Salvinia (Salvinia molesta)
Close up of Salvinia (Salvinia molesta)
Salvinia is declared a Class B (growth and spread to be controlled) and Class C (not to be introduced to the Northern Territory) weed in accordance with the NT Weeds Management Act and is listed as a weed of national significance because of its invasiveness, potential for spread and economic and environmental impacts.
A native of Southern Brazil and Paraguay, salvinia is thought to have been first introduced to Australia by the aquarium trade and was reported as a weed in New South Wales dating back to 1952. Since its introduction, it has been widely planted as an ornamental and has subsequently been grown in garden ponds in many other places including Alice Springs. Salvinia is found in the Northern Territory, Western Australia, South Australia, Queensland and New South Wales. Its potential distribution includes water bodies in every Australian state and territory.
Free floating Salvinia
Salvinia is a free-floating aquatic fern that can grow rapidly to form a dense mat over the water surface, severely modifying aquatic habitat for fauna, including birds, fish and invertebrates. Light is excluded and oxygen levels are reduced, leading to water stagnation and pollution. The dense mat impedes water flow, restricts stock access and provides favourable conditions for the breeding of disease-carrying mosquitoes. Individual plants are between 5–30 cm long, with 'leaves' (fronds) in whorls of 3 at each node, consisting of a pair of floating leaves and a submerged modified leaf that looks like and functions as a root. Upper surface of leaves covered with waxy egg-beater-shaped hairs; lower surface of leaves and root-like leaf covered with dark hairs.
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Salvinia Habitats
It is usually found in still or slow-moving water bodies with high nutrient levels and can survive water temperatures up to 430 and salinities up to one tenth of sea water. Its stem fragments are spread by various means including water movement. The dumping of unwanted contents of ponds and aquaria is a major reason for the spread of salvinia.
Salvinia can be sprayed with various herbicides however results can be variable as upper leaf surfaces are largely non-wettable making absorption of herbicides difficult. Large infestations are sometime gathered with mechanical harvesters and scoops, although the effectiveness of this method is limited by the ease with which the plants break into fragments. Plants deposited on the banks of water bodies can be moved away from the water’s edge, and preferably burnt, to prevent reintroduction.
Salvinia has also been recognised as a target for biological control. The Salvinia weevil (Crytobagous salviniae) has been released in Australia as a biological control agent and has been effective in tropical areas.
Click here for more information on the biological control of salvinia.
Small infestations in home ponds and aquaria can be gathered with five-woven scoops, placed in sealed plastic bags and destroyed by leaving the bags in the sun to dry out.
