HPIPM:Perennial pepperweed

Taxonomy

Domain	Eukarya
Kingdom	Plantae
Phylum	Magnoliophyta
Class	Magnoliopsida
Superorder	Rosanae
Order	Brassicales
Family	Brassicaceae
Genus	Lepidium

Scientific Name

Lepidium latifolium

Scientific Name Synonyms

Cardaria latifolia

Common Name

perennial pepperweed

Perennial pepperweed (Lepidium latifolium)

Author: Jim Jacobs, Plant Materials/Invasive Species Specialist, USDA-Montana NRCS.

Adapted from the USDA NRCS Montana Invasive Species Technical Note “Ecology and Management of Perennial Pepperweed (Lepidium latifolium L.)”

Identification and Life Cycle

Perennial pepperweed (Lepidium latifolium) is a rhizomatous perennial forb in the mustard family (Brassicaceae). The flowers are white, small (petals less than 0.1 inches long), and have four petals. They are clustered at the branch ends in ball-like groups of 6 to 8 flowers. The pod-like fruits (silicles) of perennial pepperweed have two chambers, each with a small reddish-brown seed. The silicles are small, about 0.1 inch long, rounded to ovate, and sparsely covered with long soft hairs. The pods remain on the plants at maturity and drop irregularly throughout the winter. Perennial pepperweed forms a tuft of basal rosette leaves and leaves along the floral stems that are bright green to gray-green. The basal leaves are up to 12 inches, 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 with no petiole. The leaves are waxy and have a somewhat leathery texture. Stems are typically 1 to 3 feet tall, but can reach up to 8 feet 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. Plants often grow multiple stems. 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. While roots can penetrate the soil to 10 feet or more, the majority of the root mass can be found in the upper two feet of the soil profile.

Habitats

Perennial pepperweed grows in estuaries, lake shores, water courses, riparian areas, wetlands, agricultural and urban areas, rangeland, grasslands, and woodlands. It can occur along roadways, railroads, irrigation ditches, pastures, dry hillsides, rangeland, and crops such as winter wheat and alfalfa.

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. Poisoning of horses that were fed hay contaminated with perennial pepperweed has been reported. Wildlife habitat is diminished where perennial pepperweed displaces riparian plant species important to browse and bird nesting.

Biology and Ecology

Plants begin blooming in early summer and flowering can continue until fall under good conditions. Plants can produce up to 1,000 seeds and heavy infestations can generate over six billion seeds per acre. Fluctuating temperatures stimulate germination, and seedlings emerge from mid-winter to mid-spring. 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. Local population expansion is predominantly via spreading roots, and population expansion can be as much as 10 feet per year. The creeping roots of perennial pepperweed form dense colonies that crowd out desirable plants and form near monocultures. New shoots grow from buds that form along the roots. Root fragments as small as two inches long can 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 fragments can be dispersed within and between fields by cultivation equipment and importing topsoil onto urban landscapes. Fruits with seeds can be transported long distances in river currents, irrigation ditches, contaminated hay, and by animals and birds.

Management Approaches

Integrated pest management that uses multiple management approaches provides the most successful means for controlling perennial pepperweed.

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.

Mechanical and Cultural Control

Hand pulling has reduced populations of perennial pepperweed but only where large portions of the root system were removed. Mowing can reduce perennial pepperweed. 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. Cattle and sheep will utilize perennial pepperweed where it grows with other plants but they will not graze in dense, pure stands. Sheep grazing has been reported to reduce perennial pepperweed plants without reducing native plant species. Revegetation will likely be necessary in dense, monotypic stands.

Chemical Control

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

Examples of herbicides that can be used to manage perennial pepperweed

Consult herbicide labels for additional rate, application, and safety information. Additional herbicide information can be found at http://www.greenbook.net.

Due to constantly changing labels, laws and regulations, the sponsors of this web site assume no liability for the suggested use of any chemicals noted in the management section. Contact your local pest management personnel for current information on labeled pesticides that can be used for the intended plant disease, insect pest or weed.

References

For more information and images please visit IPM Bugwood. http://www.ipmimages.org/search/action.cfm?q=perennial%20pepperweed