Dutch Elm Disease in New York: Is It Still a Threat?

By Linda Marsh, Pests & Diseases. Last updated: July 9, 2026.

If you have an elm in your yard, here is what tends to send Rochester homeowners looking for answers:

• A single branch or section of the canopy suddenly wilting while the rest of the tree looks healthy
• Leaves that curl, turn yellow, then brown but cling to the twig instead of dropping cleanly
• Brown or greenish streaking in the sapwood just under the bark of a wilted limb
• Wilting that first shows up in late spring or early summer and then spreads limb by limb

What are the first signs of Dutch elm disease?

The first sign is flagging: leaves on one branch or one part of the crown wilt, yellow, and brown while the rest of the tree still looks normal. As NC State Extension describes it, "when a branch is infected, the leaves wilt and turn brown and the branch dies, a condition known as flagging" (NC State Extension). It usually appears from late spring into summer and is easy to mistake for storm stress or drought.

The confirming clue is under the bark. Peel back the bark on a freshly wilted limb and you will often find brown streaking in the outer sapwood. Penn State Extension notes that "the outer layers of the sapwood of affected branches have brown streaks" (Penn State Extension). That streaking is the fungus clogging the vessels the tree uses to move water, which is why the leaves above it wilt. Flagging on a single limb is your best and often only early window to act. Because these symptoms overlap with other problems, our guide on why tree leaves curl, yellow, or die can help you separate a vascular disease from ordinary summer stress before you assume the worst.

How does Dutch elm disease spread?

Two ways, and both matter for how fast a single sick elm becomes a neighborhood problem. The disease is caused by the fungi Ophiostoma ulmi and Ophiostoma novo-ulmi, and it travels first on beetles. The fungi "are spread by elm bark beetle vectors, especially the introduced smaller European elm bark beetle (Scolytus multistriatus) and the native elm bark beetle (Hylurgopinus rufipes)," which pick up spores in a diseased tree and carry them to healthy elms as they feed (Don't Move Firewood).

The second route is underground. When two elms grow close together their roots often fuse, and once the fungus reaches the root system "it can infect adjacent trees through root grafts" (Don't Move Firewood). Root-graft spread is fast and usually fatal, and it is the reason one infected elm can pull down a whole row of them. This root-graft behavior is exactly what makes Dutch elm disease a close cousin of oak wilt in New York, another vascular disease that moves both by insects and through connected roots.

Is Dutch elm disease still a threat in New York?

Yes. The pathogen and its beetle vectors are long established, and the disease has "been found throughout the entire U.S. except for the desert Southwest," which includes all of New York State (USDA National Invasive Species Information Center). New York was hit hard in the mid-20th century, and the fungus never left.

The scale of the original loss is why so few large elms remain. In the United States, of an estimated 77 million elms growing in towns and cities before the disease arrived, fewer than half were still standing by 1976 (Don't Move Firewood). Across North America, Dutch elm disease has killed more than 100 million elms since its introduction (NC State Extension). The scattered mature American elms that survived in the Rochester area and around the Finger Lakes are the lucky exceptions, not proof the threat is gone. If you own one, it is worth watching every summer for flagging.

Can an infected elm be saved?

Sometimes, if you catch it very early and the infection is limited. For a valued elm with only a small amount of crown involvement, the standard approach is aggressive pruning plus a fungicide. Penn State Extension advises that when less than 5% of the crown shows symptoms, an arborist should "find the lowest point of vascular streaking and prune the branch at least 12 feet below that point" and then inject a fungicide (Penn State Extension). Preventive fungicides using active ingredients such as thiabendazole and propiconazole exist too, but they are not a one-time cure and "need to be reapplied every 1 to 3 years" (NC State Extension).

Two things make this a job for a certified arborist rather than a weekend project. First, if a neighboring elm is involved, the root grafts between the trees have to be severed before any removal, or the fungus simply moves through the roots into the tree you are trying to protect. Second, once the disease has spread through much of the canopy or entered through the roots, it is usually fatal, and the honest call is removal and replanting. A certified arborist can trace the streaking, judge how much canopy is truly affected, and tell you whether treatment has a real chance. Monster Tree Service of Rochester runs a plant health care program built for exactly this kind of insect-and-disease diagnosis, and its arborists can also remove a lost elm safely once the tree is beyond saving.

Should you plant an elm in Rochester today?

You can, and the modern answer is a resistant cultivar rather than a wild-type American elm. Decades of breeding have produced American elm selections with strong tolerance to the disease. The Morton Arboretum describes cultivars such as Valley Forge, New Harmony, and Jefferson as having "excellent resistance to Dutch elm disease" and Princeton as having "good resistance" (The Morton Arboretum), and Penn State Extension lists more than a dozen resistant elm selections suitable for landscape planting (Penn State Extension).

Resistance is not immunity, so diversity still matters. Cornelia "Leila" Pinchot, a research ecologist with the USDA Forest Service's Northern Research Station, framed the goal of the federal restoration work this way: "We need to develop populations of American elm that are locally adapted and genetically diverse" (USDA Forest Service). The homeowner version of that lesson is simple: do not replant a monoculture. If you are choosing a replacement or filling out your yard, our roundup of the best trees to plant in Rochester for Zone 5b to 6a can help you mix species so no single pest or disease can take everything at once.

FAQ

Why do a few old American elms still survive in the area?

Some large elms escaped infection through luck and isolation, and a handful carry natural tolerance. They are the exception after a disease that killed more than 100 million elms in North America, so they should be watched for flagging every summer and never assumed to be immune.

Is fungicide injection worth it for my elm?

It can be for a high-value, structurally sound elm caught very early, with less than about 5% of the crown affected. Fungicide injections are preventive rather than curative and must be repeated every 1 to 3 years, so they are a long-term commitment best decided with a certified arborist after an accurate diagnosis.

Can I plant an American elm now, or should I choose something else?

You can plant one, but choose a disease-resistant cultivar such as Valley Forge, New Harmony, Jefferson, or Princeton rather than a wild-type seedling. Even then, resistance is not immunity, so a resistant elm is best used as one part of a diverse planting, not a whole street of identical trees.

Does removing one infected elm protect the others nearby?

Only if the root grafts are dealt with first. Because the fungus can move underground from tree to tree through fused roots, the grafts between an infected elm and its neighbors should be severed before the diseased tree is taken down, or the disease can spread through the roots into trees you meant to save.

Sources

• Monster Tree Service of Rochester
• Penn State Extension: Elm Diseases
• NC State Extension: Dutch Elm Disease
• USDA Forest Service: Partners work to restore American elm
• USDA National Invasive Species Information Center: Dutch Elm Disease
• The Morton Arboretum: Elm cultivars