Spartina alterniflora • Class A

This long-lived warm season perennial typically grows from 2 to 7 feet tall and spreads extensively by long hollow rhizomes. Soft spongy stems of up to 1/2 inch in diameter emerge from the rhizomes. The flat leaf blades are from 12 to 20 inches long and tapered to a long inward-rolled tip. In Sept. and Oct. seed heads emerge at the end of the stem and are 10 to 12 inches long. 

Smooth cordgrass is an aggressive exotic salt marsh plant. It is highly invasive and considered to be one of the most aggressive weeds worldwide. It displaces native species, destroys habitat and food sources for fish, waterfowl and other marine life. It also interferes with recreational activities. 

It is found growing in intertidal zones, where it colonizes mud or sand-flats in saline or brackish water. Be-cause of its ability to trap sediment, Spartina species have the potential to change the fundamental nature of portions of Washington’s coastline. A secondary impact of this increased sediment may be changes in water circulation patterns, reducing tidal flow and leading to increased flooding at, or in the mouths of rivers. 

Some cultural control methods, such as diking, have shown moderate success in controlling the spread. 

• Seedlings can be pulled out effectively, as long as care is taken to remove both shoots and roots. 

• Mowing infestations can contain growth, and eventually kill the plants. Small clones must be mowed up to 2 or 3 times beginning with initial spring green-up and continued till they die back in the fall. Larger clones need to be mowed 9 to 10 times over two seasons for eradication. 

• Covering small Spartina clones with woven geotextile fabric has been demonstrated to be successful in some areas. The plants are mown to ground level and covered out 3 or 4 feet beyond the edges of the infestation. The covering must be anchored firmly in place and left for one or two growing seasons. 

• Since Smooth Cordgrass is found in marshes and along shorlines, the use of an herbicide formulated for aquatic settings is required. Please note that aquatic herbicides are restricted for use in Washington State to licensed applicators only. 

 Download our Flyer or visit Washington State Noxious Weed Control Board Here. Photo by Leo Michels