Old man's beard rampant growth may be arrested

Ruapehu Bulletin, Volume 14, Issue 673, 11 February 1997, Page 12

Old man's beard rampant growth may be arrested

No bigger than a sandfly, a leaf-mining fly is set to threaten the rampant growth of the intro duced weed, old man's beard. While the weed is not very common in the Waimarino, it is present and poses a real threat to any bush here, especially in the Tongariro National Park. A number of infestation sites exist, which will have to be controlled for at least 10 years to eradicate it. After six years of research, the biological control agent phytomyza vitalbae was released at a Pahiatua trial site recently. It was the first release site in the North Island and 13 more sites throughout New Zealand are planned over the next couple of months. A natural enemy of the fast growing clematis species, the fly's larvae burrows between the layers of the leaf and produces channels. It reduces the plant's growth rate and badly damaged leaves shrivel and fall off. Landcare Research project leader Richard Hill said the fly, indigenous to Germany, had been studied for the past three years along with two other agents, to ensure they would not cause significant damage to other plant life. Dr Hill, of Lincoln, said it was possible the fly might affect some ornamental plants but confirmed it would not damage native species.

Dr Hill released 200 flies at Michael and Ann Beach' s Ngaturi farm. Female flies lay about 500 eggs and can have up to five laying seasons a year, making the potential for growth huge. About 20,000 flies will be released this summer. Old man's beard is a major problem in central New Zealand, from south of Taupo through to Canterbury , where it chokes out native forest. The leaf-mining fly is the first of five biological control agents being introduced to control Old Man's Beard. The second a disease, has

been given verbal approval and an application to release a sawfly has been filed. The disease phoma attacks the plant's leaves and the old man's beard sawfly, which is in fact a wasp, eats the leaves of old man's beard. Dr Hill said he believed biological control was the only way to control the weed, but it was a long-term process with a 10-to 20-year time scale. The fly would not eradicate the plant but would bring it under control and could be used in conjunction with other methods of control. He hoped the fly would bring the plant down to a "livewith" situation but could not guarantee results. Dr Hill said old man' s beard was an unrecognised threat to the forestry industry, as it also grew on pine trees.