Canker stain of plane is a serious fungal disease that kills plane trees, and there’s currently no cure for it. It isn’t present in the UK, but it’s been spreading steadily through France, and that’s prompted us to take a proper look at how prepared the UK is, and what tree owners can learn from it now, rather than waiting until it becomes a problem here.
We first came across the detail at this year’s Arboricultural Association Conference, in a Forest Research presentation on the disease. It’s the kind of thing that’s easy to file away as “someone else’s problem”, but a bit of early awareness costs nothing and could make a real difference if the situation ever changes.
What is canker stain of plane?
Canker stain of plane, often shortened to CSP, is caused by a fungus called Ceratocystis platani. It affects plane trees (Platanus), the species behind many grand avenues and city streets, with London plane, a natural hybrid of oriental and American plane, being the one most people in the UK will recognise.
Once a tree is infected, the fungus blocks its internal transport system, the leaves wilt, and the tree typically dies within two to ten years. There’s no cure and no approved chemical treatment, which is why so much emphasis is placed on stopping it spreading in the first place.
Because of how serious it is, CSP is classed as a notifiable quarantine disease. In practice, that means anyone who suspects it should report it immediately rather than wait and see.
Is it in the UK?
Not currently. The London Tree Officers’ Association surveyed close to 3,000 London plane trees on behalf of the Forestry Commission and found no cases at all, and annual surveillance has continued since without the disease being recorded here.
It has, however, been spreading through France, historically around the Canal du Midi in the south, but more recently with isolated cases found further north too, edging it closer to the Channel. Most of that spread comes down to people rather than nature, contaminated saws, boots, gloves and machinery carrying the fungus between trees and between sites, along with root contact between neighbouring trees and, occasionally, water.
What would happen if it turned up here
The Forestry Commission has a plan ready in case a case is ever confirmed in the UK. In simple terms, a containment notice would be served, local tree work would stop pending confirmation, every plane tree within around a kilometre would be inspected, and strict limits would be placed on moving wood, soil or equipment out of the zone.
Infected trees would be felled and burned, along with those immediately around them, because plane roots graft together underground and carry the fungus between neighbours. Healthy-looking trees within 50 metres could also be removed as a precaution, given how readily spores travel through soil and water. On a street with a long run of mature plane trees, that’s a lot of trees potentially in scope from a single confirmed case. The cost of all this falls to the tree owner rather than the government, and the area would need three full years of clear monitoring before it’s considered recovered.
What France’s experience tells us
France has been dealing with CSP since the 1940s and has strict rules in place as a result. Every tree owner has a legal duty to watch for symptoms and report them straight away. Once a case is confirmed, every plane tree within a set distance is felled and burned within two months at the owner’s expense, extendable to six only with official authorisation. Anywhere in France, tools and machinery must be cleaned and disinfected every time they enter or leave a site with planes on it, and climbing standing planes on spikes is banned outright — the only exception being dismantling a tree that’s already coming down. Inside a designated outbreak zone it tightens further, with tools disinfected between every individual tree.
One rule stands out. Where a French local authority holds mapping of its plane trees, it’s obliged to hand that mapping over to the plant health service, along with the history of work done on trees in the affected area. It’s an obligation to produce what you already have rather than to go and create it, but the practical point stands either way: when a confirmed case starts a two-month clock, there’s no time to go and build a record from scratch. The lesson for the UK is simple. Knowing where your trees are, before there’s ever a problem, is what makes a fast, effective response possible.
What tree owners can do now
You don’t need to do anything drastic, CSP isn’t here, and may never arrive. But if you own or manage plane trees, a few sensible habits go a long way:
- Know what you’ve got. If you’re responsible for plane trees, whether that’s one in a garden or a whole avenue, it’s worth knowing how many there are and roughly where. A tree safety inspection is a straightforward way to get that picture, alongside a general health check.
- Ask about tool hygiene. Disinfecting tools between trees, and steering clear of metal spikes on standing trees, is good practice against all sorts of tree diseases, not just CSP. It’s a fair question to ask any tree surgeon you use.
- Keep an eye out. If a plane tree suddenly looks distressed, wilting leaves, dark staining on the bark, it’s worth getting it checked. Suspected cases can be reported through Forest Research’s TreeAlert system, or directly to APHA’s Plant Health and Seeds Inspectorate.
Trust in The Tree Fella to keep watch, not just cut back
Staying informed about emerging tree health risks, alongside the more familiar ones like ash dieback, is part of what we do as North East tree surgeons. If you manage plane trees for a business, local authority or commercial site, our commercial tree services can help, and we’re always happy to talk through what a proper record of your stock might look like. Give us a call on 0191 432 6167.