Biocontrols promising in fight against weed
Biological controls for one of the nation’s worst weeds – old man’s beard – have been released into the wild and appear to be working and spreading, a recent conference was told.
‘‘Biocontrols’’ are living creatures that kill or disrupt other living things like weeds and pests. They stand apart from chemical agents such as herbicides, and mechanical methods such as ploughing.
In the case of old man’s beard, Manaaki WhenuaLandcare
Research has identified two organisms from Europe that can only exist in the presence of the European plant.
The first is a type of sawfly. It was first released at multiple locations in 1998, but adverse weather and human disruptions meant they didn’t thrive. Landcare later concluded the populations had perished.
Researchers were therefore surprised to discover a small population near Nelson in 2015. Later investigations showed that the offspring sex ratio skewed heavily towards males. A more genetically diverse population was sourced from Serbia in 2018 and reared at Lincoln.
Thousands of larvae and mated adult females were released onto a site near Amberley, north of Christchurch, in 2019. Follow-up visits to that location since 2020 showed new generations of sawflies were active on old man’s beard.
‘‘The population has established,’’ said Arnaud Cartier, the invertebrate containment facility manager at Landcare’s Lincoln facility.
Sawflies are not great fliers, Cartier told the online conference, and won’t spread far
by themselves. But if they continue to flourish, some can be captured and moved to new sites, he said.
Sawflies and other biocontrols will never eradicate old man’s beard from New Zealand, Cartier said. That’s not how biocontrol works. Rather biocontrol restores the ‘‘balance between the weed and its natural enemies’’, he said.
The sawflies will never run out of old man’s beard on which to live, feed and mate. This gives regulators like the Environmental Protection Authority confidence that the sawfly won’t turn on native plants.
The second biocontrol is a type of eriophyid mite. It feeds on the leaves and buds of old man’s beard, producing galls and stunting growth. These creatures are tiny – 2mm – and working with them requires a microscope. But they spread through the wind, a process known as ‘‘ballooning’’.
The mites were scheduled for release in 2020, but were locked down by the pandemic. Fourteen releases were eventually made across both islands and the mite has established in Manawatū Whanganui,
Canterbury and probably elsewhere.
They’re also spreading. A new population was found near Hanmer Springs, more than 65km from an official release site near Amberley, Cartier said.
New Zealand’s early record for biocontrol was terrible. Stoats were introduced in 1879 to eat rabbits, for example, and turned on native birds and animals.
Landcare and other proponents of the practice insist they are ‘‘scrupulously regulated’’ by the EPA and must spend years jumping through scientific and legal hoops to bring overseas organisms into containment facilities, and more hoops before releases in the wild.
There was much consultation. On behalf of Ngā i Tahu, Gerry Te Kapa Coates supported the mite release. They believed the biocontrol agent posed ‘‘insignificant risk’’ and were a viable alternative to broad spectrum herbicides.
Old man’s beard is a deciduous, climbing, layering vine that can grow up to 20m in height. In suitable habitats it rapidly dominates, smothers and eventually kills all types of vegetation.