A NEW episode in the war against one of the worst weeds in southeast Australia is unravelling this week.

The invader is the English broom, also called Scotch broom, a leguminous shrub originating from Europe.

Ranked as the 31st worst established weed in Australia, English broom will face a new enemy following the first significant national release of a new biocontrol agent, a microscopic mite named Aceria genistae.

It was released last week at Dartmouth Lake in Victoria's Alpine National Park.

English broom seeds were introduced to Australia in the early 1800s as an intended substitute crop for hops.

Planted by settlers in gardens as a reminder of their country of origin, seeds rapidly escaped and broom plants began invading the bush.

Today, broom infests the cool temperate areas of Victoria, NSW, Tasmania and the Adelaide Hills.

The mite lives exclusively on English broom and originates from Europe, where it limits broom infestations.

Department of Primary Industries' quarantine manager Jean-Louis Sagliocco said years of testing in Australia under quarantine conditions had ensured no species other than English broom would be at risk of attack from Aceria genistae.

Besides herbicidal control methods, biological control has been used since the early 1990s in an attempt to control ever-expanding English broom infestations in Australia.

Mr Sagliocco said three different natural enemies of broom had been released in Victoria, mostly in the worst broom-infested areas of the Alpine National Park.

"However, the 2003 bush fires had a devastating effect, destroying old broom stands and biocontrol agent populations, but also creating open spaces for massive germination of the broom seeds still present within the soil," he said.

Mr Sagliocco said mite populations were expected to quickly establish and disperse throughout broom infestations following this week's release.

Further releases will be conducted by DPI in association with Parks Victoria and Goulburn-Murray Water every six months in the Alpine National Park and the Dartmouth catchment, he said.

For more details phone Mr Sagliocco on (03) 9785 0164.