Salvinia (Kariba weed)
Salvinia molesta
Kariba weed or Salvinia
Status: Notifiable Organism, Unwanted Organism
Description
This native of Brazil is one of the world's most damaging aquatic weeds, often completely smothering large water bodies and badly affecting water quality.
The plant is a free-floating fern. The young plants have well-spaced, small (1.5cm long) pale green leaves that lie flat on the surface of the water, attached to a horizontal stem that lies just below the water surface. Mature foliage is green to golden brown in colour and has water repellent hairs that aid the flotation of the plant. Plants are usually up to 30cm long. Leaves occur in whorls of three with only the upper two forming true leaves above the water surface, whilst the lower leaf, which resembles a root, hangs down into the water. The upper surface of the leaf is water repellent and covered with distinct white hairs with an egg beater like tip. The plant has no true roots.
Impact
Each plant can produce and shed daughter plants at the end of its horizontal axis, which in turn produce further plants until a dense mat is formed. These mats can cover entire water bodies.
These mats kill off native plants, attract breeding mosquitoes, cause flooding, block dams and irrigation systems, remove oxygen from the water, prevent recreational use and create a drowning risk for people and animals.
Where is it found?
Salvinia has been reported from the Bay of Plenty north, but only a few field sites remain active. The plants are frost-sensitive, but could move further south if they established in warm micro-climates. (Sites have been found in Hawkes Bay, Wellington and as far south as Christchurch). Most of the known sites of salvinia are now considered historic, having been clear of the plant for at least two years.
What to do
Propagation, spread, and sale of salvina is prohibited under the Biosecurity Act 1993. All sightings must be reported to Biosecurity New Zealand on 0800 80 99 66.
MAF contracts a monitoring and control programme aimed at eliminating salvinia from New Zealand.
Page last updated: 22 May 2008