Weed Alert! Salvinia molesta
Escapes in NC

Stratford H. Kay, Associate Professor
Crop Science Department, North Carolina State University
 Raleigh, NC 27695

Giant salvinia (Salvinia molesta) first appeared in North Carolina in October 1998 at an aquatic nursery display at the State Fair. This highly invasive, floating aquatic plant subsequently was found in wetland nurseries, water garden dealerships, and ornamental pools in 19 NC counties, but was not known to exist outside of cultivation until this summer. Following a tip received in August from a commercial aquatic applicator, this weed was found in several ponds on a golf course in Brunswick Co. In September, the weed was reported in two ponds on another golf course at Wilmington. The identity of the weed at these sites was confirmed by personnel from the North Carolina Department of Agriculture and Consumer Services (NCDA&CS) and North Carolina State University (NCSU).

During a pond management workshop on September 20 in Kinston, a property owner brought in a live sample of giant salvinia from a pond in Jacksonville, and another aquatic applicator reported a large infestation in a swamp pond within a subdivision adjacent to the Northeast Cape Fear River east of Burgaw. Thursday, September 28, a joint task force of personnel from NCSU, NCDA&CS, the North Carolina Department of Environment and Natural Resources Division of Water Resources, the Cooperative Extension Service office at Wilmington, and the U.S. Army Corps of Engineers, Wilmington District, visited the sites at Wilmington, Jacksonville, and near Burgaw. Both ponds at the golf course in Wilmington were completely covered with giant salvinia, and small patches of plants were present in a drainage ditch into which the lower pond flowed. Data collected using GPS equipment indicated that the upper and lower ponds were about 0.25 and 0.5 acres, respectively, and the ditch was 0.1 acre. Both ponds had been infested for more than two years.

The site in Jacksonville was of much higher concern as flooding two weeks earlier had washed large masses of giant salvinia from a small pond (0.25 acre) into the adjacent wetland, which flows into Northeast Creek. Very little salvinia remained in the pond. A survey of the wetland revealed large mounds of plants piled against the tree line and smaller patches of live plants on wet soil up to 100 yards from the pond. A few plants were found within 25 ft. of the creek in the wetland. Giant salvinia has been in this site since 1999. No plants were found downstream at this time, but there is concern that flooding in the fall of 1999 and mid-September 2000 may have washed plants into Northeast Creek and the adjacent wetlands downstream.

The site currently of greatest concern is the swamp pond beside the NE Cape Fear River. Property owners here indicated that this weed has been present for at least three or four years. Giant salvinia is present in the open water that encircles a swampy wetland. Plants were visible well back into the trees in the wetland and in a small drainage canal paralleling the road just east of this site. Some waterhyacinths also were seen in the canal. The pond, including the encircled wetland, occupies 15 acres, and has been flooded several times. In fall 1999, ten to twelve ft. of water covered the road next to the pond. Dead salvinia was found hanging in trees ten to twelve ft. above the ground, where they were stranded during the flooding following Hurricane Floyd in 1999. This site is only 100 ft. from the Northeast Cape Fear River, and stranded plants were found in trees within 30 ft. of the river. It is highly probable that giant salvinia has been distributed widely downstream into the swamps along the river. Control of giant salvinia in sites such as this is essentially impossible due to obstructions preventing herbicide treatment. Surveys of adjacent wetlands will be conducted during the next two weeks by NCDA&CS. Updates will follow pending the findings of this survey.

For more information, contact Stratford Kay: stratford_kay@ncsu.edu.