Privet on the menu

Following our story last week on privet growing on Franklin roadsides, Auckland Council released the information that they were releasing a small weapon to help combat the noxious weed.

Particularly aimed at Chinese privet, a tiny lace bug has been given the job to feast on the weed and has recently been released in the Hunua Ranges Regional Park by the Auckland Council’s biosecurity team.

Privet is the bane of many hay fever sufferers, with its perfume thought to cause sinus and itchy eyes.

It can also displace native plants, and the leaves and fruit are poisonous.

The lace bug is an example of biological weed control (biocontrol), which is control using a weed’s natural enemy.

Both the adults and the nymphs of the bug pierce and suck the mesophyll tissues from privet leaves. Mesophyll is the green material of a leaf that allows the plant to photosynthesise, so the bug’s actions leave the foliage looking bleached.

It can also lead to defoliation and reduced vigour of the plant, meaning other species can more easily compete.

“Privet is banned from sale and distribution in Auckland and council does some site-led control, however it is so widespread that it makes control very expensive and our resources are limited,” says Holly Cox, Senior Biosecurity Advisor for Plants. This is why biocontrol is such an important tool, particularly against widespread, entrenched weed species. Successful biocontrol can provide long-term, low-cost weed control and allow resources to be used in other areas,” she says.

Like the weed, Chinese privet lace bug is native to China. It was first imported to New Zealand in 2013 for study and testing and it was approved for release in the field by the Environmental Protection Authority in 2015.

Biocontrol does not eradicate a weed but weakens it and reduces its abundance, making it easier to control with other methods and allowing native species to compete.