Common Sycamore Tree Diseases and How to Treat Them

Most of what looks like a disease on a sycamore is anthracnose: disfiguring, alarming, and almost never fatal. The one that actually kills is canker stain, and it usually arrives on somebody's pruning saw. Telling those two apart is the whole job of this page.

Everything below refers to the Platanus sycamores — the American sycamore (Platanus occidentalis), the London plane (Platanus × acerifolia) and their close relatives. It does not cover the British "sycamore," which is a maple (Acer pseudoplatanus), or the sycamore fig (Ficus sycomorus). Those are unrelated trees with unrelated problems.

Start with the symptom you can see, not the pathogen name

Almost every diagnostic page in this niche is organized by fungus. That is backwards for the person standing under the tree. Here is the same information the other way round.

Anthracnose: the one you will almost certainly meet

Sycamore anthracnose is caused by Apiognomonia veneta (its asexual stage is Discula platani), a fungus that overwinters in cankers on infected twigs and in dead leaves on the ground. In spring it releases spores that rain and wind carry onto the expanding buds.

What it does, in the order you notice it

Young leaves brown and die as they emerge from the bud. Where infection comes slightly later, you get brown blotches on either side of the main leaf vein, and those blotches enlarge and run together until much of the leaf is dead. Tan dead areas expanding along the veins are the signature; round, scattered, isolated spots point somewhere else.

The fungus also kills young shoots and forms sunken cankers at the base of twigs, girdling everything beyond that point. Black fungal fruiting structures are visible on the bark of newly killed twigs early in spring, and can be found with a hand lens along the leaf veins.

If the year is bad, the tree defoliates — sometimes everything but the terminal leaves — in late spring. This is the part that panics owners, and it is also the part that resolves itself: the tree pushes a second set of leaves in midsummer and finishes the season looking almost normal.

Why some springs are catastrophic and others are clean

This is the most useful number on the page, and hardly anyone gives it. Severity is set by temperature in the two weeks after the tree leafs out. If the average daily temperature over that window stays below 55 °F, the disease is severe. Between 55 and 60 °F it tapers off. Above 60 °F you may see little or nothing at all.

That single fact explains most of what people mistake for a declining tree. A wet, cool spring produces a defoliated sycamore; a warm one produces a healthy-looking sycamore; the tree did not change. It also explains why the same species is a wreck in the Pacific Northwest and largely clean in central Texas, and why the American sycamore suffers far more than the London plane.

What years of it do to the shape of the tree

Repeated bud death has a permanent consequence. When a terminal bud is killed, dormant lateral buds are stimulated into growth; those shoots get infected and die the following spring, and the cycle repeats at the same point. The result is a broom-like proliferation at branch ends and a crooked, angular branching pattern that stays with the tree for the rest of its life. Old cankers also act as a reinfection source every year.

What actually works

Sanitation, mostly. Rake and destroy fallen leaves and twigs, and during dormancy prune out dead twigs and small branches, cutting three to four inches below the canker. On a mature sycamore this is a partial measure and the extension services say so plainly: it is difficult when the affected twigs are small, numerous, and out of reach in a 75-to-115-foot crown.

Fungicide is where most advice goes wrong. A protective spray program means covering the entire canopy when the buds swell and again ten days later — two full-canopy applications in the narrowest window of the year. That is realistic on a nursery tree and not realistic on a mature shade tree with a hose-end sprayer. For a genuinely high-value tree, the option that exists is trunk injection performed by a licensed applicator, which has given good control in field trials. For everyone else, sanitation plus keeping the tree properly watered is the honest answer.

Canker stain: the one that is worth knowing about

Canker stain of plane is caused by Ceratocystis platani (older literature calls it Ceratocystis fimbriata f. sp. platani). Unlike anthracnose, it kills. Infected trees die within roughly two to ten years, and there is no way to save one.

How to recognize it

The crown thins: sparse foliage, undersized leaves, sometimes a single branch wilting first and the rest following. On the trunk and larger branches you find sunken cankers that are elongated or lens-shaped, and that roughen and blacken with age. Beneath the canker the wood is stained bluish-black or reddish brown; cut across, the discolored wood is wedge-shaped, with the point of the wedge running toward the center of the trunk. That wedge is the diagnostic feature.

How it gets in — and why this section matters more than the rest of the page

The fungus enters only through wounds. Fresh pruning cuts, wind damage, bird and insect damage, and mechanical injury from mowers and equipment are the doorways. The spores are produced within days of the first infection, in slimy masses on the wound surface, and they stick readily to saws, ropes, ladders, gloves, boots and clothing. Sap-feeding beetles move them too, and the fungus can pass between neighboring trees through root contact and through water — that last route is how the famous plane avenue along France's Canal du Midi became infected.

In other words, the disease mostly spreads because people move it. That is bad news and good news at once: the prevention is entirely in your hands and costs nothing.

The rules that follow from that

• Prune only in December and January, and only in dry weather. Infection is least likely in those two months.
• Disinfect tools immediately after working on any sycamore or London plane, before moving to the next one. Alcohol works.
• Never use wound paint or pruning sealer on a Platanus. This is the counterintuitive one. Contaminated brushes move spores from tree to tree more efficiently than saws do. Sealing a sycamore wound is worse than leaving it open.
• There is no effective chemical treatment. Removing and burning infected wood and roots is the only reliable control, because the fungus survives for months or years in dead material.

Two honest caveats. Canker stain is present in some western and eastern US states, but for reasons that are not understood it has become less significant in the United States in recent years — most American homeowners will never see it, while it is doing serious damage in Greece and southeastern France. And the pruning rules above are worth following anyway, because they cost you nothing but a calendar date and a bottle of alcohol.

Bacterial leaf scorch: browning that comes back worse every year

Xylella fastidiosa is a bacterium that colonizes the xylem — the tissue that carries water up from the roots — and blocks it. The result is a scorch that starts at the leaf margins and works inward.

On sycamore the pattern is specific. The oldest leaves brown along their margins and then between the veins, beginning in mid to late summer, on one branch or a few branches in the inner and lower part of the crown. A brown band sometimes develops between the dead tissue and the still-green tissue; that band is a useful tell. Symptoms progress outward toward branch tips, and they recur every year with more branches involved. Infected trees also break bud late in spring and produce smaller-than-normal leaves — a detail worth knowing, because drought damage does not do that.

Leafhoppers and spittlebugs carry the bacterium from tree to tree. Strains are host-specific enough that the X. fastidiosa found in elm does not infect sycamore, and vice versa.

There is no cure. Antibiotic injection (oxytetracycline) suppresses symptoms for the season it is applied and delays their appearance by a couple of weeks; the bacterial population rebounds each year, so it has to be repeated for the rest of the tree's life and it never eliminates the infection. It is a cosmetic treatment for high-value trees, not a cure. The rest of the management is keeping the tree unstressed and accepting a slow decline. Get a laboratory confirmation before you commit money to anything — scorch symptoms have several causes and this one is expensive to guess at. Worth noting for anyone choosing a replacement: American sycamore is susceptible enough that bacterial leaf scorch can kill it, while Mexican sycamore is reported resistant.

Powdery mildew, decay and root problems

Powdery mildew (Microsphaera) shows up as heavy white growth on the upper surface of leaves in late summer and fall, badly distorting leaf shape. It looks serious and is not: little damage occurs to the tree beyond appearance, and no control is recommended unless the tree is exceptionally valuable. Do not thin the canopy for it — you would be opening pruning wounds in the growing season, which is exactly what canker stain is waiting for.

Wood decay is a different category of problem. Old sycamores hollow out routinely; hollow sycamore trunks are a well-documented den site for raccoons, wood ducks and chimney swifts, and a hollow trunk is not by itself a diagnosis of ill health. What matters is whether enough sound wood remains. Bracket fungi or mushrooms at the base or emerging from the trunk mean decay fungi are working inside, and that is a structural risk question for a qualified arborist with the tree in front of them, not something you spray.

Root problems on this species are usually not a pathogen. The American sycamore is a floodplain tree that tolerates temporary flooding and compacted urban soil, so waterlogging alone rarely explains a decline. Grade changes, severed roots from trenching, and soil compaction from construction are the far more common causes, and they show up as a thinning crown a year or two after the work, not immediately.

Three things that look like disease and are not

Bark falling off. The single most common false alarm on this tree. Sycamores shed bark in plates because the outer bark cannot stretch as the trunk expands, and the pale patches underneath are the newer bark. It happens more during the growing season, when the trunk is putting on girth. If this is what brought you here, the mechanism is explained in full on our page about sycamore tree bark.

Leaf drop in high summer. A sycamore dropping leaves in July or August during dry weather is showing water stress, not infection. The signature is leaves that go brown, brittle and curled rather than blotched along the veins, sometimes with stress cankers on the branches. Water deeply and infrequently, wetting the whole root zone out beyond the edge of the canopy; shallow daily watering keeps the roots at the surface and makes the problem worse next year. We cover the full set of causes in why a sycamore drops its leaves.

Insect damage read as disease. Sycamore lace bugs feed on the undersides of leaves and produce fine white stippling that turns to bronzing by late summer; aphids leave sticky honeydew and sooty mold. Both are cosmetic on a mature tree and both are diagnosed by turning a leaf over — see sycamore tree pests for what to look for.

Do resistant cultivars solve this?

Partly, and the fine print matters. The anthracnose-resistant selections you will be offered — 'Bloodgood', 'Liberty', 'Columbia', Exclamation!™ — are London plane cultivars, not American sycamores. If a nursery sells you a "resistant American sycamore," check the label.

Resistance is also partial and climate-dependent, and the extension services do not fully agree. Penn State lists 'Bloodgood', 'Columbia' and 'Liberty' as resistant London planetree cultivars. The Pacific Northwest Plant Disease Management Handbook reports 'Bloodgood' and 'Liberty' as resistant but 'Columbia' and 'Yarwood' as susceptible in western Oregon. Both are correct: a cultivar bred and tested in the eastern United States can perform badly in a cool, wet western spring, which is precisely the weather that drives this disease. Nothing on this list is immune, and buying by cultivar name without asking how it behaves in your climate is how people end up disappointed.

What to do next

If the tree defoliated in spring and releafed by midsummer, you have anthracnose and a rake is your main tool. If you find a sunken, elongated canker on the trunk with stained wood beneath it, stop pruning and get a diagnosis before anyone touches the tree again. If browning starts at the leaf margins in August and comes back worse each summer, ask for a laboratory test before paying for treatment.

Call an arborist when there is decay in the trunk or major limbs, when a canker on the trunk needs identifying, when you want a lab-confirmed diagnosis, or when treatment would require working in the canopy. Everything else on this page is a homeowner job, and most of it is done in December with clean tools. For the routine that prevents most of these problems in the first place, start at our sycamore tree care hub, and see the sycamore through the seasons for when each task falls in the year.