Elm Yellows vs Dutch Elm Disease

Elm yellows (sometimes called elm phloem necrosis) is the most commonly misdiagnosed lookalike for Dutch Elm Disease. Both kill elms, both produce wilting symptoms, and both spread between trees — but the cause, progression pattern, and management strategy are completely different.

What elm yellows is

Elm yellows is caused by a phytoplasma, a type of bacteria-like organism without cell walls. It is spread by leafhoppers (primarily white-banded elm leafhopper, Scaphoideus luteolus) that feed on the phloem of healthy elms after acquiring the pathogen from infected trees. Once in a tree, the phytoplasma colonizes the phloem and disrupts sugar transport.

Where they overlap

Both elm yellows and DED:

Cause wilting, yellowing, and eventual tree death

Affect American elm and other native North American elms

Spread between trees (different vectors, but transmission happens)

Have no cure once a tree is infected

How to tell them apart

Feature | Dutch Elm Disease | Elm yellows
Speed of symptom onset | Branch by branch, over weeks | Whole tree at once, often over 2–4 weeks
Pattern within tree | Single flag → spreads | Generalized canopy yellowing simultaneously
Vascular streaking | Brown streaks in xylem | Yellow-brown discoloration of phloem (inner bark)
Wintergreen smell | None | Yes — fresh inner bark smells of wintergreen / methyl salicylate
Vector | Elm bark beetles | Leafhoppers
Geographic range | Widespread N. America, Europe | Mostly central/eastern US, less common elsewhere
Asian elm cultivars | Generally resistant | Generally susceptible
Tree response after symptoms | Branch dieback over months | Total tree collapse within 1–2 seasons

The wintergreen test

This is the single most useful field test for distinguishing the two diseases:

Cut a small piece of bark from a wilting branch

Scrape the inner bark (phloem) surface

Sniff the freshly scraped surface

A wintergreen or methyl-salicylate odor indicates elm yellows rather than DED. The smell comes from compounds the tree produces in response to phytoplasma infection. Dutch Elm Disease produces no such odor.

Why misdiagnosis matters

Treating elm yellows with fungicide injections (the DED treatment) will fail completely. Phytoplasmas are not fungi; they're not affected by propiconazole or thiabendazole. Money spent on fungicide is wasted, and the tree continues declining.

There is no effective chemical treatment for elm yellows. Management options:

Remove infected trees promptly to reduce phytoplasma source for leafhoppers

Some Asian elm cultivars resist elm yellows (different resistance from DED resistance)

Tetracycline injections show experimental success but require repeated annual applications

When to suspect elm yellows over DED

Strongly consider elm yellows if:

The whole canopy yellowed within a few weeks (not flag-by-flag)

You smell wintergreen in the inner bark

You're in central/eastern US (Ohio Valley region in particular)

Trees are dying in clusters within 1–2 years rather than over multiple seasons

DED-resistant Asian cultivars in the area are dying alongside American elms

Get lab confirmation

Both diseases can be confirmed through PCR testing. State plant diagnostic labs offer phytoplasma-specific assays. Don't rely on visual diagnosis alone for a high-value tree.

Related pages

What Are the Symptoms of Dutch Elm Disease?

Differential Diagnosis Guide

Who Should I Contact if I See Dutch Elm Disease?

Dutch Elm Disease Symptom Checker

References

Sinclair, W. A., & Griffiths, H. M. (1995). "Epidemiology of a slow-decline phytoplasmal disease: elm yellows in central New York." Phytopathology, 85(5), 511–518.

Sinclair, W. A., Townsend, A. M., & Sherald, J. L. (2000). "Elm yellows in North America." In The Elms: Breeding, Conservation, and Disease Management (pp. 121–136). Kluwer Academic Publishers.

Conti, M., D'Agostino, G., Casetta, A., & Mela, L. (1988). "Some characteristics of elm yellows transmission by Macropsis mendax." Acta Horticulturae, 234, 275–278.