Hornwort control on Centennial Park Lake successful
28 April 2008
A survey to monitor the effect of control work for the invasive aquatic weed hornwort (Ceratophyllum demersum) at Centennial Park Lake, Timaru has revealed no visible signs of the weed, MAF Biosecurity New Zealand said today.
Hornwort was identified in Centennial Park Lake and the north branch of the Otipua stream in February 2006. A survey of the lake in January 2008 showed hornwort was still present, although none was found at any site surveyed outside of the lake.
In March the aquatic herbicide endothall (Aquathol K/Aquathol Super K) was applied to hornwort in the lake. Previous treatments with the herbicide diquat weren't successful in eradicating hornwort from the lake.
"We are very pleased with the outcome of the hornwort control work in Centennial Lake, as it significantly reduces the risk of hornwort being spread to other South Island water-bodies," said Victoria Lamb, Senior Adviser - Pests and Pathways Team, MAF Biosecurity New Zealand.
"The lake will be surveyed again in December this year, once the weather warms up and any remaining plants have had time to grow large enough to be identified. Regular monitoring of the lake will continue for the next five years. If no hornwort is found at the site during this time, hornwort will be declared eradicated from the lake.
"Exclusion of hornwort from the South Island is the goal of MAF Biosecurity New Zealand's National Interest Pest Response for hornwort, and this latest result supports this goal."
Ms Lamb said the restricted place notice put in place in February 2006, which closed the lake and affected stream areas to all use (including paddling, fishing, kayaking and swimming), will remain in place until after the survey in December, after which a decision will be made on whether the notice will be revoked or changed.
Hornwort is an invasive weed established in the North Island. It is not yet thought to be established in the South Island. It grows rapidly, forming dense mats that choke waterways and is difficult to eradicate.
Hornwort is a free-floating plant with no roots. It has long, dark green stems with forked leaves arranged in whorls of 7-12. Hornwort may be found in waterways and garden ponds. Members of the public are asked to keep a look out. Any sightings should be reported to MAF Biosecurity New Zealand on 0800 80 99 66. For more information about hornwort go to www.biosecurity.govt.nz/pests/hornwort.
- For further information contact Judith Hamblyn, Senior Communications Adviser on 04 894 0687 or 029 8940687.