New Weapon In War Against Noxious Weed

One of New Zealand's worst weeds, old man's beard, may be in for a shave, with the release of a hungry insect that attacks it.

Old man's beard (Clematis vitalba) is one of the top five noxious weeds in the country. It gets its common name from its beard-like feathery seed heads. An aggressive climbing vine, it grows up to ten metres a year, smothering vegetation in its path. It can also spread up into trees, eventually pulling them down with its weight. Traditionally a problem in native forests, old man's beard is now infesting plantation forests as well.

Landcare Research scientists and Wellington Regional Council staff have made the first large-scale release of the old man's beard sawfly (Manophadnus spinolae). The sawfly's caterpillars damage the weed by eating the leaves off at the base.

Landcare Research technician Hugh Gourlay says 400 caterpillars were placed on old man's beard plants near Upper Hutt. In a month's time, council staff will check on the caterpillars' progress.

Mr Gourlay says scientists will observe the sawflies' progress over the next two or three years, to see how much damage they have done to the weed. "We hope they will spread far and wide, and reduce the plant's vigour.

"We are confident that the sawflies will attack only old man's beard. Exhaustive tests have shown the sawflies are not a risk to native plants or other commercially valuable plants."

Mr Gourlay says Landcare Research will now focus on breeding more sawflies for other regional councils, for release throughout NZ. "At this early stage, none are available for members of the public, as we need to focus on building up numbers to supply to local authorities.

"In the meantime, anyone with old man's beard on their property should rip it out, and apply herbicide to the stumps. It is essential to double-check afterwards that the vine has been killed, and has not sprung back."

Landcare Research is also investigating a new insect to attack the stems of old man's beard. The bark beetle (Xylocleptes bispinus) has the greatest potential to do damage to old man's beard in New Zealand. Studies are underway in Europe to determine how specific the beetle is to old man's beard.

Two other control agents, a leaf miner (Phytomyza vitalbae) and a fungus, (Phoma clematidina), are already waging war on the weed, and have successfully established and spread throughout New Zealand, thanks to the efforts of regional councils and the Department of Conservation.

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