C-DRONE GUIDE · 2 SEPTEMBER 2026

Canker stain of plane trees: drone-assisted diagnosis, 35-metre buffer mapping and mandatory felling

A plane tree turning yellow in midsummer is not necessarily sick — but if it is, the law leaves no room to manoeuvre: felling within two months, a 35-metre preventive buffer around the tree, a ten-year ban on replanting plane trees. Canker stain, an incurable quarantine pathogen, has already cost the Canal du Midi more than 33,000 plane trees out of 42,000 — the very tree canopy that earned it UNESCO World Heritage status. Diagnosis remains a laboratory matter, but scouting, mapping the statutory buffer and monitoring replanting across dozens of kilometres of alignment are concrete ground for a drone. Here is what it genuinely adds, and what it cannot replace.

Published on 2 September 2026, reviewed on 11 September 2026 — regulations in force as of September 2026.

A quarantine pest, not an ordinary tree ailment

Canker stain of plane trees is caused by a microscopic fungus, Ceratocystis platani, accidentally introduced from North America in the mid-twentieth century. It blocks sap flow and typically kills the tree within two to five years, with no known cure. Under EU Implementing Regulation 2019/2072, the pathogen is classified as a quarantine organism across the European Union, subject to mandatory control: in France, the framework is set by the order of 31 January 2025 on the control of Ceratocystis platani, which replaced the earlier 2006 and 2015 orders without changing the overall logic.

As soon as an approved laboratory confirms the fungus on a plane tree, the owner — a commune, a building manager, a private operator, a waterway authority — must, at their own expense, have the tree felled, stump-removed or devitalised, then incinerate the contaminated wood on site, within two months of the notification. That deadline can be extended to six months with the regional prefect's authorisation, provided measures guarantee the pathogen does not spread in the meantime. Around the diseased tree, a 35-metre radius requires preventive felling of every neighbouring plane tree, considered probably already infected even without visible symptoms; and across a wider 50-metre radius, planting any new plane tree remains banned for ten years, matching how long the fungus persists in the soil.

What a drone genuinely adds — and what it cannot replace

The reference diagnosis still happens on the ground: an expert spots crown decline, bark necrosis and reddish staining under the bark, takes a wood sample, and an approved laboratory confirms it by PCR or water test. No drone replaces that step. What an aerial camera adds is a first pass over ground that ground-based inspection covers poorly: canal banks hard to reach outside the towpath, private alignments at the back of a plot, tall park plane trees whose crown only reads from a distance and from above. On early cues — yellowing, partial wilting of the foliage, before trunk necrosis is even visible from the ground — a multispectral or hyperspectral camera on board picks up signatures the naked eye cannot yet see.

A study by Jasmine Abdulridha, Ozgur Batuman and Yiannis Ampatzidis, published in 2019 in Remote Sensing, shows that a UAV-mounted hyperspectral system detects citrus canker — another canker-causing disease — at different severity stages, with classification accuracy above 95 % (see the study on Google Scholar). A second study, led by Run Yu and a team from Beijing Forestry University and published in 2022 in Frontiers in Plant Science, shows on pine wilt disease — another quarantine organism subject to mandatory felling — that repeated drone-borne hyperspectral monitoring detects tree stress several weeks before symptoms are visible on a standard RGB image or during a ground survey (see the study on Google Scholar). Applied to plane trees, this kind of monitoring does not replace experts' annual field surveys: it helps prioritise them, across dozens of kilometres of alignment where every single tree cannot be examined on foot with the same frequency. Our guide to drone multispectral detection of spruce bark beetle details a comparable method for another forest health emergency.

Mapping the 35-metre radius and quantifying the felling

Once a diagnosis is confirmed, the manager must produce a precise document: the exact perimeter of the 35-metre radius around the infected tree, with the list of plane trees concerned and, often, the neighbouring plots and owners to notify. Along a river or a canal, where bank ownership changes every few dozen metres, that surveying-chain delineation work is slow and error-prone. A georeferenced drone orthophoto, aligned on the land registry, traces that radius precisely and produces, within hours, the map that accompanies each prefectural notification.

A drone also helps after felling: a photogrammetric pass over the cleared area lets managers calculate the volume of wood to incinerate or remove under sealed tarpaulin — a figure the forestry works contractor and the site manager use to cost and check the demolition contract. An operator managing several infestation clusters along the same stretch gains a mapped inventory, year after year, of trees lost and of how the contamination front is advancing — a use close to what our guide to municipal tree inventory by drone already describes, applied here to a pathology rather than a plain census.

The Canal du Midi, a national case study

France's most documented outbreak remains the Canal du Midi, a UNESCO World Heritage site precisely for its two-century-old tree canopy. The first outbreak was identified there in 2006 near Agde; twenty years on, Voies navigables de France (VNF), the state waterway authority, counts, according to figures released in January 2026, 33,350 plane trees felled out of the 42,000 that lined the canal before the disease arrived. More than 22,000 trees have already been replanted, with a deliberate diversification into seven species — oak, pine, maple, chestnut, poplar, lime and nettle tree (hackberry), the latter chosen as the identity species expected to eventually cover around 40 % of the route, since replanting plane trees there is no longer legally possible. VNF puts the investment already committed at close to €110 million, out of an estimated €220 million total budget for the whole felling, replanting and bank-consolidation operation.

Today, VNF's annual survey is still carried out on the ground by tree experts, with sampling and laboratory analysis confirming each suspected outbreak. Along several hundred kilometres running through Toulouse and Béziers among other towns, regular drone overflight — even partial, targeted at the most exposed sections — would add a monitoring layer between two field campaigns, and a tool for tracking young trees' survival photographically over several years, comparable to what our guide to drone reforestation and replanting survival monitoring describes.

Steps and price of a mission in 2026

A mission of this kind runs in three stages. First, a scouting pass over the alignment or site concerned, in visible or multispectral light depending on the season — foliage needs to be developed, so ideally May to September — to prioritise which sections need ground examination. Then, if an outbreak is confirmed by the laboratory, precise mapping of the statutory 35-metre radius and the plots concerned. Finally, once works are complete, a check and volume-calculation pass over the cleared area, followed by spaced-out photographic monitoring if replanting is under way. The regulatory information on this page reflects the rules in force in September 2026.

Orders of magnitude observed in 2026 (excl. VAT):

For a mission of this kind, whether for a commune, a river management syndicate, a waterway authority or a private operator, request a quote stating the length of alignment concerned and whether a laboratory has already confirmed an outbreak: that information directly shapes the nature of the mission.

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