Perennial pepperweed

Lepidium latifolium

Background

Identification

• Smooth, green-grayish leaves.
• Up to over 6 feet high, typically 3 to 4 feet.
• Dense aggregations of tiny white flowers (< 1/4 in.).
• Has horizontal underground stem (rhizome), which can be viewed by uprooting a plant.

Identification key in: Hickman, J. ed. 1993. The Jepson Manual: Higher Plants of California. University of California Press.

Growth and spread

• Can reproduce from pieces of underground stems, or by seed.

Habitat and local distribution

• Can establish dense colonies in a wide variety of environments, including marshes, meadows, saline soils, riparian areas, beaches, and disturbed areas such as roadsides, agricultural fields and irrigation channels.
• Native of Eurasia. Arrived at the East Coast of the US about 1924. In 1941 the plant was present in Solano county, and in subsequent years has spread to all 9 Bay Area counties. Present in large quantities in the South Bay and Delta, and in limited amounts in the Central Bay (May 1995).

Impacts

• Can grow in dense linear patches along sloughs and levees to the exclusion of all other vegetation; able to displace native pickleweed and other native species.

Prevention and Control

Prevention

• Plant natives or spread native seed in disturbed areas.

Manual or mechanical control

• Mechanical methods such as disking do not provide control alone since plants can rapidly resprout from fragments left in soil (Young et al. 1995).
• Prescribed burning—not effective method of control alone; typical infestations may not be able to maintain burning (Howald 2000).
• Flooding—may be successful if area is flooded for a prolonged period of time; plant abundance reduced at West Navy Marsh (Contra Costa County) when tidal action returned to diked marsh (May 1995).

Biological control

• Biological control agents—testing of biological agents not a likely control method due to the risk posed to commercial crop plants in the mustard family (Brassicaceae) and native Lepidium species (Young et al. 1995).

Chemical control

• Application of herbicides—chlorsulfuron, triclopyr (as Garlon3A® and Garlon4®), and glyphosate (as Rodeo® and Roundup®) have shown to be effective in controlling perennial pepperweed in studies at Grizzly Island Wildlife Area in Suisun Marsh (Howald 2000).
• Estimated costs: costs for materials and application by a contractor are approximately $250 per acre for glyphosate, depending on size of treatment area, scale of treatment, and herbicide dosage. It is recommended to contract a licensed professional for herbicide applications (Gibbons et al. 1999).

References and more information