Weed enemy to make national debut

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Boneseed leafroller larva

www.landcareresearch.co.nz

Weed enemy to make national debut

A South African moth will be released into New Zealand for the first time tomorrow, on Waiheke Island, weather permitting. This biocontrol agent is ready to battle boneseed, a highly invasive coastal plant.

Boneseed has spread rapidly in the past 20 years. It is scattered along coastlines throughout the North Island and parts of the South Island, particularly Nelson and Marlborough, and parts of Christchurch and Dunedin. Fast-growing and a prolific seeder, boneseed can rapidly replace native plants, and its dense thickets can also restrict people’s access to beaches.

Landcare Research is mass-rearing boneseed leafroller caterpillars (Tortrix s.l. sp.“chrysanthemoides”) for release. The caterpillars are rapacious feeders of the shrub’s foliage, and in some cases can kill entire plants. They web leaves together to make homes for themselves, hence the name “leafroller”.

Landcare Research technician Chris Winks has been rearing the caterpillars since their release from quarantine in January. Mr Winks says the insects will serve an important role.

“Many areas where boneseed grows are inaccessible and environmentally delicate. Often the cost of control is prohibitive, or the use of herbicide is environmentally undesirable. The caterpillars will be of most help in those cases.

“They will never eradicate the plant, but they may slow boneseed down enough to prevent a monoculture, and give our native plants a better chance of competing with it.”

Mr Winks says the leafroller moth is expected to have three generations per year, and will hopefully build up to large numbers on boneseed plants next summer.

He says extensive tests in South Africa by Landcare Research and by Australian researchers show that the risk of leafrollers eating anything else but boneseed is negligible.

The research and release of the boneseed leaf-rollers is part-funded by the Auckland Regional Council. ARC Biosecurity Manager Jack Craw says boneseed is now common on Auckland’s coastline, including many of the Hauraki Gulf islands.

Landcare Research weed scientists are working with other councils to release boneseed leafrollers into other parts of the country.

They are also working with colleagues in South Africa to test a promising rust fungus, which may also be suitable to be brought here to attack boneseed.

ENDS

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