Herbicide Tolerance Study
Successful native restoration depends on controlling weeds, which are the most common cause of planting failure. Herbicides, when used carefully, remain the most cost-effective tool for large-scale weed control. However, we often lack good information on how New Zealand native plants respond to commonly used herbicides. This means field teams either need to be overly cautious, or run the risk of unintentionally damaging the very plants we are trying to protect.
With support from the Brian Mason Trust, we set out to fill some of these knowledge gaps. Our team tested the herbicide tolerance of five understudied native species frequently used in Styx Living Laboratory plantings. Over 700 plants were grown in controlled field plots and exposed to the herbicides our teams use in real restoration work.
What We Found
Some native species were more vulnerable than expected to the broadleaf herbicides clopyralid and triclopyr, especially when plants are young.
Others, including several monocots and Coprosma species, showed higher tolerance and can be safely sprayed around with suitable care.
Drift from a diluted glyphosate mix—simulating careful spraying around native plants—caused little to no harmto most species tested.
We also identified opportunities to refine weed-control strategies and reduce unnecessary caution where species show strong tolerance.
These results give us a clearer understanding of where herbicide risks are highest, and how to target weed control to keep native plantings safe while still being effective.
A New Guide for Restoration Field Staff
Alongside the experiment, we compiled a wider New Zealand herbicide tolerance reference table, bringing together our findings and previous research from around the country. This guide summarises known tolerances and vulnerabilities for dozens of native species and provides colour-coded practical advice for field workers.
Read the Full Resources
Read the full research report: Identifying Herbicide Tolerances of Understudied Native Plants to Improve Restoration Outcomes
Download the Field Workers’ Herbicide Tolerance Lookup Table
These resources are designed to help restoration teams plan safer, more efficient weed-control programmes and reduce losses in the critical first years after planting.
This project was made possible through the generous support of the Brian Mason Trust, and the hard work of the Styx Living Laboratory field team.
