Darwin’s barberry (Berberis darwinii) is what is called a “garden escape”. It was originally introduced to New Zealand for its ornamental value, but thanks to its bird-dispersed seed, it literally flew over the garden fence to invade our native forests and shrublands. Its distribution in New Zealand is scattered from just north of Auckland to as far south as Stewart Island.
Darwin’s barberry is one of the few weeds in New Zealand that can actually establish and persist under a forest canopy. In addition to this, research by Kate McAlpine (DOC, Science and Research) has shown that Darwin’s barberry is able to produce copious amounts of viable seed which can be spread hundreds of metres by birds. All told, this makes Darwin’s barberry a serious threat to New Zealand’s indigenous biodiversity.
On Stewart Island, history has it that Darwin’s barberry made its first appearance there as a hedge plant at Halfmoon Bay (Oban). Much like the gorse story we all know so well, Darwin’s barberry refused to stay put like a well behaved hedge, and has spread up to 35 kilometres from the main seed source.
In October 2001, a multi-agency eradication programme got underway. Southland District Council, Environment Southland and DOC joined forces to eradicate Darwin’s barberry from Stewart Island. Eradication means eradication, and Darwin’s barberry has to be cleared away from everywhere – including private property. Stewart Islanders have been consulted right from the start, with door to door visits and flyers advertising the eradication work. Community response to the programme has been great, with many people approaching DOC for advice and help. And the Eradication Crew have plenty of advice to give, as they now have a finely honed procedure and techniques. They have discovered that the most effective method of control is to handsaw smaller shrubs or chainsaw big ones, and then treat cut sumps and stems with Vigilant Gel (dyed blue to keep track of which stumps have been treated). A disturbing discovery has been that when cut stems are left lying on the ground, they are able to form roots (‘layering’). But this is no problem for the Eradication Crew who transfer all cuttings to vacant land near the local sewage pond where they are burned.
Now in its second season, the Stewart Island Darwin’s barberry eradication programme is making great progress. Although there is a long way to go yet, the Eradication Crew are maintaining a strategic approach and are keeping sight of the forest for the trees…so to speak.
The rest of the country can draw inspiration from the successful control work happening on Stewart Island; and even though Darwin’s barberry is now scattered throughout New Zealand, we can stop its spread.
We can all help by removing it from our own gardens and keeping an eye out for any growing wild. Darwin’s barberry is easiest to recognise when it is heavy with golden/yellow flowers (mostly from late spring to early summer), that are followed with dark purple berries with a whitish tinge. For the rest of the year you’ll know it by its small, prickly, holly-like leaves. For advice on control or to report any infestations, get in touch with your friendly weeds staff.