Lagarosiphon is also known as oxygen weed. It is a perennial plant, which grows fully submerged in water to depths of 6.5 metres. The plant has spiralled, green leaves on slender, brittle stems up to 5 metres long. It forms large mats of interwoven stems below the water surface. It has an exceptional ability to reproduce and spread. The plant is spread by vegetative fragmentation. Dispersal of fragments is by water flow, or by people transporting fragments on their boats, trailers and fishing nets.
Reasons for the Strategy
Lagarosiphon is an aggressive freshwater weed that shades out native aquatic plants. By modifying habitats and smothering other useful species, Lagarosiphon may displace food sources of value to Maori such as watercress. Dense stands will impede water flow and interfere with water utilisation. Surface beds spoil water for aesthetic and recreational purposes. Lagarosiphon liberates oxygen as it grows, but heavy infestations diminish oxygen available to fish by reducing water circulation and through the decomposition of dead plants.
Lagarosiphon is assessed at “4” on the infestation curve. There are numerous sites in garden and farm ponds and some waterways in Tasman District, including Golden Bay. Extensive areas of suitable habitat, and the potential for it to cause significant adverse effects, mean the benefits of containment control far outweigh the costs. As Lagarosiphon is so difficult to control, the focus will be on educating the public and continuing to investigate effective control methods for existing infestations. A rule requiring control of Lagarosiphon is inappropriate, given how difficult it is to control.
To address the adverse effects of Lagarosiphon in the Tasman-Nelson region during the term of the Strategy.
The alternative option of “do nothing” or relying on voluntary control will not achieve the objective of containing Lagarosiphon, and will result in significant additional costs to the community with respect to lost natural values, and the increased cost of control in the future. Requiring total control is not practical, as the control methods may not be effective in every situation.
Strategy Rule for Gorse
The occupier shall manage Lagarosiphon to prevent it spreading to other water bodies.
Biosecurity Act Requirement
No person shall knowingly sell, propagate, breed, release or commercially display Lagarosiphon, under Sections 52 and 53 of the Act