Are uncrewed aerial spraying systems the future for forestry pesticide application?

Abstract

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 Unpublished reports from the New Zealand Forest Research Institute Ltd and Forest Growers Research Ltd were also considered.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.