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Norfolk Pines and herbicides

Norfolk PinesThis report was commissioned by Tauranga City Council as part of an investigation into the ailing Norfolk Pines at Marine Parade and Pilot Bay.

Investigation of ailing Norfolk pines at Mt Maunganui

The report, by arborists Paul Kenny and Gerald Collett, links the the Norfolk trees’ decline to active ingredients found in some formulas of prickle-weed spray.
Broadleaf herbicides are used to target weeds in turf, most notably prickle-weed.
Active ingredients in the broadleaf herbicides used by the Council to treat prickle-weed are picloram, tricolpyr and clopyralid.
Until we have more information, broadleaf herbicides will no longer be used by Tauranga City Council in areas where the chemicals could come into contact with tree roots.


Mid 2013 Staff first started looking seriously at the decline of Norfolk Pines.
July 2013 Scion were engaged to assess the trees and test for any bacteria, virus and pathogens present in both the trees and the soil. The cause of the disorder could not be determined.
October 2013  Scion commenced a treatment trial aimed at improving tree health using nutrient plugs and injections of phosphite. Twenty one trees showing the most decline were selected. Seven trees were injected with phosphite, seven trees were injected with phosphite and nutrient plugs and seven trees were kept as controls with no treatment.
October 2013  The turf areas surrounding the Norfolk Pines along Marine Parade up to number 60, and Pilot Bay, were sprayed with humic acid. Humic acid enhances the moisture holding ability of the soil and works to enhance a plant’s natural defences against toxins and disease.
February 2014 Paul Kenny was engaged to check the structural integrity and life expectancy of the two most severely affected trees. Paul was also asked if he could identify any cause of the decline. Paul investigated the likely cause and this has resulted in the final report.
May 2014  Tree 16 was removed.
August 2014 TCC received the report from Paul Kenny on 31 August 2014.

Media Release: Norfolk Pine mystery solved

Media release: Norfolk Pine mystery solved

Last Reviewed: 08/02/2017