United States Department of Agriculture 

NATURAL RESOURCES CONSERVATION SERVICE 

Invasive Species Technical Note No. MT-11 

April 2007 

Ecology and Management of Perennial Pepperweed [Lepidium latifolium L.]

By 

Jim Jacobs, NRCS Invasive Species Specialist, Bozeman, Montana 

Jane Mangold, Restoration Ecologist, USDA, Agricultural Research Service, Burns, Oregon 

Figure 1. Perennial pepperweed infestation. Photo by Michael Carpinelli. 

Abstract 

Perennial pepperweed, also called tall whitetop and often confused with whitetop (Cardaria 

draba), is a rhizomatous perennial weed threatening riparian areas, irrigation ditches, and 

floodplain meadows in Montana. This weed in the mustard family (Brassicaceae) spreads by 

creeping roots and rhizomes, and prolific seed production. Found most often in seasonally 

flooded areas, perennial pepperweed can also spread to upland and rangeland sites, and it is 

adapted to salt-affected soils. It can form dense patches that compete with crops, forage plants, 

and riparian plants (see Figure 1). Infestations reduce crop yield and increase production costs, 

reduce livestock carrying capacity, and its control is costly. 

Perennial pepperweed is native to southeastern Europe and western Asia. The first record of 

perennial pepperweed in Montana is from Gallatin County in 1935 along a roadside near 

Manhattan. By 2002 it had been reported from 17 counties (http://invader.dbs.umt.edu) with a 

total of 2,750 acres infested. In Montana it has been found along roadways, railroads, the 

Missouri River, irrigation ditches, in winter wheat, alfalfa, Conservation Reserve Program, 

pastures, on dry hillsides, and in rangeland. Perennial pepperweed is ranked as a Category 2 

noxious weed in Montana, meaning it is currently present and believed to be rapidly spreading 

from existing infestations. 

Perennial pepperweed can be temporarily suppressed using herbicides that contain metsulfuron, 

chlorsulfuron, or imazapic as active ingredients. Long-term herbicidal control requires repeated 

applications. Cattle, sheep, and goats will graze perennial pepperweed, but the effects on 

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population fitness of long-term grazing with these animals are not known. Mowing and sheep 

grazing reduce stand density for up to one year. There are no approved biological control insects 

for release on perennial pepperweed. 

Biology and Ecology 

Roots. There are few white-flowered mustards that grow from creeping roots, therefore once it 

is established, this characteristic can help identify perennial pepperweed. The roots penetrate 

deeply into the soil and spread horizontally (see Figure 2). While roots can penetrate the soil to 

ten feet (2 m) or more, the majority of the root mass can be found in the upper two feet of the 

soil profile making perennial pepperweed competitive for soil moisture and nutrients. The roots 

are coarse with minimal development of fine roots or root hairs, are widely spaced, and form a 

network through connecting branches. The coarse root architecture suggests perennial 

pepperweed requires high nutrient substrate compared to finely-rooted plants like grasses. The 

creeping roots form dense colonies of perennial pepperweed that crowd out desirable plants and 

form near monocultures. New shoots grow from buds that form along the roots. Roots enlarge 

at the soil surface and form a woody crown from which shoots grow. Root fragments as small as 

two inches (5 cm) long can re-generate new plants, and root or rhizome fragments dried for three 

days in the sun and open air can re-sprout on moist soil. Root carbohydrate reserves are lowest 

at initiation of flower stalks bolting. 

Figure 2. Creeping roots displaying vegetative reproduction. Photo by Clare Poulsen. 

Stems. Perennial pepperweed stems normally grow from one to three feet (1 m) tall, but can 

reach up to eight feet (2 m) in wet areas. Stems are hairless, erect, stiff, and branching. The 

stem base is semi-woody. Stems die back to the base each year, drying to a light tan color, and 

dead stems can persist for several years (see Figure 3). Plants often grow multiple stems. Stems 

can form adventitious roots when plants are inundated with flood water for three or more days, 

and populations can tolerate flooding for up to 50 days. 

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Figure 3. Old stems of perennial pepperweed showing persistent, light tan color. 

Photo by Michael Carpinelli.

Leaves. Perennial pepperweed forms a tuft of basal rosette leaves and leaves along the floral 

stems that are bright green to grey-green. The basal leaves are up to 12 inches (30 cm) long by 

0.5 to 3.2 inches (8 cm) wide, with entire or toothed margins, have a prominent white mid-rib, 

and taper to an elongated petiole at the point of attachment to the stem. The stem leaves are 

smaller than the basal leaves and have a less defined mid-rib, no petiole, but do not clasp the 

stem as the leaves of whitetop (Cardaria draba). The leaves are waxy and have a somewhat 

leathery texture. 

Flowers. The flowers are white, small (petals less than 0.1 inches long), and have four petals 

and six stamens. They are clustered at the branch ends in ball-like groups of six to eight flowers 

arranged in a raceme (see Figure 4). Plants begin blooming in early summer and flowering can 

continue until fall under good conditions. 

Figure 4. Perennial pepperweed flowers. Photo by Michael Carpinelli. 

Fruits. The pod-like fruits (silicles) of perennial pepperweed have two chambers, each with a 

small reddish-brown seed (see Figure 5a). The silicles are small, about 0.1 inch (2 mm) long, 

rounded to ovate, and sparsely covered with long soft hairs (pilose). The pods remain on the 

plants at maturity and drop irregularly throughout the winter. Plants can produce up to 1,000 

seeds and heavy infestations can generate over six billion seeds per acre. Seeds produce a 

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mucilaginous coating when wet, which possibly helps them adhere to substrates and survive dry 

periods (see Figure 5b). 

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 Figure 5a and Figure 5b 

 Figure(s) 5a and b. Perennial pepperweed silicles and seed (a) and mucilaginous coat 

 around wet seed (b). 

Life History. There is little published information on the phenology of perennial pepperweed. 

Few seedlings have been observed in field populations indicating that it does not spread locally 

by seed and that local population expansion is predominantly via spreading roots. Seed viability 

is reportedly very high. Fluctuating temperatures stimulate germination, and seedlings emerge 

from mid-winter to mid-spring. Salinity has little effect on the germination of seeds or resprouting from root fragments. Rosettes grow from roots in late winter or early spring making 

perennial pepperweed competitive for early spring moisture and nutrients. In established 

infestations, early spring canopy cover and litter buildup shade desirable plants. Floral shoots 

bolt in late May, blooming begins in mid-June, and seed pods form throughout the summer. 

Plants die back to root crowns under drought conditions or after a hard frost (see Figure 3). 

Individual plants are believed to survive for several years. Stands as old as 15 years have been 

reported. Perennial pepperweed is saline tolerant and is a salt pump, absorbing salt from the soil, 

accumulating it in the leaves, and then depositing it on the soil surface upon leaf fall. 

Spread. Perennial pepperweed spreads by seed, creeping roots, and root fragments. Population 

expansion is mainly through the extensive spreading root system and can be as much as ten feet 

(2 m) per year. Root fragments can be dispersed within and between fields by cultivation 

equipment and imported topsoil onto urban landscapes. Roots and rhizomes of hand-pulled 

plants can remain viable for three days when left on the soil surface and in the sun. Fruits with 

seeds can be transported long distances in river currents, irrigation ditches, contaminated hay, 

and by animals and birds. In eastern Oregon, it is believed that perennial pepperweed is 

commonly spread by haying infested meadows and then moving the hay offsite carrying seeds 

along with it (see Figure 6). 
Figure 6. A hay meadow infested with perennial pepperweed. 

Perennial pepperweed can be spread in contaminated hay. 

Habitat. Perennial pepperweed grows in estuaries, lake shores, water courses, riparian areas, 

wetlands, agricultural and urban areas, rangeland, grasslands, and woodlands. In Montana, 

perennial pepperweed is a weed of riparian habitats that are periodically flooded or have a moist 

soil surface, however it is adapted to dryer upland sites as well. It has been found along 

roadways, railroads, the Missouri River, irrigation ditches, in winter wheat, alfalfa, CRP fields, 

pastures, on dry hillsides, and in rangeland. Infestations in Wyoming are found within 100 feet 

(30 m) of riparian areas. The aboveground biomass production of perennial pepperweed declines 

in soils without nutrient inputs (particularly phosphorous), and periodic nutrient inputs from 

flooding may help keep perennial pepperweed competitive with other plants in riparian areas. 

Economic impacts. Perennial pepperweed infestations reduce livestock carrying capacity by 

displacing nutritive forage plants. Hay contaminated by perennial pepperweed has lower 

nutrient content than weed-free hay. Wildlife habitat is diminished where perennial pepperweed 

displaces riparian plant species important to browse and bird nesting. 

Perennial pepperweed has been used medicinally. An infusion of the plant has been used for 

liver and kidney diseases and as a remedy for treatment of skin diseases. Leaves can be eaten 

raw or cooked and have a very hot cress-like flavor. The roots have been grated and made into a 

hot, pungent sauce used as a substitute for horseradish. The seed has also been used as a 

condiment. 

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Management Alternatives 

Herbicide.1/ Metsulfuron (1.0 oz product/ac.) applied to actively growing plants, but before full 

bloom, or chlorsulfuron (1.0 oz. product/ac.) applied during bud to early bloom are the most 

effective herbicide treatments and can suppress perennial pepperweed for one to two years. A 

nonionic surfactant is needed when using chlorsulfuron or metsulfuron. Imazapic (8-12 oz. 

product/ac.) mixed with methylated seed oil (1 qt./ac. MSO) applied after full bloom until plants 

start to die will provide similar control. Shoots of perennial pepperweed can be killed using 

2,4-D (2 qt. product/ac.), but root crowns will re-sprout new foliage. Glyphosate (2 qt. 

product/ac.) provides similar control as 2,4-D, however glyphosate is non-selective and revegetation may be needed to restore competitive plants (see Figure 7). Repeated herbicide 

applications are needed to sustain population reductions regardless of the product used. 

Figure 7. Perennial pepperweed plants spot-treated with glyphosate. 

Hand Pulling. Hand pulling has reduced populations of perennial pepperweed but only where 

large portions of the root system were removed. Because roots can re-sprout new foliage after 

1/

Any mention of products in this publication does not constitute a recommendation by the NRCS. It is a violation 

 of Federal law to use herbicides in a manner inconsistent with their labeling. 

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drying for up to three days, pulled root fragments should be burned, or bagged and placed in the 

trash. Though labor intensive, hand pulling may be practical for small infestations or to 

eliminate re-growth after herbicide application.

Mowing and Grazing. Mowing has been shown to reduce perennial pepperweed by 46 percent 

for one year. It is recommended to mow to a four-inch or greater stubble height to maintain the 

vigor of native and desirable plant species. Mowing should be applied at the first sign of 

flowering when root carbohydrates are lowest usually around mid-June, and before the 

development of seeds to prevent spread. It is likely that perennial pepperweed will re-grow 

flower shoots after mowing and follow-up management will be needed to prevent seed 

production. Mowing combined with herbicide application to re-growth has been shown to 

improve the effectiveness of chlorsulfuron and glyphosate in controlling perennial pepperweed. 

Mowing should only be re-applied to sites with plant species that are tolerant of repeated 

mowing. 

Cattle and sheep will utilize perennial pepperweed where it grows with other plants but they will 

not graze in dense, pure stands. In one study, grazing reduced perennial pepperweed in a pasture 

by 78 percent for one year. Sheep grazing has been reported to reduce perennial pepperweed 

plants without reducing native plant species. Perennial pepperweed seed will remain viable after 

passing through animal digestive tracts. One study found germination rates of seeds following 

rumen incubation were increased by five to 40 percent. Grazing animals that may have ingested 

seeds should be contained and fed weed-free forage for five days before moving to weed-free 

areas. Poisoning of horses that were fed perennial pepperweed-contaminated hay has been 

reported. 

Biological Control. There are no biological control agents approved for release on perennial 

pepperweed largely due to the risk of damage to valuable crops that are closely related 

taxonomically, including canola, mustard, and cabbage, and there is a potential non-target threat 

to an endangered native Lepidium species. 

Tillage. Perennial pepperweed, like other perennial rhizomatous weeds, may be controlled by 

persistent repeated tillage. However, tillage also spreads root fragments and should be followed 

by herbicidal control and cropping or re-vegetation. 

Re-vegetation. Where perennial pepperweed forms dense near-monocultures, re-vegetation may 

be needed to establish competitive plants after control procedures. Establishing competitive 

perennial grasses on disturbed land, followed by prescribed grazing management to maintain 

grass vigor will suppress perennial pepperweed and prevent re-establishment and spread by 

rhizomes and seed. Refer to Montana Plant Materials Technical Note 46, ‘Seeding Rates and 

Recommended Cultivars,’ and Extension Bulletin EB19 ‘Dryland Pasture Species for Montana 

and Wyoming’ for recommended re-vegetation species and their appropriate seeding rates. State 

and area resource specialists can help determine the most appropriate, site-specific species mix, 

timing of seeding, and seeding methods. Where herbicides have been applied, chemical 

carryover should be assessed prior to planting permanent vegetation. 

Integrated Pest Management (IPM). Integrated pest management is the application of two or 

more management alternatives so they are complimentary in weed suppression, increase the 

longevity of control procedures, and improve production or conservation of resources. Mowing 
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prior to herbicide application has been shown to improve the herbicidal control of perennial 

pepperweed. To reduce the frequency of herbicide re-applications, prescribed grazing with 

sheep, goats, or cows can be applied to prevent re-establishment from roots that survive 

herbicide treatment (follow herbicide label guidelines for grazing after herbicide treatment). On 

cropland, tillage followed by herbicide treatment will be more effective than either treatment 

applied alone. 

References 

Eiswerth, M.E., L. Singletary, J.R. Zimmerman, and W.S. Johnson. 2005. Dynamic benefit-cost 

analysis for controlling perennial pepperweed (Lepidium latifolium): A case study. Weed 

Technology 19:237-243. 

Krueger, J. and R. Sheley. 2004. Perennial pepperweed (Lepidium latifolium). Montana State 

University Extension Service Montguide A-10. 3 p. 

Renz, M.J., and J.M. DiTomaso. 2006. Early season mowing improves the effectiveness of 

chlorsulfuron and glyphosate for control of perennial pepperweed (Lepidium latifolium). Weed 

Technology 20:32-36. 

Young, J.A., C.D. Clements, and R.R. Blank. 2002. Herbicide residues and perennial grass on 

establishment perennial pepperweed sites. Journal of Range Management 55:194-196. 

Young, J.A., C.E. Turner, and L.F. James. 1995. Perennial pepperweed. Rangelands 17:121-

123.