Egeria densa - Brazilian Elodea - A Probem Aquatic Plant in the Western USA

Egeria densa - Brazilian elodea

The Western Aquatic Plant Management Society

Description and Variation Comparison of Egeria densa and Elodea canadensis

Brazilian elodea looks very much like a larger, more robust version of its commonly-found native relative, Elodea canadensis (waterweed). The photograph at the right compares two strands of Elodea canadensis (upper left) to Egeria densa (the large robust plant to the right). Brazilian elodea leaves are 1-3 cm long, up to 5mm broad, and are in whorls of four to eight. The leaves are minutely serrated, linear, and its short internodes frequently give the plant a very leafy appearance. The leaves and stems are generally a bright green. The lowest leaves are opposite or in whorls of 3, while the middle and upper leaves are in whorls of 4 to 8. Stems are erect, cylindrical, simple or branched and grow until they reach the surface of the water where they form dense mats. The 18-25mm white flowers have three petals, are dioecious (male and female flowers on separate plants), and float on or rise above the water's surface on thread-like hypanthiums produced from apical double nodes. White or pale slender roots are unbranched. Adventitious roots are freely produced from double nodes on the stem.

Economic Importance

Brazilian elodea is a popular aquarium plant and can be found for sale in most pet shops, usually under the name Anacharis, although the sale of this plant in Washington is illegal. The trouble starts when Brazilian elodea is accidentally or deliberately introduced into lakes and ponds. The characteristics that make Brazilian elodea a good aquarium plant, also make it a nuisance plant out of its native habitat. Brazilian elodea forms dense monospecific stands that restrict water movement, trap sediment, and cause fluctuations in water quality. Dense beds interfere with recreational uses of a waterbody by interfering with navigation, fishing, swimming, and water skiing. An estimated 1500 acre feet of storage capacity were lost annually in Lake Marion, South Carolina due to sedimentation caused by Brazilian elodea growth. In New Zealand, electric generating plants were shut down when fragments of Brazilian elodea clogged intake structures on the Waikato River. In Washington State, local and state government and lake residents spend thousand of dollars every year to manage Brazilian elodea infestations.

Geographic Distribution

Brazilian elodea is native to the central Minas Geraes region of Brazil and to the coastal areas of Argentina and Uruguay. Due to its popularity as an aquarium plant, Brazilian elodea has also spread to New Zealand, Australia, Hawaii, Denmark, Germany, France, Japan, and Chile. In the United States, this plant has run wild in fresh inland waters from Washington to Massachusetts, California, and Florida. State officials in Oregon consider Brazilian elodea to be their worst aquatic plant problem. Brazilian elodea is causing major problems in the Sacramento Delta region of California.

Habitat

Brazilian elodea is a submersed, freshwater perennial herb, generally rooted on the bottom in depths of up-to-20 feet or drifting. It is found in both still and flowing waters, in lakes, ponds, pools, ditches, and quiet streams. It tends to form dense monospecific stands that can cover hundreds of acres and can persist until senescence in the fall. High water temperatures (greater than 30 degrees centigrade) and high light intensities can cause senescence.

History

The earliest report of Brazilian elodea in the United States was from Millneck, Long Island where the plant was collected in 1893. It was offered for sale in the United States in 1915, where it was recommended as a good "oxygenator" plant. The first European record of this species outside of cultivation was in a canal in Leipzig, Germany in 1910.

Growth and Development

In Long Lake, Kitsap County in Washington State about 25 percent of the biomass overwinters along the bottom in a dormant-like, evergreen condition. The plants initiate growth when water temperatures reach 10 degrees centigrade. Getsinger describes the life cycle of Brazilian elodea in Lake Marion, South Carolina as follows: Two major growth flushes occur in spring and fall. Each of these flushes are followed by periods of senescence, with a loss of biomass through sloughing and decay of tips and branches. Flowers are produced in late spring and again in the fall. The intensity of flowering varies from year to year. During the summer, profuse branching forms a canopy. The branches form dense, tangled mats on the water's surface.

Reproduction

Seeds and/or female flowers have never been reported from Brazilian elodea populations established in the United States. The absence of sexual reproduction in introduced populations of Brazilian elodea emphasizes the importance of the vegetative growth phase of the plant. Specialized nodal regions described as double nodes occur at intervals of 6 to 12 nodes along a shoot. A double node consists of 2 single nodes separated by a greatly shortened internode. Double nodes produce lateral buds, branches, and adventitious roots. Only shoot fragments of Brazilian elodea which contain double node regions can develop into new plants. The plant fragments readily and each fragment containing a double node has the potential to develop into a new plant. Plant root crowns also develop from double nodes along an old shoot. When a shoot sinks to the bottom during fall and winter senescence, a new root crown may develop at one or several double nodes along the new shoot. Brazilian elodea lacks specialized storage organs such as rhizomes or tubers and stores carbohydrates in stem tissues.

Response to Herbicides

Westerdahl and Getsinger report excellent control of Brazilian elodea with diquat and complexed copper, endothall dipotassium salt, and endothall and complexed copper. Good control was obtained with acrolein, diquat, and fluridone. California reports good control achieved using complexed copper alone.

Fluridone (Sonar®) was used to treat Brazilian elodea in Lake Limerick, Washington in 1995 with excellent results. A year after treatment Brazilian elodea biomass had declined about 95 percent throughout the lake. However, some surviving stem ends initiated new growth during 1996.

Response to Cultural Methods

Localized control (in swimming areas and around docks) can be achieved by covering the sediment with a opaque fabric which blocks light from the plants. Managers of reservoirs and some lake systems may have the ability to lower the water level as a method of managing aquatic plants. Goldsby and Sanders reported that consecutive drawdowns in Black Lake, Louisiana eradicated Brazilian elodea. They noted that consecutive drawdowns may be more effective than an individual drawdown. The success of a drawdown is dependent on several factors such as degree of desiccation (drawdowns in rainy western Washington and Oregon are often ineffective), the composition of substrate (sand vs. clay), air temperature (the exposed sediments need to freeze down to 8-12 inches), and presence of snow.

Response to Mechanical Methods

Because this plant spreads readily through fragmentation, mechanical controls such as cutting, harvesting, and rotovation (underwater rototilling) should be used only when the extent of the infestation is such that all available niches have been filled. Using mechanical controls while the plant is still invading, will tend to enhance its rate of spread. Harvesting removes surfacing mats and creates open areas of water.

Biocontrol Potentials

It is unknown what insects or pathogens have biocontrol potential for Brazilian elodea. However, recent research in Brazil has identified a fungus (Fusarium sp.) which damaged Brazilian elodea in laboratory tests. This may have potential as a biological control agent for Brazilian elodea.

Fortunately triploid grass carp find Brazilian elodea highly palatable and they have been successfully employed as a management tool in Devils Lake, Oregon and Silver Lake, Washington to control Brazilian elodea populations. Brazilian elodea is highly preferred over most native species and theoretically, it should be possible to remove Brazilian elodea while favoring the growth of native species. However, in practice, grass carp often remove the entire submersed aquatic community and should be used with great care. Grass carp are also not suitable for use in waterbodies where inlets and outlets cannot be screened.

References

Barko, J.W. and R.M. Smart. 1981. Comparative influences of light and temperature on the growth and metabolism of selected submersed freshwater macrophytes. Ecological Monographs 51: 219-235.

Catling, P.M. and W. Wojtas. 1986. The waterweeds (Elodea and Egeria, Hydrocharitaceae) in Canada. Canadian Journal of Botany 64: 1525-1541.

Cook, C.D.K. and K. Urmi-Konig. 1984. A revision of the genus Egeria (Hydrocharitaceae). Aquatic Botany 19: 73-96.

Getsinger, K.D. 1982. The life cycle and physiology of the submersed angiosperm Egeria densa Planch. in Lake Marion, S.C. pHd Dissertation.

Gibbons, M.V., H.L. Gibbons, Jr., and M.D. Sytsma. 1994. A citizen's manual for developing integrated aquatic vegetation management plans, first edition. Washington State Department of Ecology, Olympia, WA.

Goldsby, T.L. and D.R. Sanders. 1977. Effects of consecutive water fluctuations on the submersed vegetation of Black Lake, Louisiana. Journal of Aquatic Plant Management. 15:23-8.

Hogan, W.D. and S.B. Hopkins. 1978. Improved efficacy in aquatic vegetation control. Proceedings of the Southern Weed Science Society 31: 237.

Hotchkiss, N. 1972. Common marsh, underwater and floating-leaved plants of the United States and Canada. Dover Publications, Inc., New York.

Lazor, R.L. 1975. The ecology, nomenclature and distribution of hydrilla (Hydrilla verticillata Casp.) and Brazilian elodea (Egeria densa Planch.). Proceedings of the Southern Weed Science Society 38: 269-273.

Manning, J.H. and D.R. Sanders. 1975. Effects of water fluctuation on vegetation in Black Lake, Louisiana. Hyacinth Control Journal 13: 17-24.

Pieterse, A.H. and K.J. Murphy. eds. 1993. Aquatic Weeds The Ecology and Management of Nuisance Aquatic Vegetation. Oxford University Press.

Tarver, D.P., J.A. Rodgers, M.J. Mahler, and R.L Lazor. 1986. Aquatic and Wetland Plants of Florida. Bureau of Aquatic Plant Research and Control, Florida Department of Natural Resources, Tallahassee, Florida 32303.

Welch, E.B., E.G. Kvam, and R.F. Chase. 1994. The independence of macrophyte harvesting and lake phosphorus. Verh. Internat. Verein. Limnol. 25:2301-2304.

Westerdahl, H.E. and K.D. Getsinger, eds. 1988. Aquatic plant identification and herbicide use guide, volume II: Aquatic plants and susceptibility to herbicides. Technical report A-88-9. Department of the Army, Waterways Experiment Station, Corps of Engineers, Vicksburg, MS.

Whitley, J.E., B. Basset, J.G. Dillard, and R.A. Haefner. 1990. Water Plants for Missouri Ponds. Missouri Department of Conservation, P.O. Box 180, Jefferson City, MO 65102.