Özet:

Invasive wilding conifer species are a major threat to biological conservation in New Zealand. Scattered individual plants are particularly problematic as these are very costly to treat and once they reach reproductive maturity can act as point sources for further invasion. A novel method is described in this paper that delivers a precise dose of oil-based herbicide mixtures into the tree crown via a hand held lance using a helicopter as a platform. Using this method the objective of this research was to test the efficacy of six triclopyr based herbicides in an oil carrier, on isolated naturally occurring Pinus contorta (Dougl.) and P. nigra subsp. laricio (Poir.) Maire. Methods: For each species and treatment combination treated trees covered a wide range of heights, ranging from ca. 0.5 to 16 m. Measurements of mortality taken 24 months post herbicide application were used to examine variation in efficacy of these herbicides, where successful treatment was defined by a mortality rate of 85% or higher. Logistic regression models were fitted for each species and from these models we determined the threshold tree height at which 85% mortality occurred, H85. Results: For both species treatment efficacy significantly (P ≤ 0.05) declined as tree height increased. The two most effective treatments for both species were a 500 mL dose that included 60 g triclopyr in oil with addition of 1% alkylsilicone surfactant (20 G OM 500 mL) and a 1 litre dose that included 120 g triclopyr and 20 g picloram in oil (10G T20). Values of H85 for 10G 20T and 20 G OM 500 mL were, respectively, 7.7 m and 8.0 m for P. contorta and 7.1 m and 6.8 m for P. nigra. Conclusion: Spot application of triclopyr based herbicides, in an oil carrier, onto the tree crown was found to be an effective means of controlling two of the most vigorous New Zealand wilding conifer species.

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