United States Department ofAgriculture

Field Guide for Managing

Whitetop in the Southwest

Forest 

Service

Southwestern

Region TP-R3-16-20 Revised June 2017
Cover Photos

Top left: Chris Evans, Illinois Wildlife Action Plan,Bugwood.org 

Top right: Steve Dewey, Utah State University, Bugwood.org 

Lower right: Chris Evans, River to River CWMA,Bugwood.org

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1 

Whitetop (Cardaria draba (L.) Desv., formerly known as Lepidium draba) 

Mustard family (Brassicaceae)

Whitetop is listed as a noxious weed in Arizona and New 

Mexico. This field guide serves as the U.S. ForestService’s 

recommendations for management of whitetop in forests, 

woodlands, and rangelands associated with its

Southwestern Region. The Southwestern Region covers 

Arizona and New Mexico, which together have 11 national

forests. The Region also administers 4 national grasslands

located in northeastern New Mexico, western Oklahoma, 

and the Texas panhandle.

Description

Whitetop (synonyms: heart-podded hoary cress, hoary 

cardaria, whiteweed, peppergrass) is an introduced,

creeping, perennial plant that grows up to 2 feet tall. It is 

similar in appearance to two closely related Cardaria 

species: C. chalepensis (lens-podded hoary cress) and C. 

pubescens (globe-podded hoary cress). These three exotics

are members of the mustard family (Brassicaceae) and are

often grouped together because they invade similar sites

and are equally difficult to control. The primary

distinguishing characteristic between these species is the 

type and shape of the fruit, which is an indehiscent 

(remaining closed at maturity) pod called a silicle. C. 

draba has heart-shaped pods that become flattened with 

prominent veins as they dry. C. chalepensis has oval or 

lens-shaped pods that do not become flattened and veins 

are not prominent. C. pubescens has globose, hairy 

purplish pods that remain inflated when dry.

Growth Characteristics

• Herbaceous, broadleaved, perennial plant; typically 

grows 16 to 20 inches tall.

• Deep, long-lived taproots that store carbohydrates; 

extensive creeping root system.

• Plants have a gray-green, soft-hairy appearance; 

grayish stems grow upright or along ground without

rooting at the nodes (procumbent); lower portion of 

plant tends to be hairier and have more leaves; 

branching occurs primarily in upper portion of plant.

• Leaves alternate; rosette leaves and basal leaves of 

mature plants taper to a petiole. When mature, lower 

leaves are long and slender; upper leaves are obovate 

with smooth to slightly toothed margins; arrowheadlike lobes of leaves clasp the stem; leaves covered 

with short, white hairs.

• Flat-topped inflorescence (corymb of racemes) has 

white 4-petalled flowers; flowers have 6 stamens; 1 

pistil; sepals are green; petals are spoon-shaped.

• Indehiscent fruits are heart-shaped, 2-chambered 

silicles with a distinct beak (a persistent style) on the

end opposite the notch; one ovoid, reddish-brown 

seed per chamber.

Ecology

Impacts/Threats

Whitetop produces low quality forage; dense infestations 

can crowd out desirable plants and reduce animal diversity. 

The foliage contains glucosinolates, which are toxic to

cattle and decompose into allelopathic compounds that can

impede germination and growth of desirable plants.

Invasions of whitetop often occur in sensitive areas, which 

can limit control options.

Site/Distribution

Although whitetop grows on soils ranging from moderately 

saline to acidic, it favors disturbed, unshaded areas with 

moderately moist, alkaline soils. Whitetop is widely 

distributed across the western U.S. and can be found along 

roadsides or irrigation ditches, and in rangeland meadows, 

sub-irrigated pastures, and hay fields. 

Spread

Seed is dispersed by water, wind, and animals; seed may

move great distances as a contaminant in other types of 

seed. New shoots are commonly grown from root 

fragments that can be spread broadly in displaced soil, hay 

bales used for erosion control, or alfalfa hay. Seed or root 

fragments may adhere to surfaces and undercarriages of 

vehicles and road maintenance equipment.
2 

Invasive Features

Whitetop is adaptable to a wide range of habitats. It

produces up to 4,800 seeds per plant that are viable for up 

to 3 years in soil. In warmer climates, whitetop may 

produce several seed crops during a growing season. It

also has a deep taproot and a creeping lateral root system. 

Large carbohydrate reserves within the roots enable shoots 

to emerge early and grow rapidly in the spring thereby 

allowing it to outcompete other species. Root fragments 

less than 1-inch long may re-sprout to form new shoots. 

Management

Due to the extensive creeping root system associated with 

whitetop, large populations of this species are a challenge 

to eradicate if not an impossibility once established. 

Components of a successful control program include

repeated treatments, monitoring of treated areas, and 

measures taken to control missed plants, re-sprouts, and 

newly emerged seedlings. Combining control methods 

should always be considered in a long-term approach to

control whitetop.

The following actions should be considered when planning 

an overall management approach:

• Maintain healthy plant communities to limit whitetop 

infestations. This may involve preventing excessive 

grazing and reseeding areas with desirable grasses 

and forbs after disturbance.

• Practice prevention and eradicate new populations of 

whitetop as early as possible.

• Use certified weed-free hay; use pellets to feed horses 

in backcountry areas.

• Periodically check areas where hay bales are used to 

control erosion or where soils have been imported for 

presence of whitetop.

• Combine mechanical, cultural, biological, and 

chemical methods for effective whitetop control.

• Implement annual monitoring and follow-up 

treatment for missed plants and seedlings.

• Detect, report, and map extensive infestations. Keep 

annual records of reported infestations.

Table 1 summarizes some management options for 

controlling whitetop under various situations. Further

details on these management options are explained below. 

Choice of individual control method(s) for whitetop 

depends on many factors including the extent and density

of infestation; current land use and site condition; 

accessibility, terrain, and microclimate; and nontarget flora 

and fauna present. Other considerations include treatment 

effectiveness, overall cost, and the number of years needed 

to achieve control. More than one control method may be 

needed for a particular site.

Physical Control

Although labor intensive and costly, physical methodsthat

are consistently and repeatedly used can be effective at

controlling whitetop. Effectiveness of physical methodsis 

usually improved when combined with herbicide control.

Manual Methods

Hand removal – Hand digging or grubbing may be

feasible for small, isolated populations or for plants located

in sensitive areas such as riparian corridors. Ideally, the

entire root system should be dug out before the seed forms.

Debris should be disposed of by burning piled plants or by

bagging and then depositing the bags in a landfill.

Mechanical Methods

When using machinery to manage whitetop, the equipment

should be cleaned after use to prevent movement ofseeds

or root fragments into un-infested areas.

Mowing – By itself, mowing is not recommended as it can 

contribute to further spread and increased densities of 

whitetop. In agronomic lands or areas with level ground 

where mowing is practical, cutting the weed in

combination with later well-timed herbicide applications 

will improve control effectiveness. Mow whitetop early in 

the growth season when it is at flower bud stage. Allow the 

shootsto re-sprout and then apply herbicide when plants 

again reach flower bud stage. Mowing causes the plant to 

produce larger leaves that are perpendicular to the ground 

which gives better access of herbicide into the lower third 

of leaves. An alternative is to spray plants in late summer

to early fall and then mow in the spring. New shoots will 

likely be produced, and repeat spraying is usually
3 

Table 1. Management options*

Site Physical Control Cultural Control Biological Control Chemical Control

Roadsides,

fence lines,

or non-crop

areas

Mow at late bud to early

flower stage; apply

herbicide to re-sprouts.

Remove small patches by

hand pulling.

Use seed, mulch, and fill 

materials certified to be 

weed-free.

Clean machinery following

activity in infested areas.

Train road crews and the

public to identify and report 

infestations; map reported

populations.

Biocontrol agents are 

currently unavailable.

Spray at bud to early flower

stage.

For ground application, use 

truck-mounted or tractorpulled spraying equipment.

Wash under vehicle after

application to prevent spread.

Rangelands,

pastures, or

riparian

corridors 

For seedlings, use initial

deep cultivation followed

by repeat cultivation at a 4 

to 5-inch depth every 5 to

10 days during the growth 

season; repeat for 2 to 4 

consecutive years.

Prescribed burning is NOT

recommended.

Use seed and forage hay 

certified to be weed-free;

use pellets for horses in 

backcountry areas.

Monitor areas where soil

was imported or hay bales

were used for erosion 

control.

Reseed with competitive

desirable plants.

Although slightly toxic to 

cattle, prescribed grazing 

with sheep or goats may be

considered in combination

with other methods. Closely

manage grazing to prevent 

overuse of desirable species. 

Biocontrol agents are

currently unavailable.

For extensive and dense

infestations, use ground or

aerial broadcastspraying. 

For sparse infestations, use 

backpack or hand-held

sprayer.

Wilderness,

other natural

areas, and/or

small

infestations

Hand dig or grub small

patches; remove as much

of the root as possible; bag 

and dispose of debris

appropriately.

Use seed and forage hay 

certified to be weed-free;

use pellets for horses in 

backcountry areas.

Educate the public to

identify and report 

infestations.

After passing through

infested areas, inspect and

remove any seed or root

fragments from animals,

clothing, and vehicles.

Same as above. Use backpack or hand-held

sprayers or use wick method

for IPT.

Broadcast spraying may be

used on thicker stands, if

allowed.

*Choice of a particular management option must be in compliance with existing regulations for the land resource.

necessary for further control.

Tillage – Cultivation is effective with seedlings and in

areas where the population is not yet well established. Till

plants below the depth of lateral and vertical roots, and 

plan to repeat cultivation shortly after new shoots emerge. 

Thismay require tillage that is needed every 10 to 15 days 

for 6 to 8 weeks during the growing season which may be 

followed by less frequent tillage. Speed of eradication 

depends upon timing and frequency of cultivation, and 

this practice usually has to be repeated for at least 2 

consecutive years. Even infrequent cultivation before 

seed set can reduce whitetop infestation. Combining 

tillage with well-timed herbicide use can further improve

effectiveness.

Prescribed Fire

Since 75 percent of whitetop’s total biomass is below 

ground, populations rebound rapidly following fire.

Therefore, this practice is not recommended as a control

method. Burning is an acceptable means to dispose of plant

debris.

Flooding

When feasible, flooding an area with 6 to 8 inches of water 

for 2 months can be an effective control method.
4 

Cultural Control

Prevention is key to controlling whitetop, and early

detection and plant removal are critical for reducing its

spread. Educating land managers, the local public, and 

others to identify nonnative noxious species is important so 

they can help report all suspected infestations. Weed 

screens for irrigation ditches should be considered as a

means of preventing seed dispersal via waterways. Seed 

and materials used for mulch, forage, or fill should be 

certified to be weed-free; pellets may be used for horses in 

backcountry areas. Reseeding with desirable shrub and 

perennial grass species that are competitive with whitetop 

should be considered for areas not recovering naturally 

following suppression efforts.

Biological Control

Grazing

Although palatability is low, goats and sheep will graze 

whitetop from the rosette stage until early flowering. 

Whitetop reportedly is toxic to cattle if consumed in great 

enough quantities, but livestock generally make very little 

use of this weed. 

Classical Biological Control

Research is underway; however, there currently are no 

classical biocontrol agents (insects, pathogens, etc.) 

approved by USDA for management of whitetop.

Chemical Control

Whitetop grows in many different crop and rangeland 

situations, which complicates the choice for best chemical

control. Herbicides commonly used to control mustards 

generally work well on whitetop; but these chemicals often

control a wide range of other broadleaf plants as well,

some of which are desirable. For example, legumes such as

alfalfa are sensitive to most herbicides that are effective

with whitetop and could be lost if sprayed.

All herbicides recommended in table 2 will effectively 

control whitetop when properly applied. Aquatically 

approved formulations of glyphosate, imazapic, or 

imazapyr are acceptable for use in areas near water. Each

herbicide product will have different requirements and

restrictions according to the label. Read and understand the

label prior to any application. To prevent development of 

resistance in whitetop from repeated treatments, the label 

should be consulted for guidelines on rotating herbicide

active ingredients. Consult the registrant if you have 

questions or need further detail.

Herbicide Application

In general, herbicide applications should be made during 

the flower bud stage to early flowering when carbohydrate 

root reserves are lowest. Chlorsulfuron or metsulfuron 

methyl provide effective whitetop control in noncropland 

areas, but timing is important. Spraying with these 

products should be done in early spring or preferably in the 

fall before winter dormancy. Ester or amine 2,4-D 

formulations provide fair to good control or suppression 

when sprayed in early spring.

Herbicides may be applied in several ways including 

wicks, backpack or hand-held sprayers, ATV or UTV 

sprayers, or conventional boom sprayers that are pulled or 

attached to a tractor or truck. Any equipment used to spray 

herbicide should be calibrated. For sparse populations, one 

person or a small team can spray or wick whitetop in an 

area using the individual plant treatment (IPT) method. 

Spray plants directly by wetting the foliage and stems to 

the point of dripping while using an adjustable spray 

nozzle attached to a hand-held or backpack sprayer.

To suppress whitetop in riparian areas while allowing 

desirable plant species to reestablish, wick individual 

plants with 100 percent solution of 2,4-D for several 

consecutive years. Where water is not present year-round, 

chlorsulfuron may be used as long as the herbicide has 

time to degrade in the soil before water returns.

Management Strategies

Early detection and removal of new infestations soon after

discovery is the most effective weed managementstrategy

for whitetop control. Small or isolated infestations on 

otherwise healthy sites should be given high priority for 

treatment, followed by treatment of whitetop in 

passageways with a high potential for spread such as 

waterways and irrigation canals. In areas where whitetop 

has become well established, containment should be a 

management priority. Containment can be achieved
5 

Table 2. Herbicide recommendations

Common

Chemical

Name (active 

ingredient)

Product

Example1

Broadcast 

Treatment 

(rate per 

acre)

Spot 

Treatment 

(spray 

solution)2

Time of

Application Remarks

Chlorsulfuron Telar XP 1 ounce 1–2% Bud to early

bloom.

Selective; safe for labeled grasses; provides 1–2 

years control. Not for use near waterbodies.

Use 0.25% v/v NIS3

. If area is mowed before 

herbicide applied, lower rate is effective.

Metsulfuron

methyl

Escort,

Ally

0.75–1 ounce 1% Same as above. Selective; safe for most perennial grasses. Not for 

use near irrigation water.

Add 0.25% v/v NIS3

. May apply in fall if part of 

plant is still green.

Chlorsulfuron +

metsulfuron

Cimarron

Plus

1.25 ounces 1% Same as 

above.

Broad spectrum; most broadleaved plants and 

certain grasses are susceptible; pre-emergent and

post-emergent activity.

Add 1/16% – 1/18% v/v NIS3

; 1 to 2 inches of 

rainfall is required after application to move

herbicide into root zone.

Aminopyralid + 

metsulfuron

Chaparral 2.5–3.33

ounces

1% Spring (rosette

to bolt) or fall

(seedling to

rosette).

Broad spectrum; most broadleaved plants (including 

legumes and woody plants) and certain grasses are

susceptible. Not for use near surface water.

Tank mix with 2,4-D for bolt to early flower stages. 

Add 0.25% v/v NIS3

. 

Glyphosate Rodeo,

Roundup Pro 

[others 

available] 

3 quarts 

Rodeo

4 quarts 

Roundup Pro

Rodeo: 0.75–

2% + NIS3

Roundup Pro: 

2%

Flower bud 

stage.

Nonselective. Rodeo is labeled for use in or near

aquatic areas.

If infestation is dense, mow and then apply 

glyphosate when regrowth reaches flower bud stage.

2,4-D ester or 

amine4

several

products

available

2 quarts 1–5% Before bud 

stage.

Selective; acceptable for use in/near aquatic areas.

Apply annually for 2 years or more to control

established stands. If infestation is dense, mow first

and then spray regrowth. 

Imazapyr Arsenal,

Habitat 

[others 

available] 

2–3 pints 0.5–5% Flower bud to

flowering

stage; apply to

actively 

growing plant

parts.

Nonselective; pre-emergent and post-emergent; 

broad-spectrum control. In addition to spray drift, 

nontarget plants may also be killed or injured by 

imazapyr through runoff, residue movement in soil, 

or root exudates from treated plants.

Habitat is labeled for use near water.

Add 0.25% v/v NIS for post-emergent use.

Imazapic Plateau 12 fluid

ounces

5% Same as above. Selective herbicide but may retard growth ofsome

grasses. This herbicide is the preferred alternative to

imazapyr if protection of desirable plants is needed.

1 Trade names for products are provided for example purposes only, and other products with the same active ingredient(s) may be available. Individual product 

labels should be examined for specific information and appropriate use with whitetop.

2 Spray solution is the herbicide/water ratio in a spray mix that may be used for spot treatment with backpack or hand-held sprayers. The amount of product 

applied during an annual growing season must not exceed the maximum application rate per acre as specified by the product label – refer to the product label 

for the site type and application.

3 NIS is an abbreviation for nonionic surfactant, which is an additive commonly recommended for post-emergent foliar application of herbicides.

4 2,4-D is a restricted use pesticide in New Mexico only. A certified applicator’s license is required for purchase and use.
6

by managing the outside perimeter to prevent further 

spread.

Monitoring and follow-up applications after treatment are 

needed over a minimum of several years to attain longterm control. Monitoring should be conducted in early

spring and late summer to find rosettes that form the 

leading edge of expanding infestations. To enhance longterm control, efforts should be made to encourage return of

desirable plants such as shrubs and perennial grasses that 

will compete with whitetop for water, nutrients, and space.

Management of whitetop should involve careful planning 

and a long-term commitment, as persistence is a must for 

whitetop control. Whatever the management approach, 

control will likely require several consecutive years of 

treatment that uses an integrated approach. Since it is 

ordinarily useless to treat an area only one time without retreatment, it is especially important to allocate sufficient 

resources to the area where control is attempted. After 

initial treatment, resources should also be available to 

respray or retreat the treated area as necessary. 

References and Further

Information

Bossard, C. And D. Chipping. 2000. Cardaria draba. In 

C.C Bossard et al. (eds.) Invasive Plants of 

California’s Wildlands. Univ. California Press.

Berkley, CA. Available at http://www.cal-ipe. 

org/ip/management/ipcw/online.php (accessed Sept. 

2010)

Colorado State Parks. 2003. Best Management Practices 

Weed Profile: Whitetop/Hoary Cress. Availableat 

http://parks.state.co.us/SiteCollectionImages/parks/ 

Programs/ParksResourceStewardship/Whitetop.pdf 

(accessed Sept. 2010)

Davison, J.C., E. Smith, and L.M. Wilson. 2007. Livestock 

Grazing Guidelines for Controlling Noxious Weeds

in the Western United States. A WesternRegion 

Sustainable Agriculture, Research and Education

Project. EB-06-05. Pp. 24-25. Available at http://

www.cnr.uidaho.edu/rx-grazing/Livestock_Graizng 

_Guidelines%28Davison_et_al.%202007%29.pdf 

(accessed Sept. 2010)

Duncan, K., K. McDaniel, and M. Renz 2005. Chemical 

Weed and Brush Control for New Mexico

Rangelands. New Mexico State University College 

ofAgriculture and Cooperative Extension Service. 

Pp. 6-7.Available at http://aces.nmsu.edu/pubs/_ 

circulars/CR_597.pdf (accessed Sept. 2010)

Encycloweedia Datasheets by California Department of 

Food and Agriculture. Available at http://www.cdfa. 

ca.gov/phpps/ipc/weedinfo/cardaria.htm (accessed

Sept. 2010)

Invasive Plant Atlas of the United States. Available at

http://www.invasive.org/weedus/index.html 

(accessed Sept. 2010)

Jacobs, J. 2007. Ecology and Management of Whitetop. 

USDA/NRCS Technical Note MT-12. Available at

http://www.mt.nrcs.usda.gov/technical/necs/ 

invasive/management/technotes-ai.html (accessed 

Sept. 2010)

Lyons, K. E. 1998. Element Stewardship Abstract for 

Cardaria draba (L.) Desv. Available at http://www. 

invasive.org/weedcd/html/esas.htm (accessed Sept. 

2010)

NMSU Factsheet: Hoary cress. Available at http://weeds. 

nmsu.edu/factsheet.php?weed_id=21 (accessed 

Sept. 2010)

Tu, M., C. Hurd, and J.M. Randall. 2001. Weed Control 

Methods Handbook: Tools and Techniques for 

Natural Areas. Available at http://www.invasive. 

org/gist/products/handbook/methods-handbook.pdf 

(accessed Sept. 2010)

USDA Forest Service. 2006. Weed of the Week:Whitetop 

(Cardaria draba (L.) Desv.). Available at http:// 

na.fs.fed.us/fhp/invasive_plants/weeds/whitetop.pd

f (accessed Sept. 2010)

USDA Plants Database. 2010. Available athttp://plants.

usda.gov/java/profile?symbol=CADR (accessed

Sept. 2010)
7 

Zouhar, K. 2004. Cardaria spp. In Fire Effects Information 

System. USDA, Forest Service, RMRS, Fire 

Sciences Lab (Producer). Available at http://www. 

fs.fed.us/database/feis/ (accessed Sept. 2010)

Suggested Web Sites

CABI database:

http://www.cabi.org/?page=1017&pid=2257&site=170

For information on invasive species:

National Invasive Species Information Center

http://www.invasivespeciesinfo.gov/

Invasive.Org

http://www.invasive.org/weedus/index.html

For information about calibrating spray equipment: NMSU 

Cooperative Extension Service Guide A-613, 

Sprayer Calibration. Available at

http://aces.nmsu.edu/pubs/ _a/A-613.pdf

Herbicide labels online:

http://www.cdms.net/
For more information or

other field guides, contact:

USDA Forest Service 

Southwestern Region

Forest Health

333 Broadway Blvd., SE 

Albuquerque, NM 87102

Or visit the Southwestern Region’s 

website for invasive species:

http://www.fs.usda.gov/goto/r3/invasivespecies

The use of trade or firm names in this publication is for reader 

information only and does not imply endorsement of any 

product or service by the U.S. Department of Agriculture. 

Recommendations made here for 

pesticide use are not obligatory, 

nor do they imply that discussed 

uses have been registered. All 

uses of pesticides must be 

registered by appropriate State 

and/or Federal agencies before 

they can be applied.

CAUTION: Pesticides can be 

injurious to humans, domestic 

animals, desirable plants, and fish or other wildlife—if they 

are not handled or applied properly. Use all pesticides 

carefully and lawfully. Follow recommended practices for the 

disposal of surplus pesticides and pesticide containers.