'Check, clean, dry' still best way to control didymo

24 July 2007

The latest findings from MAF Biosecurity New Zealand's Didymosphenia geminata (didymo) science programme were presented to the Didymo Technical Advisory Group and Long-Term Management partners at a seminar held in Wellington today.

Dr Christina Vieglais, Didymo Science Programme Leader, MAF Biosecurity New Zealand (MAFBNZ) said the seminar was invaluable in transferring information to partners and stakeholders.

"With the development of a long-term management programme for didymo, partners will need information to help them make decisions about how to best manage and respond to didymo in their area.

"Two-and-a-half years of coordinated research conducted by science providers, under contract to MAFBNZ, has provided a body of scientifically sound information regarding the detection, distribution, impacts, containment and control/eradication of didymo. We now know much more about didymo than when it was first discovered in Southland in 2004."

Dr Vieglais said the latest research findings into the ecological impact of didymo indicate the effect on aquatic invertebrate populations, on which trout and other fish feed, may be less severe than first thought.

"Firstly, the studies have found increased numbers of bottom-dwelling invertebrates living in association with didymo algal mats. This is meaningful for our native fish, most of which feed on these types of invertebrates.

"Secondly, the studies have found the highest densities and biomass of drift invertebrates near the river sites with medium to high didymo biomass. The main sources of food for trout are invertebrates which emerge from the river bottom and drift downstream.

"These findings are preliminary, and the potential long-term ecological impacts of didymo are still unclear. The findings don't diminish the impact didymo has on aesthetics, recreation and irrigation activities and MAF Biosecurity New Zealand is committed to slowing its spread," said Dr Vieglais.

Results of field trials of the chelated copper control tool confirmed its potential as a control tool for didymo.

"It may be possible to use the chelated copper control tool in certain situations to control didymo, but we have to be mindful that any control action must not create more environmental problems than it might solve. A decision to develop this tool further, and whether that work is best led by MAFBNZ, will be made in August once all the results from the research have been analysed.

"However, it is clear New Zealand-wide eradication of didymo is not possible based on the work done to date. The best way to control the spread of didymo is for all freshwater users to check, clean and dry their equipment between waterways. That is our best defence against didymo," said Dr Vieglais.

The didymo science programme has focused on three main areas: control of the alga (including decontamination, containment, suppression, elimination, and eradication); distribution (including detection, distribution, mapping, and sampling and analysis protocols); and impacts (including impacts on the economy, environment, and trout).

Other research results presented at the seminar were:

  • Ecological studies of didymo in New Zealand, 2006 - 2007
  • Effects of didymo biomass on invertebrate drift & trout growth
  • Predicting the potential distribution of didymo in New Zealand
  • Current surveillance methods to detect presence/absence of didymo
  • Extreme low-level genetic detection of didymo: a new surveillance tool
  • Didymo sample database: a web-based tool
  • Survivability of didymo and development of the Check Clean Dry method
  • Natural control of didymo in spring-fed waters
  • Stalk degradation as a potential didymo mitigation method
  • Development of a potential didymo control tool

The final peer-reviewed reports will be available on the MAF Biosecurity New Zealand website as they are finalised. This is expected to be by the end of August.

For more information contact:

Judith Hamblyn, Senior Communications Adviser
Ph 04 894 0687 or 029 894 0687

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