Issue 10, June 25, 2010

Aquatic Invasives: Brazilian Elodea and Hydrilla

There are two invasive species threatening America's waterways- Brazilian elodea (Egeria densa) and hydrilla (Hydrilla verticillata). Hydrilla is a persistent problem throughout North America while Brazilian elodea only survives in the north. Aquarium dealers still sell Brazilian elodea; be sure to purchase alternatives such as Canadian Elodea or American Waterweed when stocking your aquarium.

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These plants look fairly similar. They are both light green, with long slender stems and leaves growing in whorls. Brazilian elodea has leaves growing in whorls of 4-6 and the leaves are much larger and smoother. Leaves on hydrilla grow in whorls of 5 and have small teeth on the underside of the midrib. Hydrilla also produces tubers (yellowish bulbs attached to the root tips) and turions (buds in the leaf axils). Both grow submerged in freshwater habitats.

Since these plants lack any natural predators in this country, they are able to easily outcompete native plants and quickly dominate an area, filling up the body of water, and “topping out" at the surface as large mats. Once established, hydrilla and Brazilian elodea can clog irrigation and flood control canals. Stands of the plants also interfere with boating and can be spread further if fragments of the plants get attached to a boat or trailer.

There are several options for control of hydrilla. Drawdown, a process that removes water from a lake or pond and allows the plants to die before water is let back in, and mechanical harvesting using chopping machines are possible options. Herbicides have been shown to be temporarily effective but will not completely eliminate the problem. Brazilian elodea has proven to be more difficult to control; mechanical harvesting will simply allow the plants to spread. However, Brazilian Elodea can be controlled by herbicides. Grass carp has been suggested as a possible control because of their large appetite for plants. However, once placed in the ecosystem, grass carp is very difficult to recapture and can cause further problems for native plants.

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If you suspect you have either of these plants on your property, contact: Illinois Cooperative Pest Survey.--Stephanie McLaughlin

Kelly Estes

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