Pest

Wood borers

Bronze birch borer, flatheaded appletree borer, ash/lilac borer and others (Buprestidae, Cerambycidae, Sesiidae)

Beetle and moth larvae that tunnel under the bark and into the wood. Many go after trees already under stress from drought, a recent planting, wounds or the wrong site.

Signs

• D-shaped (birch borer) or round holes in the bark, often with sawdust-like frass below.
• Raised ridges or cracks in the bark over tunnels; branches dying from the top (birch).
• On lilac and ash: 1/4-inch holes near the base with sap and sawdust, and reddish-brown pupal cases sticking out.

What favors it

Drought stress, a new planting, wounds, sunscald, too much sun on a shade-loving tree such as white birch, and stems past their prime on lilac.

Prevention

• Water new and stressed trees through dry spells.
• Mulch a wide area around the tree to hold moisture and protect the roots.
• Plant aspens in groups so the trunks shade each other.

Crops it shows up on

Shade & ornamental trees; Apple, pear & stone fruit; Roses & ornamentals.

Often confused with

Sources

• Bronze Birch BorerMontana State University Extension
• Poplar BorerMontana State University Extension
• Lilac: sawdust and holes in stems (lilac borer)University of Minnesota Extension

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