Evaluation of perennial pepperweed (Lepidium latifolium) management in a seasonal wetland in the San Francisco Estuary prior to restoration of tidal hydrology

  • Published source details Whitcraft C.R. & Grewell B.J. (2012) Evaluation of perennial pepperweed (Lepidium latifolium) management in a seasonal wetland in the San Francisco Estuary prior to restoration of tidal hydrology. Wetlands Ecology and Management, 20, 35-45.


This study is summarised as evidence for the following.

Action Category

Use herbicide to control problematic plants: brackish/salt marshes

Action Link
Marsh and Swamp Conservation
  1. Use herbicide to control problematic plants: brackish/salt marshes

    A replicated, randomized, paired, controlled, before-and-after study in 2007–2009 in a brackish marsh invaded by perennial pepperweed Lepidium latifolium in California, USA (Whitcraft & Grewell 2012) found that spraying the vegetation with imazapyr herbicide reduced the richness and cover of non-target vegetation over two years, but that spraying the vegetation with 2,4D had no significant effect on these metrics. After two years, imazapyr-treated plots contained only 0.5 non-pepperweed plant species/0.25 m2 (vs 2,4D: 2.0 species/0.25 m2; untreated: 2.1 species/0.25 m2) and only 7% cover of plants other than pepperweed (vs 2,4D: 70%; untreated: 66%). Imazapyr-treated plots had only 1% cover of pepperweed (vs 2,4D: 26%; untreated: 31%), and above-ground pepperweed biomass was only 7 g/m2 (vs 2,4D: 29 g/m2; untreated: 40 g/m2). The pattern of results was similar after one year, although not the values of some metrics (e.g. only 3–34% cover of plants other than pepperweed). Before intervention, plots destined for each treatment had similar non-pepperweed richness (2.0–2.6 species/plot), non-pepperweed cover (30–35%), pepperweed cover (27–39%) and pepperweed biomass (87–110 g/m2). Methods: Thirty-six plots were established (in six blocks of six) in a degraded, historically tidal, brackish marsh. In 2007 and 2008, twelve plots (two plots/block) received each of three treatments: spraying with dyed imazapyr (Habitat®), spraying with dyed 2,4D (Weedar®) or no herbicide (spraying with dyed water only). Vegetation was surveyed in April before (2007) and after (2008, 2009) intervention. Plant species and cover were recorded in three 0.25-m2 quadrats/plot. Pepperweed was cut from three 0.125-m2 quadrats/plot then dried and weighed.

    (Summarised by: Nigel Taylor)

Output references
What Works 2021 cover

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 21

Go to the CE Journal

Discover more on our blog

Our blog contains the latest news and updates from the Conservation Evidence team, the Conservation Evidence Journal, and our global partners in evidence-based conservation.

Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape ProgrammeRed List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Mauritian Wildlife Supporting Conservation Leaders
Sustainability Dashboard National Biodiversity Network Frog Life The international journey of Conservation - Oryx Cool Farm Alliance UNEP AWFA Bat Conservation InternationalPeople trust for endangered species Vincet Wildlife Trust