November 2001
Hydrilla
(Hydrilla verticillata)

Map of Current Hydrilla Reports in New England

Hydrilla verticillata in pan	Hydrilla in situ - Stonington, CT June 21, 1996	Hydrilla in situ same spot, 18 days later

Click on thumbnails to see larger image.

Hydrilla, Hydrilla verticillata (L. f.) Royle, has been recently reported at 2 new sites in southern New England. This highly invasive aquatic plant is often confused with the native Elodea canadense and Elodea nuttallii, both of which are widespread in the region and the introduced Brazilian waterweed Egeria densa.

Hydrilla has leaves in whorls of 3 to 8 at each node and small tubers (usually less than 1 cm long) that grow in the soil at the bottom of the lake or stream. These tubers often break off and may not be present on free-floating plant parts. Hydrilla was originally discovered in New England in 1989 in a small artificial pond (less than 1 acre) in Stonington (New London County) Connecticut. Unfortunately it went unreported until 1995 because it had been misidentified. That same year a second population was reported from a larger pond (around 3 acres) a few miles away. The first pond was dredged and the material removed was dried (and frozen) under black plastic to kill the tubers. This pond was subsequently restored. The second, larger pond was treated with herbicide. Eradication appears to have worked at the small pond but in 2001 Hydrilla was again found at the larger pond. It has again been treated with a herbicide.

In the spring of 2001 a third New England occurrence was discovered in Wilton (Fairfield County) Connecticut. It was discovered in an artificial pond by aquatic weed control experts and reported to the Connecticut Department of Environmental Protection. This pond has also been treated with herbicide. All 3 sites will be monitored in 2002.

In October, Hydrilla was reported from a large pond in Barnstable (Barnstable County) Massachusetts. Residents notice increased aquatic plant growth and contacted someone licensed in aquatic weed control in Massachusetts. They in turn contacted Dr. Barre Hellquist of Massachusetts Liberal Arts University in North Adams an authority on New England's aquatic flora, who confirmed the identification. The Massachusetts Lakes and Ponds Program was notified and they have already visited the site and will formulate a plan to remove this invasive before it has the chance to spread.

Hydrilla spreads very easily either by floating plant parts or the turions that grow in the bottom of the pond moving from one body of water to another. Movement can be facilitated by birds and by unintentional human transport on boats, boat trailers, bait pails and other objects. It can also be introduced into a body of water as a contaminant with water garden plants or by dumping aquaria in which this has be used as an oxygenating plant.

For more information on hydrilla see:

http://nas.er.usgs.gov/taxgroup/plants/docs/hy_verti.html