KEY POINTS:
A decade of study has convinced government researchers to seek environmental approval for release of a sap-sucking lace bug to control woolly nightshade.
The South American tree is a pest in New Zealand, and Landcare Research scientists are preparing to apply to the Environmental Risk Management Authority (Erma) for approval to release the bugs.
They will have to prove that the bugs will not pose a danger to useful plants in the same genus, Solanum, as the nightshade, including potatoes, tomatoes and the native poroporo.
"Of the species tested, eggplant appeared to be the most at risk," said Lynley Hayes, Landcare's programme leader for biological control of weeds.
But she said open field trials in South Africa - rather than in a glasshouse - showed the bugs were unlikely to attack eggplant under normal conditions.
Terry Olckers of KwaZulu-Natal University said there were indications the bug could reduce the leaves, stems and roots of potted woolly nightshade plants by about a third.
It seemed to prefer shaded sites, which could be an advantage along the margins of NZ's native forests and pine plantations, where the nightshade is a particular pest. The trees grow to 9m.
"All the information that is available suggest the lace bug is a valid candidate as a bio-control agent for woolly nightshade in NZ," said Richard Hill, who wrote a report recommending use of the lace bug.
But he warned that a single agent was not likely to be enough against nightshade, which can regenerate from cut stumps.
Landcare researchers are planning to later evaluate a flowerbud-feeding weevil for release.
WOOLLY NIGHTSHADE
* Also known as tobacco weed, flannel weed, kerosene plant and eared nightshade.
* An aggressively invasive pest.
* Can grow up to 10m tall and put forest regeneration at risk.
- NZPA
