How Does Dutch Elm Disease Look Like?

Recognizing Dutch Elm Disease early is crucial for tree management. The disease causes distinctive symptoms that progress over time as the fungus spreads through the tree's vascular system. For a comprehensive list of symptoms, also see What Are the Symptoms of Dutch Elm Disease?

Early Symptoms

Leaf Wilting and Yellowing

Flagging: Individual branches develop yellowing, wilting leaves while other parts of the tree remain healthy

Pattern: Often starts on one side of the tree or in upper branches

Timing: Symptoms typically appear in late spring to early summer

Branch Dieback

Affected branches begin to die back from the tips

Leaves on dying branches may turn brown but often remain attached

Dead branches become brittle and may fall

Advanced Symptoms

Vascular Staining

Brown streaking: Cut branches reveal dark brown or black streaks in the wood

Location: Staining appears in the outer rings of wood (sapwood)

Pattern: Streaks may form complete or partial rings

Rapid Decline

Acute form: Tree may die within a few weeks of showing symptoms

Chronic form: Tree decline occurs over 1-2 years

Whole tree: Eventually the entire tree becomes affected

Distinctive Signs

Beetle Galleries

Bark beetles: Small holes in bark from elm bark beetles

Galleries: Intricate tunneling patterns under bark created by beetle larvae

Frass: Fine sawdust-like material around beetle holes

Root System

Root grafts: Connected root systems can show disease spread between nearby trees

Secondary infections: Weakened trees become susceptible to other diseases and pests

What to Look For

On Leaves:

Sudden wilting of leaves on individual branches

Yellowing progressing to brown

Leaves curling and dropping prematurely

On Branches:

Branch dieback starting at tips

Brown streaking visible when bark is peeled back

Brittle, dead wood

On Trunk:

Bark beetle entry holes

Possible fungal growth or cankers

Overall decline in tree vigor

Seasonal Timing

Spring: New leaves may fail to emerge on affected branches

Early Summer: Classic flagging symptoms appear

Late Summer: Advanced dieback and tree decline

Fall/Winter: Dead branches become more apparent

Confirming the Diagnosis

Visual symptoms alone may not be sufficient for definitive diagnosis. Professional confirmation often requires:

Laboratory testing of wood samples

Microscopic examination for fungal spores

Consultation with certified arborists or plant pathologists

For suspected Dutch Elm Disease cases, see Who Should I Contact if I See Dutch Elm Disease? for reporting guidance and professional referrals.

Related Information:

Understanding the disease: What Causes Dutch Elm Disease?

Internal spread: How Does Dutch Elm Disease Spread in a Tree?

Treatment options: Can Dutch Elm Disease Be Treated?

Prevention strategies: What Preventative Treatments Exist for Dutch Elm Disease?