Staff and volunteers of the Kern River Preserve have spent over a decade fighting invasive species. These efforts have paid off with one of the most native forests in western North America.

For many years staff of the Kern River Preserve and partners have spent thousands of hours attempting to eradicate purple loosestrife and perennial pepperweed from South Fork Valley lands.

Each of us can help prevent the spread of invasive plants and animals. You can help by learning which species can become invasive and eradicate these from your own yards. Help to educate your local nurseries about the problem with invasives and get them to stop selling problem plants. Contact your legislator and local agriculture commissioner to make sure no invasives are sold or promoted in your county or town.

The article that follows is a tutorial on perennial pepperweed: one of a series of articles staff of the Kern River Preserve are preparing to educate about local invasives and some steps each of us can take to help eradicate them.

(Lepidium latifolium), from bank to bank and shore to shore, this noxious newcomer to the South Fork is native to southern Europe and western Asia. It spreads by mostly by creeping roots and seed under many different environmental conditions. 
This perennial plant has glabrous (hairless) bright green to gray-green leaves. It is distinguished from the another invasive hoary cress or whitetop (Lepidium draba) by the stalked leaves that do not clasp the stem like the cress. Rosette leaves are ovate to oblong with entire to serrate margins on long petioles. Rosette leaves are about 4 to 11 inches long and 1 to 3 inches wide. Stem leaves are sessile and lanceolate, have entire to toothed margins, and become smaller toward the top of the stem.

The plant grows up to six feet tall forming dense thickets that crowd out native plants. Mature plants have numerous erect, semi-woody stems that originate from large, interconnected roots. Roots are long, minimally branched, and enlarged at the soil surface forming a semi-woody crown. It normally flowers in summer but as with most plants in the mustard family can flower at any time conditions are right. The flowers are small white and form dense clusters at the end of the branches. The fruit (seed housing) is a two seeded, reddish brown, slightly hairy, 1/16" long capsule.

Native to southern Europe and western Asia, it grows in waste areas, wet areas, ditches, roadsides, cropland, along waterways, and dry habitats such as road cuts and fills. Robust, deep-seated spreading roots and numerous seeds make this weed very difficult to control. Past attempts at mechanical removal have actually caused the spread of the plant and an increase in numbers.

Recent surveys identify perennial pepperweed as a weed problem in nearly all of California, and both the California Department of Food and Agriculture (CDFA) and California Invasive Plant Council (Cal-IPC) list it as a noxious weed of greatest ecological concern. Small to moderate infestations of perennial pepperweed are found along the South Fork Kern River from Tulare to Kern County, and large infestations are found along the Susan River (Lassen County), the Lower Klamath Wildlife Refuge (Siskiyou County) and the Truckee River (Washoe County, Nevada) Scattered infestations occur along the Sacramento River north of Lake Shasta (Shasta County), as well as along roadways in Lassen County and Washoe County, Nevada.

Management in Home Landscapes

Prevention is the best management strategy for avoiding problems with perennial pepperweed in and around home landscapes. If perennial pepperweed is found growing in landscaped areas, immediately control the plant before it can spread. Pulling plants (try to remove as much of the root as possible) is an effective way of controlling a few scattered plants growing within landscaped areas. Contact a licensed pesticide applicator if you would like to control any weeds chemically.

Management in Fields, Crops, etc.

Established perennial pepperweed populations are difficult to control and require multiple years of intensive management. Suppressing the extensive root system is critical for successful control. A management program should include prevention, monitoring, and treatment of small satellite populations before plants develop extensive roots. Make sure root fragments and seed are not transported to other sites. Always clean vehicles, machinery, and clothing after visiting infested areas.