DATE 13 October 2005
Warning against unapproved cleaning methods, testing progresses.
Biosecurity New Zealand has become aware of a number of alternative cleaning methods being promoted for cleaning river
equipment. This has occurred without consultation with Biosecurity New Zealand, and the methods have not been laboratory
tested on Didymo.
There are doubts about the ability of some of the proposed methods to kill Didymo. Not using the approved cleaning
methods would put the user at risk of breaching the controlled area conditions where they are in place, as well as
potentially spreading Didymo to an unaffected waterway.
Biosecurity New Zealand is working to assess these methods, but reiterates that in the meantime, the approved cleaning
methods, available online but repeated below, should be used. Advice is being developed for recommended cleaning options
for specific items and will be online shortly at www.biosecurity.govt.nz/didymo.
If any more cleaning methods are approved, Biosecurity New Zealand will advise of these in a further update. In the
meantime, the following approved measures should be followed.
To ensure you do not spread Didymo, wherever possible restrict equipment, boats, clothing and other items for exclusive
use in a single waterway.
If you are moving items between waterways you must:
1. Inspect: Before leaving the river, remove all obvious clumps of algae and look for hidden clumps. Leave them at the
affected site. If you find any later, do not wash them down drains. Treat them with the approved cleaning methods below,
dry them and put them in a rubbish bin.
2. Clean: Soak and scrub all items for at least one minute in either, hot (60°C) water, a two percent solution of
household bleach or a five percent solution of salt, nappy cleaner, antiseptic hand cleaner or dishwashing detergent. A
two percent solution is 200 ml, a five percent solution is 500 ml (two large cups), with water added to make 10 litres.
3. Dry: If cleaning is not practical (i.e. livestock), after the item is completely dry to touch, wait an additional 48
hours before contact or use in any other waterway.
Meanwhile, Didymo testing in the North Island is well in hand despite weather delays, and testing in the Southern third
of the South Island started today.
Inclement weather and resulting high river levels forced the postponement of some North Island sampling for sample
quality and safety reasons, but should be completed by next Wednesday. The delays should not extend the completion date
Yesterday the survey headquarters moved from Turangi to Alexandra in Central Otago, where planning of the survey for the
Southern third of the South Island has been completed for the start of testing today. When testing in that region has
been completed, the exercise will be repeated for the central third of the South Island.
All testing should be completed by next Friday, with results announced as soon as possible. Biosecurity New Zealand
still intends to release the results by geographic area to avoid any confusion in the event of any positive samples. The
results of the survey will guide BNZ’s further short-term containment and longer term management options for Didymo. The
controlled areas that have been put in place will be reassessed when the survey is completed.
So far the only rivers to have been confirmed with Didymo are the six rivers mentioned in previous updates – the Waiau
(upper and lower), Mararoa, and Oreti Rivers in Southland, the upper Clutha and Hawea in Otago, and the Buller River in
the Tasman District.
Biosecurity New Zealand has also requested proposals for potential chemical, biological and mechanical control methods
for Didymo. The first draft of an economic impact assessment for Didymo is expected by the end of October.