Brian Richardson

Invasive conifers are widespread and impactful weeds, resulting in significant ecological change and management costs. Treatments to control invasive species are expensive and require long-term commitment, yet their effectiveness under operational conditions is rarely quantified. The effectiveness of two operational control approaches – aerial application of foliar herbicides and ground-based manual methods – applied to manage invasive pines in New Zealand (NZ) in typically high-density and low-density infestations, respectively, was assessed. The objective was to quantify the effectiveness of each method in reducing Pinus contorta populations and to characterize the post-treatment population structure over time to assess reinvasion risk. Pine mortality and regeneration were surveyed in operationally treated infestations 1–4 years after control across a range of invaded environments in NZ. Mortality following aerial boom spray exceeded 90% on average across all height classes 3 years after treatment. Ground-based methods achieved high mortality among larger individuals but were significantly less effective for pines shorter than 60 cm. Both operational approaches allowed populations to persist via surviving individuals in the initial years post-treatment; however, the resulting population structures differed between treatments. Reinvasion risk also differed between treatments. Following aerial boom spray, reinvasion was driven primarily by surviving larger trees, whereas following ground-based control, it was driven by missed seedlings that persisted after treatment. Despite high mortality, aerial boom spray left an estimated 1,094 surviving pines ha ^-1 4 years after treatment, approximately half of which exceeded 2 m in height. In contrast, the large number of seedlings missed by ground treatments could lead to rapid invasion recovery. Follow-up treatment within 2–4 years is likely to be necessary for both control methods, although management should target contrasting residual population structures and reinvasion pathways.

Large-scale tree planting with indigenous trees is one approach to combatting climate change and environmental degradation. However, a significant challenge with establishing planted indigenous forests at scale, particularly in New Zealand, is that our knowledge and capacity to achieve this in highly modified environments, covered by invasive species, is relatively poor. The purpose of our study was to quantify the survival and growth of five indigenous tree species (three gymnosperms, two angiosperms) planted either on their own (weed-free) or in association with an indigenous (Leptospermum scoparium J.R. Forst) or exotic (Cytisus scoparius (L.) Link) shrub species. We monitored survival and growth following planting for 2.5 years. Results showed that survival for the gymnosperms was > 90% for all treatments. In contrast, survival of the two angiosperms was poor, and, in general, not significantly related to the presence or absence of neighbouring vegetation. The response to vegetation management for tree height was similar across all species: weed-free treatment > L. scoparium treatment > C. scoparius treatment. Diameter growth was also highest for all tree species in the weed-free treatment, compared to the two other vegetation management treatments, but the extent of the increase varied by tree species. We found no direct evidence for neighbouring vegetation facilitating early survival and growth of the five indigenous tree species tested at our study site. However, the outcomes require testing at scale and across environments to underpin future forest restoration efforts.

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.

Background: Pesticide application is a primary method for managing weeds, insect pests and pathogens in New Zealand’s forests. Apart from some manual spot spraying, most pesticide applications are made using helicopters, with herbicides the most widely used pesticide class. Current aerial application practices have evolved into efficient operations designed to provide a balance between performance criteria, i.e. maximising treatment efficacy, minimising unwanted environmental impacts (e.g. spray drift), and maximising productivity while minimising cost. Over the last decade, there has been a proliferation of relatively small, battery-powered, multi-rotor uncrewed aerial spraying systems (UASS) but their use to date in New Zealand forestry has been limited. This paper assesses the potential role of UASS in forest management and, where opportunities exist, identifies barriers slowing their adoption. Methods: Publications on spray application in New Zealand forestry and use of UASS in both New Zealand and internationally were identified by conducting a Google Scholar literature search using a range of relevant keywords, and the retrieved studies were reviewed systematically. Unpublished reports from the New Zealand Forest Research Institute Ltd and Forest Growers Research Ltd were also considered. Information from the reviews was assessed critically, synthesised, and used to evaluate several potential forestry use cases for UASS. Results: Several potential use cases for UASS were identified along with a set of research and development needs to support and accelerate the adoption of UASS into forest management operations and to provide regulators with the means to apply appropriate risk management measures. Based on the literature analysis, the opportunity for UASS, at least in the near term, is to realise the concept of ‘precision spraying’ rather than to replace conventional aircraft carrying out broadcast applications over large areas. Conclusions: Recent UASS technology improvements have provided the potential for a step-change for at least some pesticide application niches within New Zealand forestry. Significant opportunities for UASS in forestry include herbicide spot spraying, treatment of boundaries close to sensitive areas, low-volume fungicide or insecticide applications, especially for small areas or in pest eradication operations; and applying variable treatments to individual plants or zones within a target area defined by remote sensing tools. A coordinated research and development programme is needed to optimise UASS use and to provide performance data to underpin regulatory processes.

BACKGROUND: Multicopters are used for releasing particulates seeds, fertilizer and spray. Their low cost and high manoeuvrability make them attractive for spraying in steep terrain and areas where overspray is undesirable. This article describes a model of multicopter wake and its influence on particulate dispersion, which is computationally economical compared to many computational fluid dynamics (CFD) approaches, yet retains reasonable accuracy. RESULTS: A model was successfully implemented in OpenFOAM . It features source terms for the rotor wash, Lagrangian particle tracking, an evaporation model, and a porous medium approach to model the effect of the ground vegetation. Predictions were validated against the field tests of Richardson et al. which used a DJI Agras MG‐1 multicopter in three different flights with airspeeds of 3.2–4.9 m s ⁻¹ , ground speeds of 2.1–2.9 m s ⁻¹ and cross‐wind speeds of 0.04–2.2 m s ⁻¹ . The effective swath width (30% line separation) was predicted to within one standard deviation. Sensitivity to a rotor rotational speed, flight height, flight velocity, multicopter roll and yaw angles, surface roughness length, plant height and leaf density was checked. CONCLUSION: In all flight trials, the modelled swath was closest to the experimentally obtained swath when the surface roughness of the fetch was equal to 0.5 m (bushes) and the rotational speed of all rotors was equal to 2475 rpm with 0.75R (0.2 m) tall plant canopy (grass) introduced to the model. The model showed acceptable validity for flight velocities of ≤2.8–5 m s ⁻¹ when flight parameters can be approximately estimated. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Myrtle rust is a serious fungal disease caused byAustropuccinia psidiiaffecting a number of Myrtaceae species in New Zealand and elsewhere. Control with fungicides or biologicals provides a mechanism to reduce the build-up of inoculum in the short-term while other strategies are being developed or deployed for long-term management. This study evaluated the efficacy of fungicides for control of myrtle rust under controlled conditions and identified adjuvants that would promote spreading of fungicidal active ingredients across the leaf surface. The spread of fungicide on detachedM. excelsaleaves was assessed by applying three different adjuvants in combination with seven fungicides. Subsequently,M. excelsaplants were treated with three fungicides/mixes, (azoxystrobin + epoxiconazole, triademinol or a natural tea-extract) at a single rate followed by inoculation withA. psidiiurediniospores on day 0, 7, 14 or 21 days after spraying. The response to infection inM. excelsaplants based on different inoculation timings at days 0, 7 and 21 significantly differed among fungicide treatments. The fungicide azoxystrobin + epoxiconazole was the most effective with infections significantly lower on the adaxial leaf surface than abaxial, despite good surface coverage of fungicide being achieved on both leaf surfaces. There were significant differences among fungicides based on the proportion of infected leaves onM. excelsaplants. Day 21 post-spray inoculation indicated a significant interaction between inoculation time and fungicide on leaf disease ratings. However, this was not the case at either 28 or 35 days post-inoculation. This research contributes to fungicide options for myrtle rust control in New Zealand.

Background While unmanned aerial vehicles (UAVs) are increasingly being used to deliver small‐scale aerial pesticide applications there remains uncertainty over their efficiency in terms of uniformity of spray deposition and their application efficiency. Consequently, a field study was designed to quantify factors influencing the uniformity of spray deposition from a multi‐rotor UAV that is operated commercially in New Zealand. Two sampling systems for measuring spray deposition, a continuous horizontal string and steel plates placed on the ground, were compared. Results The spray deposit distribution characteristics and calculated lane separation values (distance between flight lines that produce a maximum coefficient of variation (CV) of 30% for spray deposits) were strongly influenced by wind speed, nozzle position, release height, ground speed, and droplet size. Lane separation values ranged from 1 to >5 m. Swath distribution parameters (spread and position of peak deposition) derived from plates were not significantly different to those derived from string. However, total deposition on strings relative to plates increased with small droplets. Reducing plate sampling intensity from 0.25 m intervals to 0.5 m and even 1.0 m had only a minor effect on estimates of swath parameter values. Conclusions The potential for precision spraying from UAV platforms has yet to be achieved with improvements required in hardware and software. Further, mechanistic models are needed to quantify how complex interactions among multiple operating and meteorological variables influence spray deposition.

Forest health can be adversely affected by invasive organisms. Biosecurity measures to prevent the establishment of harmful invasive organisms at national points of entry (e.g., airports or shipping ports) are vital to protect forest health. Innovations in pest eradication technologies are being developed based on their efficiencies and effectiveness. However, the question of whether people find them acceptable is rarely considered. In New Zealand, research is underway into the use of highly targeted pesticide spraying using unmanned aerial vehicles (UAVs) as a novel technology to eradicate pest species that impact forest, food, and fibre sectors. Public approval for such technologies, however, can be a critical aspect for their success. A tool can be technically effective (achieve eradication), but uptake may be impossible if communities do not trust the technology. We developed a method for enabling discussions about the use of UAVs and their acceptability in general before being operationalized for biosecurity. This paper presents an investigation of how “participatory-design”, an often tactile, visual, and inclusive process of community engagement can improve the acceptance of technology use in the public sphere. We asked people, both scientists and citizens, to evaluate the acceptability of a range of UAV uses (including biosecurity) along a continuum and then explored the reasons for their placement. Key criteria for acceptable and unacceptable uses were subsequently developed to help technology designers and operators consider aspects of social acceptability during design processes. Our tool and approach facilitated discussions around technology acceptability that were subsequently adopted by our technical design team for the development and the use of acceptable UAVs for biosecurity. This research shows how systematic approaches to design can help uncover and mitigate social acceptability issues through inclusive design under increasing threats of biosecurity, whether related to challenges of trade or climate change.