Controlling the pinewood nematode: finding the best balance between cost and effectiveness
INRAE - National Research Institute for Agriculture, Food and Environment
image:
Maritime pines on the east cost of Ile d'Yeu in France
view moreCredit: INRAE - Jean-Marie BOSSENNEC
The pinewood nematode (Bursaphelenchus xylophilus) is the most devastating parasite of pine forests across Eurasia. To combat the pinewood nematode, European regulation requires that Member States clear-cut all susceptible tree species within a 500 metre radius of infested trees. However, this measure has not made it possible to eradicate the disease in Portugal, and a previous modelling study1showed it was not effective in vast, pine-only forests. In this new modelling study, scientists compare the cost-effectiveness of clear-cutting within a 500 metre radius of the infestation site versus selective felling, where only infested trees that display symptoms of the disease are cut inside the 20 km x 20 km area around the infestation site in a homogenous stand of maritime pines. To do so, scientists simulated different methods and intensities of ground-based and aerial forest monitoring.
A comprehensive model for assessing different methods of controlling the pinewood nematode
This study is based on a dispersal model of the pinewood nematode’s insect vector, Monochamus galloprovincialis (Robinet C. et al. 2019, Robinet C. et al. 2020), and the transmission of the pinewood nematode, with adjustments for the insect’s flight behaviour and the location of pines. The model simulates different monitoring methods and their effectiveness in the Landes forest in southwest France: ground-based visual monitoring from forest roads and paths; ground-based monitoring combined with trapping of the insect vector; and aerial monitoring combined with AI-assisted image analysis. The scientists also incorporated the costs associated with monitoring and analyses to identify the nematode, along with the different types of felling (clear-cutting or selective), and the loss of income linked to the felling of healthy trees. Cost-effectiveness was calculated for several scenarios of nematode introduction (number of dispersing insect vectors), several monitoring methods and intensities, and different proportions of symptomatic trees among infested trees.
Selective felling offers the best cost-effectiveness, provided monitoring is stepped up
The results show that aerial monitoring is better than ground surveys. Rapid advances in remote sensing combined with artificial intelligence to detect declining pines should enable even more effective monitoring in the years ahead. For the time being, however, ground surveys remain the only method used. Research is currently under way to make remote sensing more operational (see below).
Whatever the strategy –– selective felling or clear-cutting –– eradication of the pinewood nematode is only possible under optimal conditions for detecting the pinewood nematode: namely, if monitoring is carried out several times by aircraft with high detection efficiency at the times when trees infested by the nematode show symptoms. Under these optimal conditions, selective felling of trees could cost as much as 200 times less than clear-cutting, as it avoids the costs associated with the loss of non-infested trees.
Under non-optimal conditions, eradication is impossible regardless of the cutting method, in which case the objective is to reduce the impact of the nematode by containing the disease. The selective felling of declining trees still offers the best cost-effectiveness ratio.
These results show that improving monitoring is essential in order to effectively limit the spread of the pinewood nematode.
Advances and hope in research on remote sensing to monitor forests
Monitoring of the nematode in France currently relies on ground surveys and a network of traps for insect vectors (Mariette et al. 2023). However, research on remote sensing to monitor forests is expanding rapidly. Satellite remote sensing now makes it possible to identify clusters of declining trees fairly well, such as patches of mortality due to spruce bark beetle attacks (the FORDEAD method; Dutrieux et al. 2024). In the case of the pinewood nematode, declining pines are more isolated, scattered across the landscape, and need to be detected individually. For the moment, European satellite images lack the resolution necessary for this. Likewise, drones cannot be used to monitor forest landscapes because the area to be covered is too large. It is therefore necessary to use aircraft or microlights (the method considered in this article), but this detection method is still at the experimental stage. Another important line of research is the processing of these images using AI, which requires a large training dataset and is still under development. Finally, detecting a declining tree does not mean that the cause of its decline is the pinewood nematode. Research is therefore underway to identify the spatio-temporal distribution pattern of symptomatic trees likely damaged by the pinewood nematode. Three of the article’s authors are involved in FORSAID https://forsaid.eu/), a European project aimed at developing a diagnostic tool that combines high-resolution imagery and AI-based analysis.
References
Dutrieux R., Ose K., de Boissieu F., Féret J.-B. (2024). Fordead: a python package for vegetation anomalies detection from Sentinel-2 images. Zenodo. DOI: 10.5281/zenodo.12802456.
Mariette N., Hotte H., Chappé A.-M. et al. (2023). Two decades of epidemiological surveillance of the pine wood nematode in France reveal its absence despite suitable conditions for its establishment. Annals of Forest Science, 80 :21. https://doi.org/10.1186/s13595-023-01186-8
Find out more about Pinewood nematod with our overview in 8 questions and answers
Journal
Journal of Applied Ecology
Article Title
How to eradicate an invasive forest pest without clear-cutting
Article Publication Date
11-Mar-2026
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