowers. Generally, Dalmatian toadflax is

found on dry, rocky foothill sites and yellow toadflax is found

on cooler, wetter sites along streams or in mountain meadows.

• Dalmatian toadflax produces multiple stems at the base that

grow to 3 feet tall. The leaves are oval, blue-green, waxy, and

clasp the stem. The flowers are yellow with orange throats

and a long spur on the upper ends of the stems. The plants

produce flowers throughout the summer before taking on a

dry, wilty appearance in the fall.

• Yellow toadflax, commonly referred to as butter-n-eggs,

grows 1-2 feet tall. The leaves are narrow and very similar in

appearance to leafy spurge, but lack the milky latex. Flowers

of yellow toadflax are similar to those of Dalmatian toadflax,

but more clustered toward the top of the plant.

• Both species have escaped from backyard gardens to become

invasive problems in rangeland, shrublands and forests. The

United States Forest Service estimates 10,000-20,000 acres of

yellow toadflax infest the Flattops Wilderness near Steamboat

Springs, Colorado, significantly impacting wildlife habitat.

Isolated infestations have been confirmed in the Loveland and

Berthoud areas but the majority have been found in and

around Estes Park.

à Several insect bio-control species have been introduced to

attack these toadflax plants. The most promising has been

Mecinus janthinus, a stem-boring weevil that readily attacks

Dalmatian toadflax, but unfortunately, not yellow toadflax.

Numerous releases of this weevil have been made in Larimer

County with hopes of suppressing populations and slowing the

spread of Dalmatian toadflax.

1 Mowing and grazing are not effective methods for controlling

either species. Persistent hand pulling (over 2-3 seasons) can

be effective on smaller patches.

 A fall application (when new growth appears at the plant

base) of Telar, or Plateau with a surfactant of methylated

seed oil and silicone, provides effective control of

Dalmatian toadflax. Yellow toadflax is more difficult to

control. Research results show a tank mix of Tordon,

Telar, and Overdrive is most effective.

Ornamental Weeds?

Many of the weed problems confronting Colorado

natural areas originated from backyard flower

gardens. How did this come about? Over the course

of decades, the plant nursery industry selected

showy ornamental plants from all over the world for

characteristics desirable in the western U.S. such as

drought tolerance. Unfortunately some plants

Troublesome Weeds of Larimer County

Cheatgrass

Downy brome (Bromus tectorum)

Japanese brome (Bromus japonicus) (Figure 27)

• ‘Cheatgrass’ is generally considered a collective term for

winter annual brome species. In Larimer County, and most of

Colorado, the term describes downy brome, and to a lesser

extent, Japanese brome. These grasses typically germinate in

late summer or early fall, though some germination also

occurs in spring. The leaves are covered with soft hairs from

seedling stage through all growth stages. The plants go into a

semi-dormant state through winter, often turning purple, and

are usually the first plants to green-up in early spring and

finish its life-cycle with seed set by June. The thin, dense

stems of the dry grass become a fine-fuel and a wildfire

hazard. Seed survival is 2-3 years.

• Downy brome is a List C weed species on the Colorado

noxious weed list. Due to its ubiquitous presence, cheatgrass

is not on the Larimer County Weed list. This weedy grass

was probably introduced into this country as a contaminant in

wheat seed from Asia over 100 years ago. It is now estimated

that 60 million acres of rangeland are infested with cheatgrass

across the western United States.

 At maturity, the abundant and very prickly seed heads become

a nuisance to livestock, pets and hikers.

à There are no insect agents available for cheatgrass control.

Grazing in the spring, prior to seed set, can provide

suppression, but this grass will readily re-grow and set seed

from a reduced height. Hand pulling or tillage, if feasible,

provides effective control if conducted prior to seed set.

Mowing, like grazing, can provide suppression but not

effective control.

d Herbicides can effectively control cheatgrass but attention to

timing and application rate is important so as not to injure

desired perennial grasses. Low rates of Roundup applied in

winter or early spring when perennial grasses are dormant, can

control cheatgrass with little or no injury to desirable grasses.

Matrix and Landmark provide excellent control of cheatgrass,

but grazing or haying must be restricted for one year after

application.

 The most common selective herbicide treatment for

control of cheatgrass is Plateau/Panoramic, applied in the

fall prior to emergence, or at early post-emergent stage

(pre-tillering - prior to development of secondary stems).

Plateau/Panoramic applied in the spring is ineffective.

Common mullein (Verbascum thapsus) (Figure 29)

• Common mullein is a biennial plant, which reproduces by

seed only. Plants first emerge as a fuzzy rosette in the fall or

spring, then bolt in the second season, sending up a single

thick stem 2-6 feet tall. Small yellow flowers appear along

long spikes at the top of the stem. In late summer the spikes

turn brown as seeds mature. Seed may remain viable for 80+

years.

• Common mullein is a List C weed species on the state weed

list, but not on the Larimer County weed list. Often

considered a native species, common mullein was actually

introduced from Asia and is now common across North

America. This plant often appears to have invasive

characteristics on disturbed sites such as intensively grazed

pastures, densely established prairie dog colonies, or

following wildfire.

à No insect bio-control is available for common mullein.

1 Hand pulling or digging is effective on this or any

biennial/annual species.

 The herbicides Escort, Telar and Milestone all provide

excellent control of common mullein. The addition of

methylated seed oil to the spray mix is essential for

herbicide to penetrate the hairy leaf surface.

Feral rye (Secale cereale) (Figure 28)

• Feral rye is an extremely competitive grass that has become a

nuisance to landowners across the western United States

including Larimer County. Like other winter annual species,

this grass germinates primarily in the late summer or early fall

(some spring germination as well), over-winters in a rosette

stage, resumes growth very early in the spring and reaches

maturity by mid-July. These robust plants grow 2-5 feet tall

and, and can be competitive enough to eliminate desirable

vegetation. Seed survival is about 3 years.

• Feral rye, once referred to as volunteer rye, is seldom grown as

a crop in the western United States, but has been planted as

livestock forage and as a reclamation species. This prolific

grass did not effectively serve those purposes, and the escaped

cultivar has become a major weed problem in winter wheat,

roadside rights-of-ways, rangeland and pasture. Examples of

invasiveness are very evident in the Lower Poudre Canyon,

along Glade Road, and many other sites in Larimer County.

à There are no insect bio-control agents available for control of

feral rye. Grazing in the spring, prior to seed-set, can provide

suppression but the grass will re-grow and set seed from a

reduced height.

1 Hand pulling or tillage, when practical, provides effective

control if conducted prior to seed production. Mowing, like

grazing, can provide suppression but not effective control.

 Herbicides can effectively control feral rye but attention to

timing and application rate is important so as not to injure

desired perennial grasses. Low rates of Roundup applied in

winter or early spring when perennial grasses are dormant,

can control rye with little or no injury to desirable grasses.

Matrix and Landmark applied in the fall provide excellent

control of feral rye, but careful attention to rates and sprayer

calibration is necessary or injury to perennial grasses can

occur. Also, grazing or haying must be restricted for one year

after application of these two products.

Field bindweed (Convolvulus arvensis) (Figure 33)

• Field bindweed is a deep-rooted perennial plant that

reproduces by seed or underground rootstalks. Plants emerge

in late spring producing vines that grow 1-4 feet long with

arrowhead-shaped leaves. White or pinkish, trumpet-shaped

flowers appear by mid-summer that are often confused with

morning glory. Soon after flowering, seed capsules develop

with seeds that can remain viable in the soil for 50+ years.

• Field bindweed is a List C weed species on the state weed list,

but not on the Larimer County weed list. It is a widespread

weed problem in the western United States and Colorado,

especially in farmland and along roadsides. This weed is

difficult to eradicate because of its extensive underground root

system, but is not particularly competitive in well-maintained

grassland or pasture.

 Field bindweed can accumulate toxic levels of nitrates which

cause acute respiratory difficulty, brownish discoloration of

mucous membranes, drowsiness, weakness, tremors, and

staggering gait. High enough doses of nitrate will cause

sudden death. Field bindweed also contains tropane alkaloids,

especially in the seeds, that act on the nervous system to stop

intestinal movement and cause colic.

à Insect bio-control can be an effective method of suppressing

field bindweed. A gall mite, Aceria malherbae, and to a lesser

extent a defoliating moth, Tyta luctuosa are becoming well

established in Colorado and having a significant effect on

field bindweed infestations.

1 Shallow tillage (disk, sweep) is not an effective control

method, in fact, can be counter-productive, spreading root

propagules and creating a denser, more uniform stand.

Deeper tillage such as moldboard plowing, if practical, can

provide 1-2 years control.

d The most effective herbicides for control of field bindweed

are Perspective, Tordon, Habitat, Plateau, Paramount,

dicamba and 2,4-D.

Kochia (Kochia scoparia) (Figure 26)

• An annual of the goosefoot family. Kochia typically

germinates in March, and produces flowers from July to

October. The plants are very branched with stems that are

often red. Kochia grows 1 – 6 feet tall depending on available

moisture. In fall/winter the plants break loose and become

tumbleweeds. Seed remains viable 2-3 years.

• Kochia can be a difficult plant to identify as it looks similar to

Russian thistle and can develop in many forms. Initially,

kochia will form a mat with tiny plants that appear blue-green

because of hairs covering the leaves. As it develops, it can

become quite tall and thin or quite round and bushy.

• Kochia is not listed on the state noxious weed list or Larimer

County’s Weed list. This common weed is a problem in

dryland and irrigated agriculture, rangeland and roadsides.

Kochia readily invades disturbed sites and areas of high soil

nitrates such as abandoned corrals and barnyard areas.

 Kochia can accumulate toxic levels of nitrates which cause

acute respiratory difficulty, brownish discoloration of mucous

membranes, drowsiness, weakness, tremors, and staggering

gait. High enough doses of nitrate will cause sudden death. It

may also cause liver disease and photosensitization in cattle

and sheep when enough of mature kochia is consumed.

Kochia can accumulate high levels of sulfates that will cause

poor weight gains, depression, weakness in coordination and

blindness may be seen in affected animals.

à There are no insect agents available for kochia control.

1 Small, young plants are browsed by livestock up to maturity.

Tillage or hand pulling, when feasible, is an effective method

of controlling any annual plant. Mowing is only a temporary

solution as kochia will quickly re-sprout, often creating a

stand more dense and uniform than prior to mowing.

d Because of this plant’s high degree of genetic variability, a

great deal of herbicide resistance has been selected for over

the years. A long list of herbicides are not effective for

controlling kochia including 2,4-D, Escort, Telar, Tordon,

Transline, Milestone, Plateau/Panoramic and others.

 Most effective method for control of kochia is an

application of an effective herbicide when plants are 6

inches tall or less. Dicamba, Vista, or any of the many

pre-mixes of these products with 2,4-D provide excellent

control (2,4-D alone will not control kochia). Proper

surfactant is essential to control of kochia as the young

plants are covered in fine hairs.

Mustards

Numerous mustard species are found in Larimer County, 3 of

which were added to the County Weed List in 2011 – hoary

alyssum, hoary cress and perennial pepperweed. A number

of other mustard species, all winter annuals, are not listed but

considered troublesome in some areas.

blue mustard (Figure 24), flixweed (Figure 22),

tumble mustard (Figure 23), and yellow alyssum

• Mustard species are winter-hardy plants of the cruciferae

family. The plant family name, cruciferae, implies a cross

shape, referring to the flower petal structure of 4 petals, a

distinctive characteristic of the mustard family. The species

listed above follow a winter annual life cycle – germination in

the fall or early spring and flowering and seed set in April and

May. Flowering mustards are often quite pungent, the odor is

irritating to people with allergies.

• These mustards are problematic in winter wheat, pastures and

through the first cutting of alfalfa, though inconspicuous by

mid-summer after completing the life cycle.

 Tansy mustard and flixweed may cause photosensitization in

cattle if it is the predominant forage in early spring.

à No insect bio-control agents are available for any of these

plants.

1 Hand pulling or digging is effective for controlling annual

species.

 Escort, Matrix, Plateau/Panoramic, and Telar provide

excellent control of mustard species.

Puncturevine (Tribulus terrestris) (Figure 30)

• Puncturevine is an annual, low-growing forb that first

germinates in the spring and continues to appear with multiple

flushes following rainfall throughout the summer. The plants

form mats with trailing stems 1-5 feet long. Leaflets are light

green, hairy and arranged in pairs. Small, yellow 5-petaled

flowers appear as plants mature. The flowers develop into

sharp, spiny burs containing 2-4 seeds. Seeds remain viable

for 5 years. Puncturevine is also known as ‘goathead’ because

of the sharp, menacing burs.

 Puncturevine has steroidal sapogenins that forms crystals in

the bile ducts which can cause photosensitivity. The spiny

burs can be a major contaminant in hay, cause damage to

wool, injure livestock, puncture bicycle tires and make life

miserable for a pet’s paws and human bare feet.

à Insect bio-control agents are available that feed on the

seedheads and stems of puncturevine, and provide effective

management in some areas. Unfortunately, these weevils are

not effective in Colorado’s cold climate.

1 Digging and pulling provide effective control of any annual

weed such as puncturevine. If plants have set seed, plant

material should be bagged and disposed of to prevent seed

dispersal. A handy trick to pick up multiple seeds safely is

to press a slab of Styrofoam on the ground of the infested

area.

d Numerous selective herbicides (won't injure grasses) are

effective for controlling puncturevine, the problem with

managing this persistent weed is staying after multiple flushes

that occur during the growing season. Dicamba, 2,4-D, and

Vista effectively control emerged puncturevine, but do not

provide residual control.

 For soil residual activity, Telar, Perspective and Tordon

provide season-long control.

Russian olive (Elaeagnus angustifolia) (Figure 32)

• A deciduous shrub or small tree introduced into this country

for erosion control, windbreaks and as an ornamental.

Russian olives grow to 40 feet tall, producing small yellow-

green flowers in the spring and white-brown, olive-like berries

by late summer. The stems are reddish-brown with sharp

thorns 1-2 inches long. Leaves are narrow and silver-green in

color.

• Russian olives were placed on the state noxious weed list and

prohibited sales list for Colorado nurseries in 2004. Larimer

County encourages residents to remove Russian olives, but

because of the widespread occurrence, the trees are not on the

county weed list. Russian olives have become a major

invasive plant problem along stream corridors and around

lakes and ponds. Invading trees establish dense thickets that

reduce or eliminate native trees and shrubs. Russian olive

seeds are readily spread by birds traveling between suburban

areas and river bottoms.

à There are no insect bio-control agents available for Russian

olive control.

1 Mechanical treatments, such as cutting, bulldozing and fire are

temporarily effective, though an herbicide application is

necessary to prevent subsequent sprouting. Smaller trees are

pulled out of the ground with a weed wrench.

 The most common management practice is a cut-stump

treatment, which consists of cutting the tree down near the

base and applying an herbicide on the stump to prevent

re-growth. The most effective herbicides used for this

purpose are Garlon or Habitat, applied in a mix with a

crop oil concentrate. The cut portion of the tree is typically

put through a mechanical chipper.

Russian thistle (Salsola iberica) (Figure 25)

• Russian thistle is an annual forb of the chenopodiaceae, or

goosefoot family. Russian thistle germinates in April or May,

grows 0.5 – 3 feet tall, and produces flowers mid to late

summer. The flowers are located at the base of the long,

pointed leaves. Considered the classic tumbleweed plant,

Russian thistle is very similar to kochia, where the mature

plants break loose and tumble with the wind in the winter.

Seed remains viable 2-3 years.

• Russian thistle is a common weed problem in dry land and

irrigated agriculture, rangeland and roadsides. Like kochia,

this plant readily invades disturbed sites and areas of high soil

nitrates such as abandoned corrals and barnyard areas.

Russian thistle is not listed on the state noxious weed list or

Larimer County’s Weed list.

 Russian thistle can accumulate toxic levels of nitrates which

cause acute respiratory difficulty, brownish discoloration of

mucous membranes, drowsiness, weakness, tremors, and

staggering gait. High enough doses of nitrate will cause

sudden death. It also contains oxalates which can result in

kidney failure in sheep and cattle.

à There are no insect agents available for Russian thistle

control.

1 Small, young plants are browsed by livestock up to maturity.

Tillage or hand pulling, when feasible, is an effective method

of controlling any annual plant. Mowing is only a temporary

solution as Russian thistle will quickly re-sprout, often

creating a stand more dense and uniform than prior to

mowing.

 Most effective method for control of Russian thistle is an

application of an herbicide when plants are 6 inches tall or

less. Any brand of 2,4-D, or pre-mixes of 2,4-D with

dicamba provide excellent control. Dicamba alone will not

control Russian thistle.

 Poisonous Plants

Plant poisoning of animals is dependent upon the quantity of plant

consumed, relative toxicity of the plant, growing conditions, time

of year, and animal species, age, health, stress level and size of the

animal. Animals grazing well managed pastures with abundant

forage, or fed inspected hay will for the most part not find these

plants palatable and therefore not become poisoned. Hay should

be inspected or weed-free hay purchased to ensure no poisonous

plants are contained in the bales.

If poisonous plants are suspected as the cause of an animal’s

symptoms a veterinarian should be consulted for appropriate

treatment recommendations.

The information found in this section is concise but hardly

complete. The purpose of this section is to inform landowners of

the possible dangers in and around their properties and to offer

options for the landowner to manage their land. ALWAYS consult

a professional for proper identification and before making changes

to the land as harm can be done without proper due diligence.

The following lists are some of the most important plants

poisonous to livestock in Larimer County. These lists are by no

means comprehensive. Plant names underlined are part of our top

ten poisonous plants of Larimer County and are further discussed

in the following pages. Names bolded are noxious weeds that

have poisonous qualities and are covered elsewhere in this guide.

Those bolded and italicized are troublesome weeds with poisonous

properties and are covered elsewhere in this guide.

Plants causing sudden death:

Death camas

Dogbane

Geyer larkspur

Low larkspur

Milkweeds

Poison hemlock

Water hemlock

Cyanide poisoning:

Arrow grass

Blue flax

Elderberry

Mountain mahogany

Poison suckleya

Western chokecherry

Western serviceberry

Nitrate poisoning:

Barnyardgrass

Canada thistle

Curly Dock

Field bindweed

Goldenrod

Kochia

Lambsquarter

Mallow

Nightshades

Pigweed

Ragweed

Russian thistle

Smartweed

Sorghum

Sunflower

Sweetclover

Wild oat grass

Plants causing kidney failure (Oxalates):

Curly dock

Greasewood

Kochia

Lambsquarter

Pigweed

Purslane

Russian thistle

Wood sorrel

Plants affecting the digestive system:

Any plants with sharp awns, burs, thorns, or spines (eg: cocklebur,

burdock, cheatgrass, foxtail)

Baneberry

Bitterweed

Bouncingbet

Buttercup

Corn cockle

Colorado rubberweed

Field bindweed

Leafy spurge

Nightshades

Plants causing liver disease and photosensitization

of the white skinned areas:

Blue-green algae

Buckwheat

Common cocklebur

Flixweed

Groundsel, Senecio

Houndstongue

Knotweed

Kochia

Puncturevine

St. Johnswort

Tansy mustard

Wild carrot

Plants affecting the nervous system:

Crown vetch

Fringed sage

Geyer larkspur

Horsetail

Low larkspur

Peas (perennial species)

Poison hemlock

Purple locoweed

Russian knapweed

Sand sage

Water hemlock

White locoweed

Yellow starthistle

Plants associated with congenital defects and

reproductive failure:

Broom snakeweed

Groundsel

Locoweeds

Lupine

Milk vetch

Mountain thermopsis

Poison hemlock

Ponderosa pine

Western false hellebore

Wild pea

Plants affecting the blood:

Bracken fern

Moldy yellow sweetclover

Onion

Plants affecting the musculoskeletal system:

Flatweed

Golden banner

Hoary alyssum

Selenium poisoning:

Beard tongue

Goldenweed

Gumweed

Indian paintbrush

Milk vetch

Prince's plume

Saltbush

White fall aster

Plants that effect milk production:

Bracken fern

Fringed sage

Groundsel (Senecio)

Houndstongue

Locoweeds

Lupine

Mustards

Onion

Poison hemlock

Sand sage

Plants affecting the skin:

Poison ivy (not toxic to livestock)

Poisonous Plant Quick Reference

The vertical axis are toxic plants and the horizontal axis are

animals the plants can affect. There are varying degrees of harm

from minor irritation to death. Consult this guide for management,

consult an expert immediately if you suspect poisoning.

Alpaca

Bison

Cat

Cattle

Dog

Goat

Human

Horse

Llama

Poultry

Sheep

Swine

Canada thistle

Cheatgrass

Death camas x x x x x x x x x x x x

Field bindweed x

x x

Geyer larkspur x

Hoary alyssum

Houndstongue

Kochia

Leafy spurge

Low larkspur x

x x

Myrtle spurge x

Poison hemlock x x x x x x x x x x x x

Poison ivy

Ponderosa pine

Puncturevine

Purple locoweed x

x x

Russian

knapweed

Russian thistle x

Water hemlock x x x x x x x x x x x x

Western

chokecherry

x x

White locoweed x

x x

Yellow

starthistle

Death camas (Zigadenus venenosus) (Figure 36)

• An herbaceous native perennial in the lily family. It can grow

to 2 feet tall with long, basal, grass-like leaves. The bulbs are

oval and look like onions but does not smell like onion or

garlic. The flowers are cream colored and grow in clusters

between April and July.

Death camas tends to grow in dry

meadows and on dry hillsides as well as sagebrush slopes and

montane forests.

• Can be easily confused with native garlic or onions which have

a white flowers and hollow leaves.

 Contains zygacine alkaloids that decrease blood pressure and

slow heart rate. All parts of the plant are poisonous for humans

as well as livestock. First symptoms are salivation, vomiting,

weakness, staggering gait, convulsions, then coma and death.

 Pasture management tip: Keep animals out of pastures with

death camas in the early spring when other green growing

forage is unavailable.

1 Digging and bagging scattered plants to avoid seed dispersal is

effective during and after flower.

d Herbicide treatments of 2,4-D, dicamba or Roundup applied

before flowering using a spot spray technique will control

death camas without harming desirable vegetation.

Did you know?

Milkweed species are toxic to all types of

livestock. Though not commonly ingested in

pasture, milkweed harvested with hay can be a

major problem. In 2012, nineteen horses died in

Canon City, CO from consuming hay contaminated

with whorled milkweed.

Larkspur

Geyer or foothills larkspur (Delphinium geyeri) (Figure 42)

Low larkspur (Delphinium nuttallianum) (Figure 43)

• Both species are native perennials in the buttercup family.

These plants grow to 2 to 3 feet tall. Leaves are lobed into 3-5

divisions, which are lobed again and are hairy. Flowers are

purple in geyer larkspur, low larkspur may have white sepals

with a distinct spur pointing backwards in the months of April

through July. The stems are hollow and the roots are tuberous

and woody. These plants are found from moist mountain

meadows and open forests to dry sandy sagebrush plains.

 Contain various alkaloids causing muscle weakness and

paralysis. The first symptoms are uneasiness, stiffness,

staggering, a wide stance, kneeling, lack of coordination,

sudden collapse, bloating. Cattle are most susceptible to

larkspur poisoning, while sheep and goats are only mildly

affected.

 An effective pasture management technique is to keep

livestock out of the pasture when larkspur is flowering and

until seeding has occurred.

1 Sheep and goats can be used as biological controls to graze

larkspur prior to cattle entering a pasture.

 The most effective herbicides are Escort or Tordon mixed with

a good surfactant. Apply when plants are approaching

maximum vegetative growth, but before flowers open.

Locoweed

White locoweed (Oxytropis sericea) (Figure 40)

Purple locoweed (Oxytropis lambertii) (Figure 41)

• Otherwise known as “crazy weed” locoweeds are native

perennials 2 to 12 inches tall in the legume family. Locoweeds

are found on rocky prairies, plains, hillsides, gravelly banks,

and open wooded hillsides. Leaves are basal, with leaflets on

each side and one at the tip, all covered with silky hairs. White

or purple pea-like flowers, depending on the species, in a

raceme on a leafless stem in April through August.

 Locoweeds contain the alkaloid swainsonine that is produced

by a fungus growing within the plant . Poisonous and palatable

to all livestock, especially prior to and during flowering stages,

locoweeds cause abnormal nervous behavior referred to as

“locoism”. Horses show signs of “locosim” resulting in

circling, staggering gait, lack of coordination, and falling over

backwards, making them unpredictable and unsafe to ride.

Cattle become aggressive and difficult to work. They may

have heart irregularities and lose weight. Pregnant cows and

sheep may abort or develop a condition called “water belly”,

where the uterus becomes distended with fluid. Bulls and rams

develop abnormal sperm and infertility. Pregnant animals

grazing locoweeds may produce calves or foals that are born

weak and have deformities of the limbs. Sheep develop heart

irregularities and demonstrate a loss of their flocking instinct.

The poisonous alkaloid is passed through the milk to the

suckling young. Horses with “locoism” do not recover due to

permanent effects on the brain, but cows and sheep will

recover from the reproductive effects if taken off the locoweed.

 Some locoweeds can also accumulate selenium which causes

the hair of the mane and tail to break off, and the hoof wall to

develop ridges and cracks that result in lameness.

 Pasture management tip: Create “safe” pastures that have

no locoweed to move the animals into after possible

consumption of locoweed. Try not to graze pastures with

locoweed during the summer months when palatability is high.

Overgrazing will increase the density of this plant in pastures.

 Herbicide treatments with Transline, Escort, Garlon or

Tordon with MSO will control locoweeds but re-treatment

will be necessary as the locoweed seeds stay viable for 50

years in the soil.

Poison or spotted hemlock (Conium maculatum) (Figure 39)

• A non- native biennial plant of the parsley family. Poison

hemlock grows 2 to 10 feet tall and most commonly found in

moist areas. It is an invasive weed that spreads only by seed.

Poison hemlock stems are erect, branched, ribbed, waxy, and

usually marked with purple spots near the base. Leaves are

fern-like with long-stalks below and short-stalks above, 3-4

times odd pinnately compound. The flowers are a white

umbel. Poison hemlock is commonly mistaken for wild carrot

or parsley.

 Poison hemlock contains piperidine alkaloids in all parts of the

plant. This toxin blocks the spinal cord reflexes, and causes

death within hours from respiratory failure. Young plants and

the tap root of more mature plants are most toxic. Symptoms

of poisoning include: excessive salivation, urination, and

defecation; tremors and lack of coordination; difficulty

breathing, dilated pupils, and a weak pulse. If pregnant cows

and sows eat small quantities of the plant in the first trimester

of pregnancy the newborn may have skeletal defects (crooked

calf disease) or be aborted. Goats may eat the plant without

problem as long as they have other forage available.

 Piperidine alkaloids can be passed into the milk and may be

harmful if pregnant women drink it.

1 Mowing hemlock plants to keep them short will decrease the

chance of poisoning. Do not hay areas with standing plants as

they are still toxic when dried.

 Herbicide treatment of 2,4-D, Escort, Telar, Garlon 3A, or

Rodeo provide effective control of early growth.

Did you know?

Socrates was reportedly executed by being

forced to drink poison hemlock tea.

Poison ivy (Toxicodendron radicans) (Figure 37)

• A native vine in the sumac family. Poison ivy has oval, shiny

leaves that are alternate and in groups of three. There are no

thorns on the stem. The flowers are yellowish- or greenish-

white, and present from May to July. The berry-like grayish-

white fruits mature in August. Poison ivy is common in the

foothills and canyons.

 Contains an oily resin (urishiol) that is a highly allergenic

phenolic compound that binds to the skin causing an intense

allergic reaction in people. It is not toxic to livestock, but

animal fur with the oil on it will affect humans handling the

animal. Smoke from burning poison ivy can also contain the

toxin that affect a person’s eyes and lungs. Don’t forget:

Leaves of three, let it be!

1 Mechanical removal of the plant will ensure that the oils

will not be in the area. Full body covering is recommended

while removing plants.

 Herbicide treatments of Garlon, Tordon, Roundup, or

Milestone will control poison ivy, but it may take a year to

dry up the oils.

Ponderosa pine (Pinus ponderosa) (Figure 35)

• A native tree with a very distinct orange bark with black lining

the splits. It can often be identified by its characteristic long

needles that grow in bundles of three.

 The isocupressic acid in the needles causes abortions in cattle

and bison. Affected cows will have swelling of the vulva and

udder, and there will be a vaginal discharge before and after

abortion. Weak contractions and poor dilation result in

difficult delivery and retention of the placenta which could lead

to secondary infection and future fertility problems. If a calf is

born alive the mother’s milk production may low or non-

existent. Rocky Mountain junipers are toxic to cattle in the

same way ponderosa pines are.

 Pasture management tip: Move pregnant cows during

their last trimester to a pasture without ponderosa pine

nearby, especially if there is inadequate forage for the cattle

to feed on. Cattle will eat pine needles if they are hungry.

Snow storms may cause cattle to seek shelter in the trees

and if there is nothing else accessible to them the cows will

browse on pine needles. Ensure the cattle have access to

hay in such winter conditions.

1 Create a “safe” pasture by cutting down and removing trees.

Water hemlock (Cicuta maculata) (Figure 38)

• Water hemlock is a native perennial in the parsley family.

Plants grow to 4 to 6 feet tall and are commonly found on wet

sites. Plants produce tiny white flowers with 5 petals produced

in an umbel at the ends of branches, present from June through

August. Stems are erect, stout, branched at top, often waxy,

with hollow stems; base of stem enlarged, chambered and has a

yellow, pungent fluid. Leaves are alternate, with 2 to 3 leaflets

longer than wide. The leaves have toothed margins, uppermost

leaves sometimes simple. Unlike poison hemlock that has a

taproot, water hemlock has multiple tuberous roots.

 All parts of water hemlock are highly poisonous, especially the

tuberous roots. Symptoms of poisoning include: excessive

salivation, urination, and defecation; teeth grinding and

chewing motion; seizures and violent convulsions. Livestock

will eat water hemlock especially in the spring or when other

forages are depleted. Only a mouthful or two of the young

plants or roots can be fatal.

 Pasture management tip: Remove livestock from the pasture in

the spring when the plant is often most palatable.

1 Digging and disposing of large plants is the best way to prevent

seed production and dispersal.

 Spot treating with herbicide treatments of 2,4-D, Escort,

Telar, Garlon 3A, or Rodeo is effective for control of early

growth.

Western chokecherry (Prunus virginiana) (Figure 34)

• A large native shrub in the rose family. The bark of

western chokecherry is smooth to scaly, and dull red to

gray. Leaves are ovate to broadly elliptical, rounded at

the base or slightly heart shaped, smooth or only slightly hairy,

with finely toothed margins. Flowers are white, showy, and

clustered in 2 to 5 inch long racemes at the ends of leafy shoots

in spring. The fruit matures in the fall to an edible dark

purple/black berry.

• The edible berries are bitter tasting and are best in jams and

jellies.

 The leaves, stems, and seeds contain cyanogenic glycosides

that when eaten by cattle, sheep and goats in particular, are

converted to highly toxic cyanide (the ripe fruits do not contain

cyanide). Be aware that droughted or frosted chokecherry

leaves are especially toxic. Cyanide blocks oxygen from

reaching cells and therefore prevents cellular respiration.

Sudden death occurs within 1 to 2 hours. Poisoned animals

will have labored breathing, frothing at the mouth, dilated

pupils, tremors, and convulsions. Mucous membranes will be

bright red.

 Do not plant chokecherry near animal enclosures. Animals

suspected of being poisoned by chokecherry should be seen by

a veterinarian as quickly as possible if the antidote (Sodium

thiosulfate) is to be administered in time!

1 Mechanical removal of the shrub needs to include the root ball

otherwise suckering will occur.

 A foliar herbicide treatment of Garlon or Tordon will provide

effective control of chokecherry though mechanical removal

of the limbs followed by a cut stump treatment with

triclopyr or Tordon will decrease the amount of herbicide

needed for control. Drought-stricken, dying, or frosted

chokecherry leaves are especially toxic, and broken or pruned

chokecherry branches should not be left in pastures or

animal pens.

Herbicide Reference Guide For Landowners

The purpose of this guide is to provide information helpful in

deciding which herbicide may be most appropriate for a small

acreage landowner. There is no intended endorsement of the

products listed, nor is discrimination intended towards any product

that may have been omitted. This guide is not intended to

substitute for a product label. Always read the label and keep in

mind “the label is the law.” Colorado now requires a permit

called the National Pollutant Discharge Elimination System

(NPDES) through the Clean Water Act for applications in or

near water. Check with Colorado Department of Public

Health and Environment (CDPHE ) or the Weed District

before making any applications in or near water to insure

compliance. This book references instances where aquatic

herbicides are recommended, be sure of compliance with

NPDES before proceeding with these applications. The user of

any pesticide is liable for all aspects of handling the product,

including but not limited to mixing, loading, application, spill

control and disposal of pesticides or containers.

It is a violation of federal law to use any pesticide in a manner

inconsistent with its labeling, with the following four exemptions:

- Application at a rate or frequency less than specified on the

label.

- Application on a target species not specified on the label as

long as application is to the site or use specified on the label,

unless the label specifically prohibits use on that specific pest.

- Employing any method of application not prohibited on the

label.

- Mixing with a fertilizer, as long as such a mixture is not

prohibited on the labeling.

Acronyms and Definitions for Herbicide Reference

Surfactants - Surfactants are additives to a post emergent

herbicide spray solution that enhance activity and effectiveness of

the herbicide. Surfactants increase spray coverage and penetration

on leaf surfaces, and reduce evaporation rate, thereby increasing

the amount of an herbicide that translocates into a target plant.

A common question is whether a detergent soap will suffice as a

surfactant or not. The best answer is to use the recommended

surfactant designed to enhance the activity of a specific herbicide.

When a user is investing time and money into a weed management

project, why jeopardize success over such a minor cost.

Surfactants recommended for the herbicides listed in this guide:

• COC - Crop oil concentrate is a petroleum oil based product,

typically applied at a rate of 1 quart/acre, recommended for

use with imazapyr and triclopyr on cut-stump treatments.

• MSO - Methylated seed oil is a plant oil derivative, typically

applied at a rate of 1 quart/acre, for use with imazapic and

quinclorac. Often used with other herbicides when applied

over weed species with very waxy or hairy leaves such as

common mullein or Dalmatian toadflax.

• NIS - Nonionic surfactant is an organic compound usually

mixed in at 0.25 – 0.50 % volume per volume ratio for

example .25% v/v = 1oz per 3 gal, for use with all other

herbicides listed in this guide. This surfactant is absolutely

essential for chlorsulfuron, metsulfuron methyl, and

rimsulfuron to be effective.

GUP – General Use Pesticide. Are products which are available to

the general public. All herbicides listed in this guide are general

use unless otherwise specified.

MSDS – Material Safety Data Sheet. A technical bulletin that

supplements information found on the product label. This bulletin

provides detailed descriptions of a product’s physical properties

and toxicity, and provides users and emergency personnel with the

proper procedures for handling and working with that substance.

Pesticide Label – A legal document located on the pesticide

container that provides information concerning the safe and

effective use of the pesticide. It is a violation of federal pesticide

laws to use any pesticide in a manner inconsistent with its labeling.

PPE – Personal Protective Equipment (gloves, apron, eye safety

glasses, etc.). The required PPE for a specific compound is listed

under the “Hazards to Humans” section on the label. Always use

protective equipment specified on the label. The most serious risk

of exposure from chemicals is during handling and mixing

operations with the concentrated product.

Re-entry interval - Period of time immediately after a pesticide

application when agricultural employees may not enter a pesticide

treated area without protective clothing.

RUP – Restricted Use Pesticide. The "Restricted Use"

classification restricts the purchase of a product, and its uses, to a

licensed commercial, private, or public applicator.

Landowners wishing to purchase and apply restricted use

pesticides can obtain a Private Applicator’s License through

the Colorado Department of Agriculture. Information is

available at 303-239-4186 or at:

http://www.colorado.gov/cs/Satellite/Agriculture-

Main/CDAG/1178305424099

Signal Words – Indicate the toxicity and/or hazards associated

with the use of the pesticide. Pre-mix herbicides will always have

the highest toxicity level of the mixed active ingredients.

- Caution – Category 3 or 4, least toxic. 1 ounce to 1

pint swallowed lethal to an adult.

- Warning – Category 2. 1 –3 teaspoons swallowed

lethal to an adult.

- Danger/Poison – Category 1, most toxic. 1-3

drops swallowed lethal to an adult.

Toxicity – Measured by LD

(lethal dose, 50%), describes the

dose of a pesticide that will kill ½ of a group of test animals from a

single dose. A pesticide with a lower LD

is more toxic than one

with a higher number because it takes less of the pesticide to kill

half of the test animals.

To obtain more comprehensive information regarding Colorado

and Federal pesticide laws and regulation, and an overview of the

CSU Pesticide Safety Education Program, see:

www.colostate.edu/Depts/SoilCrop/extension/CEPEP

Herbicide Index

Brand name Active ingredient Remarks Page #

Ally

Metsulfuron methyl

Amine 4

2,4-D

Aquatic

Arsenal

Imazapyr

Banvel

Dicamba

Brash

Dicamba + 2,4-D

66, 78

Chopper

Imazapyr + adjuvants

Cimarron

Metsulfuron methyl

Cimarron Max Metsulfuron methyl + 2,4-D

+ dicamba

66, 73,

Cimarron X-tra

Metsulfuron methyl +

chlorsulfuron

64, 73

Clarity

Dicamba

Clearcast

Imazamox

Aquatic

Clearstand Imazapyr + metsulfuron

methyl

72,73

Cody

Clopyralid + 2,4-D

65, 73

Confront

Clopyralid + triclopyr

65, 77

Crossbow

Triclopyr + 2,4-D

77, 78

Curtail

Clopyralid + 2,4-D

65, 78

Distinct

Diflufenzopyr + dicamba

Ecomazapyr 2

Imazapyr

Aquatic

Element 3A

Triclopyr

Aquatic

Element 4

Triclopyr

Escort

Metsulfuron methyl

Fallowmaster

Dicamba + glyphosate

66, 69

Forefront

Aminopyralid + 2,4-D

63, 78

Formula 40

2,4-D

Garlon 3A

Triclopyr

Aquatic

Garlon 4

Triclopyr

Glean

Chlorsulfuron

Grazon

Picloram + 2,4-D

Restricted

74, 76

Habitat

Imazapyr

Aquatic

Hardball

2,4-D

Hi-Dep

2,4-D

Journey

Glyphosate + Imazapic

69, 71

Landmark

Chlorsulfuron +

sulfometuron methyl

No grazing

Landmaster

Glyphosate + 2, 4-D

69, 78

Matrix

Rimsulfuron

No Grazing

Milestone

Aminopyralid

Oasis Imazapic + 2,4-D 71, 78

Opensitel

Aminopyralid + metsulfuron

methyl

63, 73

Outlaw

Dicamba + 2,4-D

66, 78

Overdrive

Diflufenzopyr + dicamba

Panoramic

Imazapic

Paramount

Quinclorac

Pathfinder II

Triclopyr + adjuvants

Pathway

Picloram + 2,4-D

Restricted

74, 78

Perspective

Aminocyclopyrachlor +

chlorsulfuron

No Grazing

62, 64

Plateau

Imazapic

Powerline

Imazapyr

Prescott

Triclopyr + clopyralid

65, 77

Pro 60 EG

Metsulfuron methyl

Rangestar

Dicamba + 2,4-D

66, 78

Redeem

Clopyralid + triclopyr

65, 77

Resolve

Rimsulfuron

Rifle

Dicamba

Rodeo

Glyphosate

Aquatic

Roundup

Glyphosate

Sahara

Imazapyr + diuron

Restricted

Starane

Fluroxypyr

Sterling

Dicamba

Telar

Chlorsulfuron

Topsite

Imazapyr + diuron

Restricted

Tordon

Picloram

Restricted

Transline

Clopyralid

Vanquish

Dicamba

Veteran 720

Dicamba + 2,4-D

66, 78

Vista

Fluroxypyr

Weedar

2,4-D

Weed B Gon

Triclopyr

Weedmaster

Dicamba + 2,4-D

66, 78

Weedone

2,4-D

Aminocyclopyrachlor

Brand Name:

Perspective with Chlorsulfuron

Other Pre-mixes:

Streamline with metsulfuron methyl

Viewpoint with metsulfuron methyl and imazapyr

Signal word

(toxicity)

Rainfast

period

Re-entry

interval

Hay harvest

(days)

Grazing interval

(days)

Caution

4 hours

Dry formulation for use in:

• Non-cropland sites such as rights-of-way, industrial sites and

fence rows.

• Range & pasture label pending – current label restricts

livestock grazing and haying for 1 year following

application.

Environmental characteristics:

• Can be applied to water’s edge, do not apply directly to

water. Not for use on irrigation ditchbanks.

• Active on target plants through foliar and root uptake.

• Applications to newly seeded grasses or under desirable

trees and shrubs may cause injury.

• The use of a nonionic surfactant, at a minimum rate of .25%

volume/volume (1oz/3 gal), is essential.

• Perspective is a dry formulation that requires vigorous

agitation to go into solution. For sprayer tanks that do not

provide agitation it is best to fill halfway with water, create

slurry in a separate container (mix enough water and granules

to agitate until granules are totally dissolved) of the measured

herbicide, then add to tank to ensure the product goes into

solution.

Primary target species:

• Perspective provides excellent control of the noxious weed

species listed in this reference guide, with the exception of

any grass species.

• CSU / Larimer County Weed District field trials have

shown Perspective to be the most effective treatment for

control of leafy spurge and field bindweed.

Aminopyralid

Brand Name:

Milestone

Pre-mixes:

Opensight with metsulfuron methyl

Forefront with 2,4-D

Capstone with triclopyr

Signal word

(toxicity)

Rainfast

period

Re-entry

interval

Hay

harvest

(days)

Grazing

interval

(days)

Caution

2 hours

12 hours

Liquid formulation, used in:

•

Range & pasture, non-cropland sites such as rights-of-way.

Environmental characteristics :

• Can be applied to water’s edge; do not apply directly to

water.

• Active on target plants through foliar and root uptake.

• Not for use on irrigation ditchbanks.

•

Caution under certain tree species. See Label.

Primary target species :

• Canada thistle, biennial thistles, knapweeds, common

mullein, common teasel, oxeye daisy, sunflowers,

cinquefoil, absinth wormwood, hawkweeds. (Plants of

composite, legume, and polygonum families).

• Not effective for controlling grass species, kochia,

bindweed, leafy spurge, toadflax, houndstongue, or most

mustard species.

• Milestone is the most frequently recommended product

for control of Canada thistle and biennial thistles in

range and pasture.

Chlorsulfuron

Brand Name:

Telar, Glean

Pre-mixes:

Cimarron X-tra with metsulfuron methyl, Perspective with

aminocyclopyrachlor, Landmark with sulfometuron methyl

Signal word

(toxicity)

Rainfast

period

Re-entry

interval

Hay harvest

(days)

Grazing interval

(days)

Caution

4 hours

Dry formulation used in:

•

Range & pasture, non-crop and industrial sites.

Environmental characteristics:

• Can be applied to water’s edge; not directly to water.

• Chlorsulfuron has soil residual activity and is active on

weeds through foliar and root uptake.

• The use of a nonionic surfactant, at a minimum rate of

.25% volume/volume (1oz/3 gal), is essential.

• Chlorsulfuron is a dry formulation that requires vigorous

agitation to go into solution. For sprayer tanks that do not

provide agitation it is best to fill halfway with water, create

slurry in a separate container (mix enough water and

granules to agitate until granules are totally dissolved) of

the measured herbicide, then add to tank to ensure the

product goes into solution.

Primary target species:

• Mustard, biennial thistles, houndstongue, common mullein,

common teasel, puncturevine (pre and post emergence),

Dalmatian and yellow toadflax.

• Not effective for controlling most grass species, kochia,

knapweed species, or bindweed.

• The pre-mix ‘Landmark’ provides excellent pre and post

emergent control of cheatgrass and feral rye. Landmark

does not have a range & pasture label, treated areas cannot

be grazed or hayed for 1 year after application.

• Telar, applied at 2.0 oz product/acre with MSO,

provides very effective control of Dalmatian toadflax.

*Restriction dependant on rate of application

Clopyralid

Brand Name:

Transline, Lontrel, Stinger

Pre-mixes:

Curtail, Cody with 2,4-D

Redeem, Confront, Prescott with triclopyr

Signal word

(toxicity)

Rainfast

period

Re-entry

interval

Hay

harvest

(days)

Grazing

interval

(days)

Caution

2 hours

12 hours

Liquid formulation used in:

• Range & pasture, forest land, and rights-of-way.

•

Cropland and turf.

Environmental characteristics:

• Water soluble, should not be applied near water.

• Some soil activity but not as persistent as Tordon.

• Transline can be safely applied near trees and shrubs.

• Active on target plants primarily through foliar uptake,

with root uptake to a lesser degree.

Primary target species :

• Canada thistle, biennial thistles, knapweeds, common

teasel, oxeye daisy, sunflowers.

• Not effective for controlling grass species, kochia,

bindweed, leafy spurge, toadflax, houndstongue, or most

mustard species.

• Safe to use over seedling grasses to control Canada

thistle and other listed weed species on re-vegetation

sites.

Dicamba

Brand Name:

Banvel, Clarity, Rifle, Sterling, Vanquish

Pre-mixes:

Brash, Outlaw, Rangestar, Veteran 720, Weedmaster with 2,4-D

Fallowmaster with glyphosate

Signal word

(toxicity)

Rainfast

period

Re-entry

interval

Hay

harvest

(days)

Grazing

interval

(days)

Caution

4 hours

24 hours

37-70*

Liquid formulation used in:

• Range & pasture, crops, rights-of-way, and turf

Environmental characteristics:

• Water soluble, should not be applied near water.

• Active on target plants primarily through foliar uptake,

with root uptake to a lesser degree.

• Do not apply near desirable trees and shrubs.

• Higher rates can cause injury to buffalograss.

• Dicamba is a volatile product that can damage off-target

vegetation through vapor drift. Do not use when

temperatures are expected to exceed 85 degrees Fahrenheit

within 24 hours of application.

Primary target species :

• Kochia and many other annual broadleaf species. At higher

rates can be used for suppression of Canada thistle, field

bindweed and biennial thistles.

• Not effective for controlling grass species.

• Dicamba is the most frequently recommended product

used to selectively control kochia in established

grassland.

*Restriction dependant on rate of application

Diflufenzopyr

Brand Name:

Overdrive, Distinct – premixes with dicamba

(Diflufenzopyr is not sold alone, available in a premix only)

Signal word

(toxicity)

Rainfast

period

Re-entry

interval

Hay

harvest

(days)

Grazing

interval

(days)

Caution

4 hours

12 hours

Dry formulation used in:

• Range & pasture, rights-of-way, corn and fallow

Environmental characteristics:

• Primarily absorbed through foliar applications, soil uptake

to a lesser degree.

• Use of surfactant recommended – nonionic or crop oil

concentrate

• Diflufenzopyr is a dry formulation that requires vigorous

agitation to go into solution. For sprayer tanks that do not

provide agitation it is best to fill halfway with water, create

slurry in a separate container (mix enough water and

granules to agitate until granules are totally dissolved) of

the measured herbicide, then add to tank to ensure the

product goes into solution.

Primary target species:

• Kochia and many other annual broadleaf species. At higher

rates can be used for suppression of Canada thistle, field

bindweed and biennial thistles.

• Not effective for controlling grass species.

• Overdrive is most often used in range and pasture to

complement the activity of other herbicides such as

aminocylopyrachlor, clopyralid, picloram, quinclorac and

triclopyr.

• Overdrive + Paramount or Overdrive + Perspective

tank mix provides very effective control of leafy spurge.

Fluroxypyr

Brand Name:

Vista, Starane

Signal word

(toxicity)

Rainfast

period

Re-entry

interval

Hay

harvest

(days)

Grazing

interval

(days)

Warning

1 hour

12 hours

Liquid formulation used in:

• Non-cropland areas such as non-irrigation ditch banks,

rights-of-way, industrial sites including grazed areas within

sites, small grains, corn and fallow.

Environmental characteristics:

• Active on target plants through foliar uptake, no soil

residual activity.

•

Not for use on irrigation ditchbanks.

Primary target species :

• Kochia, prickly lettuce, puncturevine, sunflower and plants

of the nightshade family.

• Not effective for controlling grass species, Canada thistle

or field bindweed.

• Safe to use over newly seeded grasses to control kochia

and other listed weed species on re-vegetation sites.

Glyphosate

Brand Name:

Roundup, current brand names too numerous to list

Pre-mixes:

Too numerous to list.

Signal word

(toxicity)

Rainfast

period

Re-entry

interval

Hay

harvest

(days)

Grazing

interval

(days)

Caution

1-4

hours*

4 hours

Liquid formulation used in:

•

Crop, non-crop, fallow.

Environmental characteristics

• **Non-selective herbicide (active on grasses and broadleaf

plants) that controls most annuals and perennials.

• Active through foliar uptake, has no soil activity.

• Usually surfactant is part of mix. Do not need to add extra.

• Labeled for use up to water’s edge. At least one

formulation, Rodeo, labeled for use in and around water.

An aquatic non-ionic surfactant is needed.

Primary target species:

• Effective for control of most grasses and broadleaf species.

• Selective control of winter annuals when applied at low

rates in the late winter or early spring when desirable

perennial grasses are dormant.

*Check product label.

** Not approved for the Weed District cost-share program.

Imazamox

Brand Name:

Clearcast,

Raptor – for use in alfalfa, dry bean, soybeans and other legume

crops

Signal word

(toxicity)

Rainfast

period

Re-entry

interval

Hay

harvest

(days)

Grazing

interval

(days)

Caution

2 hours

4 hours

Labeled uses (sites):

• Clearcast is labeled for control of undesirable emergent and

floating aquatic vegetation in and around standing and

flowing water. Applications may be made to control

undesirable wetland, riparian, and terrestrial vegetation

growing in and around surface water including irrigation

ditchbanks, though some limitations and restrictions exist –

SEE LABEL.

Environmental characteristics :

• Can be applied in and around standing and flowing water

including irrigation ditchbanks.

• Active on target plants through foliar and root uptake.

• Choose a surfactant that is approved for aquatic use when

applying in or near water.

• For terrestrial uses choose a non-ionic surfactant, MSO or

crop oil concentrate for best results.

Primary target species :

• Cattails, purple loosestrife, ragweed species, whitetop and

other mustard species.

• Perennial grasses and other desirable species such as sedges

and rushes may be suppressed. Degree of injury is rate

dependant.

•

Clearcast is very effective on cattails.

Imazapic

Brand Name:

Plateau, Panoramic

Pre-mixes:

Journey with glyphosate

Oasis with 2,4-D

Signal word

(toxicity)

Rainfast

period

Re-entry

interval

Hay

harvest

(days)

Grazing

interval

(days)

Caution

1 hour

12 hours

Liquid formulation used in:

•

Range and pasture and rights-of-way.

Environmental characteristics :

• Imazapic has soil residual activity, and is taken up in plants

through foliage and roots.

• This product has runoff potential and should not be used on

hillsides sloping toward water.

• Do not apply to water or inside irrigation ditches.

• Application timing, use rate and choice of surfactant can be

critical, read the label carefully.

• High rates can be injurious to cool season grasses such

as smooth brome.

Primary target species:

• Leafy spurge, cheatgrass, mustard species, Dalmatian

toadflax, field bindweed, common teasel, houndstongue,

Russian knapweed, suppression of thistle species at higher

rates.

• Not effective on kochia or diffuse and spotted knapweed.

• Imazapic is the most commonly used herbicide for

selective control of cheatgrass in newly seeded and

established grass.

Imazapyr

Brand Name:

Arsenal, Ecomazapyr 2, Habitat, Powerline

Pre-mixes:

Sahara, Topsite with diuron.

Chopper – ready to use pre-mix with adjuvants for cut-stump or

basal bark treatments.

Clearstand with metsulfuron methyl

Signal word

(toxicity)

Rainfast

period

Re-entry

interval

Hay

harvest

(days)

Grazing

interval

(days)

Caution

1 hour

Liquid formulation used in:

• Arsenal – Range and pasture (spot treatments), non-crop

areas such as industrial sites, and rights-of-way.

• Habitat – Aquatic use - for control of undesirable

emergent and floating aquatic vegetation in and around

standing and flowing water. Applications may be made to

control undesirable wetland, riparian, and terrestrial

vegetation growing in and around surface water.

Environmental characteristics :

• **Non-selective herbicide (controls grasses broadleaf

plants and brush).

• Persistent in soil, breaks down rapidly in water, uptake in

plants through foliage and roots.

• Arsenal can be applied up to water’s edge. Habitat has an

aquatic label – can be used in and around water. Not for

use on irrigation ditch banks.

Primary target species:

• Often used in mixes for total vegetative control (parking

lots, industrial sites, etc.).

• Imazapyr is very effective for control of tamarisk,

Russian olive and other woody species by foliar

application or cut-stump treatments.

Metsulfuron methyl

Brand Name:

Ally, Cimarron, Escort, Pro 60 EG, MSM 60DF

Pre-mixes:

Cimarron Max with dicamba and 2,4-D

Cimarron X-tra with chlorsulfuron

Opensight with aminopyralid

Clearstand with imazapyr

Viewpoint with aminocyclpyrachlor and imazapyr

Streamline with aminocyclopyrachlor

Signal word

(toxicity)

Rainfast

period

Re-entry

interval

Hay harvest

(days)

Grazing

interval (days)

Caution

4 hours

0-3*

Dry formulation used in:

•

Range and pasture, rights-of-way, wheat, barley, and fallow.

Environmental characteristics:

• Can be applied to water’s edge; do not apply directly to

water or under desirable trees and shrubs.

• The use of a nonionic surfactant, at a minimum rate of .25%

vol/vol (1 oz/3 gal), is essential effectiveness.

• Metsulfuron methyl is a dry formulation that requires

vigorous agitation to go into solution. For sprayer tanks that

do not provide agitation it is best to fill halfway with water,

create slurry in a separate container (mix enough water and

granules to agitate until granules are totally dissolved) of the

measured herbicide, then add to tank to ensure the product

goes into solution.

Primary target species :

• Mustards such as hoary alyssum, hoary cress, perennial

pepperweed, blue mustard, flixweed and tumble

mustard.

• Effective for control of houndstongue, common mullein,

common teasel, some brush species and assorted annual

broadleaf species.

• Not effective for controlling grass species, kochia, knapweed

species or Canada thistle.

*Restriction dependant on rate of application

Picloram – *Restricted Use Product

Brand Name:

Tordon, Outpost

Pre-mixes:

Grazon, Pathway with 2,4-D

Signal word

(toxicity)

Rainfast

period

Re-entry

interval

Hay

harvest

(days)

Grazing

interval

(days)

Caution

2 hours

12 hours

Liquid formulation used in:

• Range and pasture, fallow cropland, and non-cropland

areas.

Environmental characteristics:

• This product is soluble in water and persistent in soil.

• Do not apply on ditchbanks or bottoms, near water, or

under desirable trees and shrubs.

• Tordon is residually active in the soil, and taken into a plant

through foliar absorption and/or root uptake.

Primary target species:

• Field bindweed, Canada thistle, biennial thistles,

knapweeds, toadflax, leafy spurge, houndstongue, woody

species.

• Not effective for controlling kochia or most mustard

species.

• Not effective for grass control, though will suppress certain

established pasture grasses such as smooth brome.

* Restricted Use Products for retail sale to and use only by

Certified Applicators or persons under their direct supervision.

See criteria in the preceding ‘definitions’ section page 59.

Quinclorac

Brand Name:

Paramount, Facet, Drive

Signal word

(toxicity)

Rainfast

period

Re-entry

interval

Hay

harvest

(days)

Grazing

interval

(days)

Caution

6 hrs

12 hours

Dry or liquid formulation used in:

• Range & pasture, rice, sorghum, fallow and turf.

Environmental characteristics:

• Can be applied to water’s edge. Do not apply directly to

water or in areas where surface water is present.

• Quinclorac is active on target plants through foliar and root

uptake.

• Add methylated seed oil to tank mix at rate of 1 quart/acre

• Do not apply more than 16 oz/acre per calendar year.

• Quinclorac is a dry formulation that requires vigorous

agitation to go into solution. For sprayer tanks that do not

provide agitation it is best to fill halfway with water, create

slurry in a separate container (mix enough water and

granules to agitate until granules are totally dissolved) of

the measured herbicide, then add to tank to ensure the

product goes into solution.

Primary target species:

• Leafy spurge, field bindweed, annual grasses such as

barnyardgrass, crabgrass, and green and yellow foxtail.

• Overdrive + Paramount tankmix is one of the most

effective treatments for control of leafy spurge.

Rimsulfuron

Brand Name:

Matrix, Resolve

Signal word

(toxicity)

Rainfast

period

Re-entry

interval

Hay

harvest

(days)

Grazing

interval

(days)

Caution

4 hours

Dry formulation used in:

• Agronomic crops and control of certain invasive species,

such as cheatgrass and feral rye, in areas undergoing

restoration or re-vegetation.

• No range & pasture label – no livestock grazing or

haying for one year following application on rangeland

or pasture.

Environmental characteristics:

• Rimsulfuron is primarily active through foliar uptake, short

soil residual activity for weed control.

• The use of a nonionic surfactant, at a minimum rate of

.25% volume/volume (1oz/3 gal), is essential for this

product to be effective.

• Rimsulfuron is a dry formulation that requires vigorous

agitation to go into solution. For sprayer tanks that do not

provide agitation it is best to fill halfway with water, create

slurry in a separate container (mix enough water and

granules to agitate until granules are totally dissolved) of

the measured herbicide, then add to tank to ensure the

product goes into solution.

Primary target species:

• Annual grasses such as cheatgrass and feral rye,

puncturevine and plants of the mustard family.

• Rimsulfuron may be injurious to certain cool season

perennial grasses such as western wheatgrass.

Triclopyr

Brand Name:

Element 4, Element 3A, Garlon 4, Garlon 3A, Weed B Gon,

Capstone

Pre-mixes:

Redeem, Prescott with clopyralid

Crossbow with 2,4-D.

Capstone with aminopyralid

Pathfinder II – ready to use pre-mix with adjuvants necessary for

effective cut-stump or basal bark treatments.

Many other pre-mix products are available.

Signal word

(toxicity)

Re-entry

interval

Hay harvest

(days)

Grazing

interval

(days)

Caution –

Danger*

12 hours

Liquid formulation used in:

• Range and pasture, aquatic use (in and around water), non-

cropland, rights-of-way and turf.

Environmental characteristics :

• Ester formulation can be volatile, and is best used when

temperature is not expected to exceed 85 degrees.

• Triclopyr has some soil activity but is primarily taken up by

plants through foliage and/or vascular tissue (cut-stump or

basal bark treatment).

• Restrictions near water vary with formulation – Garlon 4 –

up to water’s edge. Garlon 3A has an aquatic label, can be

used to control target vegetation in standing water.

•

Not for use on irrigation ditch banks.

Primary target species:

• Used for controlling broadleaf weeds and woody

vegetation. Has little or no effect on grasses.

• Used as a cut-stump or basal bark treatment for control

of Russian olives, tamarisk, and other woody species.

*Signal word varies with differing triclopyr formulations

2,4-D

Brand Name:

Amine 4, Formula 40, Hi-Dep, Weedar, Weedone, Hardball, and

many others too numerous to list.

Pre-mixes:

Too numerous to list.

Signal word

(toxicity)

Rainfast

period

Re-entry

interval

Hay

harvest

(days)

Grazing

interval

(days)

Danger –

Caution*

1 hour

48 hours

Liquid formulation used in:

• A wide range of applications including range and pasture,

crops, and non-cropland.

Environmental characteristics :

• 2,4-D is the active ingredient in many compounds, and is

available in ester, amine and acid formulations.

• Ester formulations are volatile and may injure non-target

plants through vapor drift. Low volatility (LV) esters are

less susceptible to vapor drift, but may still volatilize at

temperatures above 85 degrees. Amine formulations

typically do not volatilize, and should be used during

warmer weather.

• Ester formulations penetrate foliage more readily, and are

usually used at lower rates than amine formulations.

• An acid formulation, brand name – Hardball, is nonvolatile

and labeled for aquatic and rangeland use.

• 2,4-D has little to no soil activity, uptake in plants is

through foliage.

Primary target species:

• Used for control of most broadleaf weeds. Higher rates for

control or suppression of perennials.

• Not effective for control of grasses, kochia or knapweed

species.

*Signal word varies with differing 2,4-D formulations

Sprayer Calibration

It is critical to know the output of a sprayer in order to be accurate

in adding an herbicide to the tank.

Handgun

1. Measure a calibration plot that is exactly 18.5 ft X 18.5

ft (128

of an acre).

2. Spray the plot uniformly with water, keeping the

sprayer pressure constant. Note the number of seconds

required.

3. Spray into a bucket for the same number of seconds,

again keeping the sprayer pressure constant.

4. Measure the number of ounces of water in the bucket.

5. Number of ounces of water measured from the bucket

is equal to the number of gallons per acre (GPA) the

sprayer is delivering.

Spray

Volume

(GPA)

Amount of Herbicide to Add to Each Gallon of Water

in Ounces

Recommended Herbicide Rate/Acre (from label)

1 oz

4 oz

7 oz

1 Pint

1 Quart

15 .067 .268 .469 1 2

20 .05 .2 .35 0.83 1.67

30 .033 .132 .231 0.5 1

40 .025 .1 .175 0.42 0.83

50 .02 .08 .14 0.33 0.63

2 tablespoons = 6 teaspoons = 1 fluid ounce = 29.57 milliliters

8 fluid ounces = 1 cup; 2 cups = 1 pint; 2 pints = 1 quart;

4 quarts = 1 gallon; 1 gallon = 128 fluid ounces

1ounce (dry) = 28.35 grams; 16 ounces = 1 pound

1 acre = 43,560 square feet; 1 meter = 3.281 feet

1 gallon of water = 8.3453 pounds of water

Boom or Boomless Sprayer Calibration

Volume method

1. On level ground, fill sprayer tank to a known level with

water and drift agent (if using).

2. Turn on sprayer till all nozzles have output, shut off and

refill tank to desired level.

3. Measure off ¼ of an acre, marking the start and end with a

flag.

Width of boom Linear feet to

swath in feet cover ¼ acres

2 5445

4 2723

6 1815

8 1362

10 1090

20 545

30 363

4. Drive the measured ¼ acre with the speed that you will be

using to spray, turning on the sprayer at the starting mark

and off at the ending flag.

5. Return to the level ground that you filled the sprayer at and

carefully measure the amount of water it takes to refill to

the known level from step 1.

6. Multiply the amount from above step by 4. This is GPA

(Gallons Per Acre).

Stationary method

1. On level ground, fill sprayer tank with water and drift agent

(if using).

2. Turn on sprayer and measure spray pattern width in feet.

3. Collect liquid from each nozzle for 1 minute. Measure in

ounces.

4. Divide ounces by 128 to determine GPM (Gallons Per

Minute).

5. Determine speed (MPH) you will be using during spraying.

6. With the below formula calculate GPA (Gallons Per Acre).

GPA = GPM x 495

MPH x swath width (feet)

References

More extensive information can be obtained from:

Plant identification and control:

 Larimer County Weed District - www.larimer.org/weeds

 Colorado Dept. of Agriculture Noxious Weed Program -

www.colorado.gov/ag/weeds

 Colorado Weed Management Association - www.cwma.org

 Colorado State University Extension small acreage

management- www.ext.colostate.edu/sam

 Plant identification

- www.easterncoloradowildflowers.com

- Weeds of the West

- Aquatic and Riparian Weeds of the West

- Thistles of Colorado

 Poisonous plants

- ‘A Guide to Plant Poisoning of Animals in North

America’

- Dr. Knight’s website

http://southcampus.colostate.edu/poisonous_plants

- or e-mail Dr. Knight at A[email protected]

 Seeding and soil recommendations

- NRCS office – 970-295-5655

Noxious weed awareness organizations in Larimer County:

 North Fork Weed Coop - www.northforkweedcoop.org/

 Estes Park Land Stewardship Association -

www.elsainfo.org

Weed law:

 The Colorado State Noxious Weed Act -

www.colorado.gov/ag/weeds

 Applicator education and continuing education information

- www.colostate.edu/Depts/SoilCrop/extension/CEPEP

Pesticide labels and safety information:

 Information on pesticide toxicity, environmental fate, or

mode of action 1-800-858-7378

 Rocky Mountain Poison and Drug Center 1-800-222-1222

 Chemtrec 1-800-424-9300 (Use for chemical spills.)

 www.cdms.net (Use for complete labels and MSDS)

Glossary

Alien plant – A plant species not native to the United States.

Annuals – A plant which completes its life cycle in one season,

spring through fall.

Biennials – Plants that require 2 seasons to complete life cycle.

They typically germinate in late summer, over-winter, flower, and

set seed by mid-summer of the following year.

Bolt – The initial stem arising from rosette leaves as a plant

matures. The term ‘bolting’ is often used to describe the growth

stage between rosette and flowering.

Bracts – A small leaf-like structure below the flower.

Calibration - To check, adjust, or determine spray equipment

output. (ex. Gallons Per Acre)

Containment – Defined in the Colorado Noxious Weed Act,

maintaining an intensively managed buffer zone that separates

infested regions, where suppression activities prevail, from largely

un-infested regions where eradication activities prevail.

Eradication - Defined in the Colorado Noxious Weed Act,

reducing the reproductive success of a noxious weed species or

specified noxious weed population in largely un-infested regions to

zero and permanently elimination the species or population within

a specified period of time. Once all specified weed populations are

eliminated or prevented from reproducing, intensive efforts

continue until the existing seed bank is exhausted.

Forb - A broad-leaved herb other than a grass.

Inflorescence – The flowering part of the plant.

Invasive plants – Plant species that are competitive enough to

become dominant in a particular area.

Lifecycle – A description of a plant’s duration - annuals, biennials,

perennials, simple perennials, winter annuals.

Lobed – To cut into shallow segments.

Native plant – A plant that is indigenous to Colorado.

Noxious weed - Defined in the Colorado Noxious Weed Act, as an

alien plant that have been designated by rule as being noxious, and

meets one or more of the following criteria:

(a) Aggressively invades or is detrimental to economic

crops or native plant communities;

(b) Is poisonous to livestock;

(d) The direct or indirect effect of the presence of the plant

is detrimental to the environmentally sound

management of natural or agricultural ecosystems.

Ornamental – A plant grown by nurseries with traits desirable for

landscaping, such as flower color, drought tolerance, shading, etc.

Perennials – Plants that live 3 or more years.

Raceme – An arrangement of flowers along a stem on individual

stalks about equal in length.

Restoration – A management action that results in range or

pasture improvement without re-seeding.

Re-vegetation – A management action that results in range or

pasture improvement including seeding.

Rhizomes – An underground stem, usually lateral, sending out

shoots above ground and roots below.

Rosette – A somewhat round, flattened cluster of leaves typical of

the early growth stage of many biennial plant species.

Seedling – A newly germinated plant, not yet mature.

Sessile – A plant without a stalk.

Simple perennials – Perennial plants that reproduce by seed only.

Spikes – A usually long inflorescence with sessile flowers.

Succulent – Fleshy.

Suppression - Defined in the Colorado Noxious Weed Act as

reducing the vigor of noxious weed populations within an infested

region, decreasing the propensity of noxious weed species to

spread to surrounding lands, and mitigation the negative effects of

noxious weed populations on infested lands. Suppression efforts

may employ a wide variety of integrated management techniques.

Tiller - A shoot, often one that sprouts from the base of a grass.

Winter annuals – Plants which germinate in late summer or fall,

over-winter and complete life cycle by the following spring or

summer (ex. cheatgrass, tumble mustard).

Index

2,4-D, 17, 19, 20, 21, 22,26,

27, 29, 32, 40, 41, 42, 43,

45, 50, 53, 55, 60, 61, 63,

65, 66, 71, 73, 74, 77, 78

Absinth wormwood, 63

Alpaca, 49

Aminocyclopyrachlor, See

Perspective, 60, 61, 62, 63,

Aminopyralid, See Milestone,

60, 61, 63, 73, 77

Arrow grass, 47

Baneberry, 47

Barnyardgrass, 47, 75

Beard tongue, 48

Bison, 49, 54

Bitterweed, 47

Blue flax, 47

Blue mustard, 42, 48, 63, 64,

65, 70, 71, 73, 74, 76

Blue-green algae, 47

Bouncingbet, 47

Bracken fern, 48

Broom snakeweed, 48

Buckwheat, 47

Buffalograss, 66

Bull thistle, 16, 24, 50, 63, 64,

65, 66, 67, 71, 74, 81

Burdock, 47

Buttercup, 47, 51

Canada thistle, 7, 11, 16, 26,

27, 47, 49, 63, 65, 66, 67,

68, 73, 74

Cat, 49

Cattails, 22, 70

Cattle, 20, 32, 41, 42, 45, 49,

51, 52, 54, 55, 56

Caution signal word, 59, 62,

63, 64, 65, 66, 67, 69, 70,

71, 72, 73, 74, 75, 76, 77,

Cheatgrass, 37, 38, 47, 49, 64,

71, 76, 83

Chlorsulfuron, See Telar, 58,

60, 61, 62, 64, 73

Cinquefoil, 63

Clopyralid, See Transline,60,

61, 65, 67, 77

Colorado rubberweed, 47

Common cocklebur, 47

Common mullein, 18, 38, 58,

63, 64, 73

Common teasel, 16, 27, 63, 64,

65, 71, 73

Confront, 60, 65

Conservation Districts, 3

Corn cockle, 47

Crabgrass, 75

Crazy Weed, 51

Crop oil concentrate (COC),

35, 44, 58, 67, 70

Crown vetch, 48

Curly dock, 47

Cypress spurge, 16, 20

Dalmatian toadflax, 16, 35, 36,

58, 63, 64, 65, 71, 74,

Danger/Poison signal word,

59, 77, 78

Death camas, 46, 49, 50

Dicamba, 17, 19, 26, 27, 29,

32, 40, 42, 43, 45, 50, 60,

61, 66, 67, 73

Diffuse knapweed, 16, 30, 63,

64, 65, 71, 73, 74, 78

Diflufenzopyr, See Overdrive,

60, 61, 67

Dog, 49

Dogbane, 46

Downy brome, 37

Elderberry, 47

Escort, 19, 27, 28, 29, 33, 38,

41, 42, 51, 52, 53, 55, 60,

Feral rye, 39, 64, 76

Field bindweed, 40, 47, 49, 62,

66, 67, 68, 71, 74, 75

Flatweed, 48

Flixweed, 42, 48, 63, 64, 65,

70, 71, 73, 74, 76

Fluroxypyr, See Vista, 61, 68

Foxtail, 47, 75

Fringed sage, 48

Garlon 3A, 22, 35, 44, 52, 53,

54, 55, 56, 60, 77

Garlon 4, 35, 44, 52, 54, 56,

60, 77

Geyer larkspur, 46, 48, 49, 51

Glean, 60, 64

Glyphosate, See Roundup, 27,

60, 61, 66, 69, 71

Goats, 32, 49, 51, 53, 56

Golden banner, 48

Goldenrod, 47

Goldenweed, 48

Greasewood, 47

Groundsel, 47, 48

Gumweed, 48

Habitat, 22, 35, 40, 44, 60, 72

Hoary alyssum, 16, 28, 42, 48,

49, 63, 64, 65, 70, 71, 73,

74, 76

Hoary cress, 16, 29, 42, 48, 63,

64, 65, 70, 71, 73, 74, 76

Horse, 23, 28, 31, 48, 49, 52

Horsetail, 48

Houndstongue,16, 29, 47, 48,

49, 63, 64, 65, 71, 73, 74

Humans, 32, 43, 49, 50, 54, 59

Imazapic, See Plateau, 56, 59,

Imazapyr, See Habitat, 58, 61,

Indian paintbrush, 48

Japanese brome, 37

Knotweed, 47

Kochia, 41, 42, 45, 47, 49, 63,

64, 65, 66, 67, 68, 71, 73,

74, 78

Lambsquarter, 47

Larimer County Weed District

Boundary, 6

Contacts and office map, 5

History, 7

Services, 7

Larkspur, 46. 48, 49, 51

Leafy spurge, 11, 16, 32, 35,

47, 49, 62, 63, 65, 67, 71,

74, 75

Llama, 49

Locoism, 52

Locoweeds, 48, 49, 51, 52

Low larkspur, 46, 48, 49, 51

Lupine, 48

Mallow, 47

Matrix, 38, 39, 42, 61, 76

Mediterranean sage, 16, 18, 19

Methylated seed oil (MSO),

36, 38, 52, 58, 64, 70, 75,

Metsulfuron methyl, See

Escort, 58, 60, 61, 62, 63,

64, 72, 73

Milestone, 19, 21, 23, 25, 26,

27, 31, 38, 41, 54, 61, 63

Milk vetch, 48

Milkweeds, 46

Mountain mahogany, 47

Mountain thermopsis, 48

Musk thistle, 16, 24, 25, 50,

63, 64, 65, 66, 67, 71, 74,

Myrtle spurge, 16, 20, 36, 49

Nightshades, 47

Nonionic surfactant (NIS), 19,

58, 62, 64, 69, 70, 73, 76

NPDES, 4, 57

NRCS, 14, 15, 81

Onion, 48, 50

Orange hawkweed, 16, 21, 36,

Overdrive, 36, 61, 67, 75

Oxeye daisy, 63, 65

Paramount, 32, 40, 61, 67, 75

Pawnee Buttes Seed Co., 2

Peas, 48

Perennial pepperweed, 16, 33,

42, 48, 63, 64, 65, 70, 71,

73, 74, 76

Personal Protective Equipment

(PPE), 59

Perspective, 25, 26, 31, 32, 40,

43, 61, 62, 64, 67

Pesticide Safety Education

Program, 59

Picloram, See Tordon, 60, 61,

67, 74

Pigweed, 47

Plateau, 27, 28, 29, 31, 32, 33,

36, 38, 40, 41, 42, 61, 71

Poison hemlock, 46, 48, 49,

53, 55

Poison ivy, 48, 49, 54

Poison suckleya, 47

Ponderosa pine, 48, 49, 54, 55

Poultry, 49

Prickly lettuce, 68

Prince's plume, 48

Private Applicator’s License,

Puncturevine, 43, 47, 49, 64,

68, 76

Purple locoweed, 48, 49, 51

Purple loosestrife, 16, 22, 36,

Purslane, 47

Quinclorac, See Paramount,

58, 61, 67, 75

Ragweed, 47, 70

Rifle, 61, 66

Rimsulfuron, See Matrix, 58,

61, 76

Rocky Mountain junipers, 54

Rodeo, 22, 27, 53, 55, 61, 69

Roundup, 12, 38, 39, 50, 54,

61, 69

Russian knapweed, 16, 23, 31,

48, 49, 63, 64, 65, 71, 73,

74, 78

Russian olive, 36, 44, 72, 77

Russian thistle, 41, 45, 47, 49

Saltbush, 48

Saltcedar, See Tamarisk

Sand sage, 48

Scotch thistle, 16, 24, 25, 50,

63, 64, 65, 66, 67, 71, 73,

74, 81

Senecio, 47, 48

Sheep, 32, 41, 45, 49, 51, 52,

Smartweed, 47

Smooth brome, 32, 71, 74

Sulfometuron methyl, 61, 64

Sorghum, 15, 47, 75

Spotted knapweed, 16, 30, 63,

64, 65, 71, 73, 74, 78

St. Johnswort, 47

Sudangrass, 15

Sunflower, 21, 47, 63, 65, 68

Sweetclover, 47, 48

Swine, 49, 53

Tamarisk, 16, 34, 72, 77

Tansy mustard, 42, 47

Telar, 19, 25, 26, 27, 28, 29,

31, 33, 36, 38, 41, 42, 43,

53, 55, 61, 64

Tordon, 12, 19, 21, 23, 25, 26,

29, 30, 31, 32, 36, 40, 41,

43, 51, 52, 54, 56, 61, 65,

Transline, 21, 23, 25, 26, 27,

30, 31, 41, 52, 61, 65

Triclopyr, See Garlon, 56, 58,

60, 61, 63, 65, 67, 77

Tumble mustard, 42, 48, 63,

64, 65, 70, 71, 73, 74, 76,

Vista, 42, 43, 61, 68

Warning signal word, 59, 68

Water hemlock, 46, 48, 49, 55

Western chokecherry, 47, 49,

Western false hellebore, 48

Western serviceberry, 47

Western wheatgrass, 76

White fall aster, 48

White locoweed, 48, 49, 51

Wild carrot, 47, 53

Wild oat grass, 47

Wild pea, 48

Wood sorrel, 47

Yellow alyssum, 42

Yellow starthistle, 16, 23, 48,

Yellow sweetclover, 48

Yellow toadflax, 16, 35, 36,

63, 64, 65, 74

Photograph credits:

Anthony Knight

Sue Burke

Bugwood.com

Colorado Department of

Agriculture

Jim Sebastian

Kelly Uhing

Larimer County Weed

District Staff

Alex Somero

Notes