Compound 'promising' in fight against didymo

Scientists are testing a promising new compound in the battle against the highly invasive algae didymo, or rock snot, that is clogging South Island waterways.

The copper-based formulation devised by National Institute of Water and Atmospheric Research (Niwa) scientists in Christchurch has proved effective in killing didymo in laboratory tests, while having little effect on other organisms.

Niwa scientist Barry Biggs said trials of the compound so far had proved "very promising".

"It's got a low level of toxicity to fish within the range that we would use on didymo," Dr Biggs said.

The next set of trials was scheduled in about three weeks.

Part of those tests would determine how toxic it might be to native fish, such as whitebait, and organisms that live on the bottom of rivers, such as mayflies and other insects.

"We need to be sure we are protecting those species," Dr Biggs said.

"Killing didymo is one thing but we don't want to be killing everything else."

Dr Biggs said he and his fellow scientists were "pretty excited" by the discovery and the copper compound's potential as a tool in the battle to control the invasive algae that was first discovered in a Southland river in 2004.

Didymo had since spread rapidly to several South Island waterways, including the lower reaches of the Waitaki River.

Dr Biggs said the new compound was the culmination of almost two years of research that began soon after didymo was first discovered.

"It hasn't been difficult to kill didymo but it's been extremely difficult to kill didymo and not kill everything else," he said.

"The reason we're excited about our discovery now is that this particular compound we've developed appears to be killing didymo but with a low level of toxicity to other organisms in the river."

Dr Biggs stressed the new compound was not a "magic bullet".

"It will not kill didymo or eradicate didymo forever. It's going to be part of an ongoing surveillance and control strategy that will need to be developed for certain waterways."

He urged water users to continue their vigilance by checking, cleaning and drying any equipment before using it in another waterway to avoid spreading the algae, which appeared to be "coming back rapidly" this spring.

Biosecurity New Zealand spokesman Phil Barclay said while results of the Niwa work, done under contract to the Government agency, were "really pleasing" the compound still needed to be tested in the natural environment.

River bug

Didymo is a freshwater type of algae that lives on the bottom of streams and rivers smothering rocks. It thrives in cold, running water.

Didymo was first found in New Zealand in 2004 in the lower Waiau and Mararoa Rivers in Southland.

Since September 2005 it has been found in the Bulla, Hawea, Clutha, Waitaki, Von and Oreti rivers. Yet to reach the North Island.

Didymo's arrival in New Zealand is the first recorded occurrence in the Southern Hemisphere.

It originates from Europe and has been found in the United States, Alaska, Canada, United Kingdom, Russia, Norway, Poland, Hungry, Romania, China and India.

Biosecurity New Zealand predicts didymo could cost the country $157 million a year.

- NZPA