Anthracnose on Rochester Shade Trees: Why Sycamore, Oak, and Ash Leaves Look Scorched in Spring

By Linda Marsh, Pests & Diseases. Last updated: June 25, 2026

Every spring around Monroe County, homeowners send the same alarmed photos: a big sycamore on the tree lawn that pushed out leaves, then went brown and crispy along the veins within a couple of weeks. The instinct is to assume the tree is dying. In most cases it is not. The culprit is anthracnose, a group of fungal diseases that thrive in exactly the cool, damp spring our region serves up most years.

What is anthracnose and why does it hit Rochester trees in spring?

Anthracnose is not one disease but a family of related fungal infections, each fairly host-specific. Sycamore and London planetree get their own anthracnose fungus, oaks get another, and ash, maple, and dogwood each have their own as well. What they share is timing and behavior. The fungi overwinter in fallen leaves and in small twig cankers, then release spores during cool, wet weather as buds break and the first tender leaves expand.

Rochester gives these fungi nearly ideal conditions. Our springs run cool and wet, and those cool stretches in the 50s with frequent rain are the sweet spot for infection. Locally it does not help that moisture off Lake Ontario tends to keep things damp longer than a few miles inland. When that pattern holds through April and into May, anthracnose flares hard. In a warm, dry spring it can be almost invisible.

Why do the leaves look scorched, curled, or frost-bitten?

The classic look is browning that follows the leaf veins, irregular dead blotches, and curling or distortion of leaves that were infected while still expanding. On sycamore you often see the tree drop a flush of young leaves entirely, then releaf later in the season, which alarms people even though the tree is defending itself.

This scorched appearance is exactly why anthracnose gets misdiagnosed. It mimics several other problems:

• Late frost damage. A hard frost after budbreak browns tender foliage too, but frost hits uniformly across the exposed canopy in one event, while anthracnose spreads progressively and concentrates on lower, interior, shaded foliage where leaves stay wet longest.
• Herbicide drift or root uptake. Lawn weed-killer damage causes cupping and strapping of leaves, but it usually shows odd new-growth distortion rather than vein-following brown blotches.
• Leaf scorch from heat and drought. True scorch shows up in hot, dry mid to late summer along leaf margins, not in cool wet spring along the veins. When you are not sure which problem you are looking at, our Rochester homeowner's diagnostic guide to a sick tree walks through how to narrow it down.

If you are working through a broader pattern of discoloration and decline, our pillar on why tree leaves curl, yellow, and die walks through how to tell these causes apart step by step.

Which Rochester shade trees are most affected?

In Monroe County, a handful of species account for most of the anthracnose calls:

• American sycamore and London planetree. The most dramatically affected by far. Sycamore anthracnose can cause repeated early leaf drop and a zigzag, witch's-broom growth habit over years as twigs die back. This is the species most likely to look alarming and is a real concern across Upstate New York.
• Oak (especially white oak group). Oak anthracnose causes brown blotches and some leaf curl, usually on lower branches, and is rarely serious.
• Ash. Ash anthracnose adds another stress on a genus already devastated by emerald ash borer. If you have ash, the borer is the far bigger threat. See our breakdown on how to spot and stop emerald ash borer in Monroe County.
• Maple and dogwood. Both get their own anthracnose. It is generally cosmetic on maples, while dogwood anthracnose can be more damaging on flowering dogwoods over time.

Because the symptoms overlap with other spring leaf diseases, it helps to compare. Maple owners often confuse anthracnose blotches with the raised black spots of maple tar spot, which is a different fungus entirely and even less harmful.

Will anthracnose kill my tree?

For an established, otherwise healthy shade tree, the honest answer is almost never from a single season. Anthracnose is mainly a stress and cosmetic disease. A vigorous sycamore can defoliate in May and releaf by June with no lasting harm.

The exception is repeated, severe infection year after year, especially on sycamore, where chronic twig dieback gradually thins and deforms the canopy. Trees already weakened by drought, compacted clay soil, root damage, or girdling roots are the ones that decline. So watch the underlying health of the tree, not just the spotted leaves. Buried trunks and girdling roots in particular are a quiet, fixable cause of that decline, which we cover in root collar excavation for buried trunks and girdling roots in Rochester.

How do you manage anthracnose without overreacting?

For the vast majority of Rochester yards, anthracnose is managed culturally, not chemically:

• Rake and remove fallen leaves and twigs in autumn and again in spring. This is the single most effective step because the fungus overwinters in that debris.
• Prune out dead twigs on chronically infected sycamores during dry weather to remove twig cankers and open the canopy for faster drying.
• Improve tree vigor: correct mulch volcanoes, relieve soil compaction, and water deeply during summer drought so the tree can outgrow the damage.
• Skip the fungicide in most cases. Foliar fungicides only work preventively, applied at budbreak before symptoms show, and the timing is genuinely hard to hit in our unpredictable springs. For a high-value specimen sycamore with a history of severe infection, a certified arborist may recommend properly timed treatment, but for most trees it is not worth it.

When a tree shows alarming symptoms and you cannot tell anthracnose from a more serious disease or pest, that is the moment to get a professional eye on it. You can schedule an arborist evaluation with Monster Tree Service rather than guess.

FAQ

Is anthracnose contagious to my other trees? Mostly no, because each anthracnose fungus is fairly host-specific. The sycamore fungus will not jump to your oak or maple. A bad sycamore can spread spores to nearby sycamores, but it will not infect unrelated species.

Should I spray a fungicide for anthracnose? For most Rochester yard trees, no. Fungicides only work preventively at budbreak, the timing is hard to nail in our variable springs, and the disease is rarely damaging enough to justify it. A certified arborist may advise treatment only for a high-value specimen with a history of severe infection.

My sycamore lost all its young leaves in May. Is it dying? Probably not. Early defoliation followed by a second flush of leaves in June is the classic, survivable sycamore anthracnose pattern. A healthy tree routinely recovers, though repeated years of this warrant a professional evaluation.

How do I tell anthracnose from frost or herbicide damage? Frost browns the canopy uniformly in a single event, herbicide tends to distort and cup new growth, and anthracnose spreads progressively along leaf veins and concentrates on shaded, slow-drying interior foliage. When in doubt, have an arborist confirm it.

Sources

• Cornell Garden-Based Learning (Cornell University)
• USDA Forest Service, tree and forest health information
• New York State Department of Environmental Conservation, Forests and Trees
• Monster Tree Service of Rochester (our editorial pick)