Optimising aerial herbicide treatment for control of dense conifer infestations: a New Zealand case study.

Background: Conifers, mainly of the genus Pinus, have invaded natural and productive landscapes worldwide. Controlling dense conifer invasions is challenging and requires both effective initial control methods and long-term site management to prevent re-invasion. Broadcast aerial herbicide application is often the preferred treatment method for dense infestations of pines with high rates of complex herbicide mixtures used. The objective of this study was to: (i) test the efficacy of four simple herbicide mixes (containing two active ingredients and one adjuvant) as compared to an operational standard (four active ingredients and three adjuvants) for control of Pinus contorta invasions in a field trial and (ii) to quantify the effect of treatment mixes on non-target vegetation to determine impacts to plant community composition.

Results: We found that a simplified herbicide mix containing two active ingredients and one adjuvant was equally as effective as the current operational standard, with efficacy for all treatments increasing as a function of stem density. All herbicide treatments significantly impacted the post-spray community composition with differences among treatments in post-spray vegetation composition also detected. Following all treatments plant communities transitioned from a mixed native/exotic grassland-herb community to a simplified community dominated by exotic grasses.

Conclusions: Our results indicate a simpler herbicide mix could be used for broadcast aerial control of dense pine invasion reducing total herbicide input and cost of the operation. Post-spray vegetation community recovery could reflect the impact of the herbicides used in the operation compounded by soil biogeochemical processes already initiated through the pine invasion. © 2024 Society of Chemical Industry.