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Overview:
Spartina, commonly called cordgrass, is a perennial grass which typically grows on tidal mudflats and in salt marshes. One species of cordgrass, S. foliosa, is native to the west coast of the United States. It is found from Baja California, Mexico to Bodega Bay. Historically, extensive native Spartina salt marshes existed throughout San Francisco Bay and its estuaries.
Over the years four species of non native, invasive Spartina have been introduced into San Francisco Bay; S. alterniflora, S. anglica, S. patens, and S. densiflora. Three of these occur in Marin. The species, S. alterniflora, has successfully hybridized with the native Spartina to create an extremely vigorous hybrid.
The areas in Marin with the largest populations of invasive Spartina are:
The Corte Madera Creek Complex, including Creekside Park, Piper Park, Corte Madera Marsh Reserve and areas surrounding the Larkspur Landing Ferry Terminal. S. densiflora is the species found most abundantly in Corte Madera Creek; however two other species do occur, especially in Creekside Park.
Blackies pasture and creek in Tiburon. The area around Blackies is mainly infested with hybrid Spartina, although S. densiflora occurs there as well.
Invasive cordgrasses are a threat to San Francisco bay estuaries because they can clog flood channels, displace native vegetation, significantly raise mudflat elevation, and reduce habitat of fish, shellfish, shorebirds and migratory waterfowl.
The Invasive Spartina Project (ISP) was established in 2000 by the California Coastal Conservancy to address the rapid spread of invasive Spartina in the San Francisco Bay/Estuary. ISP uses a range of control methods including manual, mechanical and chemical.
In 2005 Imazapyr was approved in California for use in estuaries for controlling Spartina. Imazapyr is a systemic broad-spectrum herbicide that is applied to the foliage. It is then absorbed and translocated throughout the plant and down into the belowground roots and rhizomes. Because Spartina spreads rapidly via rhizomes, the translocation of the herbicide into the rhizomes effectively prevents further spreading of the clone once the aboveground portion of the plant has died.
Because the application of herbicide is highly effective with very low environmental impact compared to non-chemical control methods, it is the preferred control option on about 95% of the Spartina treatment sites.
