Common Name: smooth cordgrass Scientific Name: Spartina alterniflora Symbol: SPAL Group: Monocot Family: Poaceae Growth Habit: Graminoid Duration: Perennial

What does it look like?

It is important to be able to identify this invasive species in the grass family, whose major characteristics are round jointed stems which are hollow between the nodes, with two arrangements of leaves in vertical rows and an open leaf sheath. Smooth cordgrass is an erect perennial that can grow up to 5 feet tall. Leaves are spiky and flat (when fresh), hairless, and they taper to a sharp tip. Its large stems are round and hollow between the joints, and red (or purple) streaks mark the base of healthy young plants. Roots are white and fleshy with underground runners, which can lead to aggressive spreading (SWP 2005). This cordgrass can be easily confused with the native California cordgrass (S. foliosa), which is generally less than four feet tall and only shows red pigment on decaying tissues, not young, healthy green shoots (Bossard et al. 2000).

Note: One main determining characteristic of smooth cordgrass is the ligule with fine hairs; other plants have papery sheaths or no ligule at all. The ligule is a collar tissue between the sheath and stem of the grass (SWP 2005).

The most rapid growth period occurs between April and September, while dead plant material is washed away by winter tides. Plants usually begin to flower after two to three years, in late July to September, but few seeds are produced in most plants. Ripe seeds fall from October to January and those that are trapped in the mud can germinate from February to May, but most seedlings do not survive the first winter. Seedlings that do survive can spread very rapidly the following spring, and vegetative fragments may spread year-round. Infestations of cordgrass on mudflats begin as isolated, circular patches which spread outward by vegetative shoots until they fuse together and form continuous meadows of cordgrass (Bossard et al. 2000).

Where does it grow?

Smooth cordgrass is native to the Atlantic and Gulf Coast marshes of North America and was brought to San Francisco and Padilla Bay for salt marsh restoration and erosion control projects (Spicher and Josselyn 1985 in Bossard 2000). It is rapidly spreading in Marin County and South San Francisco Bay. It was in Humboldt Bay in the early 1980s and eradication projects have been unsuccessful.

This invasive cordgrass is often found in large, monospecific stands, in intertidal mud or sand areas with minimal wave action. It can grow as low as eelgrass in the intertidal zone. (SWP 2005) It cannot grow on wave-swept beaches and freshwater marshes that lack saltwater influence.

Is it in our watershed?

Though this grass has not yet been identified in the Mattole, several yellow “cards” released by the Spartina Watch Program of Portland State University, have been found on the Mattole Beach, near the estuary. These cards were released from either Humboldt or San Francisco Bay to determine what areas are at risk for invasion of Spartina species.

What problems does it cause?

Non-native cordgrasses are invading and damaging many Pacific Coast estuaries. They colonize as dense stands in open mudflats and intertidal areas that serve as important shorebird feeding habitat along with oystering and recreational fishing areas (Pfauth, 1998). Dense growth of smooth cordgrass can also trap sediments, which alters hydrology and can clog flood control and navigation channels. Native California cordgrass stands are under threat of hybridization or are being replacement by smooth cordgrass (Daehler and Stron, 1997 in Bossard 2000).

How do you get rid of it?

Mechanical/Manual Control

Hand pulling: Hand pulling is the best method for early infestations (one to a few plants) on soft substrates, where rhizomes can be gently pulled from the mud. It is important to be careful not to leave any rhizomes that might break off, to prevent further regeneration. On harder substrates, shovels may be necessary, and it is more likely to overlook rhizomes, so it is important to take care in these areas. After removal, carry the plant material above high tide mark, where it will dry out and die. The removal site should be marked appropriately and monitored, starting a few months after removal, to ensure successful eradication (Bossard, 2000).

Solarization: Small infestations may be covered with black plastic tarp or geotextile fabric. First, cut back stems with a weed whacker or similar tool and then cover with 100 percent shadecloth or heavy-duty black plastic. It is best to begin covering in spring. The covered area should extend at least one meter beyond the plant diameter and be anchored with sandbags or deep stakes. Completely covered infestations may die within four months, but eradication success rates are higher after one year or more (Bossard, 2000).

Mowing: This technique has been successful on infestations outside California, if shoots are mown to mud level in the late fall. In California, where plants grow year round, it is necessary to mow eight or more times a year to kill smooth cordgrass. Occasional mowing will not kill plants but may lead to increased shoot density (Daehler, pers. observation in Bossard, 2000).

Author:
Unity Peterson, Invasive Plant Program Coordinator, Mattole Restoration Council, Petrolia, CA.

Photograph:
Erik Grijalva

References:
Bossard, CC., J.M. Randall and M. Hoshovsky. (eds.) 2000. Invasive Plants of California’s Wildlands. University of California Press, Berkeley, CA. Online version:groups.ucanr.org/ceppc/Invasive_Plants_of_California's_Wildlands/

Pfauth, Mary and Mark Sytsma. Key to West Coast Spartina Species: Based on Vegetative Characters. Biology Department. Portland State University. January 1998.

SWP 2005. Spartina Dispersal Study. The Spartina Watch Program. Portland State University. www.clr.pdx.edu/projects/spartina