The regional council’s biosecurity team leader Shane Grayling referred to two relatively recent studies, one by Auckland Allergy Clinic in 2015 and the other by the University of Auckland, that both concluded privet was not a significant allergen.
The conclusion from the Auckland Allergy Clinic trial stated: “Most of the people who are experiencing symptoms during the privet flowering season are reacting to the more allergenic pollens like grasses, weeds (mainly English plantain) or trees like birch and olive.”
“All these plants have a flowering season that overlaps with the privet flowering season.”
A biocontrol project started seven years ago could signal hope for those who are convinced privet is affecting them. In 2015, the regional council undertook a biocontrol project by releasing a type of lace bug that specifically targets privet around several sites in the Western Bay.
“In the last seven years, there have been nine releases of the lace bug across the region as a biocontrol agent for Chinese privet,” Grayling said.
“Encouragingly, based on the last round of monitoring, heavy damage to the privet trees has been present at four separate sites and some damage at another three.”
However, he said it would often take a number of years for a biocontrol agent to show signs of impact.
“The degree of lace bug establishment can vary quite significantly between sites and years, hence the ongoing monitoring. If a population establishes well on a site, there is the potential to move the breeding bugs to other sites, which will further increase the distribution and hopefully the impact.”
Over recent years, Whakatāne District Council has come under community pressure to eradicate the pest plant from the escarpment above the town. However, Whakatāne District Council open spaces manager Ian Molony told Local Democracy Reporting previous trials to do so had been unsuccessful.
“The council has previously run a trial on an area of the Whakatāne escarpment behind Wairaka where privet was poisoned and left standing, and native vegetation was interplanted between the privet. The trial found control of regeneration of privet from seed was difficult on the steep slopes of the escarpment, and this regeneration eventually smothered the native vegetation which was planted.”
The trials also showed the poisoning of privet could cause erosion of the escarpment.
“The large poisoned privets which were left standing also created concerns when they eventually rotted and fell away. This exposed the slope in various locations, which could lead to erosion. As a result, Council received numerous concerns from the community about this at the time.”
Molony said due to the scale of the problem and issues caused by the trial and research indicating that privet was not an allergen for the majority of people, the council had not investigated the issue further.
The fact that a large percentage of privet in the Whakatāne district was on private land also added to the difficulties.
