A. Rolando, B. Richardson and T. Paul
Scion, 49 Sala Street, Rotorua, 3010, New Zealand
Wilding conifers, particularly Pinus contorta (Dougl.), P. mugo Turra, P. nigra Arnold and Pseudotsuga menziesii (Mirb.) Franco, present a national-scale weed problem in New Zealand with an estimated 1.7 million hectares of land infested. Currently, herbicides are the main tools used in the management of conifer infestations, ranging from isolated and scattered trees to dense canopy cover (Gous et al. 2014). Whilst herbicides are effective, current recommendations use very high rates and are, as a result, costly. There is potential to improve control recommendations by (i) increasing the targeting efficiency of application platforms, and (ii) understanding the dose-response relationships and factors driving uptake and translocation of key herbicides. We will present an overview of our research that directly addresses these two factors with an overall aim of increasing the efficiency of herbicide use and reducing unwanted environmental impacts.
One of the biggest challenges for conifer control is the ability to efficiently use herbicides where conifers are clumped and/or scattered, and canopy cover is between 30 to 70% of the infested land area. In such situations, broadcast herbicide spraying is not appropriate as there are too many off-target effects on vegetation. An aerial ‘autoboom methodology’ could provide a cost-effective method for precision herbicide treatment of scattered and clumped conifers with minimal off-targets effects. The aim would be for the aircraft to fly at a constant speed along pre-determined flight lines to provide an optimal path that passes over any target tree crowns. The tree crown envelopes and positions would be programmed into the aircraft’s spray computer as target zones and as the aircraft passes over each target zone the boom, or sections of the boom, would automatically switch on and off. We conducted a preliminary trial to test the potential of such an aerial autoboom system and also evaluated the challenges and limitations on the implementation of this technology using aerial platforms. We will present our findings to date and outline the technology required to overcome the limitations we have identified in preliminary tests.
We are also investigating the use of multi-rotor unmanned aerial vehicles (UAVs) for conifer control. UAVs have the potential to achieve a level of precision beyond what is practical by helicopters, predominantly because of their slower operating speeds and lower spray release heights. We have faced many challenges working with UAVs and will present some of the work we have conducted in evaluating their targeting precision and spray coverage capabilities, particularly for spot spraying of conifers. At present, the downside of using UAVs is a small payload and low endurance, but the technology is rapidly improving and warrants further investigation for application to wilding conifer control.
As UAV-based herbicide application is an emerging technology for spot control, we have been investigating the relationship between herbicide dose and placement (foliar or bark) to better understand the amount of herbicide that is required to kill trees of different sizes. For this research, we tested the use and efficiency of a UAV (AGRAS MG-1) for foliar application of herbicides to the tree crown. An understanding of the efficacy of low volume foliar applications of herbicides for different tree sizes will enable us to fast track the potential to use these application platforms as tools for control of isolated conifers. We will present the results of our work and implications for further research on spot application of herbicides with UAVs and other aerial platforms for the control of invasive conifers.
Gous S., Raal P. & Watt M. S. (2014) Aerial spot treatment using an oil carrier to apply ester based herbicides for control of Pinus contorta and P. nigra in New Zealand. N. Z. J. For. Sci. 44: 23.