Perennial Pepperweed

Perennial pepperweed is an herbaceous perennial in the Brassicaceae (mustard) family. It produces multiple erect stems from a semi-woody crown that may reach between 2 to 4 feet tall. These stems may branch near the tips. Basal leaves may be between 4 and 12 inches long and have petioles. Stem leaves are alternately arranged, hairless, and have a distinct white midvein. Leaves are directly attached to stems, and leaf margins may be smooth or slightly toothed. Leaves may be up to 12 inches long and 1 to 2 inches wide. Perennial pepperweed flowers from late spring to late summer. Flowers occur in dense clusters at the end of stems. Each flower is small, white, and contains 4 petals. Perennial pepperweed has both a deep taproot and creeping, lateral roots. Seeds are produced in capsules and are small, flattened, and reddish brown in color.

Perennial pepperweed is native to Eurasia and was possibly introduced to North America in 1936 as a contaminant in crop seed. It spreads by seeds and creeping roots creating dense infestations. It can be transported to new locations by seeds and root fragments. Perennial pepperweed is frequently found in riparian areas and on gravel bars in Teton County. It can also be found in disturbed sites, pasture, and livestock paddocks.

Prevention and cultural control strategies should be utilized as much as possible. Clean Drain Dry your watercraft, including rafts and paddleboards, to prevent spreading perennial pepperweed to other riparian areas.

There are not any biological controls for perennial pepperweed currently available.

Hand pulling and digging out of the taproot and all lateral roots can effectively eradicate small patches of perennial pepperweed, but great care must be taken to ensure that all of the root system is removed. Tillage is strongly discouraged as this is likely to fragment and spread reproductive roots. Grazing can prevent seed production, but will not eradicate root stock.

Large infestations and areas where manual removal is not practical can be controlled with herbicides. Spring treatments prevent flowering and seed production, and fall treatments may be effective at killing the root system. Read the label before using any herbicide. Contact TCWP if you have any questions about application rates or how to use an herbicide.

• Field Guide for Managing Perennial Pepperweed in the Southwest (2017) United States Department of Agriculture: Forest Service.
• Perennial Pepperweed (Lepidium latifolium). Wisconsin Department of Natural Resources.
• Perennial Pepperweed: Integrated Pest Management for Home Gardeners and Landscape Professionals (2015) Wilson, R.G. University of California Agriculture and Natural Resources: Statewide Integrated Pest Management Program.
• Perennial Pepperweed (Lepidium latifolium). Washington State Noxious Weed Control Board.
• Perennial Pepperweed: Foreign invader of California’s wetlands (2010) Renz M., Bell, C.E., Wilen, C., and DiTomaso, J.M. University of California WEED Research and Information Center.