Salvinia Molesta

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q Current q Potential (in waterbodies)

Salvinia (Salvinia molesta)
The problem
Salvinia is a Weed of National Significance. It is regarded as one of the worst weeds in Australia because of its invasiveness, potential for spread, and economic and environmental impacts.Salvinia is an aquatic weed that can choke waterways. It floats on still or slow-moving water and can grow rapidly to cover the entire water surface with a thick mat of vegetation. This shades out any submerged plant life and impedes oxygen exchange, making the water unsuitable for fish and other animals. Salvinia infestations reduce the natural beauty and biodiversity of wetlands. A salviniainfestation can reach up to 400 tonnes of wet weight per hectare. Infestations are a major obstacle to the enjoyment and use of water. They block irrigation, cause flooding, pollute drinking water, and prevent recreational activities such as swimming, fishing and boating. Infestations can be dangerous to animals and people because the mats look like solid ground, and they provide an ideal breedingenvironment for disease-carrying mosquitoes. oval-shaped hairy fronds. A brown frond, consisting of many hairy filaments, also occurs at each node and trails in the water, looking and acting like a root. Salvinia changes as it matures and becomes more crowded. In low densities the primary invading plants have a few small floating fronds (10–15 mm wide) which lie flat on the water. However, in thedense infestations that cause mats, the many floating fronds are folded, up to 60 mm wide, overlapping and tightly packed together in a concertina-like fashion. The surfaces of the floating fronds have numerous distinctive egg-beater-shaped hairs that repel water and assist floatation. This hair shape is characteristic of Salvinia molesta. • Salvinia is a major aquatic weed threatening waterwaysaround Australia. • Infestations are widespread on the east coast of Australia but could spread elsewhere. • Public education will help to prevent spread because infestations are caused by human activities. • Because of salvinia’s ability to rapidly spread from single plants, only small infestations are likely to be eradicated. • In warm temperate, sub-tropical and tropical areas, biological controlis very effective. • Biological control can be integrated with chemical and physical control in cooler areas.
Salvinia forms dense mats that can cover entire waterbodies. Photo: Colin G. Wilson

Salvinia – Salvinia molesta

Key points

The weed
Salvinia is a free-floating fern that forms dense mats on water. It consists of manybranched horizontal stems, 1–2 mm in diameter, which float justbelow the water surface. At each node, or joint, on the stem is a pair of floating, green,

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Growth calendar
May Aug Mar Nov Dec Sep Apr Feb Oct Jun Jan Jul

New growth Active growth Spore formation Spore drop Germination

No viable spores yet found in Australia

General growth pattern

Growth pattern under suitable conditions

Salvinia grows best when the water temperature isbetween 20 and 30°C; growth is limited or absent under 10°C. As salvinia is found throughout tropical, sub-tropical and temperate regions, these climatic conditions will occur at different times of the year. It grows faster when nutrients are abundant, often after rainfall has washed nutrients from the land into water bodies. Salvinia is a fern and does not produce flowers. Although many ferns doproduce spores, salvinia has never been known to produce spores in Australia and is considered to be a sterile clone. survive for many months if the water body dries up, particularly in shaded environments or on soils that hold water. Salvinia also thrives in nutrientrich waters such as agriculture run-off or wastewater. These attributes allow it to colonise most water bodies. Salvinia is a...