The war with the weed broom may have slightly tilted in favour of land managers, with the release in Southland last week of a new gall mite.
Mites have previously been released in Canterbury after being imported by Landcare Research on behalf of the Canterbury Broom Group, but this was the first release in Southland.
Environment Southland's senior biosecurity officer Keith Crothers said the mite, which was native to Western Europe, was released at Nokomai and Te Anau.
It would take 12 to 24 months to determine if the release had been successful.
Meanwhile, a leaf-eating beetle introduced to control the California thistle and released on several sites in South Otago over the past couple of years, appears to have survived winter.
Clutha Agriculture Development Board consultant Graeme Pringle said mild weather in August and September had helped, with signs the beetles had not only survived but reproduced.
Colder weather since then had tempered activity and Mr Pringle expected to see further signs in the New Year.
Last autumn a stem and root-eating weevil was released in West Otago, but Mr Pringle said the site had not yet been inspected to see if they had survived.