Perennial Pepperweed
(Lepidium latifolium):
Foreign invader in California's wildlands

Where is it now?

Today, perennial pepperweed is a weed problem in all of the 48 contiguous states except Arizona. In California, only the very wettest areas of the northwest coast and the driest areas of the Lower Colorado River Desert, are not currently infested with perennial pepperweed. Infestations are also reported in Canada, Mexico, and Australia.

Perennial pepperweed can survive in a wide variety of habitats, from open areas in coniferous forests at elevations over 9000 feet to coastal marshes at sea level. Infestations are often found along roadsides, in hay fields, and in disturbed soils. The preferred habitat is a wetland, especially in saline or alkaline soil. Perennial pepperweed thrives best in a Mediterranean climate characteristic to most of California.

Why is it a problem?

Perennial pepperweed has invaded thousands of acres of natural habitat, especially riparian zones, throughout California and other western states. It is also an agricultural weed, infesting thousands of acres of rangeland, grass pasture, hay and row crops. Perennial pepperweed root fragments or seed are often transported when hay or straw are used to feed horses or mules in backcountry areas or used as mulch in natural areas. Once introduced from seed or root fragment, perennial pepperweed can rapidly occupy disturbed sites.

Over time, this invasive plant will eventually displace the native plant community. Loss of the native vegetation generally leads to a decrease in nesting sites for birds and habitat for native rodents, reptiles, and mammals. Native trees, such as willow and cottonwood, do not establish well in the thick stands of perennial pepperweed. Furthermore, dense stands along a section of stream or riverbank do not adequately bind soil, thus resulting in increased erosion during floods.

Perennial pepperweed also acts as a ‘salt pump, bringing salts from deep in the soil up through the roots and depositing them on the soil surface. The increased soil salinity further inhibits growth of existing native plants or prevents them from re-establishing in an infested area. Left uncontrolled, perennial pepperweed will completely transform native habitats to more saline areas dominated by salt-tolerant nonnative species.

Perennial pepperweed readily invades riparian areas and prevents the establishment or regeneration of native trees and herbaceous plant species.

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