Canker Stain of Plane Trees: A Silent Legacy of World War II
Plant Health Risk Analyst, Defra.
Canker Stain of Plane Trees: A Silent Legacy of World War II
Picture yourself on holiday taking a stroll beneath a canopy of majestic plane trees, somewhere in the South of France, or Italy perhaps? While enjoying the cooling shade provided by the lofty trees, you could be forgiven for thinking all is well in the world, however, just scratch the surface a little and beneath the bark of these towering trees lies a tale of war, resilience, and an unrelenting pathogen. Canker stain of plane (caused by the fungus Ceratocystis platani) may be a rather obscure pathogen to most, but its story intertwines with one of history’s most turbulent chapters: World War II.
The Fungus Among Us
The disease, caused by the fungus Ceratocystis platani, Canker stain of plane specifically targets plane trees (Platanus species), which have long been prized for their shade and aesthetic value in urban landscapes from antiquity to modern times. They have been featured in Homer’s “The Iliad” as well as the writings of Herodotus, who in the 5th century described a plane of such impressive size it was prised by the Persian emperor Xerxes, who adorned its branches with golden ornaments. So useful is the shade and the pollution filtering abilities of the tree’s bark that they have been widely planted in cities across Europe and the UK. The infection often finds its way into a tree through wounds to the outer bark. Once this wound parasite has found a way in, it creeps through the tree under the bark, blocking the vascular tissues of the tree that are essential to the tree’s ability to transport water and nutrients. Symptoms include cankers, sunken wounds with orange and purple discoloration of the surrounding wood, and sudden wilting of foliage often just on one branch that then spreads through the tree crown. This disease is usually fatal and can kill a tree within two to five years, leading to a slow, yet inevitable death for the infected tree.
An Unlikely Stowaway
The connection to World War II begins with the transportation of supplies across Europe made form infected plane wood from the Americas. During the war, wooden crates and ammunition boxes crafted from infected plane wood were shipped to regions where the fungus had not yet established. These unsuspecting carriers became the Trojan horse for Ceratocystis platani, introducing the pathogen to new countries. Once present it then spread like wildfire, wreaking havoc in Italy, France, and other parts of Europe. The busy and often overstressed wartime supply chains acted as unwitting accomplices and couriers, ensuring the spread of the fungus that then found fertile ground wherever it went.
France’s Plane Tree Crisis
One of the most profound impacts of canker stain has been in southern France, where magnificent rows of plane trees once lined the Canal du Midi—a UNESCO World Heritage site. These trees, celebrated for their beauty and historical significance as well as the welcome shade they provide, have been decimated by the fungus, transforming lush banks into stark landscapes. Efforts to replant and protect these trees are ongoing, but the scars left by the introduction of this fungus still remain.
Lessons from History
The story of Ceratocystis platani is a cautionary tale about how human activity—particularly during times of war—can inadvertently disrupt ecosystems. It’s a reminder of how interconnected our world is, where even the most unassuming actions, like the choice of wood for crates, can have far-reaching consequences. We do not believe that canker stain of plane is present in the UK. And we’d like to keep it that way. The impact of the disease on plane trees in the greenspaces of cities such as London could be significant. Good biosecurity is essential, and we all have a role to play in preventing the introduction and spread of harmful organisms.
Hope on the Horizon
Though canker stain continues to pose challenges, researchers and arborists are exploring ways to mitigate its effects. From breeding resistant varieties of plane trees to implementing strict biosecurity measures, there is hope for the preservation of these iconic trees.
So next time you stroll under the shade of a plane tree, take a moment to appreciate its resilience—not just against the forces of nature but also against the unintended consequences of human history. Its story is a testament to survival, both of the trees and the lessons from history we can learn.
You can learn more about the pests and diseases associated with plane trees on the Observatree website. If you think that you have seen symptoms of a possible Ceratocystis platani, or the pest plane lace bug (reported in the London area in 2024) please report them through TreeAlert.