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

Published source details Tobias V.D., Block G. & Laca E.A. (2016) Controlling perennial pepperweed (Lepidium latifolium) in a brackish tidal marsh. Wetlands Ecology and Management, 24, 411-418.
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This study is summarised as evidence for the following.

	Action	Category
	Use herbicide to control problematic plants: brackish/salt marshes Action Link

Use herbicide to control problematic plants: brackish/salt marshes

A replicated, paired, controlled, before-and-after study in 2007–2009 in a brackish marsh invaded by perennial pepperweed Lepidium latifolium in California, USA (Tobias et al. 2016) reported that spraying the vegetation with herbicide typically reduced native plant cover. Results summarized for this study are not based on assessments of statistical significance. Over two years, cover of the two dominant native species (Pacific pickleweed Sarcocornia pacifica and alkali heath Frankenia salinia) declined in sprayed plots in 8 of 12 cases (from 5–85% before intervention to 0–45% after two years) but was stable or increased in unsprayed plots in six of six cases (before: 12–67%; after: 24–70%). Cover increased in only one of the remaining cases in sprayed plots (from 17% to 45%). The size and direction of the effect of on native cover depended on the species, herbicide composition and location within the marsh (see original paper). The number of pepperweed stems decreased in plots treated with herbicide (from 21–36 stems/m² before intervention to <1 stem/m² after two years) compared to an increase in untreated plots (from 27 stems/m² to 32 stems/m²). Methods: Thirty-six 16-m² plots were established in a pepperweed-invaded brackish marsh. In May 2007 and 2008, twenty-one plots were sprayed with herbicide: 10 with imazapyr (Habitat®) and 11 with mixed imazapyr and glyphosate (Rodeo®). Fifteen plots were not sprayed, but pepperweed flowerheads were removed. In May 2007–2009, vegetation was surveyed in the central 1 m² of each plot.

(Summarised by: Nigel Taylor)