Lightning-Struck Elm: Assessing Damage and Managing Insects

A lightning strike on a mature elm creates a wound that attracts borers, ants, and decay. Quick action and patience are both required.

Immediate Steps

• Remove hazards: Cut off the shattered branch and any loose, hanging bark.
• Do not paint or seal wounds: Let the tree compartmentalize naturally.
• Spray for borers: Apply a borer-control insecticide (permethrin or bifenthrin) to the trunk and major limbs now to deter egg-laying.

Prognosis: Wait Until Spring

Lightning effects vary wildly. Some trees die quickly; others survive for years. Hardwoods like elm have better survival odds than conifers. Wait until leaf-out next spring to assess:

• Does the tree leaf out fully?
• Is canopy density normal?
• Are there signs of progressive dieback?

Bark Management

Loose bark that pulls away easily can be carefully trimmed back to firmly attached bark (a technique called "bark tracing") using a sharp knife or chisel. Do not cut into sound wood. This encourages clean callus formation.

Long-Term Care

• Fertilize lightly in spring to support recovery.
• Water deeply during dry spells.
• Monitor for recurring borer activity; retreat if needed.
• Consult a certified arborist for structural assessment if the tree is near structures.

Key Insight

The insects are secondary invaders exploiting lightning damage. Treating them helps, but the tree's own vigor determines survival. Patience and observation are your best tools.