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Controlling perennial pepperweed (Lepidium latifolium) in a brackish tidal marsh


Perennial pepperweed (Lepidium latifolium) is an aggressively invasive species that spreads by vegetative growth and seeds. Common methods for removal such as hand-pulling and mowing are impractical in brackish marsh environments. We evaluated the effects of two herbicide treatments (imazapyr and imazapyr + glyphosate) against a non-herbicide control (flower head removal) on invasive pepperweed and native vegetation in three habitats (bay edge, channel edge, and levee) in brackish marshes. Both herbicide treatments produced significantly better control of pepperweed than the control, but imazapyr alone took 2 years of treatment to produce levels of control that were similar to one year of the imazpyr + glyphosate treatment. Both herbicide treatments also reduced native cover, but the effects were more severe in plots treated with imazapyr + glyphosate than in plots treated with imazapyr alone. Effects on pepperweed were similar across the three habitats, but impacts on native vegetation were less severe in bay edge environments. Managers should consider the tradeoffs when choosing a treatment plan for pepperweed: the quick reduction of pepperweed achieved by the combination of imazapyr and glyphosate may come at the expense of creating opportunities for reinvasion by causing bare ground and/or patches of litter that are slowly recolonized by native species.

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This experiment was part of a set of studies on perennial pepperweed control at San Pablo Bay National Wildlife Refuge. Funding for these studies was provided by U. S. Fish and Wildlife Service Inventory and Monitoring Program, National Fish and Wildlife Foundation, California Department of Fish and Wildlife, U.S. Fish and Wildlife Service Invasives Program, U.S. Fish and Wildlife Service Coastal Program, and the Marin-Sonoma Mosquito and Vector Control District. We also wish to thank our partners, Point Blue (formerly Point Reyes Bird Observatory)’s Students and Teachers Restoring a Watershed Program, Sonoma Land Trust, Friends of San Pablo Bay NWR, Renee Spenst (Ducks Unlimited), Ingrid Hogle (Invasive Spartina Project), and Shelterbelt Builders.

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Correspondence to V. D. Tobias.

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Tobias, V.D., Block, G. & Laca, E.A. Controlling perennial pepperweed (Lepidium latifolium) in a brackish tidal marsh. Wetlands Ecol Manage 24, 411–418 (2016).

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  • Invasive species
  • Wetland
  • Management
  • Brackish marsh
  • Imazapyr
  • Glyphosate