Mite might trim old man's beard
18 July 2018
A gall mite may be introduced to New Zealand to control the pervasive weed old man’s beard, if an application to the Environmental Protection Authority (EPA) succeeds.
“This weed forms dense, permanent masses with heavy layered stems that smother and collapse underlying vegetation,” says Dr Clark Ehlers, EPA senior advisor New Organisms.
“Heavy infestations prevent regeneration, leading to loss of native species in affected areas. This can open vegetation to invasion by other weeds. Old man’s beard can also scramble over the ground, destroying low-growing plant communities on riverbanks, and in coastal and other sensitive habitats.”
“It colonises open forests, forest margins, shrublands, riversides, cliffs, bushtracks and hedgerows. It is also a troublesome urban weed. The vines can extend as far as 20 metres.”
Horizons Regional Council has applied to the EPA to introduce the gall mite, Aceria vitalbae, on behalf of the National Biocontrol Collective, comprised of 14 regional councils and the Department of Conservation.
While old man’s beard, Clematis vitalba, is a member of the Ranunculaceae family, of which there are nine native Clematis species and four native genera in the same subfamily, laboratory tests and overseas experience suggest the gall mite is unlikely to colonise other species of Clematis.
Manaaki Whenua – Landcare Research is the science provider for the application, and consulted widely before choosing six exotic Clematis species or hybrids for host range testing at the University of Belgrade in Serbia.
According to the applicant, the results suggest that the gall mite is expected to effectively colonise only old man’s beard in New Zealand. Occasional galls may be expected on exotic, non-target Clematis species, but the presence of low numbers of mites is unlikely to cause them damage.
The application says that old man’s beard causes environmental damage throughout most of New Zealand, often in distant or inaccessible areas of high conservation value. Most infestations go unmanaged.
Biological control by the gall mite could provide a safe and sustainable alternative to mechanical and chemical methods of control, the applicant says. The gall mite could also disperse to isolated infestations that are inaccessible, or unknown to land owners. It would persist from year to year.
“Adult gall mites are less than one millimetre long,” Dr Ehlers notes. “They do not fly, but disperse on the wind. They attack old man’s beard by sucking out plant juices and creating tumour-like galls on leaves and shoots. This often leads to the death of that part of the plant.”
The applicant notes that successful biological control of the weed would mean reduced costs for regional councils, the Department of Conservation and other land owners. Five regional councils recently estimated they spend approximately $760,000 per year to fight old man’s beard.
Public submissions on this application open on Wednesday 18 July 2018 and close at 5pm on 29 August 2018.