Leafy elodea is a submerged aquatic perennial plant that thrives in shallow, nutrient-rich, slow-moving or stationary water to depths of around seven metres. More cold tolerant than many other aquatic weeds, it thrives in southern Australia.
Leafy elodea was traded as an aquarium and pond plant. Unfortunately, it has escaped and causes problems including restricting water flow, increasing siltation, reducing aquatic plant and animal biodiversity, and interfering with swimming, boating and fishing.
Leafy elodea is native to parts of South America. It has become a problem throughout North and South America, and in England, Japan, New Zealand and South Africa.
The distribution of leafy elodea in Australia includes rivers, lakes, ponds and dams in coastal and inland southern New South Wales (NSW) and south-east Queensland. It is uncommon in other states and has been banned from sale in the Northern Territory, South Australia, Tasmania and Western Australia.
The plant spreads when stem pieces break from the main plant. This occurs easily from actions such as boat wash and mechanical harvesting, but also from natural means. The plant is spread from site to site through movement of plant fragments, both deliberate and accidental. Fragments caught on boat trailers, fish traps or other equipment can survive long enough to cause a new infestation when equipment re-enters water. The plant has also been deliberately planted for commercial harvesting purposes.
The freshwater plant has cylindrical stems that grow up to 1.5 m long (occasionally up to 5 m). Stems take root at the lower nodes but float for most of their length.
The leaves are oval- to oblong-shaped, generally 1.5–4 cm long, 2–5 mm wide, and found in groups (whorls) of 4–5 at the stem nodes. Lower stem leaves may be opposite or in whorls of 3, while the middle and upper leaves can grow in whorls of 4 to 8. Very fine teeth, only visible by a hand lens, are found along the leaf margins. Dense clusters of leaves appear at the ends of branches which often grow to reach the water surface.
The white flowers (1.2–2 cm wide) are found at the water surface on stems up to 8 cm long. These flowers have three large petals centred by a cluster of generally nine yellow anthers. Male and female flowers grow on separate plants, although only male plants have been found in Australia. Seed production has not been recorded.
Rebecca Coventry, Andrew Petroeschevsky, Syd Lisle and Peter Gorham.
Preventing this weed escaping into waterways is the best way of managing it, particularly in areas that are currently free of the plant.
Remove this plant from aquariums and garden ponds. Dispose of plant material by drying in the sun and burying fragments. Never dump or grow aquarium plants in waterways.
Mechanical harvesting can reduce the bulk of the species but has little value in preventing regrowth and long-term control. Often more plant fragments are produced and these spread further downstream.
The long-term management of this plant is likely to involve both increased and variable water flows and reduced nutrient loading.
See Using herbicides for more information.
Diquat 200 g/L
Rate: 5 L /megalitre water
Comments: Apply by injection below the surface or as a surface spray.
Withholding period: 1 day in pasture, 10 days in treated water.
Herbicide group: L, Inhibitors of photosynthesis at photosystem I (PSI inhibitors)
Resistance risk: Moderate
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Locally Controlled Weed
The plant must not be sold, propagated or knowingly distributed