Invasive Plants of California's Wildland

Salt-meadow cordgrass (Spartina patens) is a long-lived grass one to four feet tall, with thin wiry stems and tightly furled leaf blades, both of which are narrow (less than one-fifth of an inch) at the base. The inflorescence is open, composed of two to thirteen spike-like branches, which emerge about sixty degrees from the central axis, the lowest of which rarely overlaps (Hickman 1993). Other California coastal cordgrass species have compact inflorescences with spike-like branches appressed to the main axis. When plants are not blooming, the extremely narrow stem and angled leaf distinguish this plant from other cordgrasses. Salt-meadow cordgrass has a reddish purple base and no basal leaf sheath (Pattens, pers. comm.).

Salt-meadow cordgrass is found in coastal salt marshes, sand dunes, and swales in California coastal counties from Santa Barbara County north to Sonoma County (Calflora reports). In Benecia State Park marsh, east of the Carquinez Strait, it occurs in the high salt marsh zone. It can tolerate a wide range of salinity levels (Silander 1979). In salt marshes it prefers moderately saline to brackish conditions in the middle to upper zone (Chabreck and Condrey 1979). Salt-meadow cordgrass occurs with pickleweed (Salicornia virginica), fleshy jaumea (Jaumea carnosa), salt grass (Distichlis spicata) (Whitlow 1980), and sea lavender (Limonium californica), as well as soft bird’s beak (Cordylanthus mollis ssp. mollis) in the mid-upper salt marsh zone (Brown pers. observation). It has invaded two additional Pacific Coast locations, Suislaw Estuary on Cox Island in Oregon (Frenkel and Boss 1988) and Dosewallips State Park, in Washington on the west side of Puget Sound (Frenkel 1987).

This cordgrass is native to the coastal regions of the Gulf of Mexico and the Atlantic Ocean from Texas to Newfoundland (Frenkel and Boss 1988). It may have been introduced as packing material in association with unofficial plantings of eastern oysters (Crassotrea virginica) in Oregon and Washington (Townsend 1896, Frenkel and Boss 1985). The source of the population in California is unknown (Spicher, pers. comm.), but it was first reported thirty-five years ago (Munz 1985). Dense, monotypic circular patches form from a single genetic group, and proliferation and reestablishment of colonies appears to be a function of seed dispersal (Frenkel and Boss 1988). Reduced interspecific competition and the presence of barren or disturbed areas near established colonies also facilitate invasion.

Since its introduction to Cox Island, salt-meadow cordgrass has expanded exponentially, with new outlying patches appearing in native vegetation (Frenkel and Boss 1988). As colonies expand, the dense stems impede growth of native species, often collapsing onto adjacent plants and smothering them (Frenkel and Boss 1988). Accretion coupled with expansion of the cordgrass community ultimately may result in conversion of low marsh to monotypic higher-elevation marsh. Dense mats of roots and rhizomes occupying depths of up to eight inches (Clark 1994) may further impede recolonization by native species. Seedlings can easily be overlooked and pose additional problems for eradication.

In August 1997 the Benicia State Park marsh population of salt-meadow cordgrass was localized in a 341 square foot area (Spicher and Brown, pers. observation). Its proximity to the rare plant species Cordylanthus mollis ssp. mollis, now federally listed, warrants close attention, since current restoration efforts in this marsh may alter conditions and favor expansion.

Radial expansion of cordgrass colonies is clonal. New plants arise from tillers, which produce abundant rhizomes and roots inside the patch perimeter.

Salt-meadow cordgrass flowers from July through October. Seed heads form within two to three years after seedling emergence (Pattens, pers. comm.) The number of flowers is proportional to colony size (Frenkel and Boss 1988). Seed production is highly variable and most likely dependent on pollen viability (Frenkel, pers. comm.). In the marsh environment, selection seems to favor genotypes with higher vegetative biomass and lower reproductive output (Silander 1979). In its native area, seeds mature in August or September and germinate in April or May when conditions are warmer (Clark 1994).

The best method for removing salt-meadow cordgrass depends on the size of the population and the local conditions in which it grows. Unfortunately, effective means for complete eradication of this species have yet to be discovered. Since the plant often grows among other species in tidally influenced marshes, great care is required in implementing treatments.

Manual/mechanical methods: Combined with excavation of subterranean plant parts, hand pulling may be effective for small patches. Seedlings are easily pulled as the root system is still shallow. Clipping inflorescences and seed heads in small patches may help prevent establishment of new colonies in adjacent areas, although existing clonal patches will be unaffected. Mowing with a weed eater has been used with variable success in Washington, but it must be done before plants set seed (May-June).

Solarization: Geotech fabric (tightly woven plastic mat) has been effective in controlling salt-meadow cordgrass in areas with moderate tidal range in Washington. Cloth is tucked into the ground beyond the tillering edge with a shovel, then staked every ten feet (3 m). Rope or cable is criss-crossed over the surface of the plastic and cinched to the stakes. Sand bands and bricks are then placed onto the cloth to secure it (Clark 1994). The cloth should be left in place for at least four growing seasons. This method is less effective in lower elevations of marsh or in areas where drift wood accumulates (Pattens, pers. comm.).

Potential agents for this species have not been investigated. Salt-meadow cordgrass establishment in barren, disturbed areas may be impeded by planting another vigorously growing native species such as pickleweed or saltgrass.

Wicking with 20 percent glyphosate (as Rodeo) has been effective for portions of the Washington state population. In California Rodeo® must be applied by a certified pesticide applicator. While this method may be appropriate for small peripheral stands and patches, problems with calibration and excessive dripping have been reported (Moore, pers. comm.). Backpack sprayers using 5 percent Rodeo® may be an effective alternative for larger populations.